data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0001-8585-1717 Laszlo L. Kiss Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. Kristine Lam Discovery of two
warm mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0002-9910-6088 Jacques
Laskar Discovery of two warm mini-Neptunes with contrasting densities orbiting
the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS data
observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0003-2634-789X Baptiste Lavie Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0001-8884-9276 Christophe
Lovis Discovery of two warm mini-Neptunes with contrasting densities orbiting
the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS data
observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0001-7120-5837 Demetrio Magrin Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0003-0312-313X Luca
Marafatto Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0002-8822-6834 Pierre Maxted Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0003-3794-1317 Scott
McDermott Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. Djamel Mékarnia Discovery of two warm mini-Neptunes with
contrasting densities orbiting the young K3V star TOI-815††thanks: This study
uses TESS data, CHEOPS data observed as part of guaranteed time observation
programs CH_PR10031 and CH_PR10048, and ESPRESSO data collected with the ESO
3.6 m telescope under programs 105.20P7.001, 109.23DX.001, and 110.2481.001
(PI: Bouchy). The photometric and radial velocity data in this work are only
available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0001-5000-7292 Christoph Mordasini Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0002-1013-2811 Felipe
Murgas Discovery of two warm mini-Neptunes with contrasting densities orbiting
the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS data
observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0001-9087-1245 Valerio Nascimbeni Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0001-9770-1214 Louise D.
Nielsen Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0002-5254-2499 Göran Olofsson Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0003-3747-7120 Roland
Ottensamer Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0001-5684-5836 Isabella Pagano Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0001-9573-4928 Enric
Pallé Discovery of two warm mini-Neptunes with contrasting densities orbiting
the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS data
observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0003-0987-1593 Gisbert Peter Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0001-6101-2513 Giampaolo
Piotto Discovery of two warm mini-Neptunes with contrasting densities orbiting
the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS data
observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0002-9937-6387 Don Pollacco Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0001-9850-9697 Didier
Queloz Discovery of two warm mini-Neptunes with contrasting densities orbiting
the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS data
observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0002-3012-0316 Roberto Ragazzoni Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0002-7697-5555 Devin
Ramos Discovery of two warm mini-Neptunes with contrasting densities orbiting
the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS data
observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0009-0002-2478-4308 Nicola Rando Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. Heike Rauer Discovery of two
warm mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0002-6510-1828 Christian
Reimers Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0002-2334-1620 Ignasi Ribas Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0002-6689-0312 Sara
Seager Discovery of two warm mini-Neptunes with contrasting densities orbiting
the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS data
observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0002-6892-6948 Damien Ségransan Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0003-2355-8034 Gaetano
Scandariato Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0003-2029-0626 Attila Simon Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0001-9773-2600 Alexis M.
S. Smith Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0002-2386-4341 Manu Stalport Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0003-0996-6402 Manfred
Steller Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0003-2459-6155 Gyula Szabó Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0002-0606-7930 Nicolas
Thomas Discovery of two warm mini-Neptunes with contrasting densities orbiting
the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS data
observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. Tyler A. Pritchard Discovery of two warm mini-Neptunes with
contrasting densities orbiting the young K3V star TOI-815††thanks: This study
uses TESS data, CHEOPS data observed as part of guaranteed time observation
programs CH_PR10031 and CH_PR10048, and ESPRESSO data collected with the ESO
3.6 m telescope under programs 105.20P7.001, 109.23DX.001, and 110.2481.001
(PI: Bouchy). The photometric and radial velocity data in this work are only
available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0001-9227-8349 Stéphane Udry Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0001-7576-6236 Carlos
Corral Van Damme Discovery of two warm mini-Neptunes with contrasting
densities orbiting the young K3V star TOI-815††thanks: This study uses TESS
data, CHEOPS data observed as part of guaranteed time observation programs
CH_PR10031 and CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m
telescope under programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI:
Bouchy). The photometric and radial velocity data in this work are only
available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. Valérie Van Grootel Discovery of two warm mini-Neptunes with
contrasting densities orbiting the young K3V star TOI-815††thanks: This study
uses TESS data, CHEOPS data observed as part of guaranteed time observation
programs CH_PR10031 and CH_PR10048, and ESPRESSO data collected with the ESO
3.6 m telescope under programs 105.20P7.001, 109.23DX.001, and 110.2481.001
(PI: Bouchy). The photometric and radial velocity data in this work are only
available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0003-2144-4316 Eva Villaver Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0003-4936-9418 Ingo
Walter Discovery of two warm mini-Neptunes with contrasting densities orbiting
the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS data
observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0002-5839-1521 Nicholas Walton Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/. 0000-0003-3983-8778 Cristilyn
N. Watkins Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. Richard G. West Discovery of two warm mini-Neptunes with
contrasting densities orbiting the young K3V star TOI-815††thanks: This study
uses TESS data, CHEOPS data observed as part of guaranteed time observation
programs CH_PR10031 and CH_PR10048, and ESPRESSO data collected with the ESO
3.6 m telescope under programs 105.20P7.001, 109.23DX.001, and 110.2481.001
(PI: Bouchy). The photometric and radial velocity data in this work are only
available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/. 0000-0001-6604-5533 Discovery of two warm mini-Neptunes with
contrasting densities orbiting the young K3V star TOI-815††thanks: This study
uses TESS data, CHEOPS data observed as part of guaranteed time observation
programs CH_PR10031 and CH_PR10048, and ESPRESSO data collected with the ESO
3.6 m telescope under programs 105.20P7.001, 109.23DX.001, and 110.2481.001
(PI: Bouchy). The photometric and radial velocity data in this work are only
available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm
mini-Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.Discovery of two warm mini-Neptunes with contrasting densities
orbiting the young K3V star TOI-815††thanks: This study uses TESS data, CHEOPS
data observed as part of guaranteed time observation programs CH_PR10031 and
CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under
programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy). The
photometric and radial velocity data in this work are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/.Discovery of two warm mini-
Neptunes with contrasting densities orbiting the young K3V star
TOI-815††thanks: This study uses TESS data, CHEOPS data observed as part of
guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO
data collected with the ESO 3.6 m telescope under programs 105.20P7.001,
109.23DX.001, and 110.2481.001 (PI: Bouchy). The photometric and radial
velocity data in this work are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/.

We present the discovery and characterization of two warm mini-Neptunes
transiting the K3V star TOI-815 in a K-M binary system. Analysis of its
spectra and rotation period reveal the star to be young, with an age of
$200^{+400}_{-200}$ Myr. TOI-815b has a 11.2-day period and a radius of 2.94
$\pm$ 0.05 $\it{R_{\rm\mathrm{\oplus}}}$ with transits observed by TESS,
CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-815c, has a radius of 2.62
$\pm$ 0.10 $\it{R_{\rm\mathrm{\oplus}}}$, based on observations of three
nonconsecutive transits with TESS; targeted CHEOPS photometry and radial
velocity follow-up with ESPRESSO were required to confirm the 35-day period.
ESPRESSO confirmed the planetary nature of both planets and measured masses of
7.6 $\pm$ 1.5 $\it{M_{\rm\mathrm{\oplus}}}$ ($\rho_{\mathrm{P}}$ =
1.64${}^{+0.33}_{-0.31}$ g cm-3) and 23.5 $\pm$ 2.4
$\it{M_{\rm\mathrm{\oplus}}}$ ($\rho_{\mathrm{P}}$ = 7.2${}^{+1.1}_{-1.0}$ g
cm-3), respectively. Thus, the planets have very different masses, which is
unusual for compact multi-planet systems. Moreover, our statistical analysis
of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets
tend to have higher bulk densities compared to those undergoing strong
irradiation. This could be ascribed to their cooler atmospheres, which are
more compressed and denser. Internal structure modeling of TOI-815b suggests
it likely has a H-He atmosphere that constitutes a few percent of the total
planet mass, or higher if the planet is assumed to have no water. In contrast,
the measured mass and radius of TOI-815c can be explained without invoking any
atmosphere, challenging planetary formation theories. Finally, we infer from
our measurements that the star is viewed close to pole-on, which implies a
spin-orbit misalignment at the 3$\sigma$ level. This emphasizes the
peculiarity of the system’s orbital architecture, and probably hints at an
eventful dynamical history.

