F.-J. Zickgraf

Identification of a Complete Sample of Northern ROSAT All-Sky Survey X-Ray Sources. III. The Catalog

We present a catalog of optical identifications of a representative sample of northern (δ > -9°) ROSAT All-Sky Survey (RASS) sources. A full identification has been carried out for a count-rate- and area-limited complete RASS subsample comprising 674 sources. All sources are within six study areas outside the Galactic plane (| b | > 196), one area being near the north Galactic pole and one near the north ecliptic pole.

THE NEW LONG-PERIOD AM HERCULIS SYSTEM RX J2157.5)0855

The identification and study of the optical counterpart of the ROSAT-discovered AM Her system RX J2157.5+0855 is reported. We present high time-resolution spectrophotometric, spectropolarimetric, and multicolor CCD-photometric observations of this polar obtained when the system was actively accreting. The 3.375 hr orbital period of the system places it among a few long-period AM Her objects. The emission lines clearly reveal the presence of at least two different line components with different widths and radial velocity variations. The Balmer emission lines contain significant contribution from the X/UV-illuminated hemisphere of the secondary star. The Hα line is deblended into two components, which we identify with the secondary star and the accretion stream. The circular polarization unambiguously confirms the magnetic nature of this newly discovered cataclysmic variable with ≈20 MG strength deduced by cyclotron emission modeling. Combining radial velocity and light curves with polarization variations provides additional information about the system geometry.

The new AM Her system RX J0704.2+6203 Northern twin of BL Hydri

We report here on the identication and study of the optical counterpart of the ROSAT source RX J0704.2+6203. Extensive spectral and photometric observation showed that the object belongs to the class of magnetic Cataclysmic Variables. We determined the orbital period of the system to be 97: m 27 and estimated the strength of its magnetic eld to be on the order of 20 MG. The system was observed in both high and low states, common for its class. Other parameters of the magnetic close binary system were estimated. The spectral and photometric behavior of the object is similar to that of the well studied polar BL Hyi.

The new ultrashort-period cataclysmic variable RX J0757.0+6306

A new cataclysmic variable is identified as the optical counterpart of the X-ray source RX J0757.0+6306. The emission lines bear evidence of a strong disc with an S-wave with period of 75±1.4 min, which we identify with the orbital period of the system. CCD photometry reveals an additional period of 8.45 min. which is stable over five nights. We assume it is the spin period of the accreting primary. We tentatively identify RX J0757.0+6306 as an intermediate polar.