# Original Research By Young Twinkle Students (ORBYTS): Ephemeris Refinement
of Transiting Exoplanets II

Billy Edwards  Department of Physics and Astronomy, University College London,
London, WC1E 6BT, United Kingdom  Blue Skies Space Ltd., 69 Wilson Street,
London, EC2A 2BB, United Kingdom  Lara Anisman  Department of Physics and
Astronomy, University College London, London, WC1E 6BT, United Kingdom
Quentin Changeat  Department of Physics and Astronomy, University College
London, London, WC1E 6BT, United Kingdom  Mario Morvan  Department of Physics
and Astronomy, University College London, London, WC1E 6BT, United Kingdom
Sam Wright  Department of Physics and Astronomy, University College London,
London, WC1E 6BT, United Kingdom  Kai Hou Yip  Department of Physics and
Astronomy, University College London, London, WC1E 6BT, United Kingdom  Amiira
Abdullahi  London Academy of Excellence Stratford, Broadway House, 322 High
Street, Stratford, London, E15 1AJ, United Kingdom  Jesmin Ali  Hammersmith
Academy, 25 Cathnor Road, London, W12 9JD, United Kingdom  Clarry Amofa  Ark
Globe Academy, Harper Road, London, SE1 6AF, United Kingdom  Antony Antoniou
Preston Manor School, Cartlon Avenue East, Wembley, HA9 8NA, United Kingdom
Shahad Arzouni  Hammersmith Academy, 25 Cathnor Road, London, W12 9JD, United
Kingdom  Noeka Bradley  Forest School, Snaresbrook, London, E17 3PY, United
Kingdom  Dayanara Campana  Ark Globe Academy, Harper Road, London, SE1 6AF,
United Kingdom  Nandini Chavda  Preston Manor School, Cartlon Avenue East,
Wembley, HA9 8NA, United Kingdom  Jessy Creswell  Ark Globe Academy, Harper
Road, London, SE1 6AF, United Kingdom  Neliman Gazieva  Preston Manor School,
Cartlon Avenue East, Wembley, HA9 8NA, United Kingdom  Emily Gudgeon-
Sidelnikova  Hammersmith Academy, 25 Cathnor Road, London, W12 9JD, United
Kingdom  Pratap Guha  London Academy of Excellence Stratford, Broadway House,
322 High Street, Stratford, London, E15 1AJ, United Kingdom  Ella Hayden
London Academy of Excellence Stratford, Broadway House, 322 High Street,
Stratford, London, E15 1AJ, United Kingdom  Mohammed Huda  Hammersmith
Academy, 25 Cathnor Road, London, W12 9JD, United Kingdom  Hana Hussein
Hammersmith Academy, 25 Cathnor Road, London, W12 9JD, United Kingdom  Ayub
Ibrahim  Hammersmith Academy, 25 Cathnor Road, London, W12 9JD, United Kingdom
Chika Ike  Hammersmith Academy, 25 Cathnor Road, London, W12 9JD, United
Kingdom  Salma Jama  London Academy of Excellence Stratford, Broadway House,
322 High Street, Stratford, London, E15 1AJ, United Kingdom  Bhavya Joshi
Preston Manor School, Cartlon Avenue East, Wembley, HA9 8NA, United Kingdom
Schet Kc  Preston Manor School, Cartlon Avenue East, Wembley, HA9 8NA, United
Kingdom  Paris Keenan  Ark Globe Academy, Harper Road, London, SE1 6AF, United
Kingdom  Charlie Kelly-Smith  Hammersmith Academy, 25 Cathnor Road, London,
W12 9JD, United Kingdom  Aziza Khan  Preston Manor School, Cartlon Avenue
East, Wembley, HA9 8NA, United Kingdom  George Korodimos  Hammersmith Academy,
25 Cathnor Road, London, W12 9JD, United Kingdom  Jiale Liang  London Academy
of Excellence Stratford, Broadway House, 322 High Street, Stratford, London,
E15 1AJ, United Kingdom  Guilherme Luis Nogueira  London Academy of Excellence
Stratford, Broadway House, 322 High Street, Stratford, London, E15 1AJ, United
Kingdom  Neil Martey-Botchway  Ark Globe Academy, Harper Road, London, SE1
6AF, United Kingdom  Asan Masruri  Preston Manor School, Cartlon Avenue East,
Wembley, HA9 8NA, United Kingdom  Osuke Miyamaru  Hammersmith Academy, 25
Cathnor Road, London, W12 9JD, United Kingdom  Ismail Moalin  Preston Manor
School, Cartlon Avenue East, Wembley, HA9 8NA, United Kingdom  Fabiana
Monteiro  Ark Globe Academy, Harper Road, London, SE1 6AF, United Kingdom
Adrianna Nawrocka  Hammersmith Academy, 25 Cathnor Road, London, W12 9JD,
United Kingdom  Sebri Musa  Ark Globe Academy, Harper Road, London, SE1 6AF,
United Kingdom  Lilith Nelson  Hammersmith Academy, 25 Cathnor Road, London,
W12 9JD, United Kingdom  Isabel Ogunjuyigbe  Hammersmith Academy, 25 Cathnor
Road, London, W12 9JD, United Kingdom  Jaymit Patel  Preston Manor School,
Cartlon Avenue East, Wembley, HA9 8NA, United Kingdom  Joesph Pereira  Forest
School, Snaresbrook, London, E17 3PY, United Kingdom  James Ramsey
Hammersmith Academy, 25 Cathnor Road, London, W12 9JD, United Kingdom  Billnd
Rasoul  Ark Globe Academy, Harper Road, London, SE1 6AF, United Kingdom  Tumo
Reetsong  Ark Globe Academy, Harper Road, London, SE1 6AF, United Kingdom
Haad Saeed  Hammersmith Academy, 25 Cathnor Road, London, W12 9JD, United
Kingdom  Cameron Sander  Forest School, Snaresbrook, London, E17 3PY, United
Kingdom  Matthew Sanetra  Hammersmith Academy, 25 Cathnor Road, London, W12
9JD, United Kingdom  Zainab Tarabe  Preston Manor School, Cartlon Avenue East,
Wembley, HA9 8NA, United Kingdom  Milcah Tareke  Hammersmith Academy, 25
Cathnor Road, London, W12 9JD, United Kingdom  Nazifa Tasneem  London Academy
of Excellence Stratford, Broadway House, 322 High Street, Stratford, London,
E15 1AJ, United Kingdom  Meigan Teo  Forest School, Snaresbrook, London, E17
3PY, United Kingdom  Asiyah Uddin  London Academy of Excellence Stratford,
Broadway House, 322 High Street, Stratford, London, E15 1AJ, United Kingdom
Kanvi Upadhyay  Preston Manor School, Cartlon Avenue East, Wembley, HA9 8NA,
United Kingdom  Kaloyan Yanakiev  Preston Manor School, Cartlon Avenue East,
Wembley, HA9 8NA, United Kingdom  Deepakgiri Yatingiri  Preston Manor School,
Cartlon Avenue East, Wembley, HA9 8NA, United Kingdom  William Dunn
Department of Physics and Astronomy, University College London, London, WC1E
6BT, United Kingdom  Anatasia Kokori  Department of Physics and Astronomy,
University College London, London, WC1E 6BT, United Kingdom  Birkbeck,
University of London, Malet Street, London, WC1E 7HX, United Kingdom  Angelos
Tsiaras  Department of Physics and Astronomy, University College London,
London, WC1E 6BT, United Kingdom  Edward Gomez  Las Cumbres Observatory, 6740
Cortona Dr, Suite 102, Goleta, CA 93117, USA  Cardiff University, School of
Physics and Astronomy, 11-14 The Parade, Cardiff, CF24 3AA, United Kingdom
Giovanna Tinetti  Department of Physics and Astronomy, University College
London, London, WC1E 6BT, United Kingdom  Blue Skies Space Ltd., 69 Wilson
Street, London, EC2A 2BB, United Kingdom  Jonathan Tennyson  Department of
Physics and Astronomy, University College London, London, WC1E 6BT, United
Kingdom  Blue Skies Space Ltd., 69 Wilson Street, London, EC2A 2BB, United
Kingdom

