Alert Notice 737: HST observing schedule for TW Hya - final set of observations

April 2, 2021

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Further to AAVSO Alert Notices 731 and 733, Dr. Fred Walter (Stony Brook University) informs us that the final set of HST observations of the T Tau star TW Hya will take place as follows:

05 Apr 2021 03:49:55 - 04:42:57 UT
05 Apr 2021 13:21:38 - 14:14:40
06 Apr 2021 13:10:56 - 14:03:58
07 Apr 2021 13:00:14 - 13:53:16
08 Apr 2021 12:52:27 - 13:45:29

As was needed for the previous set of HST observations, Dr. Walter says that "the important thing is to get dense-enough establish trends and periodicities."

Observations are requested in four bands (B,V and either Cousins RI (preferred) or Sloan ri). Once the HST observations are completed, please continue to monitor TW Hya through April 15, but at a lower cadence, with one observation per night. The satellite TESS has completed its observations of TW Hya.

"TW Hya is fairly bright, with a mean V ~ 11, and a historical range from 10.6 to 11.3 (from VSX). The typical day-to-day range of variability is +/- 0.1 mag. I seek to extract colors accurate to better than 2% (0.02 mag), which requires CCD photometry accurate to better than 0.01 mag."

TW Hya is being observed as part of the ODYSSEUS pre-main sequence star program that is underway. As noted in Alert Notice 731, 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.

Coordinates (2000.0): 11 01 51.91 -34 42 17.0 (from VSX page for TW Hya)

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

Please submit observations to the AAVSO International Database using the name TW HYA.

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



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