Vol 42, No 5 (2016)

We have compiled a catalog of 903 candidates for type 1 quasars at redshifts 3 < z < 5.5 selected among the X-ray sources of the “serendipitous” XMM-Newton survey presented in the 3XMMDR4 catalog (the median X-ray flux is ≈5 × 10⁻¹⁵ erg s⁻¹ cm⁻² in the 0.5–2 keV energy band) and located at high Galactic latitudes |b| > 20° in Sloan Digital Sky Survey (SDSS) fields with a total area of about 300 deg². Photometric SDSS data as well infrared 2MASS and WISE data were used to select the objects. We selected the point sources from the photometric SDSS catalog with a magnitude error δ_mz′ < 0.2 and a color i′ − z′ < 0.6 (to first eliminate the M-type stars). For the selected sources, we have calculated the dependences χ²(z) for various spectral templates from the library that we compiled for these purposes using the EAZY software. Based on these data, we have rejected the objects whose spectral energy distributions are better described by the templates of stars at z = 0 and obtained a sample of quasars with photometric redshift estimates 2.75 < z_phot < 5.5. The selection completeness of known quasars at z_spec > 3 in the investigated fields is shown to be about 80%. The normalized median absolute deviation (Δz = |z_spec − z_phot|) is σ_Δz/(1+z_spec) = 0.07, while the outlier fraction is η = 9% when Δz/(1 + z_спек.) > 0.2. The number of objects per unit area in our sample exceeds the number of quasars in the spectroscopic SDSS sample at the same redshifts approximately by a factor of 1.5. The subsequent spectroscopic testing of the redshifts of our selected candidates for quasars at 3 < z < 5.5 will allow the purity of this sample to be estimated more accurately.

The nearest neighbor distance distribution law is generalized to fractal stellar media. The asymptotics of the distribution law for the magnitude of a large random force has been derived for them. An expression for the effective mean interparticle distance in such a medium has been found. The derived asymptotics for a power-law change in conditional density is shown to coincide closely with the results obtained within the framework of a general approach. We conclude that the large random forces in a fractal stellar medium are entirely attributable to the nearest neighbors (clumps) located in a sphere with an effective radius determined from a generalized Holtsmark distribution.

In this work the light curves (LCs) solutions along with the radial velocity curve of the semidetached binary systemXZ And are presented using the PHOEBE program(ver 0.31a). Absolute parameters of the stellar components were then determined, enabling us to discuss structure and evolutionary status of the system. The analysis indicates that the primary is a non-synchronous (i.e., F1 = 3.50 ± 0.01) Main Sequence (MS) star and the secondary is a bit more evolved, and fills its Roche critical surface. In addition, times of minima data (“O − C curve”) were analyzed. Apart from an almost parabolic variation in the general trend of O − C data, which was attributed to a mass transfer from the secondary with the rate ̇₂ = (9.52 ± 0.41) × 10⁻¹⁰M_⊙ yr⁻¹; two cyclic variations with mean periods of 34.8 ± 2.4 and 23.3 ± 3.0 yr, modulating the orbital period, were found, which were attributed to a third body orbiting around the system, and magnetic activity cycle effect, respectively.