Alert Notice 801: GM Aur and BP Tau monitoring for HST and TESS

December 1, 2022

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Dr. Frederick Walter (Stony Brook University) requests AAVSO observers' assistance in monitoring the classical T Tau stars GM Aur and BP Tau in support of observations with HST and TESS scheduled for now through mid-January 2023.

Dr. Walter provides the following information and instructions:

"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. Please read other Alert Notices (starting from AAVSO Alert Notice 725) and forum notes on this program for more details.

Observations of the final 2 HST/ULLYSES/ODYSSEUS targets, GM Aur and BP Tau, are underway. "These are monitoring targets, so the HST will obtain 4 sets of UV spectra of each star over an interval of about 3 weeks (3 rotation periods). In addition, both targets are in TESS sector 59, which will be observed continuously for 27 days, 26 November through 23 December.

Target Details:
    Target        RA  (J2000)  Dec               <V>      Range           HST  observation dates
1. GM Aur    04 55 10.98 +30 21 59.4    12.2     11.8-12.6 V    2022 26 November - 13 December
2. BP Tau     04 19 15.83 +29 06 26.9    12.1     11.5-12.7 V    2022 12 December - 2023  7 January

"I ask that those of you who can obtain CCD filter photometry (BVRI preferred, and U if you can) at least nightly for these targets:

1. GM Aur: now through 23 December

2. BP Tau: now through 7 January

"Please try to obtain 1% S/N (0.01 mag), so that colors are accurate to about 2% (0.02 mag).

"Additional exact times of the HST observations will be announced in an Alert Notice and in the above forum threads when available, " the hopes of obtaining exact simultaneity on occasion. But the important thing is to establish the trends in the color variability. Typical variability timescales are a few hours. TESS will catch the flares. Note that there will be no TESS coverage of BP Tau for the second half of the HST observations (23 December - 7 January); during this interval your photometry will be even more important.

"Thanks again for contributing to a very successful and productive program.

HST observations are currently scheduled for:

  1. Start time: 26 Nov 2022 20:57:24               End time: 26 Nov 2022 21:49:53  (completed)
  2. Start time: 28 Nov 2022 09:28:09               End time: 28 Nov 2022 10:20:38  (completed)
  3. Start time: 29 Nov 2022 18:47:44               End time: 29 Nov 2022 19:40:13  (completed)
  4. Start time: 01 Dec 2022 08:54:28               End time: 01 Dec 2022 09:46:57
  5. Start time: 02 Dec 2022 18:15:05               End time: 02 Dec 2022 19:07:34
  6. Start time: 04 Dec 2022 06:45:49               End time: 04 Dec 2022 07:38:18

  7. Start time: 06 Dec 2022 06:22:58               End time: 06 Dec 2022 07:15:27
  8. Start time: 07 Dec 2022 07:48:19               End time: 07 Dec 2022 08:40:48
  9. Start time: 09 Dec 2022 07:28:00               End time: 09 Dec 2022 09:11:19
10. Start time: 10 Dec 2022 11:56:02               End time: 10 Dec 2022 12:48:31

"Times are UT. Photometry leading up to, or during the HST observations, will be particularly useful."

Charts with comparison stars for these targets may be created using the AAVSO Variable Star Plotter (VSP).

Please submit observations to the AAVSO International Database using the names GM AUR or BP TAU, respectively.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen using material provided by Dr. Walter.


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