###### Key Words.:

planets and satellites: detection – planets and satellites: composition -
planets and satellites: formation - techniques: photometry – techniques:
radial velocities

##  1 Introduction

The Transiting Exoplanet Survey Satellite (TESS; Ricker et al. 2015) and the
Kepler space mission have profoundly transformed our understanding of planets
by detecting thousands of exoplanets using the transit method, particularly
those with radii below 4 $\it{R_{\rm\mathrm{\oplus}}}$ and relatively short
orbital periods. Fulton et al. (2017), using precise planet radius
measurements, identified a clear bimodal distribution in the radii of small
planets. It appears that close-orbiting planets predominantly fall into two
categories: super-Earths (below 1.8 $\it{R_{\rm\mathrm{\oplus}}}$) or sub-
Neptunes (2 to 4 $\it{R_{\rm\mathrm{\oplus}}}$), with very few planets
occupying the intermediate range (the so-called radius valley). Four
mechanisms have been proposed to explain the origin of these two populations:
photoevaporation of the H-He envelopes due to high-energy radiation from the
host star (Lopez & Fortney 2013; Owen & Wu 2017; Jin & Mordasini 2018; Rogers
& Owen 2021; Attia et al. 2021), atmospheric mass-loss fueled by the cooling
luminosity of a planet’s core (Ginzburg et al. 2018; Gupta & Schlichting
2019), a combination of ex situ formation and photoevaporation (Venturini et
al., 2020), and an in situ gas-poor formation scenario (Lee et al. 2022).
These mechanisms predict different compositions for the mini-Neptunes, ranging
from dry planets composed of a H-He envelope atop a rocky core (Owen & Wu,
2017; Jin & Mordasini, 2018; Gupta & Schlichting, 2019; Lee et al., 2022) to
water worlds with a thin or no H-He atmosphere (Venturini et al., 2020). The
mechanisms also predict distinct relationships between stellar and planetary
mass, as well as differing locations of the valley (in the period-radius-mass
space) and varying occurrence rates relative to the age of the systems (Berger
et al., 2020; Petigura et al., 2022).

Numerous ongoing follow-up programs are dedicated to characterizing the masses
of super-Earth and mini-Neptune planets located close to the “radius valley”
of short-period orbits. However, there is limited coverage of mini-Neptunes
with low stellar irradiation (less than 30 $\it{S_{\rm\mathrm{\oplus}}}$) and
long orbital periods (greater than 15 days). We started a radial velocity (RV)
follow-up campaign with the Échelle SPectrograph for Rocky Exoplanets and
Stable Spectroscopic Observations (ESPRESSO; Pepe et al. 2021) dedicated to
the characterizations and precise density measurements of warm mini-Neptune
planets that transit FGK dwarfs. Currently, there are known 17 exoplanets in
this parameter range with stars brighter than V=12 and well-constrained
densities111$\sigma_{\mathrm{M}}/M$ $\leq$ 25$\%$ and $\sigma_{\mathrm{R}}/R$
$\leq$8$\%$ according to the PlanetS catalog222Available on the Data &
Analysis Center for Exoplanets (DACE) platform (https://dace.unige.ch) (Otegi
et al. 2020).

Multi-planet systems provide the opportunity to study planets of different
densities and compositions within a single system, and to compare such planets
with each other. One observed trend in the diversity of planetary systems is
that planets seem to resemble “peas in the pod,” that is to say, multi-
transiting systems tend to have planets with similar sizes and geometrically
spaced orbital distances (Weiss et al., 2018; Otegi et al., 2022; Mishra et
al., 2023). Understanding these trends is crucial since they can elucidate
underlying physical processes and constrain formation theories.

In this work we present the discovery of two mini-Neptune planets transiting
TOI-815, a V=11.2 mag K3V star. The innermost planet, designated TOI-815b, has
an orbital period of 11.2 days. This planet’s transits were captured by TESS
during Sectors 6, 36, and 63, as well as by the CHaracterising ExOPlanet
Satellite (CHEOPS; Benz et al. 2021), the Antarctic Search for Transiting
ExoPlanets (ASTEP) telescope (Guillot et al. 2015), and the Las Cumbres
Observatory Global Telescope (LCOGT; Brown et al. 2013). As for the outer
planet, TOI-815c, TESS detected three transits during the aforementioned
sectors; however, a unique period could not be determined. Additionally,
targeted CHEOPS photometry was performed to investigate potential period
aliases, leading to the confirmation of a 35-day orbital period for TOI-815c.
The planetary nature of both objects has been confirmed via RV follow-up using
ESPRESSO.

The paper is structured as follows: In Section 2 we provide a detailed
description of the space- and ground-based observations with TESS, CHEOPS,
ASTEP, and LCOGT, as well as the ESPRESSO RV observations. Section 3 details
how we determined the host star parameters by combining high-resolution
spectra. In Section 4 we present our global photometric and RV analysis and
its results. Finally, in Section 5 we present a discussion of the system, and
we conclude in Section 6.

##  2 Observations

###  2.1 TOI-815 in a binary system

Behmard et al. (2022) searched for stellar companions to TESS objects of
interest (TOIs; Guerrero et al. 2021) by cross-matching them with the Gaia
Early Data Release 3 (EDR3) catalog. TOI-815 was identified to be in a binary
system with the nearest known neighbor in the TESS Input Catalog Version 8
(TICv8; Stassun et al. 2019), TIC 102840237 (Gaia DR3 5415648821874435584)
that is located approximately 359 AU ($\sim 6\aas@@fstack{\prime\prime}4$)
north of TOI-815 (Figure 1). According to the TICv8 catalog, TIC 102840237 is
an M-dwarf with $T_{\mathrm{eff}}$ = 3766 $\pm$ 157 K and is 2.5 magnitudes
dimmer than TOI-815 in the G band. To compensate for flux contamination in the
photometry, we included a dilution factor for the light curves, as presented
below.

###  2.2 TESS photometry

The TOI-815 system (TIC 102840239) was observed in TESS Sector 9 (2018
December 12 to 2019 January 06) in 30-minute cadence and Sectors 36 (2021
March 07 to 2021 April 01) and 63 (2023 March 10 to 2023 April 06) in
20-second cadence. In Sectors 9 and 36, the target was imaged on CCD 2 of
camera 2, and in Sector 63, on CCD 1 of camera 2. The 30-minute full frame
image light curves were extracted by the MIT Quick Look Pipeline (QLP; Huang
et al. 2020), resulting in the simple aperture photometry (SAP) flux and the
QLP Kepler Spline SAP (KSPSAP; Vanderburg & Johnson 2014) flux. The 2-minute
and 20-second cadence photometry was produced by the Science Processing
Operations Center (SPOC; Jenkins et al. 2016) pipeline at the NASA Ames
Research Center, resulting in the SAP (Twicken et al., 2010; Morris et al.,
2020) flux and the Presearch Data Conditioning SAP (PDCSAP; Smith et al. 2012;
Stumpe et al. 2012, 2014) flux.

On 2019 June 21, the TESS data public website333https://tev.mit.edu/data/
announced the discovery of a 11.2-day TESS TOI (Guerrero et al. 2021),
TOI-815b. The SPOC detected the transit signature of TOI-815b in searches of
Sector 36, and a search of Sectors 36 and 63 with a noise-compensating matched
filter (Jenkins 2002, 2010, 2020), and the signature was fitted with an
initial limb-darkened transit model (Li et al. 2019) and passed all the
diagnostic tests presented in the Data Validation report (Twicken et al.
2018). In particular, the difference image centroiding test for the multi-
sector search located the host star within 1.4 $\pm$ 3.4 arcsec of the transit
source. Seven transits with a depth of 1301 $\pm$ 54 ppm and a duration of
3.06 $\pm$ 0.43 hours were identified in Sectors 9, 36, and 63 (Figure 15).
However, TOI-815 showed one additional transit in each sector with a transit
depth of 1004 $\pm$ 73 ppm and a duration of 2.53 $\pm$ 0.59 hours, suggesting
a second transiting companion. As presented in this work, with follow-up
observations using ESPRESSO and CHEOPS, we confirmed the planetary nature and
characterized the second planet.

