Vol 74, No 3 (2019)

Stellar photometry in nine fields around the giant elliptical galaxy M87 in the Virgo cluster is obtained from archival images of the Hubble Space Telescope. The resulting Hertzsprung-Russell diagrams show populated red-giant and AGB branches. The position of the tip the red-giant branch (the TRGB discontinuity) is found to vary with galactocentric distance. This variation can be interpreted as the effect of metal-rich red giants on the procedure of the measurement of the TRGB discontinuity or as a consequence of the existence of a weak gas-and-dust cloud around M87 extending out to 10’ along the galactocentric radius and causing I-band absorption of up to \(0\mathop .\limits^{\rm{m}} 2\) near the center of the galaxy. The TRGB stars located far fromtheM87 center yield an average distancemodulus of (m-M) = 30.91 ± 0.08, which corresponds to the distance of D = 15.4± 0.6Mpc. It is shown that stars in the field located between M86 and M87 galaxies at angular separations of 37’ and 40’ are not intergalactic stars, but belong to the M87 galaxy, i.e., that the stellar halo of this galaxy can be clearly seen at a galactocentric distance of 190 kpc. The distances are measured to four dwarf galaxies P4anon, NGC4486A, VCCA039, and dSph-D07, whose images can be seen in the fields studied. The first three galaxies are M87 satellites, whereas dSph-D07 is located at a greater distance and is a member of the M86 group.

We present an optical spectrum of the star V1648 Aql (IRAS19386+0155) obtained at the 6-m SAO RAS telescope with a spectral resolution of R ≥ 60 000. Heliocentric radial velocity was measured from numerous metal absorptions is V_r = 10.18 ± 0.05 km s^-1 (V_LSR = 18.1 km s^-1). We determined the atmospheric, circumstellar, and interstellar components in the profile of the Na I D lines at V_r = 9.2, -3.4, and -12.8 km s^-1 respectively. The averaged over 20 identified DIBs velocity V_r = -12.5 ± 0.2 km s^-1 coincides with the interstellar Na I component. Weak emissions with an intensity of about 10% of the local continuum level were detected in the spectrum; they are identified as low-excitation metal lines. Their central position, V_r = 8.44 ± 0.28 km s^-1, points to the presence of a weak velocity gradient in the upper layers of the stellar atmosphere. Based on the spectroscopic data and taking into account the interstellar and circumstellar reddening, we estimated the star’s luminosity M_V ≈ -5^m and also obtained the lower estimate of distance d ≥ 1.8 kpc. Using the model atmosphere method, we determined the fundamental parameters and chemical abundances in the atmosphere confirming the status of a post-AGB star for V1648 Aql.

Magnetic-field measurements for Herbig Ae/Be stars are analyzed to determine the distribution functions of root-mean-squared magnetic field strengths \(\mathcal{B}\) (in G) and magnetic fluxes Φ (in G cm²) for Herbig stars with measured magnetic field. The \(\mathcal{B}\) and Φ values are approximated by log-normal functions with the means equal to 〈log \(\mathcal{B}\)〉 = 2.0 and log 〈Φ Φ〉 = 25.5, respectively, and with the widths of \({\rm{log}}(\sigma)_\mathcal{B}=0.3\) dex and log(σ_Φ) = 0.4 dex, respectively. The inferred distribution widths are close to the typical values for main-sequence (MS) AB-type stars, whereas the mean logarithms of magnetic fields and magnetic fluxes proved to be significantly (by up to one order of magnitude) lower than the corresponding values for MS stars (2.5 and 26.4, respectively). The origin of these differences and the evolution of magnetic fields for intermediate-mass pre-MS stars are discussed.

We present the photometric and spectroscopic observations of the polar 1RXSJ152506.9-032647. The observations were carried out at the 6-m and Zeiss-1000 telescopes of the SAO RAS, and at the 1.5-m Russian-Turkish telescope RTT150. The determined orbital period of the system is \(0\mathop .\limits^{\rm{d}} 06462793\). The object was observed in the intermediate \(\langle{R_c}\rangle=17\mathop .\limits^{\rm{m}}8\) in 2013 and 2017 and high states \(\langle{R_c}\rangle=16\mathop .\limits^{\rm{m}}8\) in 2016. The light curve analysis showed that the accretion in the system occurs towards two magnetic poles of the white dwarf. The spectra of the object was typical of polars with strong hydrogen emissions of the Balmer series (HI), of neutral (He I), and ionized (He II) helium, and weaker lines of heavier elements (Fe II, CII, CIII, and Mg II). Hydrogen and helium emission lines showed a two-component structure. We determined the parameters of the system: M₁ = 0.56 ± 0.04M_⊙, M₂ = 0.133 ± 0.008M_⊙, q = 0.24 ± 0.001, i = 79° ± 1°, R_L2 = 0.16 ± 0.01R_⊙, R_L2/R₂ = 1.04, and A = 0.6 ± 0.02R_⊙.

A technique for computing the spectrograph for astrophysical studies based on the basic input and output parameters of the optical system. In the framework of the proposed technique, it is possible to determine the main properties of the spectrograph components: the focal length of the collimator, the focal length of the projection camera, the blaze angle of the grating, the frequency of the grating. The following parameters are used as the basic ones: the required spectral resolution, the spectral range studied, the spectrograph entrance aperture, the height of the detector in the direction of dispersion, and the available length of the diffraction grating. Recommendations are proposed on the choice of the schematic of the spectrograph based on the computed magnification in the optical system of the device inferred from the basic parameters.