ODYSSEUS V: Observations of GM Aur

American Association of Variable Star Observers (AAVSO)
Fri, 10/08/2021 - 15:13

ODYSSEUS is an international collaborative campaign to understand the processes involved in the formation of low mass stars, their circumstellar disks, and their planets, via the time-variability of these systems.
To date ODYSSEUS observations, with contributions from the AAVSO, have supported monitoring observations of TW Hya, RU Lup, BP Tau, and snapshot
observations of a few dozen other young stars, and resulted in 3 papers published, in press, or submitted.

The final monitoring target for the first year of the HST ULLYSES program is the low mass pre-main sequence star GM Aur. HST will observe the star 12 times over 3 stellar rotation periods, beginning October 13, with about a 1.4 day interval between observations. I request CCD photometry in the B,V,R, and I bands in support of the UV spectroscopy from the HST. GM Aur is also in the TESS field of view from September 16 through November 6.

GM Aur J2000 Position:   4 55 10.981 +30 21 59.38
       Brightness:  V=12.2 (Simbad)   Range: 13.1-13.9p (VSX)
       Rotation period: 6 days  (VSX)

As of today, the first 4 HST observations are scheduled: (Times are UT)
  Start time: 13 Oct 2021 11:54:10      End time: 13 Oct 2021 12:46:38
  Start time: 15 Oct 2021 06:46:59      End time: 15 Oct 2021 07:39:27
  Start time: 16 Oct 2021 16:08:03      End time: 16 Oct 2021 17:00:31
  Start time: 17 Oct 2021 20:46:03      End time: 17 Oct 2021 21:38:31
The other 8 observations will occur between October 18 and November 1; times will be posted when available.

The purpose of ground-based photometric support is to obtain optical colors, and to look for color variations, during the time of the HST campaign. These
help us to interpret brightness variations in the single-band TESS light curve, and to interpret the optical and UV spectroscopy.
Please try to get 1% BVRI photometry or better (0.01 mag precision), so we can determine colors to 2% or better.

While observations simultaneous with the HST windows are important, so is a continuous record, so please try to observe on every clear night Oct 12 - Nov 1.

V-band observations in the AAVSO database from the 2020 observing season scatter between about V=11.9 and 12.5.
TESS observations in 2019 showed variations of about +/-0.02 mag, and trends of about 0.01 mag/day.

Ground-based imaging is particularly important in this case.
The star 2MASS J04551015+3021333, which is about as bright as GM Aur, is 28 arcsec to the south. Very little is known about this star, although
the GAIA parallax suggests it is a background giant. This star will be blended with GM Aur in the 21 arcsec TESS pixels, so we will need ground-based data
to verify that this star is not contributing to the variability.

Please report magnitudes for both GM Aur and 2MASS J04551015+3021333.

Thank you for your contributions to the first 3 parts of the ODYSSEUS campaign.
Your participation in this campaign is a big part of its success.

Please upload any data you get to the AAVSO database. Thanks in advance for your contributions to this campaign.


American Association of Variable Star Observers (AAVSO)
2MASS J04551015+3021333

Does 2MASS J04551015+3021333 need an AUID?