For the analysis of the 30-minute cadence data we used the KSPSAP flux. For
the 2-minute and 20-second cadence light curves, we used the uncorrected SAP
flux and accounted for the systematic noise with the juliet package (Espinoza
et al. 2019) using Gaussian process (GP) models with an approximate Matérn 3/2
kernel.

In order to check the existence of contaminant sources, we plotted the target
pixel file (TPF; Figure 1) along with the aperture mask used for the SAP flux.
The plot was generated using tpfplotter (Aller et al. 2020). The apertures
used for extracting the light curves in all three sectors were contaminated by
TIC 102840237 (Section 2.1) and therefore we included a dilution coefficient
during the modeling of the TESS light curves. Our TESS light curve analysis is
described in more detail in Section 4.4.

Figure 1: TESS TPF of TOI-815 created with tpfplotter (Aller et al. 2020). The
orange pixels define the aperture mask used for extracting the photometry.
Additionally, the red circles indicate neighboring objects from the Gaia DR2
catalog, with the circle size corresponding to the brightness difference
compared to the targets (as indicated in the legend). Our target is marked
with a white cross. Pixel scale is 21$\arcsec$/pixel.

###  2.3 CHEOPS observations

CHEOPS is a 32 cm aperture ESA telescope dedicated to the characterization of
transiting exoplanets. It performs high-precision photometry in a broad
optical passband (330 to 1100 nm). The instrument is optimized for bright
stars, making it an ideal facility to observe small-amplitude transits created
by low-mass planets (e.g., Delrez et al. 2021; Leleu et al. 2021), or
characterize the minute emission signals of hot Jupiters at optical
wavelengths (Lendl et al., 2020; Krenn et al., 2023). Among various scientific
goals, the CHEOPS space mission is also suited to improve the radius precision
of known exoplanets discovered by TESS (Bonfanti et al., 2021a) by observing
additional transits and to recover the true period of double transit
candidates detected by TESS (e.g., Osborn et al. 2023; Ulmer-Moll et al. 2023;
Garai et al. 2023). TOI-815 was jointly observed by two programs within the
CHEOPS guaranteed time observation (GTO): one targeting improved radius
precision for multi-planet systems detected by NASA TESS (CHESS; PR0031) and
the other targeted on confirming the orbital periods of long-period candidates
found by TESS (DUOS; PR0048). The observations had an exposure time of 60 s,
typical duration of 5-7 orbits (8.2-11.4 hours), and achieved efficiencies
between 51 and 73% (e.g., due to Earth occultations, Earth’s stray light
contamination and South Atlantic Anomaly crossings). CHEOPS data are
automatically processed with an automatic aperture photometry pipeline (Hoyer
et al., 2020). We however re-extracted the photometry using point spread
function (PSF) photometry with the PIPE
package444https://github.com/alphapsa/pipe (Brandeker et al. 2022), which, due
to the large asymmetric PSF of CHEOPS, typically results in photometry with
less influenced by external factors such as companion stars, roll-angle
trends, etc. PIPE takes into account the flux contamination from nearby stars
by subtracting a synthetic image using the PSF and Gaia DR2 parameters for the
neighbor stars. Therefore, the dilution factor for the CHEOPS light curves was
fixed to one.

###  2.4 Ground-based photometry

The TESS pixel scale is $\sim 21\arcsec$ pixel-1 and photometric apertures
typically extend out to roughly 1$\arcmin$, generally causing multiple stars
to blend in the TESS aperture. To determine the true source of transit signals
in the TESS data, improve the transit ephemerides, and check the SPOC pipeline
transit depth after accounting for the crowding metric, we conducted
photometric ground-based follow-up observations with ASTEP and LCOGT of the
field around TOI-815 as part of the TESS Follow-up Observing Program
(TFOP)555https://tess.mit.edu/followup/ Sub Group 1 (Collins, 2019). We used
the TESS Transit Finder, which is a customized version of the Tapir software
package (Jensen, 2013), to schedule our transit observations.

####  2.4.1 ASTEP

We observed TOI-815 with ASTEP on 2021 April 04 but could only rule out an
ingress of TOI-815b that was, at the time, predicted to occur at BJD
2459309.02. Subsequent analysis (see Section 5.5) shows that as a result of
transit timing variations (TTVs), the prediction was incorrect, and that the
ingress should have started at $2459309.93\pm 0.0285$, later than the end of
this first series of observations. On 2022 September 13, using an improved
camera system (Dransfield et al., 2022; Schmider et al., 2022) we observed the
target again (Figure 2), with 15 second exposures, at wavelengths ranging from
about 700 to 1000 nm (Schmider et al. 2022). The data were processed on site
with an IDL-based aperture photometry pipeline (Abe et al., 2013; Mékarnia et
al., 2016). We detected an on-time 2.0 ppt transit of TOI-815b, using a 13.9
arcsec target aperture. While the ingress was clearly evident, the egress was
affected by sky brightening, with a Sun at about $12^{\circ}$ below the
horizon at end of the observation sequence.

Figure 2: Phase-folded TESS, ASTEP, and LCOGT light curves of TOI-815b (top
panel) and TESS light curves of TOI-815c (bottom panel). The data are binned
to 30 minutes (purple and orange circles).

####  2.4.2 LCOGT

We observed an intended full transit window of TOI-815b on 2021 February 18
(Figure 2) in Pan-STARRS $z$-short band using the LCOGT 1.0 m network node at
South Africa Astronomical Observatory (SAAO). However, after updating the
ephemeris from TESS Sector 36 data, we determined that the follow-up
observations were out of transit by approximately one day. Therefore, these
data are not considered further in this work. We observed a partial transit
window of TOI-815b on 2023 March 11 using the same band-pass and LCOGT network
node. The images were calibrated by the standard LCOGT BANZAI pipeline
(McCully et al., 2018) and differential photometric data were extracted using
AstroImageJ (Collins et al., 2017). We used circular photometric apertures
with radius $3\aas@@fstack{\prime\prime}9$. The target star aperture was
diluted by 0.85$\%$ by the neighbor star (Section 2.1). The best zero, one, or
two detrending vectors were retained if they decreased the Bayesian
information criterion (BIC) for a fit by at least two per detrend parameter.
We found that a proxy for sky transparency and the Y-centroid of the target
star on the detector detrending pair provided the best improvement to the
light curve fit that was justified by the BIC values.

###  2.5 Spectroscopic follow-up with ESPRESSO

We acquired 34 high-resolution spectroscopic observations of TOI-815 using
ESPRESSO on the 8.2 m Very Large Telescope (VLT) located in Paranal, Chile.
The observations were carried out between 2021 April 04 and 2022 December 04
as part of the observing programs 105.20P7.001, 109.23DX.001 and 110.2481.001
(PI: Bouchy), dedicated to the characterization of warm mini-Neptune
transiting exoplanets. The observations have an integration time ranging from
600 to 700 s, a median resolving power of 140,000 using 2 $\times$ 1 binning,
and a wavelength range of 380-788 nm. The RVs and activity indicators were
extracted using version 3.0.0. of the ESPRESSO pipeline, and we computed the
RVs by cross-correlating the Echelle spectra with a G2 numerical mask.

The ESPRESSO pipeline was devised to correct the residual atmosphere
dispersion, that is, after atmospheric dispersion corrector correction. This
reduces significantly the chromatic effects on the data. Out of the total
observations, six were identified as unreliable since the flux correction was
not applied and therefore were excluded from the global modeling. The average
uncertainty of the RV data is 0.68 m s-1 and the RMS is 0.74 m s-1. We report
the ESPRESSO RV measurements and their uncertainties, along with the full
width at half maximum (FWHM), bisector, contrast, S-index and H$\alpha$-index
in Table 4. The excluded data points are noted in the same Table. The RV time
series and the phase-folded RVs for TOI-815b and TOI-815c are shown in Figure
3.

