A model of the Algol type close binary TT Hydrae

Abstract

UBV photometric observations and elements of TT Hydrae obtained by Kulkarni and Abhyankar (1980) are combined with the radial velocity curve of Popper (1979, personal communication) to derive the absolute dimensions and a model of this important Algol system. While the photometric ratios of radii in V and B are in agreement giving k = 0.3812 for a limb darkening coefficient of x = 0.6, application of Irwin's (1947) method gives x = 0.4 for U. The primary is found to be a main sequence A1 V star of mass 2.61M_⊙ and radius 2.01 R_⊙, and the secondary is classified as a K1 III star of mass 0.70 M_⊙ and radius 5.33 R_⊙. The observed Fourier coefficients for the light outside the eclipse agree with those calculated from theory for the reflection and ellipticity effects. The system shows an ultraviolet excess of 0.5 to 0.6 magnitudes during primary eclipse, which is attributed to an asymmetric circumstellar distribution of matter around the primary. The evolutionary status of the secondary, which does not appear to fill its Roche lobe completely, is discussed.