The Coefficient of Limb Darkening for YZ (21) Cassiopeiae in Red Light.

The eclipsing variable YZ Cassiopeiae has been observed with a red-sensitive caesium-cell photo- electric photometer, resulting in a light-curve having the necessary degree of precision for the calculation of darkening coefficients. Descriptions of the methods used for observing and for analysis are given. The color class of the secondary component was determined as F5, in agreement with earlier work. The darkening coefficient of the A3 component is 0.33, that of the F5 component is 0.5 at a mean wave length of X6700. INTRODUCTIO