|
Description
A new method for combined calculations of proper motions (PMs) based on accurate measurements of POSS1 and POSS2 epoch plates is given. The positional accuracy of various surveys and catalogues is estimated, and statistical weights for each of them are established. To achieve the best positions, weighted averaging of direct measurements on DSS1/DSS2, and data from APM, MAPS, USNO-A2.0, USNO-B1.0 and GSC 2.3.2 catalogues were used. The rms accuracy of positions achieved for POSS1 is 119mas in each coordinate and 168 mas total and for POSS2 is 69mas in each coordinate and 98mas total. Using these accurate positions and the large separation in years between POSS1 and POSS2, we have calculated the best possible proper motions: 3.9mas/yr in each coordinate and 5.5mas/yr total. We have worked out methods to control and exclude accidental errors that appear in any survey. We have compared and combined our PM with those given in USNO-B1.0, SDSS DR7, and Tycho-2 catalogs and obtained even better results: 3.0mas/yr in each coordinate and 4.2mas/yr total PM. This approach has been applied to the First Byurakan Survey blue stellar objects containing a significant number of white dwarfs and subdwarfs. Altogether 640 objects have been revealed with PM>=10mas/yr, the detection limit for this method; and an electronic table of these objects is given. For more confident proper motions, we adopt the limit 20mas/yr (333 objects). Adopting 50km/s as an upper limit for tangential velocities, we have calculated maximum distances and absolute magnitudes and estimated luminosity types for these objects and obtained 185 probable white dwarfs (M>8mag), 69 possible white dwarfs (6mag<M<8mag), and 42 candidate sd/WDs (3mag<M<6mag). Given that we have re-discovered 141 genuine white dwarfs among the classified objects, the success rate of discovery of white dwarfs is estimated as 83% and 38% for our probable and possible white dwarfs, respectively.
|
