Lux, Mugrauer & Bischoff

Oliver Lux, Astrophysikalisches Institut und Universitäts-Sternwarte Jena,
Schillergäßchen 2, D-07745 Jena, Germany.

# The deep eclipses of RW Aur revisited by long-term photometric and
spectroscopic monitoring††thanks: Based on observations obtained with
telescopes of the University Observatory Jena, which is operated by the
Astrophysical Institute of the Friedrich-Schiller-University.

Oliver Lux  Markus Mugrauer  Richard Bischoff  Astrophysikalisches Institut
und Universitäts-Sternwarte Jena<EMAIL_ADDRESS>
(2023; 2023; 2023)

###### Abstract

RW Aurigae is a young stellar system containing a classical T Tauri star as
the primary component. It shows deep, irregular dimmings, first detected in
2010. At the University Observatory Jena, we carried out optical follow-up
observations. We performed multiband (BVRI) photometry of the system with the
Cassegrain-Teleskop-Kamera II and the Schmidt-Teleskop-Kamera between
September 2016 and April 2019, as well as spectroscopy, using the Fibre Linked
ÉCHelle Astronomical Spectrograph between September 2016 and April 2018. We
present the apparent photometry of RW Aur, which is consistent with and
complementary to photometric data from the American Association of Variable
Star Observers. The V-band magnitude of RW Aur changed by up to three
magnitudes during the timespan of our monitoring campaign. For the observing
epochs 2016/2017 and 2017/2018 we report a decreasing brightness, while in the
epoch 2018/2019 the system remained in a relatively constant bright state. In
the color-magnitude diagram, we see that RW Aur lies close to a track for grey
extinction. The spectra show a decreasing equivalent width of the
$\rm{H}\alpha$ emission line for decreasing brightness, whereas the equivalent
width of the $[\rm{O}I]$ line increases, indicating an increased outflow
activity during the obscuration. Both gives further evidence for the favored
theory that the obscurations are caused by a hot dusty wind emerging from the
inner disk.

###### keywords:

stars: individual (RW Aur) – stars: variables: T Tauri stars – techniques:
photometric, spectroscopic

††articletype: Article Type

##  1 Introduction

Figure 1: The light curve of RW Aur in optical filters between 2006/04/01 and
2023/04/07, taken from AAVSO. Blue stars give B-band, green squares V-band,
red diamonds R-band and purple hexagons I-band magnitudes. Black triangles
indicate upper limits. The dark-grey dashed lines mark the beginning and end
of our photometric monitoring campaign, respectively.

T Tauri stars (TTS) are low-mass pre-main sequence stars with masses up to
about 2 $\rm{M}_{\odot}$ (Joy, 1945; Shenavrin ., 2015), which are usually
surrounded by circumstellar disks made of gas and dust. They show significant
variability on different timescales, which is mainly caused by strong surface
magnetic fields leading to cool spots, as well as mass accretion leading to
hot spots (Herbst ., 1994). TTS which show both phenomena are usually referred
to as classical TTS, while weak-line TTS lack the accretion activity.

Table 1: Stellar parameters of RW Aur A.

Parameter | Value | Reference
---|---|---
RA (J2000) | 05 h 07 m 49.6 s | 1
Dec (J2000) |  $+$30 d 24 m 05 s | 1
$\mu_{\text{RA}}$ |  $4.906\pm 0.329$ mas/yr | 1
$\mu_{\text{Dec}}$ |  $-24.578\pm 0.255$ mas/yr | 1
$\varpi$ |  $5.4541\pm 0.3324$ mas | 1
Distance |  $185\pm 10$ pc | 2
Mass | $1.34\pm 0.18\,\rm{M}_{\odot}$ | 3
SpT | $\rm{K}2\pm 2$ | 4
$T_{\rm eff}$ |  $5040_{-420}^{+240}$ K | 5
log $L[\rm{L}_{\odot}]$ | $0.23\pm 0.14$ | 3
X-ray count rate | $0.020\pm 0.009\,\rm{s}^{-1}$ | 6
Accretion rate | $1.5\text{ - }2.0\times 10^{-8}\,\rm{M}_{\odot}/\rm{yr}$ | 7,8
Age |  $3\pm 1$ Myr | 9

(1) Gaia Collaboration . (2022), (2) Bailer-Jones . (2021), (3) White Ghez
(2001), (4) White Hillenbrand (2004), (5) Pecaut Mamajek (2013), (6) König .
(2001, ROSAT HRI), (7) Ingleby . (2013), (8) Koutoulaki . (2019), (9) Dodin .
(2020)

Table 2: Observing log for our photometric monitoring of RW Aur. We list for each observing epoch, the covered span of time, the used instrument, the number of nights when observations were carried out ($N_{\text{Obs}}$), the detector integration times ($DIT$ in units of seconds), and the diameter in pixel ($\diameter$) of the used apertures in the B-, V-, R-, and I-band. Epoch | Dates | Instrument | $N_{\text{Obs}}$ | $DIT(\rm{B})$ | $\diameter$ | $DIT(\rm{V})$ | $\diameter$ | $DIT(\rm{R})$ | $\diameter$ | $DIT(\rm{I})$ | $\diameter$
---|---|---|---|---|---|---|---|---|---|---|---
I | 2016/09/07 - 2017/04/20 | CTK-II | 19 | 90 | 5 | 30 | 5 | 30 | 5 | 30 | 5
IIa | 2017/09/05 - 2017/09/19 | STK | 3 | 30 | 4 | 10 | 4 | 10 | 4 | 10 | 5
| 2017/10/15 - 2018/01/15 | STK | 6 | 30 | 4 | 5.0 | 4 | 5.0 | 4 | 5.0 | 5
IIb | 2018/01/30 - 2018/03/29 | CTK-II | 10 | 90 | 4 | 30 | 4 | 30 | 4 | 30 | 4
III | 2018/08/16 - 2018/11/18 | STK | 30 | 30 | 6 | 5.0 | 5 | 5.0 | 5 | 5.0 | 5
| 2019/01/18 - 2019/04/21 | STK | 29 | 10 | 6 | 2.5 | 5 | 2.5 | 5 | 2.5 | 5

RW Aurigae (RW Aur) was one of the first stars to be identified as a TTS (Joy,
1945). The star is a target for photometric observations for more than 50
years and long known to be variable. Its basic stellar parameters are
summarized inTable 1. RW Aur is located in the Taurus-Auriga star forming
region at a distance of about $185\pm 10$ pc (Bailer-Jones ., 2021),
consistent with the Gaia DR3 parallax distance of $183\pm 11$ pc (Gaia
Collaboration ., 2022). Today it is known to be a multiple system, where the
primary star, RW Aur A, is a classical TTS with spectral type $\rm{K}2\pm 2$
(White Hillenbrand, 2004) and a mass of $1.34\pm 0.18\,\rm{M}_{\odot}$ (White
Ghez, 2001). The secondary star in the system, RW Aur B, is separated from its
primary by about 1.49 arcsec (based on Gaia DR3 astrometry, Gaia Collaboration
., 2022), which corresponds to a projected separation of about 270 au. RW Aur
B is a weak-line TTS, which has a spectral type $\rm{K}6\pm 1$ (White
Hillenbrand, 2004) and a mass of about 0.8 $\rm{M}_{\odot}$ (Shenavrin .,
2015). It was investigated in detail and classified as an UX Ori type variable
star by Dodin . (2020). Ghez . (1993) reported the discovery of a tertiary
component, RW Aur C, which is probably a substellar companion with a mass of
less than 0.045 $\rm{M}_{\odot}$ (Ghez ., 1997). It exhibits an angular
separation to RW Aur B of 0.12 arcsec (or 20 au of projected separation).
Hence, RW Aur is a hierarchical triple system.

