Photometric monitoring of T Tauri stars, RS CVn stars and related objects

Abstract

A program of photometric monitoring of T Tauri stars, Ae-irregular variables, and RS CVn stars is in its third year of operation at Van Vleck Observatory. Results from the first year were published by Herbst, et al. (1982; Paper I), and from the second year will appear in the November 1983 issue of AJ, (Paper II). Stars observed so far include the following: T Tauri (RW Aur, SU Aur, RY Tau, T Tau, CO Ori); Herbig Ae/Be (BD+40 ° 4124, BD+4~ 3731, BD+6~1283, BD+46 ° 3471, BD+61 ° 154, AB Aur, Z CMa); Ae-Irregular (BF Ori, UX Ori, WW Vul); RS Cvn and related (FK Com, DM UMa). On the program this year, in addition to several of the stars listed above, are T Ori, GW Ori and HH Aur. We are very interested in coordinating observations of these or other similar stars with the efforts of spectroscopists, IUE observers, or infrared observers. Anyone wishing to propose a collaborative effort should contact W. Herbst. Observations are made with a single-channel photometer attached to the 60 cm Boller and Chivens reflector (the Perkin telescope) of the Van Vleck Observatory. A GaAs tube is used permitting UBVRI (Cousin's system) data to be obtained. Narrow and intermediate band filters centered on Ha and the K-line of CaII are also used. Our limiting magnitude, set by the extremely bright sky at our on-campus location, is V ~13. We prefer to work considerably brighter than that. All observations are made differentially. There have been roughly 40 useful nights per 6-month observing season during the past few years. Data handling and reduction are highly automated (through an LSI 11/02 microprocessor linked to Wesleyan's mainframe computer), permitting quicklooks, and an easy, efficient observing environment. An award from the Dudley Observatory to W. Herbst and H.L. Nations has made it possible for us to begin construction of a fully automated photometric system, capable of being operated remotely. Hopefully the new system will be in place by next Fall. As a single example of results obtained so far from our program, we discuss in this paper, data obtained on five T Ori stars and its interpretation. A T Ori star is one which exhibits large, aperiodic drops in brightness by ~0.5 to 3 mag on timescales of ~i week, followed by an equally rapid recovery. Between minima, most stars remain close to maximum light with only small amplitude, irregular fluctuations. There are five T Ori stars on our program, the three Ae-irregular variables plus the two G-type T Tauri stars, CO Ori and SU Aur. Last year's light curve for UX Ori is shown in Paper II and is an example of typical T Ori-type behaviour. Near maximum light, the spectra of all five program stars are predominantly photospheric in nature, with relatively weak He emission. To substantially reduce the