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Astron. Astrophys. 338, 947-956 (1998)

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Phase-resolved optical photometry and spectroscopy of the supersoft X-ray binary 1E 0035.4-7230 *

A. van Teeseling 1, K. Reinsch 1, M.W. Pakull 2 and K. Beuermann 1

1 Universitäts-Sternwarte Göttingen, Geismarlandstrasse 11, D-37083 Göttingen, Germany
2 Observatoire de Strasbourg, URA 1280 du CNRS, F-6700 Strasbourg, France

Received 7 May 1998 / Accepted 3 August 1998

Abstract

We present phase-resolved optical photometry and spectroscopy of the supersoft X-ray binary 1E 0035.4-7230 (= SMC 13). The average U, B, V, and R light curves show an almost perfect sinusoidal [FORMULA] mag modulation on the 4.1 hr orbital period, but in individual binary orbits there can be significant deviations from the average light curves. There is a significant [FORMULA] variability with a standard deviation of 0.04 mag, and which may be related to the orbital phase. The binary appears to be bluest [FORMULA] in orbital phase before optical minimum. Modeling of the light curves indicates an orbital inclination of [FORMULA] and a mass ratio [FORMULA] (with [FORMULA] the mass of the accreting star). The observed optical modulation is probably dominated by the changing aspect of the irradiated companion star, which has effective temperatures on the irradiated side [FORMULA] K. Our spectra show variable He II [FORMULA] emission, and broad Balmer absorption lines. The latter appear more prominent when the companion star is closest to us. Modeling the optical spectrum of the irradiated companion star by a composition of normal stellar spectra reproduces the observed colour and amplitude of the modulation, but predicts too strong Balmer absorption lines which must be significantly weaker because of strong irradiation.

Key words: accretion, accretion disks – stars: individual: 1E 0035.4-7230 – novae, cataclysmic variables – white dwarfs – X-rays: stars

* Based on observations collected at the European Southern Observatory, La Silla, Chile: ESO No 56.D-0589, 58.D-0275

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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998
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