A redetermination of the luminosity, distance, and reddening of beta Lyrae.

Abstract

The authors have redetermined the distance to β Lyrae and found that it probably lies between 345 and 400 pc, with the most likely value being 370 pc. With the corresponding true distance modulus of 7.8 mag, they find that the eclipsing system of β Lyrae has a maximum absolute visual magnitude of -4.7 mag. Using Wilson's model, the authors conclude that the average absolute visual magnitude of the primary component is -4.1 mag, so that the star is best classified as B8.5 or B9 II-Ib. The visual absolute magnitude of the secondary component is -3.3 mag. The color excess is small, E(B-V) = 0.04 mag. These data are based on optical and IUE scans of the brightest visual companion to β Lyrae, HD 174664, and on an analysis of the hydrogen line profiles in its spectrum. The authors find that the star is mildly evolved within the main-sequence band. Its effective temperature (14250K) and surface gravity (log g ≅ 4.0) correspond most closely to those of stars classified as B6 V. This conclusion creates a certain evolutionary dilemma, since the age of HD 174664 should not exceed 20 - 30 million years if the basic model of β Lyrae as an Algol-type binary is correct while the authors' result is 48×10⁶yr.