An Automated Search for Variability in Chromospherically Active Stars

We have completed an automated photometric survey of 66 potential or known chromospherically active late-type stars with the 0.4 m Vanderbilt/Tennessee State robotic telescope. The precision of the observations from this telescope matches that predicted from photon and scintillation noise alone and represents a significant improvement in the precision of previous robotic telescope surveys of chromospherically active stars. Light variability has been detected and its period has been determined 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 141690 and the ellipticity effect in HD 223971. The light variations of HD 181475 are the result of pulsation while the variability mechanism of HD 99267, a newly identified member of a small group of early-F stars, is so far unidentified. High-dispersion spectroscopic observations of all the variable stars also have been obtained and analyzed to determine spectral type, υ sin ι, and velocity variability for each star. As a by-product of the spectral-type determinations, approximate abundances for a number of supposed metal-poor binaries have been determined by comparison with stars of known abundances. In most cases our abundances are much closer to the solar value than those previously measured. The minimum radius and Rossby number of each spotted star have been computed. We also have determined whether or not the spotted component of each binary system is synchronously rotating. Important questions remain about the evolutionary state or duplicity of some of our stars, including HD 17925, HD 22694, HD 29697, HD 51066, HD 72146, HD 98800, BD +13°13, BD +70°959. Candidates for Doppler imaging include HD 51066, HD 82286, HD 171488, and HD 208472