(Received May 30; 2020; Accepted July 6, 2020)

###### Abstract

We report follow-up observations of four transiting exoplanets, TRES-2 b,
HAT-P-22 b, HAT-P-36 b and XO-2 b, as part of the Original Research By Young
Twinkle Students (ORBYTS) programme. These observations were taken using the
Las Cumbres Observatory Global Telescope Network’s (LCOGT) robotic 0.4 m
telescopes and were analysed using the HOlomon Photometric Software (HOPS).
Such observations are key for ensuring accurate transit times for upcoming
telescopes, such as the James Webb Space Telescope (JWST), Twinkle (Edwards et
al., 2019) and Ariel (Tinetti et al., 2018), which may seek to characterise
the atmospheres of these planets. The data have been uploaded to ExoClock and
a significant portion of this work has been completed by secondary school
students in London.

††journal: RNAAS

##  1 Introduction

Transit photometry has yielded thousands of exoplanets over the last two
decades. While the time for the next time is well known just after discovery,
the accuracy of this prediction degrades over time to due to the accumulation
of errors on the period. Unless the ephemerides are well known, upcoming
facilities will be unable to characterise the atmosphere of a planet.
Maintaining accurate orbital ephemerides is becoming increasingly difficult
due to the sheer number of targets and will require a coordinated effort by
many groups and telescope networks.

