Alert Notice 725: Campaign on Northern T Tau Stars

Note: V510 Tau, one of the stars in this campaign, will be re-observed by HST on 2021 February 12-13 UT. Please continue your observations (highest priority are V and B, then Rc and U), obtaining a few observations each night from now through February 15.  -  Elizabeth O. Waagen, 1 February 2021

November 12, 2020

AAVSO Forum threads (scroll to the bottom of a thread for latest posts):
- Campaigns and Observation Reports: https://www.aavso.org/northern-t-tau-stars-campaign
- Young Stellar Objects: https//www.aavso.org/northern-t-tau-stars-campaign-01
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 13 Northern T Tau stars in support of a multi-site multiwavelength campaign being carried out in November and December. He provides the following information:

The HST ULLYSES project (Ultraviolet Legacy Library of Young Stars as Essential Standards – https://www.stsci.edu/stsci-research/research-topics-and-programs/ullyses); is designed to obtain a statistically complete catalog of ultraviolet observations of a set of galactic stars while the HST can still obtain UV spectra. Our interest is in a sample of T Tauri stars. This AAVSO campaign will be part of a larger program called ODYSSEUS (Outflows and Disks around Young Stars: Synergies for the Exploration of Ullyses Spectra), which includes ground-based optical and near-IR photometry and spectroscopy.

The first part of this project involves obtaining UV spectra of 13 stars in the Orion OB1 and σ Ori star forming regions in November/December 2020.

These targets will be observed with the HST while they are in the TESS field of view. TESS gets broadband (600-1000nm) optical photometry on a 10 minute cadence for typically 27 days. The HST will obtain ultraviolet spectroscopy. The goal of this observing campaign is to supplement the TESS photometry with filter photometry. It is hard to beat the time coverage of the S/N of the TESS data, or the continuous 27 day cadence, but AAVSO observers can get the color information which helps distinguish the possible causes of brightenings and fadings in the light curve, which may include magnetic flares, enhanced accretion rates, starspots, and obscuration by a warped dust disk.

The science goals are to understand the disk accretion processes that build up stars and drive their outbursts.

1.  Snapshots of Northern T Tauri Stars (November-December 2020)

13 low mass PMS stars in Orion will be observed with TESS 11/19 - 12/17/2020, and with the HST for a few hours during that window. They are listed, in order of decreasing brightness, in Table 1. The dates in Table 1 are the current windows for the HST observations. The orbits column gives the number of 96 minute orbits that will be scheduled for each target. The exact times of the HST observations will be known about 2 weeks in advance.

We ask AAVSO observers to add these targets to their observing lists.

HST observing times will 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.

Table 1: Northern Odysseus Targets

*See note below under Finder Charts about observing this star.

Timing Requirements: CCD filter photometry during the HST observations, 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 Ic, which will enable cross-calibration with TESS. Rc and U are also useful. 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 (11/19-12/17) will help us “calibrate” the TESS photometry, and correlate color changes with brightness changes.

2.  Other Photometry

The Odysseus team is arranging for other optical photometry. Among the efforts, either proposed, accepted, or scheduled are:

 - Northern hemisphere: Catania 0.91m BV RIZ+Hα; Konkoly RC80 BV RI/BV ri; Grankin 1.25m BV RI; 0.7-2.3m Thai telescopes; HOYS amateurs

 - Southern hemisphere: SAAO

 - Both hemispheres: Las Campanas Observatory u′V i

AAVSO observations will complement these other data and assist our goal of achieving dense photometric coverage on this large number of targets.

3.  Data Analysis

The HOYS (Hunting Outbursting Young Stars, https://hoys.space) project has suggested that they could take in images and process them uniformly. We will inform observers if this option becomes available. However, there will not be any requirement to share your raw images. It goes without saying that results should be submitted as usual to the AAVSO. All targets are in the VSX database.

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

Two of the targets have special observing requirements. Please follow these instructions:

a. CVSO-165, which has a 15.3 mag. companion only 5" away
- The companion is much fainter than the primary, so the primary is the target.
- If you do not have the resolution to separate them, the combined brightness will do. TESS has 21" pixels.
- Save the images - in rare cases we may want to look at them in greater detail.

b. NSV 2091 (CVSO-104), which is a pair of similar-magnitude stars separated by 2.4"
- The HST target is the western star of the pair. It is also known as Haro 5-64A and Gaia DR2 3217634157789741952. If observers can separate the pair, they should aim for the western star. The eastern star is thought to be a background G/K star, and is not known to be variable.

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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