Figure 1shows the light curve of RW Aur between April 2006 and April 2023,
created with the light curve generator from the American Association of
Variable Star Observers (AAVSO111Online available at: https://www.aavso.org/).
It can be seen that the system usually has $V=10.5\pm 1$ mag, where the
photometric variations happen on a time-scale of days (Shenavrin ., 2015). RW
Aur is very active, showing strong spectral signatures of accretion and winds
(Petrov ., 2001; Alencar ., 2005; Bozhinova ., 2016).

In 2010, the system started to show an unusual behavior, when it faded by
about 2 mag compared to its regular state. This dimming lasted for about half
a year and was followed by an even longer and deeper dimming (about 3 mag)
between 2014 and 2016. After that, until 2020, RW Aur showed strong,
unpredictable variability with amplitudes almost as in the second eclipse, but
returning to the bright state at least once per year. Since 2020, the
brightness becomes more stable, however on a slightly fainter level compared
to the original brightness and a local peak in the observing epoch 2018/2019.
The physical nature of these obscurations, and if they are all caused by the
same occulting body, is not yet fully understood.

Cabrit . (2006) discovered a trailing arm around RW Aur A, which was later
explained to be produced during the periastron passage of RW Aur B (Dai .,
2015), which happened about 500 years ago (Koutoulaki ., 2019). According to
Berdnikov . (2017), this encounter also caused a rearrangement of the inner
disk and also triggered the jet, which is observed to emerge from RW Aur A
(Hirth ., 1994). Rodriguez . (2013) suggested that the tidal arm caused the
occultation observed between 2010 and 2011.

However, Shenavrin . (2015) discovered that RW Aur shows an IR excess during
the eclipses, indicating hot dust in the line of sight (with a temperature of
about 500 to 700 K, Koutoulaki ., 2019). This would not be expected for an
occultation by a tidally induced spiral arm, which would be too distant to the
star. Due to the inclination of the outer circumstellar disk ($i=45\text{ -
}60\,^{\circ}$, Facchini ., 2016), the occultations cannot be caused by the
outer parts of the disk. Petrov . (2015) suggested that a wind emanating from
the star or the inner disk could carry large (about 1 $\mu$m) dust grains into
the line of sight, which would account for the observed grey extinction (e.g.
Antipin . 2015). The photometric and spectroscopic observations by Bozhinova .
(2016), focusing on the second deep eclipse, supported this scenario of a hot,
dusty wind.

Facchini . (2016) suggested that the occultations might be caused by a
misaligned or warped inner disk, resulting either from the tidal encounter
with RW Aur B or from a yet unknown (sub-)stellar companion around RW Aur A.
Facchini . (2016) and Koutoulaki . (2019) found unchanged signs of accretion
during the dimming, further indicating that the occulting dust layer lies
close to the primary star (within about 1 au) and only obscures the inner 0.05
to 0.1 au of the system (Koutoulaki ., 2019).

A further mechanism to explain the perturbations of the inner disk was
presented by Günther . (2018), who performed X-ray observations and detected
an increase of the coronal iron abundance of more than an order of magnitude
during the dim state. They suggested that a breakup of planetesimals or a
terrestrial planet could have enriched the inner disk with iron-rich dust,
which would then be accreted by RW Aur A, increasing the stellar iron
abundance. This scenario is further supported by Lisse . (2022), who presented
evidence for planetesimal formation, migration and destruction from IR
spectroscopy.

##  2 Observations and data reduction

We started the photometric and spectroscopic monitoring campaign in August
2016 after our discovery of the re-brightening of RW Aur after the second deep
eclipse (Scholz ., 2016). Observations of RW Aur were taken between 31 August
2016 and 21 April 2019 with instruments operated at the University Observatory
Jena, which is located near the small village Großschwabhausen about 10 km
west of Jena (Pfau, 1984). The photometry of the target was monitored in 58
nights with the Cassegrain-Teleskop-Kamera II (CTK-II from hereon, Mugrauer,
2016), and in 39 nights with the Schmidt-Teleskop-Kamera (STK from hereon,
Mugrauer Berthold, 2010). In addition, we could obtain spectroscopic
observations of RW Aur in 11 nights with the Fibre Linked ÉCHelle Astronomical
Spectrograph (FLECHAS from hereon, Mugrauer ., 2014). The photometric and
spectroscopic observations, including the data reduction, are explained in
detail in the following two subsections.

###  2.1 Photometric observations

In the course of our monitoring campaign, starting on 07 September 2016, we
observed RW Aur in total in 97 nights with the CTK-II and STK, and obtained
unresolved photometry of the target (i.e. RW Aur A and B are not individually
detected) in the B-, V-, R-, and I-band. Our observing campaign of RW Aur can
be divided into three epochs, each ranging from late summer to early spring,
corresponding to the visibility of the star. Table 2 gives the used
instruments for the different epochs as well as the detector integration time
($DIT$) used for the different filters. Three exposures per filter were taken
in each night, and the $DIT$ was adjusted dependent on the used instrument,
the seeing conditions, and the brightness of the target.

The standard reduction of all data, i.e. dark subtraction and flat-fielding,
was performed with ESO Eclipse (Devillard, 2001). For observations with the
CTK-II, for the flat-fielding we used skyflats, which were always taken in the
morning or evening twilight in the same night as the observations of the
target if possible given the weather conditions, otherwise in the next
consecutive night. For the flat-fielding of the STK data we used domeflats,
which were always taken at the end of each observing night. Dark frames for
all needed integration times were taken in each night for both instruments.
The fully reduced images were then used for the photometric analysis, which is
described in Section 3.

###  2.2 Spectroscopic observations

For our spectroscopic monitoring observations of RW Aur we used FLECHAS in its
$2\times 2$-binning mode, which yields a resolving power of about $R=7300$
over the full spectral range between 3900 and 8100 Å, covered by the
instrument. The follow-up spectroscopy of the system was carried out between
31 August 2016 and 10 April 2018. In each observing night, always three
spectra of the target were taken with $DIT$ of 900 s, 1200 s or 1800 s, chosen
dependent on the brightness of the star, to guarantee that spectra with a
sufficiently high signal-to-noise ratio ($SNR$) could be obtained ($SNR>40$).

