Aungwerojwit, A., Gaensicke, B. T., Rodríguez-Gil, P., Hagen, H.-J., Giannakis, O., Papadimitriou, C., Allende Prieto, C. and Engels, Dieter (2007) HS 1857+5144 : a hot and young pre-cataclysmic variable. Astronomy & Astrophysics, Vol.469 (No.1). pp. 297-305. doi:10.1051/0004-6361:20077276 ISSN 0004-6361.

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Abstract

Aims. We report the discovery of a new white dwarf/M dwarf binary, HS 1857+5144, identified in the Hamburg Quasar Survey (HQS).
Methods. Time-resolved optical spectroscopy and photometry were carried out to determine the properties of this new cataclysmic variable progenitor (pre-CV).
Results. The light curves of HS 1857+5144 display a sinusoidal variation with a period of Porb = 383.52 min and peak-to-peak amplitudes of 0.7 mag and 1.1mag 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 M and Twd 70 000−100 000 K, respectively. The detection of He II λ4686 absorption classifies the primary star of HS 1857+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 M and i 45◦−55◦, respectively.
Conclusions. We classify HS 1857+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 ∼105 yr ago. HS 1857+5144 will start mass transfer within or below the 2–3 h period gap.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH):	Double stars, Cataclysmic variable stars, Dwarf stars
Journal or Publication Title:	Astronomy & Astrophysics
Publisher:	EDP Sciences
ISSN:	0004-6361
Official Date:	July 2007
Dates:	Date Event July 2007 Published
Volume:	Vol.469
Number:	No.1
Page Range:	pp. 297-305
DOI:	10.1051/0004-6361:20077276
Status:	Peer Reviewed
Access rights to Published version:	Open Access (Creative Commons)
Funder:	Thailand, Particle Physics and Astronomy Research Council (Great Britain) (PPARC), Deutsche Forschungsgemeinschaft (DFG), United States. National Aeronautics and Space Administration (NASA), National Science Foundation (U.S.) (NSF), Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Andalucía, University of Texas, Ethnikon Asteroskopeion Athēnōn [National Observatory of Athens], Instituto de Astrofísica de Canarias, European Space Agency (ESA)
Grant number:	Re 353/11 (DFG), Re 353/22 (DFG)

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