Alert Notice 741: Southern T Tau Stars campaign in support of HST and TESS observations

Note:  HST will be observing Sz 76 again on August 8  from 11:27:38 through 18:56:12 UT. Please add this target to your observing queue if practical. Dr. Walter remarks that there will be no TESS data, so frequent (at least nightly) BVRI observations will be helpful for setting the context for the HST spectra.  -  Elizabeth O. Waagen, August 2, 2021

The HST observations of NSV 20468 (Sz 130) and SSTc2d J160000.6-422158 have been scheduled as follows:

 - NSV 20468 (Sz 130):  22 Jul 2021 13:17:02 - 22 Jul 2021 21:32:41
 - STc2dJ 160000.6-422158: 23 Jul 2021 04:28:52 - 23 Jul 2021 16:19:45

Please observe these targets through July 23.  -  Elizabeth O. Waagen, July 21, 2021

The HST observations have been postponed. Please continue to monitor the targets until HST can observe them, and continue to monitor targets as needed for TESS.  -  Elizabeth O. Waagen, July 6, 2021

Two targets from Table 2 have been scheduled for HST:

NSV 20468 (Sz 130)    16 00 31.25    -41 43 37.2  14.7   HST: June 20        TESS: 5/26 - 6/24

NSV 20520 (SZ 111)    16 08 54.69    -39 37 43.1 14.0    HST: June 20        TESS: 5/26 - 6/24

                                                                                              - Elizabeth O. Waagen, May 25, 2021

The HST observation dates for GQ Lup and HM Lup have been switched by the HST team. GQ Lup will be observed on May 3 and HM Lup on May 4. The times of observation are unchanged.  -  Elizabeth O. Waagen, April 29, 2021

April 23, 2021

AAVSO Forum threads (scroll to the bottom of a thread for latest posts):
- Campaigns and Observation Reports: https://www.aavso.org/hst-ulysses-southern-t-tauri-campaign-01
- Young Stellar Objects: https//www.aavso.org/hst-ulysses-southern-t-tauri-campaign
Please subscribe to these threads if you are participating in the campaign so you can be updated by the astronomer and by HQ. Join in the discussion or ask questions there!

Dr. Fred Walter (Stony Brook University) requests AAVSO observers to monitor 17 Southern T Tau stars in support of a multi-site multiwavelength campaign, including observations by HST and TESS, being carried out in April - June 2021. An 18th star is included in this request and is being observed by TESS although not by HST. He provides the following information:

"Part III of the ODYSSEUS pre-main sequence star program starts later this month. 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.

"Thanks to all of you who participated in and obtained data for Parts I (13 Northern T Tauri stars, Alert Notice 725) and II (monitoring of TW Hya, Alert Notices 731, 733, 737) of this program.

"The HST will obtain snapshots of a number of pre-main sequence (T Tauri) stars in the South over the coming months. The 17 targets for this campaign are all brighter than V~16. Most of these observations will take place while the targets are in the TESS field, yielding about 27 days of continuous 600-1000nm photometry with a 10-minute cadence.

"TESS data, both in terms of length of coverage and data quality, cannot be matched from the ground, but TESS is a single channel photometer operating in the red. We need ground-based optical photometry to place the TESS magnitudes in context, and determine what the stars may have been doing when HST was observing them.
- Pre-main sequence stars may experience enhanced accretion events or long-lived flares, either of which cause the star to become bluer, and
- they may experience variable circumstellar extinction, which may cause the star will become redder, or
- if the variable extinction is caused by optically-thick (opaque) irregularities in the circumstellar disk, their colors may not change as they fade.
Clearly, changes in extinction in particular are important for interpreting the UV spectra, which are very sensitive to the absorption.

The targets scheduled for late April through early June are given in the tables below.

Table 1: Scheduled Southern Targets

Table 2: Southern Targets - HST times to be scheduled (these targets will be moved to Table 1 as they are scheduled)

"Target Notes:

- The TESS column indicates the dates that the target is in the TESS field. CHX 18N and T Cha are near the ecliptic pole, and will be viewed for 54 days.

- Note that the HST times are preliminary and may yet change, but it is likely they will fall within the posted window. The final schedule will be posted in the forum threads given above when available.

- T Cha is not an HST target; please obtain occasional observations while the target is in the TESS window to let us correlate colors with TESS magnitudes.

- RU Lup will be monitored by the HST for 12 days during its plan window. It will not be observed with TESS.

- Information on the other targets in this campaign will be posted in the forum threads as it becomes available.

Timing Requirements: CCD filter photometry on the 3 nights surrounding the HST observation. Observe during the time of the HST observation, if possible. If not possible (2/3 of the HST observations will take place while the target is below the horizon or in daylight from any particular observatory), please get CCD filter photometry before and after the HST observations. There is no need to obtain long time series; TESS will provide that.

Filter Requirements: It is important to use standard broadband filters. Concentrate on B and V, which TESS does not observe, and on Rc and Ic, which will enable cross-calibration with TESS. T Tauri stars tend to be more variable at shorter wavelengths.

TESS color calibration: Two or more sets of BVRcIc observations during the 27-day TESS window will help us “calibrate” the TESS photometry, and correlate color changes with brightness changes.

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

HST observing times will be announced in the Discussion Forum threads given above. It is essential for observers to subscribe to these forum threads to be kept informed and plan their observing time most productively.

Finder charts: Finder charts with comparison stars for the targets may be created using the AAVSO Variable Star Plotter (VSP).

Please submit observations to the AAVSO International Database using the primary names given in Table 1.

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

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