Table 3: Observing log for our FLECHAS follow-up spectroscopy of RW Aur. We
list for each observing epoch, the Gregorian and Julian date ($JD$), the used
detector integration time ($DIT$), the signal-to-noise ratio ($SNR$) at the
peak of the $\rm{H}\alpha$ emission line in the fully-reduced spectrum, and
the mean airmass $X$ of the target during the observations.

Epoch | Date | $JD$ | $DIT[s]$ | $SNR$ | $X$
---|---|---|---|---|---
I | 2016/08/31 | 2457631.574 | 900 | 191 | 1.4
| 2016/09/02 | 2457633.557 | 1200 | 167 | 1.5
| 2016/09/13 | 2457644.569 | 1200 | 225 | 1.3
| 2016/09/15 | 2457646.581 | 1200 | 251 | 1.2
| 2016/09/21 | 2457653.499 | 1200 | 239 | 1.5
| 2016/09/29 | 2457661.458 | 1200 | 290 | 1.7
| 2017/02/15 | 2457800.391 | 1800 | 129 | 1.3
IIb | 2018/02/23 | 2458173.371 | 900 | 50 | 1.3
| 2018/02/25 | 2458175.306 | 1800 | 85 | 1.1
| 2018/03/01 | 2458179.429 | 1800 | 61 | 1.9
| 2018/04/10 | 2458219.339 | 900 | 41 | 2.0

In each observing night, directly before the spectroscopic observation of RW
Aur, we recorded three spectra of a tungsten lamp for flat-fielding, as well
as three spectra of a Thorium-Argon (ThAr) lamp for wavelength calibration,
each with an exposure time of 1.5 s. The dark-frames for the flat-fielding and
wavelength calibration were taken in the beginning of each observing night,
while the dark-frames with longer integration times, needed for the science
spectra, were taken in longer time intervals (up to a few weeks). The data
reduction was performed with the FLECHAS data reduction pipeline (Mugrauer .,
2014). The individual reduction steps covered by the pipeline are dark- and
bias-subtraction, flat-fielding, extraction of the individual spectral orders,
wavelength calibration and normalization. The long-term stability of the
instrument has been demonstrated by Bischoff . (2017) and Heyne . (2020).
Details of our follow-up spectroscopy of RW Aur are summarized in Table 3.

##  3 Photometric analysis

The photometric analysis of RW Aur was carried out utilizing aperture
photometry. At first the photometric variability of all detected stars in the
images was determined with Muniwin (Hroch, 2014), and photometric reference
stars were chosen based on the following criteria:

  * •

exhibit a minimal photometric variability throughout the whole photometric
monitoring campaign (on the 1% level or better), identified by an automatic
comparison of the photometric variability of the instrumental magnitudes of
all stars, detected in the field of view of the used instruments

  * •

be bright (within $\sim$4 mag of RW Aur during its bright state) but faint
enough to avoid saturation of the used instruments during the whole
photometric monitoring campaign

  * •

be located within 10 arcmin around RW Aur, to minimize airmass differences to
the target, and to guarantee their detection with all used instruments in all
observing epochs

Figure 2 shows a CTK-II RGB-color-composite image of RW Aur and the selected
photometric reference stars, made of images taken in the R-, V-, and B-band.

Figure 2: RGB-color-composite image of RW Aur, taken with the CTK-II on 15
September 2016. The image is made of R-, V-, and B-band images, with total
integration times of 90, 90, and 270 s, respectively. RW Aur is located in the
center of the image. The selected photometric reference stars are indicated
and marked with white circles.

We then checked the quality of all images and discarded those where RW Aur is
saturated or has a low $SNR$. In total, 1116 images (97.1 % of all) from 97
nights have sufficient quality and are therefore included in the photometric
analysis of RW Aur. In detail, photometric data of the target could be
obtained in 89 nights in the B-band, in 95 nights in the V-band, in 96 nights
in the R-band, and in 93 nights in the I-band, respectively.

In order to determine the apparent magnitude of RW Aur in the standard
(Johnson-Cousins) photometric system, the magnitudes of the reference stars in
this system are needed, which were taken from the URAT1 catalog (Zacharias .,
2015). This catalog lists the Johnson B- and V-band magnitudes, as well as the
g-, r- and i-band magnitudes from the photometric system of the Sloan Digital
Sky Survey (York ., 2000, SDSS). We convert the SDSS magnitudes of the
reference stars to their R-, and I-band magnitudes in the Johnson-Cousins
system, using the empirical color-transformation-relations:
$\rm{R}=\rm{V}-(\rm{g}-\rm{r}+0.139)/1.646$ and
$\rm{I}=\rm{R}-(\rm{r}-\rm{i}+0.236)/1.007$, determined by Jordi . (2006). The
apparent magnitudes of the reference stars for all bands are summarized in
Table 4.

We then measured the instrumental magnitudes of RW Aur and of the reference
stars in all images. Thereby, dependent on the seeing conditions, the
focussing of the instrument during the individual observing epochs, and the
used filters, we varied the aperture size between 4 and 6 pixels,
corresponding to about twice the full width at half maximum (FWHM) of the
seeing disks of the stars detected in the images. The inner and outer diameter
of the background annulus was kept constant at 10 and 20 pixels, respectively.
The used apertures for all observing epochs and filters are summarized in
Table 2.

For each object we determine the average and standard deviation of its
instrumental magnitudes in each observing night, and calculate the
differential magnitude between RW Aur and the photometric reference stars in
all filters. With the given magnitudes of the reference stars in the
photometric standard system this yields the apparent B-, V-, R-, and I-band
magnitudes of RW Aur for all observing nights. The determined apparent
magnitudes of RW Aur for all photometric bands over the whole time span of our
photometric monitoring campaign are illustrated as light curves in Figure 3and
summarized in the Appendix in Table 1. The photometric uncertainties are below
15 mmag and hence not shown in this plot, as they are smaller than the size of
the used data-points. The apparent photometry of RW Aur, measured in our
campaign, is consistent and complementary with the AAVSO photometry of the
star available for the same range of time.

Figure 3: The light curve of RW Aur for the whole span of time covered by our
photometric monitoring project. The diamonds show the apparent B-, V-, R-, and
I-band magnitudes of the star, and the black lines indicate the points in
time, when FLECHAS spectra of the star were taken.