Figure 3: Relative RV measurements with ESPRESSO and best-fit models for
TOI-815. $\it{Top}$: Time series of ESPRESSO RV measurements (in blue). The
complete inferred model, which comprises signals from two planets along with
the activity-induced signal, is represented by a continuous solid line.
$\it{Bottom}$: Phase-folded RVs for TOI-815b (left) and TOI-815c (right). In
all plots, the error bars in gray account for the estimated jitter
($\sigma_{w,\mathrm{ESPRESSO}}$).

###  2.6 High-resolution imaging

High-angular-resolution imaging is needed to search for nearby sources that
can contaminate the TESS photometry, resulting in an underestimated planetary
radius, or be the source of astrophysical false positives, such as background
eclipsing binaries. We searched for stellar companions to TOI-815 with speckle
imaging on the 4.1 m Southern Astrophysical Research (SOAR) telescope
(Tokovinin 2018) on 2019 July 14, observing in Cousins I-band, a similar
visible band-pass as TESS. This observation was sensitive to a 5.8-magnitude
fainter star at an angular distance of 1 arcsec from the target. More details
of the observations within the SOAR TESS survey are available in Ziegler et
al. (2020). The 5$\sigma$ detection sensitivity and speckle autocorrelation
functions from the observations are shown in Figure 4. No nearby stars were
detected within 3″of TOI-815 in the SOAR observations. The binary star
mentioned in Section 2.1 has a separation of 6$\aas@@fstack{\prime\prime}4$,
which places it outside SOAR’s field of view; as a result, it was not
detected.

Figure 4: SOAR speckle imaging (5$\sigma$ upper limits) of TOI-815 that rules
out the presence of stellar companions within 3$\arcsec$. The image inset
illustrates the speckle autocorrelation function.

##  3 Stellar characterization

###  3.1 Spectroscopic parameters

The stellar spectroscopic parameters ($T_{\mathrm{eff}}$, $\log g$,
microturbulence, [Fe/H]) were estimated using the ARES+MOOG methodology. The
methodology is described in detail in Sousa et al. (2021); Sousa (2014);
Santos et al. (2013); Sousa et al. (2008). For this, we used the latest
version of ARES666The last version, ARES v2, can be downloaded at
https://github.com/sousasag/ARES (Sousa et al., 2007, 2015) to consistently
measure the equivalent widths of selected iron lines on the combined ESPRESSO
spectrum of TOI-815. Because the star has an effective temperature below 5200
K, we used the appropriate list of iron lines presented in Tsantaki et al.
(2013). In this analysis we used a minimization process to find the ionization
and excitation equilibrium to converge for the best set of spectroscopic
parameters. This process makes use of a grid of Kurucz model atmospheres
(Kurucz, 1993a) and the radiative transfer code MOOG (Sneden, 1973). We also
derived a more accurate trigonometric surface gravity using recent Gaia data
following the same procedure as described in Sousa et al. (2021).

Using the stellar atmospheric parameters, we determined the abundances of Mg
([Mg/H] = $-0.03$ $\pm$ 0.09 dex) and Si ([Si/H] = $-0.03$ $\pm$ 0.06 dex),
closely following the classical curve-of-growth analysis method described in,
for example, Adibekyan et al. (2012, 2015). As for the stellar parameter
determination, we used ARES to measure the equivalent widths of the spectral
lines of these elements, and used a grid of Kurucz model atmospheres (Kurucz,
1993a) and the radiative transfer code MOOG (Sneden, 1973) to convert the
equivalent widths into abundances under assumption of local thermodynamic
equilibrium.

Finally, we estimated the projected rotational velocity, $v\sin i_{*}$, by
performing spectral synthesis around isolated iron lines in the region of Li
line at 6708 Å (discussed in Section 3.2). We used the code MOOG and the same
model atmosphere used for the abundance determination. The spectral lines are
very narrow and, despite the very high resolution of ESPRESSO spectra, we are
only able to set an upper limit of $v\sin i_{*}$ ¡ 1 km s-1. All the
parameters are presented in Table 1.

###  3.2 Mass, radius, and age

We determined the stellar radius of TOI-815 via a modified Markov chain Monte
Carlo (MCMC) infrared flux method (Blackwell & Shallis, 1977; Schanche et al.,
2020) by constructing spectral energy distributions using stellar atmospheric
models from two catalogs (Kurucz, 1993b; Castelli & Kurucz, 2003) and the
results of our spectral analysis as priors. By comparing synthetic derived
from these spectral energy distribution and the observed broadband photometry
in the following bandpasses: Gaia $G$, $G_{\mathrm{BP}}$, and
$G_{\mathrm{RP}}$, 2MASS $J$, $H$, and $K$, and WISE $W1$ and $W2$ (Skrutskie
et al., 2006; Wright et al., 2010; Gaia Collaboration et al., 2023) we derived
the bolometric flux of TOI-815. This is converted into effective temperature
and angular diameter that is subsequently combined with the offset-corrected
Gaia parallax Lindegren et al. (2021) to determine the stellar radius. To
allow for model uncertainties to propagate to our stellar radius, we used a
Bayesian modeling averaging of the radius posterior distributions produced
using the aforementioned stellar catalogs.

We determined the stellar mass $M_{\star}$ and age $t_{\star}$ by inputting
$T_{\mathrm{eff}}$, [Fe/H], and $R_{\star}$ (Table 1) along with their
uncertainties in the isochrone placement algorithm (Bonfanti et al., 2015,
2016). Following interpolation of the input parameters within precomputed
grids of PARSEC777PAdova and TRieste Stellar Evolutionary Code:
http://stev.oapd.inaf.it/cgi-bin/cmd v1.2S (Marigo et al., 2017) isochrones
and evolutionary tracks, we obtained $M_{\star}=0.776\pm 0.036\,M_{\odot}$ and
$t_{\star}=200_{-200}^{+400}$ Myr, where the error bars were computed by
adding 4% and 20% in quadrature to the internal uncertainties coming from the
interpolation scheme (as justified in Bonfanti et al., 2021a) to account for
the isochrone precision. On the one hand, the young age we derived is
apparently in disagreement with the low $v\sin{i}$ value. On the other hand,
an older main sequence star would have a smaller stellar radius differing more
than 3$\sigma$ from our $R_{\star}$ estimate.

To further assess the evolutionary stage of the star, we derived the Li
abundance by performing a spectral synthesis (Figure 16) using the same model
atmospheres and radiative transfer code as to obtain the spectroscopic
parameters and abundances (see Delgado Mena et al., 2014, for further
details). We obtain a value of A(Li)888${\rm A(Li)}=\log[N({\rm Li})/N({\rm
H})]+12$ = 1.15 dex, which is very high for stars with such cool temperatures;
their thick convective envelopes allow for the mixing of material into
interior regions hot enough to burn Li. As a consequence, Li is depleted at
early ages for cool stars. The comparison of this Li abundance to that of
stars of similar $T_{\mathrm{eff}}$ in open clusters also points to a very
young age. In particular, the stars around 4900 K in the Hyades (with an age
of $\sim$600 Myr) have A(Li) below 1 dex (see Fig. 5 in Sestito & Randich,
2005). Similar values are observed in Praesepe, with an age of $\sim$670 Myr
(Cummings et al., 2017). Therefore, TOI-815 should be younger than the Hyades
and Praesepe. On the other hand, for clusters of 150-250 Myr (e.g., M35, NGC
6475, and M34) analyzed in (Sestito & Randich, 2005; Anthony-Twarog et al.,
2018), stars with $T_{\mathrm{eff}}\sim$4900 K have Li around 1.5 dex. The
recent work on M48, a 420 Myr old cluster (Sun et al., 2023) shows that stars
with effective temperatures near 4900 K have lower Li values (around 1 dex)
than TOI-815, adding an additional constrain for an age younger than $\sim$400
Myr. The Li abundance of TOI-815 is shown with those clusters as comparison in
Figure 5.

