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Issue A&A Volume 370, Number 2, May I 2001 Page(s) 507 - 512 Section Formation, structure and evolution of stars DOI 10.1051/0004-6361:20010261

A&A 370, 507-512 (2001)
DOI: 10.1051/0004-6361:20010261

UY Ursae Majoris: A W-subtype W UMa system with a small mass ratio

Y. Yang^{1, 2, 3}, Q. Liu^{1, 2, 3} and K.-C. Leung<sup>4

1</sup>  Yunnan Observatory, Chinese Academy of Sciences, Kunming, Yunnan Province, PR China
²  United Laboratory of Optical Astronomy, Chinese Academy of Sciences, PR China
³  National Astronomical Observatories, Chinese Academy of Sciences, PR China
⁴  Department of Physics and Astronomy, University of Nebraska, Lincoln, USA

(Received 10 November 2000 / Accepted 31 January 2001)

Abstract
We present light curves and photometric solutions of the contact binary UY UMa in this paper. The light curves appear to exhibit a typical O'Connell effect, with Maximum I being 0.034 mag(V) and 0.030 mag(B) brighter than Maximum II, respectively, and Maximum I shifting to phase 0.26. The light curves are analyzed by means of the latest version of the WD program. The results show that UY UMa is a W-subtype contact binary with a small mass ratio q=0.134. The asymmetry of the light curves is explained by star spot models. From the collected data of 9 UMa contact systems with a smaller mass ratio than 0.20, the nature of the secondaries is analyzed. The results show that the luminosities and densities of the secondaries could be controlled by the primaries and that the smaller the mass ratio, the stronger the control.

Key words: stars: binaries -- starspots -- stars: variables: general

Offprint request: Y. Yang, bily@public.km.yn.cn

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