Northern T Tau stars campaign

This campaign on Northern T Tau stars is now concluded. Dr. Fred Walter, the Principal Investigator of this campaign, sends the following summary report and a thank you to the AAVSO:

Report on AAVSO Alert Notice 725: Campaign on Northern T Tauri Stars

F.M. Walter (Stony Brook University)

1. INTRODUCTION

On 12 November 2012 we issued Alert Notice 725, requesting photometric obser- vations in support of an HST program to obtain UV spectra of a sample of T Tauri stars in the Orion OB1b star forming region. The HST observations were planned to occur while the TESS spacecraft was imaging these regions.

The aim of the ground-based program is to obtain supporting optical and near- IR photometry and spectroscopy. TESS will return light curves with a 10 minute cadence nearly continuously for 27 days. The ground-based photometry will not be able to beat this, either for cadence or S/N, but will yield colors that will be indispensable for interpreting the TESS light curves (TESS operates in a single band, from approximately 600 to 1000 nm). We can also use calibrated R and I data from the ground to “calibrate” the TESS instrumental magnitudes.

The plan was to obtain good photometric coverage around the time of the HST observations, and to sample the light curves at other times during the TESS observa- tions. To supplement the Alert Notice, I requested observations from the AAVSOnet robotic telescopes during this time. We have also arranged for photometric coverage from HOYS, and from the Konkoly and Universita di Catania and other observatories in Europe.

Since the HST is scheduled without regard to ground-based considerations, and a given target is typically observable for about 1/3 of the night, the hope was that by getting many eyes on the targets we would obtain both simultaneity and a good record of the photometric behavior leading up to the time of the HST observations. This is important because the T Tauri stars vary irregularly for many reasons, in- cluding variable obscuration by circumstellar dust, brightening by accretion events, and magnetic flaring.

2. DATA AND RESULTS

It seems that the program has been successful. I thank the eleven observers (listed below) who have submitted data to the AAVSO (as of December 29). A summary of the number of observations made from November 6 through December 26 is given ’in Table 1 (the campaign formally ran 19 November through 17 December 2020). Unfortunately winter weather largely precluded getting observations simultaneously with the HST, at least from the western hemisphere.

Table 1. Observation summary

The HST data were obtained successfully. The TESS data should be on the ground and being processed. Analysis is proceeding on this and other ground-based data. Complete results will eventually be forthcoming.

ACKNOWLEDGEMENTS

I thank the AAVSO and their crew of volunteers and observers. We should all be grateful for their dedication to variable star science, and for filling in this niche which professional astronomers have largely abdicated. I thank Elizabeth Waagen for working with me on the AAVSO Alert Notice. Mostly I wish thank the eleven of you (BSEC DSN HBB HMB KSLA MGW OAAA PDM PJAD RZD SDM) who submitted observations to the AAVSO. It take a lot of observations to construct complete light curves of irregularly-variable stars, and your data will prove invaluable.

I'd like to again thank all of you who contributed to a very successful ground based photometric campaign.

But it's not over. For reasons I do not yet know, the HST observations of V510 Ori will be repeated Feb 12-13.

Because we will not have the TESS photometry, it is more important to have ground-based photometry this time around. So I'm asking any observers who can observe V510 Ori to do so now through the night of 14 February. Single snapshots each night will reveal long-trends in the variations. During the December campaign, which was very successful from a ground-based perspective,  V510 Ori appeared to have a 25 day periodic modulation with an amplitude of about 0.6 mag. But during the HST observations it brightened by 0.5 mag in the 24 hours as it recovered from what seemed to be a sharp dust dip (see http://www.astro.sunysb.edu/fwalter/SMARTS/Odysseus/v510ori.phot.html ).

I request BVRI CCD photometry. Orion is an early-evening target in February, so we'll need observers who are geographically-dispersed to ensure good coverage. Nightly snapshots suffice to establish the long-term trends; denser time coverage Feb 12-13 (exact times to be forthcoming) will help interpret the UV spectra.

UPDATED HST observing times:

The HST observations are scheduled from 0603-1328 UT on Feb 12 (the evening of Feb 11 for observers in the western hemisphere).

Unfortunately, this is best for observers in the mid-Pacific (anybody in Hawaii?). Observers in the southwestern US may be able to obtain simultaneous photometry in the hour or so before starset. Please obtain approximately nightly BVRI photometry through Feb 14, with a higher density of observations (if possible) on  Feb 12 UT.

Thanks,

Fred

AAVSO Alert Notice 728 reports on the scheduled re-observation by HST of V510 Ori, one of the targets in Dr. Walter's Northern T Tau campaign. Please see the notice for details and observing instructions.

There are threads for this campaign under the following forums:
- 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 astronomers and by HQ. Join in the discussion or ask questions there!

Many thanks, and Good observing,

Elizabeth O. Waagen, AAVSO HQ