To gain a more precise understanding of TOI-815’s age, we utilized a recently
developed kinematic-based method (Maciel et al., 2011; Almeida-Fernandes &
Rocha-Pinto, 2018) that relies on a higher probability of kinematic
disturbances and thus stellar Galactic velocity relative to known kinematic
families over the lifetimes of stars (Wielen, 1977; Nordström et al., 2004;
Casagrande et al., 2011). We compared the Galactic $U$, $V$, and $W$
velocities of TOI-815 to kinematic-age probability distributions bench-marked
using a sample of 9000 stars with well-known isochronal ages Almeida-Fernandes
& Rocha-Pinto (2018) and determine a nominal age of $\sim$470 Myr. Finally,
the gyrochronological relations of Barnes (2007) and the rotation period of
$P_{\rm rot}$ = 15.3 $\pm$ 1.2 days constrained from the photometry (Section
3.3) suggest an age of 660 $\pm$ 150 Myr.

Figure 5: Lithium abundance as a function of $T_{\rm eff}$. The green, blue,
and purple points represent the position of targets in the M35 (Sestito &
Randich, 2005; Anthony-Twarog et al., 2018), M48 (Sun et al. 2023), and
Praesepe (Cummings et al. 2017) clusters, respectively. TOI-815 is marked in
red.

###  3.3 Stellar rotation

Using the ESPRESSO RVs, we measured a median logR${}^{\prime}_{\mathrm{HK}}$ =
-4.67$\pm$ 0.03, which suggests that TOI-815 is a quite active (see Fig. 7 in
Henry et al., 1996) star. Visual inspection of the raw TESS transit light
curves shows a sinusoidal variation that is likely attributed to the stellar
activity (Figure 15). For our analysis, we used the generalized Lomb-Scargle
(GLS; Zechmeister & Kürster 2009) on the TESS SAP photometry of Sector 63 and
we identified a significant periodic signal with a period of $\sim$16.5 days,
which could be associated with the stellar rotation (Figure 17). TOI-815 was
also observed by the Wide Angle Search for Planets (WASP; Pollacco et al.
2006) transit survey in multiple years between 2006 and 2014, with the
observing season in each year spanning $\sim$ 120 nights. A total of 86 000
photometric data points was obtained using 200-mm, f/1.8 Canon lenses until
2012 and 85 mm f/1.2 Canon lenses after that. TOI-815 is by far the brightest
star in the extraction aperture. In the years 2008, 2012, and 2013 we detect a
significant periodicity with a period of 14.2-15.7 days. In each of those
years the estimated false alarm probability (FAP) is below 1%. By combining
the TESS Sector 63 and WASP photometric data, we estimate the stellar rotation
to be 15.3 $\pm$ 1.2 days.

We repeated the frequency analysis for the ESPRESSO RV measurements, as well
as for the Ca II H & K activity index (logR${}^{\prime}_{\mathrm{HK}}$) and
the cross-correlation-function asymmetry indicators (FWHM and bisector). The
GLS periodogram of the RV measurements shows a strong peak at the orbital
frequency of TOI-815c ($P_{\mathrm{orb,c}}$ $\sim$ 35 days) with a FAP ¡ 1%.
Following the subtraction of the outer planet’s signal, we found a significant
peak at the orbital period of TOI-815b ($P_{\mathrm{orb,b}}$ $\sim$ 11.2 days)
with a FAP $\approx$ 1%. Moreover, the stellar rotation period has no
counterpart in the GLS periodograms of the RVs or the activity indicators.

The most straightforward way to estimate the stellar inclination is to assume
solid body rotation (e.g., Borucki & Summers, 1984; Doyle et al., 1984):

$\sin i_{\star}=\frac{v\sin i_{\star}}{v}=\frac{v\sin i_{\star}}{2\pi
R_{\star}/P_{\mathrm{rot}}},$ (1)

where $P_{\rm rot}$ is the stellar equatorial rotation period. However,
directly using Eq. (1) to generate an $i_{\star}$ distribution is hazardous,
because $v\sin i_{\star}$ and $P_{\rm rot}$ are correlated quantities (Masuda
& Winn, 2020). To avoid such interdependence biases, we used the same
procedure as Attia et al. (2023) to derive the stellar inclination. We fitted
for $v\sin i_{\star}$ with a MCMC (using the emcee package, Foreman-Mackey et
al., 2013) based on the following formulation of Eq. (1),

$\centering v\sin i_{\star}=\frac{2\pi
R_{\star}}{P_{\mathrm{rot}}}\sqrt{1-\cos^{2}i_{\star}},\@add@centering$ (2)

and using a semi-Gaussian distribution for $v\sin i_{\star}$ (since we only
have an upper limit) as a constraint for the computation of the likelihood. We
set $R_{\star}$, $P_{\rm rot}$, and $\cos i_{\star}$ as independent jump
parameters with measurement-informed Gaussian priors on $R_{\star}$ and
$P_{\rm rot}$ (Table 1), and a uniform prior on $\cos i_{\star}$ (i.e.,
assuming an isotropic stellar inclination distribution). The number of walkers
and the burn-in phase are adjusted to ensure the convergence of the chains.
The ensuing probability distribution function (PDF) yields
$i_{\star}=32^{+15}_{-23}\leavevmode\nobreak\ {}^{\circ}$, the posterior
estimate corresponding to the median value and the error bars to the 68%
highest density interval. This result indicates that the star is spinning
faster ($v=2.5\pm 0.2$ km s-1) but we are observing it close to pole-on.

Additionally, we used the TESS photometric data to constrain the fraction of
stellar surface covered with spots. For this, we used the
SAGE999https://github.com/chakrah/sage tool to obtain flux variability models
for a given spot configuration. We fitted the observed variability using the
same procedure as described in Chakraborty et al. (2023), with uniform priors
on latitude, longitude and size of active regions. The wide priors allow spots
to be present over the entire stellar surface and the spot sizes vary from
small Sun-like spots (1∘) to large M-dwarf-type spots (15∘). To limit the
degeneracy on constraining the parameters of active regions, we fixed the
stellar inclination (to 32∘) and spot contrast in the TESS bandpass (to
0.2691). We iteratively increased the number of spots from 0 to 4 and found
that a 1-spot model is most probable and has the lowest BIC. We conclude that
at least 0.26${}^{+0.20}_{-0.05}$ % of the stellar surface is covered with
spots to match the observed photometric variability. We also estimated the
impact of these variations on the radius determination of the planets to be
below 0.31%.

Table 1: Stellar parameters for TOI-815.

| TOI-815 | Source
---|---|---
Identifiers |  |
TIC ID | 102840239 | TICv8
2MASS ID | J10232924-4350059 | 2MASS
Gaia ID | 5415648821879172096 |  Gaia DR3
TYC | 7721-01451-1 | Tycho-2
Astrometric parameters |  |
Right ascension (J2016), $\alpha$ |  10h 23m 29.25s |  Gaia DR3
Declination (J2016), $\delta$ |  $-43^{\circ}$ 50′ 05.84′′ |  Gaia DR3
Parallax (mas) |  16.825 $\pm$ 0.013 |  Gaia DR3
Distance (pc) |  59.437 $\pm$ 0.045 |  Gaia DR3
$\mu_{\rm{R.A.}}$ (mas yr-1) |  8.898 $\pm$ 0.011 |  Gaia DR3
$\mu_{\rm{Dec}}$ (mas yr-1) |  7.248 $\pm$ 0.013 |  Gaia DR3
Photometric parameters |  |
TESS (mag) |  9.360 $\pm$ 0.006 | TICv8
B (mag) |  11.145 $\pm$ 0.061 | Tycho-2
V (mag) |  10.217 $\pm$ 0.005 | Tycho-2
G (mag) |  9.9398 $\pm$ 0.0004 |  Gaia DR3
J (mag) |  8.531 $\pm$ 0.024 | 2MASS
H (mag) |  8.066 $\pm$ 0.029 | 2MASS
K (mag) |  7.999 $\pm$ 0.029 | 2MASS
Bulk parameters |  |
Spectral type | K3 |  Sec. 3.1
$T_{\rm eff}$ (K) |  4869 $\pm$ 77 |  Sec. 3.1
$R_{\star}$ ($\it{R_{\mathrm{\odot}}}$) |  0.770 $\pm$ 0.009 |  Sec. 3.2
$M_{\star}$ ($\it{M_{\mathrm{\odot}}}$) |  0.776 $\pm$ 0.036 |  Sec. 3.2
[Fe/H] (dex) |  $-0.09$ $\pm$ 0.05 |  Sec. 3.1
[Si/H] (dex) |  $-0.03$ $\pm$ 0.06 |  Sec. 3.1
[Mg/H] (dex) |  $-0.03$ $\pm$ 0.09 |  Sec. 3.1
$\log g_{*}$ (cm s-2) |  4.51 $\pm$ 0.04 |  Sec. 3.1
$v\sin i_{*}$ (km s-1) |  $<$ 1 |  Sec. 3.1
$P_{\rm rot}$ (days) |  15.3 $\pm$ 1.2 |  Sec. 3.3
$i_{\star}$ (∘) |  32${}^{+15}_{-23}$ |  Sec. 3.3
Age (Myr) | $200^{+400}_{-200}$ |  Sec. 3.2
A (Li) (dex) | $1.15\pm 0.05$ |  Sec. 3.2

  * $\bullet$

Sources: 1) TICv8 (Stassun et al., 2019) 2) 2MASS (Skrutskie et al., 2006) 3)
Gaia DR3 (Gaia Collaboration et al., 2021) 4) Tycho-2 (Høg et al., 2000).