The Exoplanet Transit Database (ETD, Poddaný et al. (2010)) provides a
platform for users to upload observations and citizen scientists have
contributed thousands of light curves. These have been used in a number of
studies (e.g. Mallonn et al., 2019; Edwards et al., 2020).
ExoClock111www.exoclock.space endeavours to stimulate engagement with citizen
scientists who have access to telescopes, allowing them to contribute to the
upcoming ESA Ariel mission. The site ranks the potential Ariel targets from
Edwards et al. (2019), prioritising those that have a large uncertainty in
their next transit time and those which have not recently been observed. These
can then be filtered by the location of the observer and the telescope size,
providing a list of exoplanet transits which would be observable in the near
future. In collaboration with ExoClock, the Exoplanet Watch project is another
coordinated effort to collect follow-up observations of exoplanet transits
with small telescopes, organised in the USA. Exoplanet Watch will deliver
similar information, focused on targets that will be observed by JWST (Zellem
et al., 2019, 2020).

Original Research By Young Twinkle Students (ORBYTS) is an educational
programme in which secondary school pupils work on original research linked to
the Twinkle Space Mission under the tuition of PhD students and other young
scientists (McKemmish et al., 2017a). Previous projects have included
calculating accurate molecular transition frequencies (Chubb et al., 2018;
McKemmish et al., 2017b; Darby-Lewis et al., 2019), studying planetary aurorae
(Wibisono et al., 2020) and spectral studies of the composition of
protostellar regions (Holdship et al., 2019).

During this project, which follows on from that detailed in Edwards et al.
(2020), the students selected suitable follow-up targets, scheduled
observations and analysed the observational data with the aim of refining
planetary transit parameters.

##  2 Methods

We selected medium and high priority targets from the ExoClock website and
obtained transit observations of TRES-2 b (O’Donovan et al., 2006), HAT-P-22 b
(Bakos et al., 2011), HAT-P-36 b (Bakos et al., 2012) and XO-2 b (Burke et
al., 2007). The observations were taken using LCOGT’s network of 0.4 m
telescopes (Brown et al., 2013) and analysed using
HOPS222https://github.com/ExoWorldsSpies/hops/. HOPS aligns the frames and
normalises the flux of the target star by using selected comparison stars
before performing a transit fit with pylightcurve (Tsiaras et al., 2016)

During the fitting, the only free parameters were the planet-to-star ratio
(Rp/Rs) and the transit mid time (T0). The other parameters were fixed to the
literature values from Öztürk & Erdem (2019); Bakos et al. (2011); Wang et al.
(2019); Bonomo et al. (2017) for TRES-2 b, HAT-P-22 b, HAT-P-36 b and XO-2 b
respectively and the limb darkening coefficients calculated from Claret et al.
(2013).

##  3 Results and Future Work

The observed transits and recovered mid-times are shown in Figure 1. For
HAT-P-36 b and XO-2 b, the literature ephemeris predicted the mid-times both
precisely and accurately, suggesting these ephemerides can be confidently used
for planning future observations. ExoClock’s algorithm had flagged as they had
not been observed for a significant amount of time. The ephemerides of TRES-2
b were also very precise but potentially less accurate as they do not agree
with our fitted mid time. A deeper analysis, with all literature data and
potentially additional observations, is needed to confirm this.

The data for HAT-P-22 b is noticeably poorer due to the brightness of the
target and because there were no other stars of a similar brightness within
the telescope’s field of view. The LCOGT network allows users to defocus the
telescope, increasing the saturation time, and this technique would be useful
for future observations. These are needed as the literature uncertainties on
this planet are relatively high and, although consistent to 1$\sigma$, our
observation appears to show a shift in the transit time.

Our data have been uploaded to ExoClock and, along with observations from
other users, will help ensure the ephemerides of these planets are well known
for potential atmospheric studies. Programmes which incorporate public
engagement, educational outreach or citizen scientists have a rich literature
of successful projects in the exoplanetary field (e.g. Lintott et al., 2013;
Wang et al., 2013; Baluev et al., 2015; Eisner et al., 2020; Nair & Varghese,
2020) and future ORBYTS projects will continue to collect transit data to help
prepare for upcoming space-based telescopes.

Figure 1: Transit observations obtained of TRES-2 b, HAT-P-22 b, HAT-P-36 b
and XO-2 b. In each case, the data is shown in black with the best-fit transit
model in red. The blue filled region indicates the predicted transit mid-time
based upon literature ephemeris while the red denotes the fitted mid-time,
both with 1$\sigma$ errors. The mid-times were converted to BJDTDB using the
tool from Eastman et al. (2010).

