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Astron. Astrophys. 328, 571-578 (1997)

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1. Introduction

Within a program devoted to the optical identification of a complete sample of northern ROSAT all-sky survey (RASS) X-ray sources we identified a new cataclysmic variable. The identification project is a collaboration of the Max-Planck-Institut für extraterrestrische Physik, Garching, Germany, with the the Landessternwarte Heidelberg (LSW), Germany, and the Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), Puebla, Tonantzintla, Mexico. A detailed description of the project is given by Zickgraf et al. (1997).

For the study areas the individual scan strips of the all-sky survey were merged to produce a final data base comprising about 1600 X-ray sources with a detection likelihood larger than 10 corresponding to X-ray detection limits of [FORMULA] cts s-1 in area near the North Ecliptic Pole and [FORMULA] cts s-1 in all other areas. Since October 1991 nearly 800 X-ray sources have been observed within the identification program. Here we report the identification and detailed follow-up observations of the ROSAT all-sky survey X-ray source RX J0719.2+6557 (= 1RXS J071913.4+655734), first results of which have been reported already earlier (Tovmassian et al. 1997).

Cataclysmic variables (CVs) are close binary systems, in which a compact white dwarf (WD) primary accretes matter from a Roche-lobe filling late-type main-sequence secondary component. Polars are a subclass of cataclysmic variables where the magnetic field of the white dwarf is strong enough to channel the accretion along the magnetic field lines, thus preventing the formation of an accretion disc and synchronizing the rotation of the white dwarf with the orbital period (Warner 1995). A hot spot (or accretion spot) which is formed as a result of a shock of accreting matter before hitting the white dwarf gives rise to hard X-ray radiation (often described with a bremsstrahlung model).

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998