Figure 4: Color-magnitude diagrams of RW Aur. The abscissas show the $(\rm{B}-\rm{V})$, $(\rm{V}-\rm{R})$, and $(\rm{V}-\rm{I)}$ colors of the stellar system, while its apparent V-band magnitude is plotted along the ordinates. The observation date is color-coded for our observations and the photometric uncertainties are indicated with error bars. Black and grey squares show data presented by Dodin . (2019) and correspond to observations taken before and after September 2010, respectively. The typical photometric errors for these observations are 0.2 mag in the B-, and 0.1 mag in the V-, R-, and I-band, respectively. The wide-dashed blue line in all diagrams indicates the color-magnitude-track of the RW Aur system for interstellar extinction according to the standard extinction law ($R_{\rm V}=3.1$), while the narrow-dashed grey line shows the track for grey extinction. A and B mark the brightness and color of RW Aur A during its bright state, and RW Aur B. Table 4: The apparent magnitudes of the selected photometric reference stars, numbered as in Figure 2. The typical photometric uncertainty of the reference stars in the different bands is 0.03 mag. Ref. star # | URAT1 ID | B [mag] | V [mag] | R [mag] | I [mag] | g [mag] | r [mag] | i [mag]
---|---|---|---|---|---|---|---|---
1 | 602-067264 | 13.217 | 12.571 | 12.202 | 11.737 | 12.832 | 12.364 | 12.132
2 | 603-068385 | 13.132 | 12.707 | 12.492 | 12.167 | 12.852 | 12.637 | 12.546
3 | 603-068220 | 13.744 | 12.316 | 11.510 | 10.769 | 13.009 | 11.821 | 11.311
4 | 603-068622 | 14.876 | 13.348 | 12.487 | 11.709 | 14.101 | 12.823 | 12.275
5 | 603-068798 | 12.936 | 12.361 | 12.043 | 11.635 | 12.589 | 12.205 | 12.030
6 | 602-067100 | 13.895 | 13.090 | 12.639 | 12.146 | 13.441 | 12.837 | 12.577
7 | 602-066917 | 13.070 | 12.353 | 11.948 | 11.471 | 12.657 | 12.130 | 11.885
8 | 602-066877 | 12.571 | 12.046 | 11.751 | 11.369 | 12.252 | 11.905 | 11.757
9 | 602-066582 | 15.164 | 13.519 | 12.594 | 11.684 | 14.319 | 12.936 | 12.255
10 | 602-066915 | 13.270 | 12.223 | 11.601 | 11.012 | 12.723 | 11.839 | 11.481
11 | 602-066898 | 13.812 | 12.535 | 11.824 | 11.114 | 13.133 | 12.101 | 11.622

The determined apparent photometry of RW Aur in all photometric bands can be
used to study the color evolution of the target, dependent on its apparent
magnitude, between its faint and bright state, which gives insights on the
nature of the obscuration. Color-magnitude-diagrams of RW Aur are shown in
Figure 4. The color-coded dots in these diagrams are the data from our
photometric monitoring campaign. These can be compared to data from Dodin .
(2019), who presented own photometric observations accompanied by data from
Herbst . (1994), Grankin . (2007) and the AAVSO. The black and grey squares in
the diagrams represent observations from before and after September 2010, when
the first deep dimming in the light curve of RW Aur was detected. The
evolution of the color of RW Aur can be compared to interstellar extinction
(Savage Mathis, 1979), indicated by the blue line, which causes rather red
colors, and grey extinction (grey line), which is connected to large dust
grains along the line of sight, resulting in rather equal obscuration in the
different photometric bands. The position of RW Aur A during its bright state
was constructed by Dodin . (2019) such that the curves for grey- and
interstellar extinction envelope most observations. The position of RW Aur B
was obtained from their resolved photometric observations of the companion.

Our measurements are consistent with the ones presented by Dodin . (2019). The
color and magnitude of the system is close to the color and magnitude of RW
Aur A during the bright state and close to the color and magnitude of RW Aur B
during the faint state. While during bright state the colors are in the middle
between the tracks for grey and interstellar extinction, we see a clear
tendency towards grey extinction when the system becomes fainter. This gives
good evidence that the obscuration is caused by large dust grains along the
line of sight.

Koutoulaki . (2019) obtained spectra of RW Aur A with X-shooter (Vernet .,
2011), one during the faint state in March 2015, and one during the bright
state in September 2016. By dividing the two spectra, they can compare the
evolution of the optical depth over wavelength with the track for interstellar
extinction (Cardelli ., 1989) as well as models for dust extinction with
different grain sizes and amounts of scattering. They find that the extinction
is between interstellar and grey for the wavelength range covered by their
observations (0.3 - 2.4 $\mu$m). This also applies to the part of their
spectra that can be compared to our BVRI photometry (0.4 - 0.9 $\mu$m).
Despite this difference to our findings in the faint state, where the
extinction is clearly grey, both studies get to the conclusion that the
obscuring screen mainly consists of large dust grains. Koutoulaki . (2019)
obtain maximum grain sizes of 15 - 150 $\mu$m, depending on the amount of
scattering and the grain types. Also note that the comparison has to be taken
with caution, because of the different methods, and because Koutoulaki .
(2019) obtained the spectrum for the faint state in an earlier epoch, when the
dimming was stronger.

##  4 Spectral analysis

Figure 5: Sections of the normalized FLECHAS spectra of RW Aur from eleven
observing epochs between 31 August 2016 and 10 April 2018, centered on the
$\rm{H}\alpha$ emission line at 6563 Å (left plot), and the $[\rm{O}I]$
emission line at 6300 Å (right plot). Spectra that were taken during the
bright state, after the second deep eclipse, are colored in red. The other
spectra were taken during faint states and are shown in black.

Figure 6: The equivalent width (EW) of the $\rm{H}\alpha$ and $[\rm{O}I]$
(6300 Å) emission line of RW Aur, and their ratio, plotted for spectra taken
between February 2013 and April 2018. EWs from our campaign are shown with
black circles, those from Bozhinova . (2016) with grey circles, respectively.