Table 2: Fitted and derived parameters for TOI-815b and TOI-815c.

Parameter | TOI-815b | TOI-815c
---|---|---
Orbital period, $\it{P_{\mathrm{orb}}}$ (days) | $11.197259^{+0.000018}_{-0.000017}$ | $34.976145^{+0.000099}_{-0.000097}$
Planet radius, $\it{R_{\mathrm{P}}}$ ($\it{R_{\rm\mathrm{\oplus}}}$) | $2.94^{+0.05}_{-0.05}$ | $2.62^{+0.10}_{-0.09}$
Planet mass, $\it{M_{\mathrm{P}}}$ ($\it{M_{\rm\mathrm{\oplus}}}$) | $7.6^{+1.5}_{-1.4}$ | $23.5^{+2.4}_{-2.4}$
Planet density, $\rho_{\mathrm{P}}$ (g cm-3) |  1.64${}^{+0.33}_{-0.31}$ |  7.2${}^{+1.1}_{-1.0}$
Orbital inclination, $i$ (degrees) | $89.36^{+0.17}_{-0.14}$ | $89.107^{+0.026}_{-0.026}$
Impact parameter, b | $0.279^{+0.058}_{-0.073}$ | $0.839^{+0.015}_{-0.016}$
Semi-major axis, $\it{a}$ (au) | $0.0903^{+0.0018}_{-0.0019}$ | $0.193^{+0.004}_{-0.004}$
Transit duration, $T_{\mathrm{14}}$ (hours) | $3.379^{+0.023}_{-0.023}$ | $2.97^{+0.09}_{-0.10}$
Scaled semi-major axis, $\it{a/\mbox{$R_{*}$}}$ |  25.2${}^{+0.6}_{-0.6}$ |  53.9${}^{+1.3}_{-1.3}$
Equilibrium temperature(a), $T_{\mathrm{eq}}$ (K) | $686^{+13}_{-14}$ | $469^{+9}_{-9}$
Atmospheric scale height(b), $H$ (km) |  288${}^{+58}_{-54}$ | $51^{+7}_{-6}$
Insolation(c), $\it{S_{\mathrm{p}}}$ ($\it{S_{\rm\mathrm{\oplus}}}$) |  36.9${}^{+2.9}_{-2.9}$ |  8.03${}^{+0.64}_{-0.64}$
Restricted Jeans escape param.(d), $\Lambda$ |  28.6${}^{+5.7}_{-5.3}$ |  145${}^{+16}_{-16}$

  * $\bullet$

Notes: (a) The equilibrium temperature is calculated using $T_{\mathrm{eq}}$ =
$T_{\rm eff}$(1-A)${}^{1/4}\sqrt{\frac{R_{*}}{2\textit{a}}}$, assuming a Bond
albedo of A = 0. (b) The scale height is calculated using $H$ =
$\frac{k_{b}T_{\mathrm{eq}}}{\mu g}$ assuming a mean molecular weight of 2.3
g/mol. (c) Insolation is calculated using $\it{S_{\mathrm{p}}}$ =
$\frac{L_{*}}{4\pi\textit{a}^{2}}$. (d) The restricted Jeans escape parameter
is calculated using
$\Lambda=\frac{GM_{\mathrm{p}}m_{\mathrm{H}}}{k_{\mathrm{B}}T_{\mathrm{eq}}R_{\mathrm{p}}}$
(Fossati et al. 2017).

##  4 Photometric and RV analysis

###  4.1 TESS-only modeling

As mentioned in Section 2.2, visual inspection of the light curves of TOI-815
in Sectors 9 and 36 revealed two similar single transits incompatible with the
known P = 11.2 days inner planet. The two transits were separated by a gap of
734.5 days, which initially led to 41 separate period aliases between 17.49
days ($P_{\rm min}$) and 734.5 days ($P_{\rm max}$), where period on aliases
shorter than this value would have produced a detectable third transit in TESS
photometry. In order to determine the most likely periods, we modeled the
system using Monotools 101010https://github.com/hposborn/MonoTools (Osborn,
2022). This uses a period-agnostic fit of the two transit events, combined
with priors from period, eccentricity and system stability to determine a
marginalized posterior probability for each period. In the case of TOI-815c,
we found that the innermost aliases are most likely, with the 23 periods
shorter than P = 40 days having probabilities greater than 1$\%$ (see Figure
6).

###  4.2 CHEOPS-only modeling

We initially scheduled 13 of the most-likely period aliases of TOI-815c (all P
¡ 25 days) with CHEOPS at varying priorities. This resulted in five
observations in 2022, light curves for which are noted in Table 6 and can be
seen in Figure 18. The most important observation occurred on 2022 March 17
(visit 3); with this observation, due to its position exactly 367.25 days
after the last transit (i.e., $t_{1}+P_{\rm max}/2$), we were able to rule out
half of all aliases. The CHESS program (PR110048) also observed a single
observation of TOI-815b, which showed little to no measurable TTVs.
Observations resumed in 2023, with a further seven aliases scheduled, of which
five were observed. One such observation, on 2023 February 28 (visit 10), was
serendipitously during the transit of planet b, adding a second CHEOPS
transit. On 2023 March 19, TESS re-observed a third transit of TOI-815c.
However, this occurred exactly 734.5 days after the previously observed
transit (i.e., $t_{2}=t_{1}+P_{\rm max}$), and therefore no period information
was gained from the observation of this transit. We extracted a quick-look
light curve using TICA (Fausnaugh et al., 2020) in order to verify the
position of this third transit and updated the ephemeris of scheduled aliases.
Thanks to these observations, very few aliases with P $<$ 40 days remained at
this point. On 2023 April 23 (visit 11), a transit of TOI-815c at a unique
transit time for the 34.97 days alias was finally observed with CHEOPS. Once a
transit had been found all other observations were stopped. The CHEOPS light
curves of TOI-815b and c are presented in Figure 7.

###  4.3 ESPRESSO-only modeling

As discussed in Section 2.5, we conducted a spectroscopic follow-up of TOI-815
using ESPRESSO over a period of 20 months. In Figure 17 we show that based on
these observations we detected TOI-815c with a statistically significant
signal at 35 days (FAP ¡ 1%) and marginally detected TOI-815b at 11.2 days
(FAP $\sim$ 1%). After fixing the transit ephemerides, the signal of TOI-815c
and b was detected at a 10$\sigma$ and 5$\sigma$ level, respectively.

Figure 6: Marginalized probabilities for each of the period aliases of
TOI-815c as calculated by Monotools from TESS-data only. The triangle
indicates the true period of the planet.

###  4.4 Joint analysis

We performed an analysis of the planetary system around TOI-815 by combining
photometric and RV data. To jointly model the datasets, we used the juliet
software package, which is a Bayesian framework capable of modeling multi-
planet systems. Juliet is an openly accessible tool that enables the
simultaneous fitting of both transit models (using the batman package,
Kreidberg 2015) and RVs (via the radvel package, Fulton et al. 2018). It
incorporates GPs to model noise (via the celerite package; Foreman-Mackey et
al. 2017). To explore the parameter space, the code uses nested sampling
algorithms with dynesty (Speagle 2020) and conducts model comparison through
Bayesian evidence (lnZ) using MultiNest (Feroz et al. 2009) in conjunction
with the PyMultiNest (Buchner et al. 2014) Python software package.

