Wing Near-Infrared, TiO-Band, andV-Band Photometry of Chromospherically Active Star Andromedae

Abstract

As a pilot program, Wing near-IR, TiO-band, and V-band photometry is being conducted of the RS Canum Venaticorum type, chromospherically active, G8 IV–III star λ Andromedae. The objective is to investigate a possible relationship between variation of the ~54 day rotationally starspot modulated visual light curve and TiO absorption strength. The TiO (γ, 0, 0) absorption band strength at λ = 719 nm is very sensitive to temperature for cool stars and manifests itself in cooler starspot regions (T ≤ 4000 K). TiO photometry has an advantage over conventional photometry in that it provides unambiguous measures of the fractional cool starspot coverage. In addition, as the stars rotate, the variation in the TiO index yields information about the longitudinal distribution of the starspots. Importantly, combining the TiO photometry with the V-band and near-IR light curves allows the discrimination of white-light faculae (=hot spot) and cool starspot contributions. Initial results of this study indicate that the observed V-band and near-IR continua light variations found for λ And primarily arise from bright spot (plage) features rather than dark starspots as is usually assumed. This is in contrast to current theories that the visual light variation is solely due to dark spots. Models using both bright and dark spot features have been developed and are being used to fit the light and TiO-index curves. The models account for cool/hot spot characteristics such as projected filling factor and temperature. The long-term variation of V light and TiO index have been investigated to search for any activity cycles.