# Secondary stars in CVs - the observational picture

Source: [Secondary stars in CVs - the observational picture](<https://www.sota2.com/research/paper/68fa24b12c2a3760193a7a21>)

Collection index: [llms.txt](<https://www.sota2.com/research/llms.txt>)

Data updated: 2025-10-24T09:26:34.495Z

Authors: K. Beuermann

Published: 1999-09-08T14:20:33.000Z

## Abstract

Recent theoretical and observational progress has substantially improved the definition of the lower main sequence and established a new basis for a comparison of main sequence stars and the secondaries in CVs. The evolutionary sequences of Kolb & Baraffe \[1999\] imply that the secondaries in many CVs are expanded compared with main sequence stars of the same mass as a consequence of unusually high mass transfer rates and/or pre-CV nuclear evolution. We show that the location of the secondaries of all well-studied CVs in the spectral type period diagram implies that they are consistent with having near-solar metallicities. We show, furthermore, that the surface brightness of K/M stars depends on gravity and metallicity and present new Barnes-Evans relations valid for dwarfs of near-solar metallicity and the secondaries in CVs of the galactic disk population. Distances derived by the surface brightness method agree with recent measurements of the trigonometric parallaxes of a few selected systems.

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## Original sources and implementation

[Original paper](<https://arxiv.org/abs/astro-ph/9909141>)

[PDF](<https://arxiv.org/pdf/astro-ph/9909141.pdf>)