We focus our spectral analysis on the $\rm{H}\alpha$ emission at about 6563 Å
and the forbidden $[\rm{O}I]$ emission at about 6300 Å. These emission lines
are typical signs of accretion in classical TTS, indicating shocked material
at the stellar surface and mass outflow, respectively (Bozhinova ., 2016;
Mohanty ., 2005). The corresponding parts of the normalized spectra are
illustrated for all spectroscopic observing epochs in Figure 5. It can be seen
that between 31 August and 29 September 2016, when RW Aur was in a bright
state, the $\rm{H}\alpha$ emission is stronger than at the later observing
epochs. In contrast, for the $[\rm{O}I]$ emission we note the opposite effect.
The equivalent widths (EWs) of the two emission lines, as measured in the
FLECHAS spectra in all observing epochs of our spectroscopic monitoring of RW
Aur, are shown in Figure 6 together with data from Bozhinova . (2016). The EWs
were measured in the individual FLECHAS spectra with IRAF and exhibit a
typical uncertainty of 0.3 mÅ for the $\rm{H}\alpha$ emission line, and 0.1 mÅ
for the $[\rm{O}I]$ emission line, respectively. The absolute value of the EW
of the $\rm{H}\alpha$ emission line of RW Aur is well above 10 Å, as expected
according to the division between classical TTSs and weak-line TTSs (Mohanty
., 2005). Our results are well consistent with the findings from Bozhinova .
(2016): When RW Aur A is in its dim state, the $\rm{H}\alpha$ emission, which
originates from near the stellar surface, is partly obscured. At the same
time, as our spectral observations cannot resolve RW Aur A and B, a larger
fraction of the continuum emission comes from RW Aur B. This effect also
reduces the $\rm{EW}(\rm{H}\alpha)$, because RW Aur B is a weak-line TTS,
which exhibits a lower $\rm{H}\alpha$ emission. The $[\rm{O}I]$ emission, on
the other hand, originates from mass outflow in the outer disk, which is not
affected by the obscuration. Therefore, the decreasing continuum emission
leads to an increase of the $\rm{EW}([\rm{O}I])$. However, compared to
Bozhinova . (2016), the $\rm{EW}(\rm{H}\alpha)/\rm{EW}([\rm{O}I])$ ratios are
surprisingly low. The measurements by Bozhinova . (2016) until April 2014 were
taken during bright state, before the second deep eclipse. Our measurements in
August and September 2016 were taken when the apparent brightness had just
recovered from the second deep eclipse, but
$\rm{EW}(\rm{H}\alpha)/\rm{EW}([\rm{O}I])$ was still lower by an order of
magnitude compared to the first observations by Bozhinova . (2016). In
particular, the $[\rm{O}I]$ emission remained almost as strong as during the
obscuration and got even stronger when the star faded again towards the end of
our observing campaign, indicating a higher mass outflow activity during this
time.

Another notable feature in the spectra of RW Aur, is the prominent P Cygni
profile of its $\rm{H}\alpha$ emission line, which is a further indicator for
wind outflow. The absorption feature is blue-shifted with respect to the peak
of the $\rm{H}\alpha$ emission line by up to 6 Å (which corresponds to a wind
velocity of about 275 km/s) and was stronger at the beginning of our observing
campaign, when the star was in its bright state. Bozhinova . (2016) also
recorded this absorbing outflow and attributed it to the reason for the
dimming. We can verify their finding that during the faint state, the
absorbing material suppresses the blue-shifted $\rm{H}\alpha$ peak. The degree
of absorption and the wind velocity are very variable. However, we note that
the outflow also exists during the bright state, so it is not directly related
to the degree of occultation. We also note that the blue-shifted peak of the P
Cygni profile is much weaker compared to the main peak, whereas Bozhinova .
(2016) found both peaks having similar strengths during the bright state. The
main reason for this difference is an increased velocity and hence a stronger
blueshift of the wind outflow: In the bright state, we get velocities of about
230 - 275 km/s, while Bozhinova . (2016) only obtained 100 - 200 km/s.
Therefore, the wind now absorbs a larger portion of the blue-shifted peak.

Besides $\rm{H}\alpha$ and $[\rm{O}I]$, the spectra show several other
emission lines with strong variations between bright and faint state. Our
fully reduced and normalized spectra will be made available for download in
the VizieR222Online available at: https://vizier.cds.unistra.fr/viz-bin/VizieR
database and can be used for more detailed studies.

Lisse . (2022) performed observations with SpeX at the NASA Infrared Telescope
Facility (Rayner ., 2003) to provide spectra in the infrared (0.7 - 5.0
$\mu$m). They show the evolution of four Hydrogen emission lines of the
Paschen series between November 2018 and October 2020. The Paschen lines only
show a single peak and, as for $\rm{H}\alpha$, they are very variable, being
stronger in the brighter states. This is in contrast to the continuum
behaviour in the infrared.

##  5 Conclusions

We monitored the photometry of RW Aur in the B-, V-, R-, and I-band between
September 2016 and April 2019, corresponding to the time after the second deep
eclipse, when it went through strong brightness variations on timescales of up
to one year, ending with a bright state in 2019. The observations were
supported by spectra taken between August 2016 and April 2018, ending during a
faint state.

The light curve fits to the photometric trend given by the AAVSO and other
authors. The CMDs show that the reddening cannot be explained by interstellar
extinction, but by large dust grains along the line of sight, related to grey
extinction. This supports the scenario of a hot dusty wind emerging from the
inner disk (Petrov ., 2015; Shenavrin ., 2015; Bozhinova ., 2016; Dodin .,
2019).

In our spectral analysis, we focused on the $\rm{H}\alpha$ and the $[\rm{O}I]$
(6300 Å) emission lines. Our results are largely consistent with Bozhinova .
(2016) in terms of an increased $\rm{H}\alpha$ EW during bright state and an
increased $[\rm{O}I]$ EW during faint state. However, in both states we obtain
$\rm{EW}(\rm{H}\alpha)/\rm{EW}([\rm{O}I])$ ratios, which are much lower than
before the start of the second deep eclipse in 2014. This shows that the re-
brightening in 2016 (Scholz ., 2016) was not equivalent to a return of the
system to its normal bright state. Instead, the outflow causing the
$[\rm{O}I]$ emission was probably even stronger during the variable phases
that occurred between 2016 and 2018, compared to the observing epoch between
2014 and 2015, reported by Bozhinova . (2016). This is no contradiction,
because the $[\rm{O}I]$ emission is only an indicator for the accretion-
induced outflow activity but not for the amount of dust carried by the wind.
Other reasons like the geometry of the system can also play a role when
explaining the repeated brightening and dimming events during the time of our
monitoring campaign.

RW Aur is an extraordinary, highly active system and a full understanding of
its variability on different timescales and in different wavebands requires a
very broad understanding of the different physical processes taking place in
this young stellar environment. In particular, it requires a broad set of
astronomical instruments and techniques to access all these phenomena. Large
progress has been made in recent years, especially since the onset of the deep
eclipses in between 2010 and 2011 as well as between 2014 and 2016. While it
is now consent that the obscurations are caused by hot dust from the inner
disk, the exact mechanisms which trigger the dust enhancement and transport it
into the line-of-sight, are still debated. It is well possible that a
combination of several proposed mechanisms is needed to explain the observed
behavior. Beginning with the tidal encounter $\sim$500 years ago (Dai ., 2015)
that might have caused a recent rearrangement or warping of the inner disk
(Berdnikov ., 2017; Facchini ., 2016; Koutoulaki ., 2019), over the formation,
migration and destruction of planetesimals (Günther ., 2018; Lisse ., 2022),
which was suggested to explain the iron overabundance in X-ray spectra, up to
the dust-laden wind that is now observed, inferred from the occultations and
the IR excess (Petrov ., 2015; Shenavrin ., 2015; Bozhinova ., 2016; Dodin .,
2019).

Ongoing research on the $\sim$3 Myr young RW Aur system will shed new light on
the story of star- and planet formation. While it is now in a relatively
constant, bright state, it will be interesting to see if there will be deep
eclipses again in the future and if they will show periodicity. Further
observations will make it possible to clarify the reasons for such dimming
events and to unravel the secrets of the spectro-photometric variability of RW
Aur and its role within the population of T Tauri stars.