Juliet employs an efficient parametrization technique for the transit model by
fitting the parameters r1 and r2, which are a combination of the planet-to-
star ratio (p) and impact parameter (b). This approach ensures a uniform
exploration of the (p, b) space. Furthermore, juliet estimates the stellar
density $\rho_{*}$, which, when combined with the orbital period, determines
the scaled semimajor axis ($\it{a/\mbox{$R_{*}$}}$).

To account for TESS photometric variability, we included a GP for Sectors 36
and 63 using a Matérn 3/2 kernel with hyperparameters amplitude
($\sigma_{\mathrm{GP}}$) and timescale ($\rho_{\mathrm{GP}}$) as shown in
Figure 15. The CHEOPS light curves exhibit correlations with certain
instrumental parameters like contamination by background stars (bg), centroid
movements (x, y) and the change in temperature of the telescope tube
$\Delta$T. Additionally, periodic noise features occur once per CHEOPS orbit
due to the satellite’s rolling motion around its pointing direction. To
account for these periodic instrumental effects, we detrended the light curves
by considering the sine or cosine of the roll angle ($\phi$). In our global
analysis, we incorporated linear models to account for both instrumental
trends and stellar variability. However, it was essential to select only the
relevant detrending parameters for each specific CHEOPS observation. To
achieve this, we employed the pycheops package (Maxted et al. 2022) that
provided us with the optimal combination of detrending terms for each visit.
The detrending terms for each CHEOPS visit are listed in Table 6.

The stellar density was fitted using a Gaussian prior based on the stellar
spectroscopic analysis conducted in Section 3. We derived the quadratic
stellar limb-darkening coefficients and their uncertainties for each
photometric filter used using the LDCU 111111https://github.com/delinea/LDCU
code (Deline et al. 2022). The LDCU code computes the limb-darkening
coefficients and their corresponding uncertainties by considering a set of
stellar intensity profiles and accounting for the uncertainties on the stellar
parameters. In our global analysis, we utilized the determined limb-darkening
coefficients from LDCU as Gaussian priors for all TESS, CHEOPS, LCOGT, and
ASTEP data.

The SPOC crowding metric calculated for TOI-815 in Sectors 36 and 63 is
$\sim$0.85. This indicates that, according to SPOC modeling after eliminating
background noise, $\sim$85$\%$ of the flux detected within the photometric
aperture originated from the target star. The remaining 15$\%$ was attributed
to various other sources, with source 2 (TIC 102840237; Section 2.1) being
particularly significant. To compensate for contamination by these additional
sources, we fixed the dilution factor for all the light curves to 0.85.

In order to prevent any potential Lucy-Sweeney bias in the eccentricity
measurement (Lucy & Sweeney 1971), we fixed the orbital eccentricity to zero.
However, to explore the possibility of noncircular orbits, we ran a separate
analysis without any constraints on the eccentricity. With the eccentricity
fitted, we found a value of e = $0.110^{+0.072}_{-0.065}$ for TOI-815b and
$0.035^{+0.064}_{-0.016}$ for TOI-815c. Therefore, the condition $e$ $>$
2.45$\sigma_{\mathrm{e}}$ is not satisfied, which suggests that the RV data
are compatible with a circular orbit. Additionally, in Table 5 we show that
the 3$\sigma$ upper limit on the eccentricity for TOI-815b and TOI-815c is
0.20 and 0.22, respectively.

Figure 7: CHEOPS light curves of TOI-815b (visits 4 and 10) and TOI-815c
(visit 11). The top light curves in the upper panel present the raw flux and
the best-fit de-correlation model. The detrending terms are presented in Table
6. The bottom light curves in the upper panel present the detrended flux, with
the best-fit transit model overlaid in black. The residuals of the models are
shown in the lower panel. The data are binned to 30 minutes (purple and orange
circles).

##  5 Discussion

Figure 8: Mass-radius diagram of small exoplanets (with radii ranging from 2
to 4 $\it{R_{\rm\mathrm{\oplus}}}$) with precise densities1 from the PlanetS
catalog2 orbiting FGK stars. The red triangles correspond to exoplanets with
stellar irradiation lower than 30 $\it{S_{\rm\mathrm{\oplus}}}$. The
composition lines of pure silicates (gray) from Zeng et al. (2016), Earth-like
planets (light-brown), and pure iron (brown) from Dorn et al. (2015) are
displayed. The purple and orange points represent TOI-815b and c,
respectively. Two composition lines (Aguichine et al. 2021) that incorporate
both water and terrestrial elements matching the equilibrium temperatures of
the two planets are plotted as purple dashed and orange dotted lines.

We report the discovery and characterization of two transiting mini-Neptune
planets around TOI-815, a young K3V star. TOI-815b is a 11.2 days period
planet with a radius of 2.94 $\pm$ 0.05 $\it{R_{\rm\mathrm{\oplus}}}$ and a
mass of 7.6 $\pm$ 1.5 $\it{M_{\rm\mathrm{\oplus}}}$. The outermost planet,
TOI-815c, has an orbital period of 35 days, a radius of 2.62 $\pm$ 0.10
$\it{R_{\rm\mathrm{\oplus}}}$ and a mass of 23.5 $\pm$ 2.4
$\it{M_{\rm\mathrm{\oplus}}}$. Based on the stellar parameters (Table 1), we
find that the semimajor axis of TOI-815b and TOI-815c are 0.0903 $\pm$ 0.0019
au and 0.193 $\pm$ 0.004 au, respectively. Assuming a zero albedo and full
heat redistribution ($f$ = 1), the equilibrium temperature of the inner planet
is $686^{+13}_{-14}$ K and its stellar insolation is 36.9 $\pm$ 2.9
$\it{S_{\rm\mathrm{\oplus}}}$. The outer planet has an equilibrium temperature
of $469^{+9}_{-9}$ K and receives a total amount of insolation equal to 8.03
$\pm$ 0.64 $\it{S_{\rm\mathrm{\oplus}}}$.

Both planets lie within the population of sub-Neptunes that are transiting FGK
stars, with 87 well-characterized exoplanet detections1 (including TOI-815b
and TOI-815c) from the PlanetS catalog2. TESS has contributed in this sample
with 46 discoveries during the past five years (Naponiello et al. 2023).
Moreover, TOI-815c adds to the population of warm mini-Neptune-sized planets
with low stellar irradiation (less than 30 $\it{S_{\rm\mathrm{\oplus}}}$);
with its inclusion, the total number of well-characterized detections is now
21. Figure 8 places TOI-815b and TOI-815c in the mass-radius diagram of small
exoplanets (2-4 $\it{R_{\rm\mathrm{\oplus}}}$) with precise densities orbiting
FGK stars (gray points). The red triangles correspond to exoplanets with
stellar irradiation lower than 30 $\it{S_{\rm\mathrm{\oplus}}}$. The
composition lines of pure silicates (Zeng et al. 2016), Earth-like planets,
and pure iron (Dorn et al. 2015) are displayed in gray, light-brown, and
brown, respectively. We also plot two other composition lines from Aguichine
et al. (2021) as dashed and dotted black lines. For TOI-815b, we plot a line
at 700 K, corresponding to its equilibrium temperature, with a composition of
45% of water and the rest as an Earth-like composition (32.5% iron-67.5%
silicates). Since TOI-815c is denser and less irradiated, we can see that it
lies on the composition lines with 10% water and an Earth-like composition at
450 K, its equilibrium temperature. Finally, we can say that if TOI-815b is
rich in water for the model under consideration, its atmosphere is inflated by
its irradiation, giving it a large radius and therefore a low density for a
quantity of water of around 45%. TOI-815c, on the other hand, would have a
lower water content of less than 10%, and its lower irradiation would not have
as much influence as its neighbor on its radius, which would explain its
higher density. Of course, this remains one possible model, and it is worth
remembering that the position of a planet in the mass-radius diagram does not
uniquely determine its composition. These planets could also have atmospheres
rich in H-He or heavier materials. A more detailed discussion of the internal
structures can be found in Section 5.3.

