AN AUTOMATED SEARCH FOR VARIABILITY IN CHROMOSPHERICALLY ACTIVE STARS

We have completed an automated photometric survey of 66 potential or k nown chromospherically active late-type stars with the 0.4 m Vanderbil t/Tennessee State robotic telescope. The precision of the observations from this telescope matches that predicted from photon and scintillat ion noise alone and represents a significant improvement in the precis ion of previous robotic telescope surveys of chromospherically active stars. Light variability has been detected and its period has been det ermined for 47 stars, 41 of which are newly discovered variables. The primary mechanism of variability is rotational modulation of a spotted surface. In addition we have detected eclipses in HD 62668 and HD 141 690 and the ellipticity effect in HD 223971. The light variations of H D 181475 are the result of pulsation while the variability mechanism o f Hf, 99267, a newly identified member of a small group of early-F sta rs, is so far unidentified. High-dispersion spectroscopic observations of all the variable stars also have been obtained and analyzed to det ermine spectral type, v sin i, and velocity variability for each star. As a by-product of the spectral-type determinations, approximate abun dances for a number of supposed metal-poor binaries have been determin ed by comparison with stars of known abundances. In most cases our abu ndances are much closer to the solar value than those previously measu red. The minimum radius and Rossby number of each spotted star have be en computed. We also have determined whether or not the spotted compon ent of each binary system is synchronously rotating. Important questio ns remain about the evolutionary state or duplicity of some of our sta rs, including HD 17925, HD 22694, HD 29697, HD 51066, HD 72146, HD 988 00, ED +13 degrees 13, ED +70 degrees 959. Candidates for Doppler imag ing include HD 51066, HD 82286, HD 171488, and HD 208472. (C) 1995 Ame rican Astronomical Society.