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## Acknowledgments

We want to thank the scientific and technical staff of the Astrophysical
Institute of the Friedrich-Schiller-University Jena for their help and
assistance in the observations. In particular, we want to thank the following
observers: Alexoudi X., Andreas C., Blümcke M., Dadalauri M., Darie J.,
Geymeier M., Gilbert H., Hartung L., Heyne T., Hildebrandt F., Hoffmann S.,
Krüger E., Michel K.-U., Munz V., Pannicke A., Pyliagin D., Schiefeneder F.,
Schulz M., Stenglein W., Trepanovski A., Wagner D., Wischer M., Zehe T.,
Zielinski P. We made use of data from the `Simbad` and `VizieR` databases,
operated at CDS in Strasbourg, France. Furthermore, we used data from the
European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia),
processed by the Gaia Data Processing and Analysis Consortium (DPAC,
https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has
been provided by national institutions, in particular the institutions
participating in the Gaia Multilateral Agreement. This work made use of the
AAVSO database, so we want to thank the many observers who provided their data
to the AAVSO, as well as the organizers for collecting the data and providing
tools like the light curve generator. Finally, we want to thank Ralph
Neuhäuser and Torsten Löhne for their helpful comments as well as Aleks
Scholz, who drew the attention of the authors to RW Aur and inspired them to
follow up on it.

## Author Biography

Oliver Lux obtained a Bachelor of Science in Physics and a Master of Science
in astrophysics at the Universities of Bochum and Bonn, respectively, gaining
knowledge about neutron stars. After that, he obtained a PhD at the University
of Jena with a work on runaway stars and supernova remnants. His further
research interests are variable stars and exoplanets.

## Appendix A

APPENDIX A: PHOTOMETRY Epoch Date $JD$ B [mag] V [mag] R [mag] I [mag] I
2016/09/07 2457638.556 $11.954\pm 0.012$ $11.164\pm 0.011$ $10.557\pm 0.010$
$~{}~{}9.789\pm 0.009$ 2016/09/13 2457644.550 $11.155\pm 0.011$ $10.490\pm
0.011$ $~{}~{}9.974\pm 0.009$ $~{}~{}9.307\pm 0.009$ 2016/09/15 2457646.563
$11.173\pm 0.011$ $10.494\pm 0.011$ $10.014\pm 0.009$ $~{}~{}9.389\pm 0.009$
2016/09/22 2457653.535 $11.593\pm 0.012$ $10.952\pm 0.011$ $10.413\pm 0.010$
$~{}~{}9.729\pm 0.009$ 2016/09/29 2457661.494 $11.179\pm 0.011$ $10.585\pm
0.011$ $10.082\pm 0.009$ $~{}~{}9.411\pm 0.009$ 2016/12/05 2457728.380
$12.218\pm 0.012$ $11.582\pm 0.011$ $11.058\pm 0.010$ $10.357\pm 0.009$
2016/12/20 2457743.323 $12.696\pm 0.013$ $12.033\pm 0.012$ $11.424\pm 0.010$
$10.656\pm 0.010$ 2016/12/21 2457744.493 $12.538\pm 0.012$ $11.879\pm 0.012$
$11.320\pm 0.010$ $10.582\pm 0.010$ 2017/01/06 2457759.533 $12.794\pm 0.013$
$12.002\pm 0.012$ $11.346\pm 0.010$ $10.523\pm 0.010$ 2017/01/19 2457773.303
$12.137\pm 0.012$ $11.434\pm 0.011$ $10.871\pm 0.010$ $10.144\pm 0.009$
2017/01/28 2457782.461 $13.011\pm 0.013$ $12.161\pm 0.012$ $11.487\pm 0.010$
$10.648\pm 0.010$ 2017/02/01 2457786.416 $12.744\pm 0.013$ $11.932\pm 0.012$
$11.311\pm 0.010$ $10.519\pm 0.009$ 2017/02/13 2457798.333 $13.280\pm 0.015$
$12.288\pm 0.012$ $11.561\pm 0.010$ $10.719\pm 0.010$ 2017/02/14 2457799.342
$13.468\pm 0.014$ $12.432\pm 0.012$ $11.693\pm 0.010$ $10.810\pm 0.010$
2017/02/15 2457800.334 $13.218\pm 0.014$ $12.330\pm 0.012$ $11.612\pm 0.010$
$10.754\pm 0.010$ 2017/03/13 2457826.410 — $11.688\pm 0.013$ $11.038\pm 0.010$
$10.243\pm 0.010$ 2017/03/27 2457840.367 $12.598\pm 0.013$ $11.839\pm 0.012$
$11.223\pm 0.010$ $10.441\pm 0.009$ 2017/03/30 2457843.295 $12.260\pm 0.013$
$11.509\pm 0.012$ $10.907\pm 0.010$ $10.175\pm 0.009$ 2017/04/20 2457864.324 —
$12.156\pm 0.013$ $11.466\pm 0.011$ $10.646\pm 0.010$ II 2017/09/05
2458001.635 $12.287\pm 0.008$ $11.398\pm 0.008$ $10.770\pm 0.004$
$~{}~{}9.960\pm 0.008$ 2017/09/12 2458008.558 $11.665\pm 0.008$ $10.850\pm
0.008$ $10.304\pm 0.004$ $~{}~{}9.564\pm 0.008$ 2017/09/19 2458015.639
$12.194\pm 0.008$ $11.412\pm 0.010$ $10.853\pm 0.004$ $10.075\pm 0.009$
2017/10/15 2458041.680 $11.198\pm 0.008$ $10.491\pm 0.008$ $10.000\pm 0.004$
$~{}~{}9.310\pm 0.008$ 2017/10/16 2458042.673 $11.081\pm 0.008$ $10.379\pm
0.008$ $~{}~{}9.929\pm 0.004$ $~{}~{}9.264\pm 0.008$ 2017/11/28 2458086.285
$12.399\pm 0.008$ $11.597\pm 0.009$ $10.987\pm 0.005$ $10.194\pm 0.008$
2017/12/07 2458095.311 $12.237\pm 0.008$ $11.488\pm 0.009$ $10.954\pm 0.005$
$10.215\pm 0.008$ 2017/12/12 2458100.279 $12.561\pm 0.008$ $11.763\pm 0.009$
$11.184\pm 0.005$ $10.410\pm 0.008$ 2018/01/15 2458133.528 — $11.726\pm 0.009$
$11.124\pm 0.005$ $10.320\pm 0.008$ IIb 2018/01/30 2458149.288 $12.880\pm
0.046$ $12.055\pm 0.032$ $11.472\pm 0.013$ $10.631\pm 0.012$ 2018/02/23
2458173.352 $13.150\pm 0.029$ $12.265\pm 0.016$ $11.596\pm 0.012$ $10.757\pm
0.010$ 2018/02/24 2458174.413 $13.111\pm 0.031$ $12.240\pm 0.017$ $11.606\pm
0.012$ $10.779\pm 0.011$ 2018/02/25 2458175.278 $13.189\pm 0.029$ $12.241\pm
0.016$ $11.557\pm 0.011$ $10.720\pm 0.010$ 2018/02/26 2458176.434 $13.057\pm
0.033$ $12.337\pm 0.018$ $11.741\pm 0.012$ $10.924\pm 0.010$ 2018/02/27
2458177.302 $13.183\pm 0.030$ $12.289\pm 0.016$ $11.618\pm 0.012$ $10.761\pm
0.010$ 2018/02/28 2458178.375 $13.054\pm 0.032$ $12.168\pm 0.017$ $11.535\pm
0.012$ $10.698\pm 0.010$ 2018/03/01 2458179.401 $12.949\pm 0.040$ $12.063\pm
0.019$ $11.452\pm 0.013$ $10.653\pm 0.010$ 2018/03/24 2458202.328 $13.309\pm
0.037$ $12.283\pm 0.018$ $11.580\pm 0.012$ $10.715\pm 0.010$ 2018/03/29
2458207.395 $13.531\pm 0.045$ $12.482\pm 0.019$ $11.719\pm 0.012$ $10.818\pm
0.010$

