Alert Notice 770: 4 T Tau stars to be observed by HST - EL Cha observations needed urgently now

February 28, 2022

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Dr. Frederick Walter (Stonybrook University) requests AAVSO observers' assistance in monitoring four T Tau stars in support of HST observations scheduled for March-April 2022.

Observations of EL Cha are needed urgently NOW through March 3 UT. The other three stars will be observed later in March and into April. The exact times for DI Cha, SY Cha, and TW Hya will be announced in the forum threads above when they have been scheduled by the HST team; approximate times are in the table below.

Dr. Walter, who thanks AAVSO observers for their contributions to this program to date, provides the following information:

"As part of the HST ULLYSES program (see earlier Alert Notices and YSO forum threads for details), the HST is scheduled to obtain UV spectra of a number of accreting T Tauri stars in the coming weeks. It would be helpful to have BVRI photometry for them in order to help interpret the UV spectra. These are southern targets, mostly in the Chamaeleon clouds (declination -78 deg).

The targets are:

Name R.A. (2000) Dec (2000) Range Mean mag HST schedule
EL Cha 08 42 39.29 -78 54 43.7 13.98-14.14 V V~14.1 2 March 2022 3:15 - 3 Mar 2022 07:10 UT
DI Cha 11 07 20.72 -77 38 07.3 10.65-10.74 V V~10.7 11 - 13 March 2022
SY Cha 10 56 30.48 -77 11 39.6 12.2-15.0 p V~12 22 - 25 March 2022
TW Hya 11 01 51.91 -34 42 17.0 10.6-11.3 V V~11 30 March 2022 - 15 April 2022 (12 observations)

Information from VSX, except for mean V (supplied by Dr. Walter)

"If you can observe these targets, please obtain digital BVRI photometry starting at least a week before the start of the HST observations, and continuing through the conclusion of the HST observations.

"It is important to get single BVRI sequences each night, but longer sets of data would be useful if they can be obtained simultaneously with the HST observations. There will not be any TESS observations", so your coverage is especially important. Note that it is extremely important to have a positive V observation 24 hours before the scheduled HST time.

Finder charts with comparison stars for the targets may be created using the AAVSO Variable Star Plotter (VSP). Sequences are being added; if they are not available at the time of your observation(s), please save your images and reduce them as soon as the sequences are available.

Please submit your observations to the AAVSO International Database using the names given in the table above.

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



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