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Astron. Astrophys. 361, 982-990 (2000)

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Evidence for a hot spot in the contact binary VW Cephei

I.B. Pustylnik 1 and P.G. Niarchos 2

1 Department of Astrophysics, Tartu observatory, Tartu region, Toravere 61602, Estonia (izold@aai.ee)
2 Department of Astrophysics, Astronomy and Mechanics, Faculty of Physics, University of Athens, Panepistimiopolis, 15784 Zografos, Athens, Greece (pniarcho@cc.uoa.gr)

Received 31 March 2000 / Accepted 3 July 2000

Abstract

We study the nature of asymmetry and the intrinsic variability in the light curves of VW Cep. We analyze our own B,V light curves as well as other data from published sources. In view of the presence of significant intrinsic brightness variations at a level of [FORMULA] on time scales comparable to the orbital period we deal only with individual light curves sampled in one-two consecutive orbital cycles. The manifold evidence for the presence of a small hot spot region close to the neck connecting both components is summarized: a) displacements of the brightness maxima from the predicted epochs of elongations suggestive of an additional energy input presumably of hot chromospheric origin, b) the overall pattern of asymmetry in brightness maxima and minima, c) systematic colour changes with the orbital phase, d) the presence of significant cosine odd harmonics in truncated series of the observed light curves. We find that a hot spot with a characteristic size of [FORMULA] and the temperature contrast [FORMULA] located on the surface of the more massive star can explain the afore-mentioned peculiarities and model light curves based on our model give a rather good fit to the observed data studied so far. The possible physical nature of the hot spot in the light of our results compared with the spectroscopic data (specifically Mg II resonance doublet) and flare activity signatures are briefly discussed.

Key words: stars: binaries: close – stars: binaries: eclipsing – stars: individual: VW Cep

Send offprint requests to: I.B. Pustylnik

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© European Southern Observatory (ESO) 2000

Online publication: October 10, 2000
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