Table 5: The apparent photometry of RW Aur during our photometric monitoring campaign. We list the Gregorian and Julian date ($JD$) of the photometric observations of the star together with the measured apparent B-, V- R-, and I-band magnitudes. In each night, the observations in the different photometric bands were performed consecutively, limiting the temporal uncertainties to only $\sim 0.006$ days. Table 1: Continued. Epoch | Date | $JD$ |  $B$ [mag] |  $V$ [mag] |  $R$ [mag] |  $I$ [mag]
---|---|---|---|---|---|---
III | 2018/08/16 | 2458346.611 | — | $10.350\pm 0.009$ | $~{}~{}9.816\pm 0.007$ | —
| 2018/08/17 | 2458347.599 | $10.735\pm 0.011$ | $10.117\pm 0.009$ | $~{}~{}9.638\pm 0.007$ | $~{}~{}9.020\pm 0.007$
| 2018/08/22 | 2458352.618 | $10.984\pm 0.011$ | $10.348\pm 0.009$ | $~{}~{}9.813\pm 0.007$ | $~{}~{}9.151\pm 0.007$
| 2018/08/23 | 2458353.611 | $11.015\pm 0.011$ | $10.354\pm 0.009$ | $~{}~{}9.830\pm 0.007$ | $~{}~{}9.185\pm 0.007$
| 2018/09/06 | 2458367.606 | $10.793\pm 0.011$ | $10.145\pm 0.009$ | $~{}~{}9.629\pm 0.007$ | $~{}~{}8.982\pm 0.007$
| 2018/09/08 | 2458369.595 | $10.860\pm 0.011$ | $10.165\pm 0.009$ | $~{}~{}9.631\pm 0.007$ | $~{}~{}9.013\pm 0.007$
| 2018/09/17 | 2458378.627 | $10.684\pm 0.011$ | $10.051\pm 0.009$ | $~{}~{}9.892\pm 0.007$ | $~{}~{}9.204\pm 0.007$
| 2018/09/18 | 2458379.644 | $10.310\pm 0.011$ | $9.731\pm 0.009$ | $~{}~{}9.290\pm 0.007$ | $~{}~{}8.776\pm 0.007$
| 2018/09/20 | 2458381.652 | $11.433\pm 0.011$ | $10.733\pm 0.009$ | $10.141\pm 0.007$ | $~{}~{}9.388\pm 0.007$
| 2018/09/21 | 2458382.632 | $11.581\pm 0.012$ | — | — | —
| 2018/09/22 | 2458383.634 | $11.079\pm 0.011$ | $10.437\pm 0.009$ | $~{}~{}9.916\pm 0.007$ | $~{}~{}9.228\pm 0.007$
| 2018/09/25 | 2458386.554 | $11.447\pm 0.011$ | $10.819\pm 0.009$ | $10.272\pm 0.007$ | $~{}~{}9.550\pm 0.007$
| 2018/09/28 | 2458389.632 | $11.301\pm 0.011$ | $10.648\pm 0.009$ | $10.098\pm 0.007$ | $~{}~{}9.392\pm 0.007$
| 2018/09/29 | 2458390.523 | $11.003\pm 0.011$ | $10.366\pm 0.009$ | $~{}~{}9.834\pm 0.007$ | $~{}~{}9.231\pm 0.007$
| 2018/09/30 | 2458391.534 | $11.014\pm 0.011$ | $10.392\pm 0.009$ | $~{}~{}9.876\pm 0.007$ | $~{}~{}9.222\pm 0.007$
| 2018/10/01 | 2458392.616 | — | $10.173\pm 0.009$ | $~{}~{}9.656\pm 0.007$ | $~{}~{}9.037\pm 0.007$
| 2018/10/06 | 2458397.620 | $11.534\pm 0.011$ | $10.824\pm 0.009$ | $10.228\pm 0.007$ | $~{}~{}9.481\pm 0.007$
| 2018/10/10 | 2458401.681 | $10.942\pm 0.011$ | $10.274\pm 0.009$ | $~{}~{}9.760\pm 0.007$ | $~{}~{}9.143\pm 0.007$
| 2018/10/11 | 2458402.677 | $10.978\pm 0.011$ | $10.392\pm 0.009$ | $~{}~{}9.887\pm 0.007$ | $~{}~{}9.212\pm 0.007$
| 2018/10/13 | 2458405.428 | $11.178\pm 0.011$ | $10.529\pm 0.009$ | $~{}~{}9.989\pm 0.007$ | $~{}~{}9.341\pm 0.007$
| 2018/10/14 | 2458406.470 | $11.431\pm 0.011$ | $10.731\pm 0.009$ | $10.193\pm 0.007$ | $~{}~{}9.535\pm 0.007$
| 2018/10/17 | 2458409.410 | $11.384\pm 0.011$ | $10.643\pm 0.009$ | $10.067\pm 0.007$ | $~{}~{}9.415\pm 0.007$
| 2018/10/21 | 2458413.358 | $11.005\pm 0.011$ | $10.390\pm 0.009$ | $~{}~{}9.848\pm 0.007$ | $~{}~{}9.191\pm 0.007$
| 2018/10/23 | 2458414.552 | $10.985\pm 0.011$ | $10.293\pm 0.009$ | $~{}~{}9.748\pm 0.007$ | $~{}~{}9.157\pm 0.007$
| 2018/11/06 | 2458428.558 | $11.149\pm 0.011$ | $10.504\pm 0.009$ | $~{}~{}9.964\pm 0.007$ | $~{}~{}9.290\pm 0.007$
| 2018/11/10 | 2458432.592 | $10.513\pm 0.011$ | $9.892\pm 0.009$ | $~{}~{}9.413\pm 0.007$ | $~{}~{}8.871\pm 0.007$
| 2018/11/14 | 2458436.650 | $10.700\pm 0.011$ | $10.067\pm 0.009$ | $~{}~{}9.579\pm 0.007$ | $~{}~{}8.995\pm 0.007$
| 2018/11/16 | 2458438.638 | — | $10.107\pm 0.009$ | $~{}~{}9.619\pm 0.007$ | $~{}~{}9.002\pm 0.007$
