Monitoring Stars in Young Clusters at Van Vleck Observatory

A program to monitor fields in young clusters with a CCD camera attached to the 0.6m Perkin telescope on the campus of Wesleyan University has been in place since 1991. Prior to that, dating from about 1982, we monitored T Tauri stars individually with a photoelectric photometer attached to the same telescope. There have probably been about 200 Wesleyan students and summer students from the Keck Northeast Astronomy Consortium involved in this work over the years, but I have lost count! Some highlights of the early work included the discovery of the rotation period of T Tauri itself and the discovery of the binodal period distribution in the Orion Nebula Cluster.

The program today concentrates on several clusters, including the ONC, NGC 2264, IC 348 and others. We have discovered several stars with odd and particularly interesting behavior including KH 15D, HMW 15 and the first T Tauri star known to show a significant change in rotation period, clearly indicative of differential rotation.

Details about the observing program are given in the papers but a brief overview is provided here. We usually have about 45 clear or partly clear nights per observing season during which we obtain useful data. Typical seeing at our site is about 2.5 arc-seconds. A typical limiting magnitude for accurate photometry (0.02 mag or better) is about I = 16 mag. Our procedure generally yields an accuracy of about 0.005 mag for stars brighter than about I = 14. This limit seems to be set by our ability to flat field, which is done with evening sky flats. In a typical season we monitor about 12 different fields containing a total of around 700 pre-main sequence stars. Most of our work has been done only in the I band of the Cousin’s system. Recently, we have done more BVRI work.

Since 2007 we have also been monitoring the bright stars of the Trapezium using extremely short exposures. Our goal in this is primarily to study the unusual eclipsing binary BM Orionis. As of 2008 we are also establishing a collaboration with Marina Romanova of Cornell to test predictions of her magnetohydronamic accretion models and to account for the unusual properties of the UX Orionis stars.

T Tauri Photometry Data Base

In the early 1990’s we assembled a data base of repeated UBVRI photometry of T Tauri stars, Herbig Ae/Be stars and FUors in order to study the nature of their variability, These data are gleaned from the literature or from our own photometry. The data base and its analysis at that time are described in the paper “Catalogue of UBVRI photometry of T Tauri Stars and Analysis of the Causes of their Variability”, Herbst et al. 1994, The Astronomical Journal 108, 1906. Much of the data came from the ROTOR program carried out at Maidanak Observatory in Uzbekistan by Valery Shevchenko and his colleagues Mansur Ibraghimov and Konstantin Grankin. Recently we have monitored potential targets for the SIM YSO project led by Chas Beichman of the Michelson Science Center.

You may access the current version of the data base at this URL:

https://wesfiles.wesleyan.edu/home/wherbst/web/TTauriDataBase/

The data can be ftp-ed and may be used for any lawful purpose. Please reference the original paper on the formation of this data base, which is:

“Catalogue of UBVRI Photometry of T Tauri Stars and Analysis of the Causes of their Variability”

Herbst, W. , Herbst, D. K., Grossman, E. and Weinstein, D. 1994, AJ 108, 1906.

For questions, problems or additions to the data base please contact W. Herbst via e-mail.

Grant Support and Acknowledgments

T Tauri monitoring has been supported at Wesleyan since 1980 by a variety of funding agencies to whom we are deeply indebted. The first photometer was attached to the Perkin telescope in 1981 and built with grants from the Research Corporation and the Perkin Fund. NSF support began in 1981 and continued well into the 1990’s. More recently, support has come from NASA through its Origins of Solar Systems program. We are also grateful to the W. M. Keck Foundation, which provided money for the first CCD camera as part of its support for the Keck Northeast Astronomy Consortium, of which Wesleyan is a member. Joint research with Valery Shevchenko’s group at Maidanak has come from the U. S. Civilian Research and Development Fund for States of the Former Soviet Union. I would be remiss in this acknowledgment not to thank the Wesleyan administration over the years for its strong support of our program, including a substantial equipment grant that allowed us to recently upgrade the CCD camera. In all of this, the Wesleyan Science machine shop and electronics shop have  been a vital component. Finally, I personally would like to thank all of the wonderful students who have not only participated in the project but moved it forward year by year.