###  5.1 Density discrepancy of lowly and highly irradiated mini-Neptunes

TOI-815c, with a bulk density of 7.2 $\pm$ 1.1 g cm-3, becomes the densest
well-characterized warm mini-Neptune (2 - 4 $\it{R_{\rm\mathrm{\oplus}}}$ and
$\leq$ 30 $\it{S_{\rm\mathrm{\oplus}}}$), with GJ 143b ($\rho_{\mathrm{P}}$ =
7.0 $\pm$ 1.6 g cm-3 and $\it{S_{\mathrm{p}}}$ = 6.0 $\pm$ 0.4
$\it{S_{\rm\mathrm{\oplus}}}$; Dragomir et al. 2019) being the second. Also,
TOI-815c is the third densest well-characterized mini-Neptune (2 - 4
$\it{R_{\rm\mathrm{\oplus}}}$), the other two being K2-292b
($\rho_{\mathrm{P}}$ = 7.4 $\pm$ 1.6 g cm-3 and $\it{S_{\mathrm{p}}}$ = 72
$\pm$ 11 $\it{S_{\rm\mathrm{\oplus}}}$; Luque et al. 2019) and Kepler-411b
($\rho_{\mathrm{P}}$ = 10.3 $\pm$ 1.3 g cm-3 and $\it{S_{\mathrm{p}}}$ = 196
$\pm$ 9 $\it{S_{\rm\mathrm{\oplus}}}$; Sun et al. 2019). We analyzed the
differences in bulk density of planets with 2 - 4
$\it{R_{\rm\mathrm{\oplus}}}$ and $\leq$ 30 $\it{S_{\rm\mathrm{\oplus}}}$
(”warm” sub-Neptunes) and planets of the same size but with $\geq$ 30
$\it{S_{\rm\mathrm{\oplus}}}$ (”hot” sub-Neptunes). In the first group, we
have 21 planets with a median density of 3.9 g cm-3. In the second, we have 65
planets with a median density of 2.9 g cm-3. We performed a resampling method
to account for uncertainties in density measurements: a large number of new
datasets (N = 10, 000 samples) are drawn, which lie within the normal
distribution of the density measurements of the planets. For each of these new
datasets, the kernel density estimation (KDE) is calculated. Similar to
histograms, its aim is to estimate an unknown probability density function
from a sample of data but in a more continuous way. We then calculated the
mean and standard deviation of all the KDEs obtained. The result for the two
groups is shown in Figure 9. There is evidence suggesting that sub-Neptune-
size planets orbiting FGK stars with low stellar irradiation (”warm” sub-
Neptunes) exhibit a slightly higher bulk density compared to those exposed to
strong irradiation. To test whether the difference in densities of planets in
these two irradiation conditions is statistically significant, we utilized a
two-sample Kolmogorov-Smirnov test, which studies whether the two data samples
come from the same distribution. With a p-value of 0.026, we find that the
densities of hot and warm sub-Neptunes belong to different distributions with
over 95% confidence. The inclusion of TOI-815b and c in the samples plays an
important role in the statistical significance of this result, as they reduce
the p-value from 0.051 to 0.026, enabling us to reach the 95% confidence
interval. This difference in density could potentially be attributed to the
cooler atmospheres of these less irradiated planets, which are more compressed
and denser. However, such a pattern could be also linked to observational bias
since more massive planets at long periods are easier to characterize using
RVs. Therefore, further precise measurements of the mass of similar exoplanets
using precise RVs are necessary.

Figure 9: KDE for the two groups of sub-Neptunes (2-4
$\it{R_{\rm\mathrm{\oplus}}}$): with an irradiation above 30
$\it{S_{\rm\mathrm{\oplus}}}$ (gray) and below 30
$\it{S_{\rm\mathrm{\oplus}}}$ (red). The solid line represents the mean of the
KDEs calculated with the 10, 000 samples drawn, and the transparent region
represents the standard deviation.

###  5.2 Similarity in the density of multi-planet systems

Well-characterized exoplanets in multi-planet systems are especially
interesting since they allow the system’s architecture to be investigated.
Otegi et al. (2022) studied the similarity of planets in radii, masses,
densities, and period ratios within a multi-planet system and revealed that
planets tend to be more similar in radius than in mass. This trend could be
linked to the significant influence of the planetary radius on density
compared to mass, and consequently, on the overall planetary composition.
Interestingly, in their work, they observed a robust correlation between
densities of adjacent planets with no clear evidence of bi-modality.

In our study we used the NASA Exoplanet
Archive121212https://exoplanetarchive.ipac.caltech.edu/ (Akeson et al. 2013)
and narrowed down our selection to planets exhibiting mass and radius
uncertainties below $\sigma_{M}/M$ $\leq$ 50$\%$ and $\sigma_{R}/R$
$\leq$16$\%$. For planets with masses characterized by TTVs we used the
catalog presented by Hadden & Lithwick (2017) and discarded the less robust
(Kepler-25b and c, Marcy et al. 2014; Kepler-18c, Cochran et al. 2011). Our
final sample consists of 116 planets within 39 multi-planet systems. In Figure
10 we plot the density of a planet (j) within our sample against the density
of the next planet (j+1) farther from the star. The points are color-coded by
the host effective temperature. The Pearson correlation test resulted in a
p-value = 0.04 that suggests a statistically significant linear correlation
between densities. It is worth noting that planets orbiting M-dwarf stars tend
to be closer to the 1:1 line compared to FGK stars with a p-value = 0.03.
However, it is important to bear in mind that this observation is based on a
limited sample of 22 planets within nine multi-planet systems. We calculated
the similarity metric for the TOI-815 system using Eq. (2) of Millholland et
al. (2017):

$\centering\mathcal{D}_{X}=\sum_{i=1}^{N_{\mathrm{sys}}}\sum_{\begin{subarray}{c}j=1\\\
P_{j}<P_{j+1}\end{subarray}}^{N_{\mathrm{pl}}-1}\left|\log\frac{X_{j+1}}{X_{j}}\right|,\@add@centering$
(3)

with $X$ corresponding to the planetary radius or planetary mass, to be
$\mathcal{D}_{R}$ = 0.05 and $\mathcal{D}_{M}$ = 0.49. The metrics indicate
that the planets in the TOI-815 system are very similar in radii but rather
different in mass. Placing the TOI-815 system in Figure 10, we clearly see
that TOI-815 is one of the least uniform systems in density. Similar to
TOI-815, the Kepler-107 system (Bonomo et al. 2023) consists of two planets,
Kepler-107b and c, with nearly identical radii (1.536 $\pm$ 0.025
$\it{R_{\rm\mathrm{\oplus}}}$ and 1.597 $\pm$ 0.026
$\it{R_{\rm\mathrm{\oplus}}}$) but significantly different densities
($5.8^{+2.7}_{-2.6}$ g cm-3 and $13.5^{+2.9}_{-2.8}$ g cm-3). Bonomo et al.
(2019) showed that this density discrepancy can be explained by a giant impact
on Kepler-107c. As presented in Section 5.4, such a mechanism can explain the
large density of TOI-815c, which suggests that the two planets have formed in
a similar way.

Figure 10: Density of a planet (j) against the density of the next planet
(j+1; farther from the star). The TOI-815 system is indicated with a star
symbol.

###  5.3 Planetary composition and internal structure

As shown in Figure 8, the TOI-815 planetary system consists of two exoplanets
that are located above an Earth-like composition line in the M-R diagram. This
already indicates that both planets include a considerable amount of volatile
materials, and for TOI-815b, a sizable atmosphere.

To explore the range of possible interior structures, we used a nested
sampling algorithm (Buchner et al., 2014) on the four-layered interior model
(Dorn et al., 2017). This model contains an iron core, a rocky mantle, a water
layer, and a H-He atmosphere. For both planets, we ran two bracketing interior
models: one where we put no constraints on the layer masses (the free model),
and one where we set the water mass fraction to zero in order to put an upper
limit on the atmospheric mass fraction (the no-water model). Additionally, for