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 119 mas in each coordinate and 168 mas total, and for POSS2 it is 69 mas in each coordinate and 98 mas total. Using these accurate positions and the large separation in years between POSS1 and POSS2, we calculated the best possible PMs: 3.9 mas yr−1 in each coordinate and 5.5 mas yr−1 total. We developed methods to control and exclude the accidental errors that appear in any survey. We compared and combined our PMs with those given in USNO‐B1.0, SDSS DR7 and Tycho‐2 catalogues and obtained even better results: 3.0 mas yr−1 in each coordinate and 4.2 mas yr−1 total PM. This approach was applied to the First Byurakan Survey blue stellar objects, containing significant numbers of white dwarfs and subdwarfs. In total, 640 objects were revealed with PM ≥10  mas yr −1, the detection limit for this method, and an electronic table of these objects is given. For more confident PMs, we adopt the limit 20 mas yr−1 (333 objects). Adopting a 50 km s−1 upper limit for tangential velocities, we calculated maximum distances and absolute magnitudes and estimated luminosity types for these objects, obtaining 185 probable white dwarfs (M > 8 mag), 69 possible white dwarfs (6 < M < 8 mag), and 42 candidate subdwarfs/white dwarfs (3 < M < 6 mag). Given that we rediscovered 141 genuine white dwarfs among the classified objects, the success rate for the discovery of white dwarfs is estimated as 83 per cent, and as 38 per cent for our probable and possible white dwarfs, respectively.

Spectral observations of 10 FBS blue stellar objects (BSO) with the OHP 1.93-m and BAO 2.6.m telescopes are reported, and overall progress in all the spectral observations and classifications of FBS BSO over 1987-2000 and in the classification of these objects based on all the accessible sources--in all, 753 out of 1103 objects--is discussed. Representative slit spectra for the major types of objects are presented and compared with digitized low dispersion spectra from the DFBS. The nature of the FBS objects is examined in terms of advances in the spectral studies. Two-color diagrams are constructed from the SDSS data and are used to find the regions occupied by the various types for further identification of objects of unknown type.

A list of comparatively faint late M and Carbon type stars detected on the Digitized First Byurakan Survey (DFBS) spectral plates in the zone with o o 49 45 + ≤ δ ≤ + covering 684 deg 2 is presented. Accurate DSS2 positions, USNO-B1.0 B and R magnitudes, 2MASS near-infrared J, H, and K S photometry, IRAS PSC/FSC fluxes (when available), approximate spectral types, and luminosity class estimates are given for 72 objects. Nine of them are newly confirmed carbon stars and 63 are M-type stars. For seven Mira variables with known pulsation periods we determined distances of 8 2 ÷ kpc using a period-luminosity relation. Distances of 115 17 ÷ pc for five M dwarfs, classified on the base of detected proper motions, were estimated using a color-luminosity relation. The object FBS 0845+466 is classified as a candidate carbon dwarf with distance 72 ≈ r pc.

A new method for the combined calculation of magnitudes based on accurate measurements of Palomar Observatory Sky Survey (POSS) epochs 1 and 2 (POSS1 and POSS2) plates is given. The photometric accuracy of various surveys and catalogues has been estimated and established and statistical weights have been calculated for each one. To achieve the best possible magnitudes, weighted averaging of data from United States Naval Observatory (USNO-A2.0), Automatic Plate Measuring (APM), Minnesota Automated Plate Scanner (MAPS), USNO-B1.0 and Guide Star Catalog (GSC 2.3.2) catalogues has been used. The root-mean-square (rms) accuracy of magnitudes achieved for POSS1 is 0.184 mag for B and 0.173 mag for R, while that for POSS2 is 0.138 mag for B and 0.128 mag for R. We have derived the best POSS1 and POSS2 magnitudes for First Byurakan Survey (FBS) blue stellar objects. We have refined the transformation formulae between POSS1 and POSS2 magnitudes and those for the Sloan Digital Sky Survey (SDSS) and a standard UBV system. Using these accurate magnitudes, we have estimated the variability of FBS blue stellar objects and revealed probable and possible variables. We have worked out methods with which to control and exclude the accidental errors that appear in any survey. We have compared and combined our results with those given in the Northern Sky Variability Survey (NSVS) data base and obtained better candidates for variability. Having excluded variables, we have combined POSS1 and POSS2 data for the remaining objects to achieve even better magnitudes and colours, the rms being smaller than 0.1 mag in both B and R and for B − R colours. This approach has been applied to FBS blue stellar objects containing a significant number of white dwarfs (WDs) or cataclysmic variables (CVs), as well as extragalactic objects (quasars, Seyferts, BL Lac objects). Altogether 336 variable objects have been revealed, with POSS2−POSS1 ≥ 3σ of the errors. An electronic table of these objects is given. Candidate variables are divided into four classes: extreme, strong, probable and possible. For a more reliable sample of variable objects we excluded possible variables from the list and were left with 161 objects. By analysing the radio and X-ray properties of these objects we have revealed their nature and rediscovered or revealed candidate active galactic nuclei (AGNs), CVs, WDs and other objects.