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Astron. Astrophys. 364, 199-204 (2000)


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Spectrophotometry and period analysis of the sdB eclipsing binary HW Virginis

L.L. Kiss 1,3, B. Csák 2, K. Szatmáry 1, G. Furész 1,3 and K. Sziládi 1,3

1 University of Szeged, Department of Experimental Physics and Astronomical Observatory, Szeged, Dóm tér 9., 6720 Hungary
2 University of Szeged, Department of Optics & Quantum Electronics, POB 406, 6701 Szeged, Hungary
3 Guest Observer at Konkoly Observatory

Received 19 July 2000 / Accepted 19 October 2000

Abstract

New CCD observations of the pre-cataclysmic binary HW Virginis are presented and discussed. The R-filtered CCD photometry was supplemented with medium-band (Cousins VRI) spectrophotometry based on low-resolution objective-prism spectra. The period variation is reanalysed by means of the standard O-C technique. The new data support the conclusions of Kilkenny et al. (2000) on the strong and continuous period change. The long-term period variation can be described approximately with two linear branches in the O-C diagram corresponding to a sudden period jump between two constant periods around JD 2448500 (1991). Additional smooth small-scale changes in the period distort the linearity. The present data do not support the hypothetical light-time effect of Çakirli & Devlen (1999).

The eclipse depths in V, R, and I do not show colour dependence, which suggests negligible continuum variations due to the cool secondary component in the far-red region (up to 8800 Å). The magnitude of the reflection effect was used to estimate the mean effective temperature of the illuminated hemisphere of the secondary. The result is 13300[FORMULA]200 K or 11000[FORMULA]200 K, depending on the primary temperature (35000 K or 26000 K). An albedo near unity is implied for the cool component.

Key words: stars: binaries: close – stars: individual: HW Vir

Send offprint requests to: l.kiss@physx.u-szeged.hu

© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000

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