A photometric and spectrographic study of RS Gruis.

Photometric (uvbyfi) and spectrographic observations of the dwarf cepheid RS Gru are described. The photometry suggests that the star is slightly reddened, E(h - y) = + . Intrinsic (b - y) and C1 values are used to derive the variations in temperature and surface gravity. The mean values are (Teff = 7620 K and (log g0 ) = 3.83. With the aid of Wesselink's method, a radius of 3.1 R0 is found. The radius and effective temperature indicate M = + 1.2 which agrees well with the value M = + 1.3 derived directly from the photometry. A mass of 2.4 9f0 is found from the radius and effective gravity. The radial -velocity data indicate that y = 82 km sec-1 and 2K = 49 km sec-1. Key words: variable star - photometry - radial velocity - pulsation