MAPPING STELLAR SURFACE FEATURES

Abstract

New photometric and spectroscopic observations of the RS Canum Venaticorum binaries cr Geminorum and UX Arietis are reported along with details of the Doppler imaging program SPOTPROF. The observations suggest that the starspot activity on a Gem has decreased to 0.05 mag in two years. A photometric spot model for September 1984 to January 1985 found that a single spot covering 2% of the surface and 1000 K cooler than the surrounding photosphere could model the light variations. Equivalent-width observations contemporaneous with the photometric observations did not show any significant variations. Line-profile models from SPOTPROF predict that the variation of the equivalent width of the 6393 A Fe i line should be ~ 1 mA. Photometric observations of UX Ari from January 1984 to March 1985 show an 0.3-mag variation indicating a large spot group must cover the surface. Contemporaneous spectroscopic observations show asymmetric line profiles. The Doppler imaging and the photometric light-curve models were used in an iterative method to describe the stellar-surface spot distribution and successfully model both the photometric and the spectroscopic variations. A number of spots covering 12% of the surface and 1000 K cooler than the surrounding photosphere are necessary to account for the observations. Estimates of the vertical component of the magnetic field yield a field strength of 2.5 kgauss. In addition, the construction of a Reticon solid-state detector system at Ritter Observatory is described. The system is capable of producing a signal-to-noise ratio of 200:1 with an image intensifier and over 400:1 without the image intensifier.