John F. Patterson

Rapid oscillations in cataclysmic variables. VIII - YY Draconis (=3A 1148 + 719)

A 16th magnitude cataclysmic variable have been found, presumably a dwarf nova, near one of the positions permitted for the hard (2-10 keV) X-ray source 3A 1148+719. The location is also coincident with the reported position of the variable star YY Draconis, cataloged as an «Algol-type» variable. Since no Algol-type system can now be found in the vicinity, it is extremely likely that the published classification of YY Dra is incorrect and that the cataloged variable is the cataclysmic binary. A serendipitous Einstein observation of the star revealed a fairly strong hard X-ray source, making it nearly certain that this is the correct identification of 3A 1148+719. The optical and ultraviolet spectra of YY Dra are fairly typical of cataclysmic variables, except that the TiO absorption bands of an M dwarf can be seen for λ > 5000 A. This shows that the accretion disk is intrinsically quite faint in quiescence, suggesting a very low accretion rate

Identification of two hard X-ray emitting Be stars using the HEAO 1 scanning modulation collimator

Using precise positions from the HEAO 1 Scanning Modulation Collimator experiment, two hard X-ray sources, 4U 0728 - 25 = 3A 0726 - 260 and 4U 2206 + 54 = 3A 2206 + 543, are identified with early-type stars. In both cases broad (10 A FWHM) H-alpha emission is detected. The UBV colors suggest that the optical counterparts are main-sequence B0-B2 stars at 2-6 kpc, implying a mean X-ray luminosity of order 10 to the 35th ergs/sq cm s (2-10 keV). The X-ray emission in both cases is highly variable, and it is suggested that they belong to the class of X-ray emitting Be stars, containing a neutron star in a widely separated binary system.

Recent optical identifications of HEAO-1 X-ray sources

The HEAO-1 satellite has produced the most complete, all-sky, X-ray survey. The sources extend to levels as faint as 1/2 Uhuru Flux Unit (UFU), with uncertain completeness below 1.25 UFU. Approximately 350 out of 840 sources have certain or highly probable optical counterparts. The identifications are necessary for estimating distances to the objects, so that properties are measured intrinsic to the source, and for establishing the classifications of the astronomical systems. There is also the opportunity to obtain TENMA and EXOSAT observations of X-ray spectra and time variability, since in general almost nothing is known of the X-ray characteristics of these weaker sources. Methods are here reviewed and the new active galactic nuclei X-ray counterparts are discussed.