| 2018/11/17 | 2458439.573 | $10.738\pm 0.011$ | $10.152\pm 0.009$ | $~{}~{}9.681\pm 0.007$ | $~{}~{}9.053\pm 0.007$
| 2018/11/18 | 2458440.516 | — | $10.186\pm 0.009$ | $~{}~{}9.721\pm 0.007$ | $~{}~{}9.145\pm 0.007$
| 2019/01/18 | 2458502.237 | $9.939\pm 0.011$ | $9.388\pm 0.009$ | $~{}~{}9.005\pm 0.007$ | $~{}~{}8.483\pm 0.007$
| 2019/01/21 | 2458505.216 | $10.334\pm 0.011$ | $9.730\pm 0.009$ | $~{}~{}9.273\pm 0.007$ | $~{}~{}8.722\pm 0.007$
| 2019/01/21 | 2458505.220 | $10.357\pm 0.011$ | $9.760\pm 0.009$ | $~{}~{}9.298\pm 0.007$ | $~{}~{}8.735\pm 0.007$
| 2019/01/31 | 2458515.230 | $10.540\pm 0.011$ | $9.931\pm 0.009$ | $~{}~{}9.471\pm 0.007$ | $~{}~{}8.874\pm 0.007$
| 2019/02/08 | 2458522.521 | — | $9.995\pm 0.009$ | $~{}~{}9.548\pm 0.007$ | $~{}~{}8.984\pm 0.007$
| 2019/02/14 | 2458529.251 | $11.674\pm 0.011$ | $10.980\pm 0.010$ | $10.351\pm 0.007$ | $~{}~{}9.601\pm 0.007$
| 2019/02/23 | 2458538.250 | $11.354\pm 0.011$ | $10.656\pm 0.009$ | $10.064\pm 0.007$ | $~{}~{}9.320\pm 0.007$
| 2019/02/24 | 2458539.255 | $10.746\pm 0.011$ | $10.103\pm 0.009$ | $~{}~{}9.573\pm 0.007$ | —
| 2019/02/25 | 2458540.256 | $10.933\pm 0.011$ | $10.247\pm 0.009$ | $~{}~{}9.689\pm 0.007$ | $~{}~{}9.039\pm 0.007$
| 2019/02/26 | 2458541.261 | $10.373\pm 0.011$ | $9.779\pm 0.009$ | $~{}~{}9.299\pm 0.007$ | $~{}~{}8.742\pm 0.007$
| 2019/02/27 | 2458542.259 | $10.989\pm 0.011$ | $10.382\pm 0.009$ | $~{}~{}9.840\pm 0.007$ | $~{}~{}9.133\pm 0.007$
| 2019/03/07 | 2458550.263 | $11.164\pm 0.011$ | $10.532\pm 0.009$ | $10.002\pm 0.007$ | $~{}~{}9.275\pm 0.007$
| 2019/03/20 | 2458563.272 | $11.123\pm 0.011$ | $10.529\pm 0.010$ | $10.002\pm 0.007$ | $~{}~{}9.281\pm 0.007$
| 2019/03/21 | 2458564.275 | $10.642\pm 0.011$ | $9.998\pm 0.009$ | $~{}~{}9.519\pm 0.007$ | $~{}~{}8.946\pm 0.007$
| 2019/03/22 | 2458565.293 | $10.960\pm 0.011$ | $10.303\pm 0.009$ | $~{}~{}9.800\pm 0.007$ | $~{}~{}9.212\pm 0.007$
Table 1: Continued. Epoch | Date | $JD$ |  $B$ [mag] |  $V$ [mag] |  $R$ [mag] |  $I$ [mag]
---|---|---|---|---|---|---
III | 2019/03/23 | 2458566.302 | $11.276\pm 0.012$ | $10.631\pm 0.011$ | $10.066\pm 0.008$ | —
| 2019/03/24 | 2458567.310 | $10.942\pm 0.011$ | $10.293\pm 0.010$ | $~{}~{}9.786\pm 0.007$ |  $~{}~{}9.184\pm$0.007
| 2019/03/29 | 2458572.286 | $10.733\pm 0.011$ | $10.180\pm 0.009$ | $~{}~{}9.722\pm 0.007$ |  $~{}~{}9.100\pm$0.007
| 2019/03/30 | 2458573.281 | $11.073\pm 0.011$ | $10.406\pm 0.010$ | $~{}~{}9.859\pm 0.007$ |  $~{}~{}9.207\pm$0.007
| 2019/03/31 | 2458574.335 | $11.277\pm 0.011$ | — | $~{}~{}9.969\pm 0.007$ |  $~{}~{}9.256\pm$0.007
| 2019/04/01 | 2458575.293 | $10.848\pm 0.011$ | $10.223\pm 0.009$ | $~{}~{}9.719\pm 0.007$ |  $~{}~{}9.119\pm$0.007
| 2019/04/10 | 2458584.312 | $10.749\pm 0.011$ | $10.201\pm 0.009$ | $~{}~{}9.713\pm 0.007$ |  $~{}~{}9.037\pm$0.007
| 2019/04/15 | 2458589.304 | $11.132\pm 0.012$ | $10.498\pm 0.010$ | $~{}~{}9.958\pm 0.007$ |  $~{}~{}9.249\pm$0.007
| 2019/04/16 | 2458590.317 | $10.900\pm 0.011$ | $10.279\pm 0.010$ | $~{}~{}9.780\pm 0.007$ |  $~{}~{}9.139\pm$0.007
| 2019/04/17 | 2458591.318 | $10.744\pm 0.011$ | $10.142\pm 0.009$ | $~{}~{}9.674\pm 0.007$ |  $~{}~{}9.062\pm$0.007
| 2019/04/18 | 2458592.307 | $11.296\pm 0.013$ | $10.608\pm 0.011$ | $10.031\pm 0.007$ |  $~{}~{}9.316\pm$0.007
| 2019/04/19 | 2458593.328 | $11.409\pm 0.012$ | $10.749\pm 0.010$ | $10.176\pm 0.007$ |  $~{}~{}9.476\pm$0.007
| 2019/04/20 | 2458594.320 | $10.809\pm 0.011$ | $10.213\pm 0.009$ | $~{}~{}9.728\pm 0.007$ |  $~{}~{}9.104\pm$0.007
| 2019/04/21 | 2458595.346 | $10.968\pm 0.011$ | $10.352\pm 0.010$ | $~{}~{}9.844\pm 0.007$ |  $~{}~{}9.188\pm$0.007