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Astron. Astrophys. 360, 627-632 (2000)

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1. Introduction

The hard X-ray source 3A 1148+719 was identified with a faint ([FORMULA] mag) cataclysmic variable (CV) by Patterson et al. (1982). They claimed that this object is identical to the variable star reported by Tsesevich (1934) and catalogued as YY Dra (Kukarkin et al. 1969). However, the co-ordinates of Tsesevich's star do not accurately agree with those of 3A 1148+719 and the types of variability are largely discordant. Arguments both for (Patterson & Eisenman 1987) and against this identification were brought (Kholopov & Samus 1988). The optical counterpart of 3A 1148+719 was given a new name, DO Dra (Kholopov et al. 1987). However, both names, YY Dra and DO Dra, are still used for 3A 1148+719 by various authors. We will use DO Dra, following GCVS.

DO Dra is an intermediate polar (IP) because besides the orbital period [FORMULA] hours (Mateo et al. 1991) it also displays a stable periodicity at 275 seconds (Patterson et al. 1992), the white dwarf (WD) spin period being 529.31 sec (Haswell et al. 1997). The ratio of the X-ray to the optical luminosity [FORMULA] is the highest of any known CV. The accretion disk is supposed to be quite faint because the absorption lines of the M secondary can be seen down to [FORMULA] nm (Patterson et al. 1992). Norton et al. (1999) argued that DO Dra is a disk-fed accretor with a weak magnetic field of the WD, so the radius at which material is captured by the field lines is relatively small. The inclination angle is moderate, [FORMULA] (Haswell et al. 1997).

Several episodes of quite a short brightening by about 5 mag were revealed on the archival plates by Wenzel (1983a,b) and Hazen (1986). They pointed to a very long recurrence time, of the order of 1000 days.

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© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000