Alert Notice 788: RU Lup monitoring needed for HST observations

August 1, 2022

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Further to AAVSO Alert Notice 751, Dr. Frederick Walter (Stony Brook University) requests AAVSO observers' assistance in monitoring the classical T Tau star RU Lup in support of observations with HST scheduled for August 10-20, 2022.

Dr. Walter writes: "The HST will monitor the pre-main sequence star RU Lup, obtaining 12 sets of ultra-violet spectra spread over roughly three stellar rotations during August 10-20. This time RU Lup will not be observed simultaneously with TESS, so ground-based observations are critical if we are to place the HST observations in a long-term context. Also unlike during last August's campaign, XMM observations of RU Lup will not take place.

"RU Lup is a bright, highly active classical T Tauri star in the Lupus star formation region. The rotation period is about 3.7 days. The system is almost pole-on, so stochastic variability dominates over rotational modulation. The VSX catalog reports it as faint as V=12.9, but it is generally closer to around V=10.8 [as of August 1, 2022, it is ~10.6 V, according to the AAVSO International Database]. The TESS data from 2019 show peak-to-peak variations of 0.8 mag.

"While you should try to get data while HST is observing, it is also important to get as complete coverage as possible from now through August 21 UT. 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.

"Filter Requirements: It is important to use standard broadband filters. Concentrate on B and V, and then Rc and Ic. T Tauri stars tend to be more variable at shorter wavelengths."

Coordinates (2000.0): R.A. 15 56 42.31  Dec. -37 49 15.5   (from VSX page for RU Lup)

Range: 9.8 - 12.9 V

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

Please submit your observations to the AAVSO International Database using the name RU LUP.

Targets for this large, multi-stage campaign (ODYSSEUS) have been announced and discussed in numerous AAVSO Alert Notices, beginning with AAVSO Alert Notice 741.

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


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