##  4 Acknowledgements

BE is the PI of the LCOGT Global Sky Partners 2020 project “Refining Exoplanet
Ephemerides” and thanks the LCOGT network and its coordinators for providing
telescope access. We are also thankful to the teachers at each of these
schools, Phil Aspery, Matt Densham, Brook Edgar, Sarah Horn and Ehsan Pedram,
for their support. BE acknowledges funding from the STFC grant ST/S002634/1.

## References

  * Bakos et al. (2011) Bakos, G. Á., Hartman, J., Torres, G., et al. 2011, ApJ, 742, 116
  * Bakos et al. (2012) Bakos, G. Á., Hartman, J. D., Torres, G., et al. 2012, AJ, 144, 19
  * Baluev et al. (2015) Baluev, R. V., Sokov, E. N., Shaidulin, V. S., et al. 2015, MNRAS, 450, 3101
  * Bonomo et al. (2017) Bonomo, A. S., Desidera, S., Benatti, S., et al. 2017, A&A, 602, A107
  * Brown et al. (2013) Brown, T. M., Baliber, N., Bianco, F. B., et al. 2013, PASP, 125, 1031
  * Burke et al. (2007) Burke, C. J., McCullough, P. R., Valenti, J. A., et al. 2007, ApJ, 671, 2115
  * Chubb et al. (2018) Chubb, K. L., Joseph, M., Franklin, J., et al. 2018, J. Quant. Spec. Radiat. Transf., 204, 42
  * Claret et al. (2013) Claret, A., Hauschildt, P. H., & Witte, S. 2013, A&A, 552, A16
  * Darby-Lewis et al. (2019) Darby-Lewis, D., Shah, H., Joshi, D., et al. 2019, Journal of Molecular Spectroscopy, 362, 69
  * Eastman et al. (2010) Eastman, J., Siverd, R., & Gaudi, B. S. 2010, PASP, 122, 935
  * Edwards et al. (2019) Edwards, B., Mugnai, L., Tinetti, G., Pascale, E., & Sarkar, S. 2019, The Astronomical Journal, 157, 242
  * Edwards et al. (2019) Edwards, B., Rice, M., Zingales, T., et al. 2019, Experimental Astronomy, 47, 29
  * Edwards et al. (2020) Edwards, B., Changeat, Q., Yip, K. H., et al. 2020, MNRAS, doi:10.1093/mnras/staa1245
  * Eisner et al. (2020) Eisner, N. L., Barragán, O., Aigrain, S., et al. 2020, MNRAS, 494, 750
  * Holdship et al. (2019) Holdship, J., Viti, S., Codella, C., et al. 2019, The Astrophysical Journal, 880, 138
  * Lintott et al. (2013) Lintott, C. J., Schwamb, M. E., Barclay, T., et al. 2013, AJ, 145, 151
  * Mallonn et al. (2019) Mallonn, M., von Essen, C., Herrero, E., et al. 2019, A&A, 622, A81
  * McKemmish et al. (2017a) McKemmish, L. K., Chubb, K. L., Rivlin, T., et al. 2017a, Astronomy and Geophysics, 58, 5.11
  * McKemmish et al. (2017b) McKemmish, L. K., Masseron, T., Sheppard, S., et al. 2017b, ApJS, 228, 15
  * Nair & Varghese (2020) Nair, S., & Varghese, J. 2020, Research Notes of the AAS, 4, 82
  * O’Donovan et al. (2006) O’Donovan, F. T., Charbonneau, D., Mand ushev, G., et al. 2006, ApJ, 651, L61
  * Öztürk & Erdem (2019) Öztürk, O., & Erdem, A. 2019, MNRAS, 486, 2290
  * Poddaný et al. (2010) Poddaný, S., Brát, L., & Pejcha, O. 2010, New A, 15, 297
  * Tinetti et al. (2018) Tinetti, G., Drossart, P., Eccleston, P., et al. 2018, Experimental Astronomy, 46, 135
  * Tsiaras et al. (2016) Tsiaras, A., Waldmann, I., Rocchetto, M., et al. 2016, ascl:1612.018
  * Wang et al. (2013) Wang, J., Fischer, D. A., Barclay, T., et al. 2013, ApJ, 776, 10
  * Wang et al. (2019) Wang, Y.-H., Wang, S., Hinse, T. C., et al. 2019, AJ, 157, 82
  * Wibisono et al. (2020) Wibisono, A., Branduardi-Raymont, G., Dunn, W., et al. 2020, Journal of Geophysical Research: Space Physics, 125, e2019JA027676
  * Zellem et al. (2019) Zellem, R. T., Biferno, A., Ciardi, D. R., et al. 2019, arXiv e-prints, arXiv:1903.07716
  * Zellem et al. (2020) Zellem, R. T., Pearson, K. A., Blaser, E., et al. 2020, PASP, 132, 054401