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arXiv · 0704.1780

HS1857+5144: A hot and young pre-cataclysmic variable

A. Aungwerojwit·B. T. Gaensicke·P. Rodriguez-Gil·H. -J. Hagen·O. Giannakis·C. Papadimitriou·C. Allende Prieto·D. Engels
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Abstract

We report the discovery of a new white dwarf/M dwarf binary, HS1857+5144, identified in the Hamburg Quasar Survey (HQS). Time-resolved optical spectroscopy and photometry were carried out to determine the properties of this new cataclysmic variable progenitor pre-CV). The light curves of HS1857+5144 display a sinusoidal variation with a period of Porb=383.52 min and peak-to-peak amplitudes of 0.7 mag and 1.1 mag in the B-band and R-band, respectively. The large amplitude of the brightness variation results from a reflection effect on the heated inner hemisphere of the companion star, suggesting a very high temperature of the white dwarf. Our radial velocity study confirms the photometric period as the orbital period of the system. A model atmosphere fit to the spectrum of the white dwarf obtained at minimum light provides limits to its mass and temperature of Mwd=~0.6-1.0 Msun and Twd=~70000-100000 K, respectively. The detection of HeII 4686 absorption classifies the primary star of HS1857+5144 as a DAO white dwarf. Combining the results from our spectroscopy and photometry, we estimate the mass of the companion star and the binary inclination to be Msec=~0.15-0.30 Msun and i=~45-55 deg, respectively. We classify HS1857+5144 as one of the youngest pre-CV known to date. The cooling age of the white dwarf suggests that the present system has just emerged from a common envelope phase ~10^5 yr ago. HS1857+5144 will start mass transfer within or below the 2-3h period gap.

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A. Aungwerojwit, B. T. Gaensicke, P. Rodriguez-Gil, H. -J. Hagen, O. Giannakis, C. Papadimitriou, C. Allende Prieto, D. Engels. 2007-04-13. HS1857+5144: A hot and young pre-cataclysmic variable. https://doi.org/10.1051/0004-6361:20077276

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