Astrophysical Bulletin最新文献

We continue to study the ultra-luminous X-ray source NGC 7793 P13 in the optical range. In this work, we are testing the model of a spherically symmetric wind atmosphere of the donor star, previously identified as a B9 Ia supergiant. The model spectrum has shown good agreement with the observed one at a relatively high mass loss rate of (dot{M}approx 6times 10^{-6}M_{odot}text{ yr}^{-1}); other parameters turned out to be close to those expected for late B-supergiants. The increased mass loss rate can be explained by the high rotation velocity of the star. In addition, we have qualitatively demonstrated the effect of X-ray irradiation on the observed spectrum and discuss the fundamental possibility of wind acceleration under conditions of powerful irradiation.

The spectroscopic material obtained from 2015 to 2021 for the young Herbig Ae star HD 179218 is described and analyzed. The profiles of the H(beta) and He I (lambda 5876) lines and their variability on different time scales are studied. Analysis of the observation results showed that the profiles of the H(beta) line in the spectrum of HD 179218 have the shape of a single emission component with local absorption features superimposed on it, the radial velocities of which vary from the blue to the red edge of the emission. On certain dates, one can simultaneously observe several components persisting for at least three days. Over 17 observation dates, the H(beta) and He I (lambda 5876) line profiles looked like the inverse profile of P Cyg, the red boundary of which (v_{textrm{red}}) varied from date to date from (+235) to (+390) km s({}^{-1}). Analysis of variations in the parameter (v_{textrm{red}}) for these lines by the Lafleur–Kinman method showed the presence of a regular component with the period (P=1.341pm 0.002) days corresponding to the expected rotation period of the star. The detected variability of HD 179218 may be a sign of magnetospheric accretion. The object’s rotation axis inclination is determined, (i=23^{circ}pm 3^{circ}). The pattern of the observed variability of HD 179218 can be explained by the peculiarities of its magnetism.

Using a previously developed technique, a study of moderate-resolution optical spectra was carried out, and sets of parameters for the dwarf novae V355 UMa, V521 Peg, VY Aqr, and PQ And were obtained. Observations of the systems in late relaxation state after a burst or in a quiescent state were carried out in 2020 and 2021 with the 6-m BTA telescope of SAO RAS. Their analysis took into account the requirement for an optimum description of the observed absorption profiles of the Balmer series lines with the model spectra of white dwarfs with radiative and convective transfer. As a result, the atmospheric parameters of the primaries were determined for all the systems, and when they were subsequently compared with models of the internal structure of white dwarf and main-sequence stars, sets of fundamental parameters of the objects were also determined. It has been established that analysis of the spectra of dwarf novae containing moderately cool white dwarfs with (T_{textrm{eff}}=12000{-}15000) K provides better accuracy of their parameters than systems with hotter primaries. A simultaneous condition to be fulfilled for increasing accuracy is to carry out observations after the objects relax to a quiescent state, since the emission lines of the accretion disk significantly narrow the region of the analyzed spectrum. It has been found that the primary components of V355 UMa, V521 Peg, VY Aqr, and PQ And have masses within the range of (M_{1}=0.59{-}0.87) (M_{odot}), and their cool companions are red dwarfs with (M_{2}=0.11{-}0.13) (M_{odot}).

Cas 1 is a Local Volume (LV) dIr. In 2019 Tikhonov, using HST images and the Tip of Red Giant Branch (TRGB) method, derived its distance (D=1.61pm 0.1) Mpc and determined the stellar metallicity of Cas 1, (z=0.0004) (or (Z_{textrm{stars}}=Z_{odot}/50)). Such an eXtremely Metal-Poor (XMP) dwarf would be a nearby analogue of I Zw 18 and a valuable object for the follow-up detailed studies. Meanwhile, the distance to Cas 1 remains debatable. Its TRGB distance of (4.5pm 0.2) Mpc, based on the deeper HST images, was presented in the Extragalactic Distance Database (EDD). It places Cas 1 in the field between groups of IC 342 ((D=3.3) Mpc) and Maffei 1/Maffei 2 ((D=5.7) Mpc). To test the suggested XMP nature of Cas 1, we conduct the 6-m telescope (BTA, SAO RAS) spectroscopy to estimate O/H in its two H II regions. We also use these spectra to derive, via the observed Balmer decrements, the upper limit of the MW extinction in Cas 1. The derived values of (12+log(textrm{O/H})) are (7.83pm 0.1) and (7.58pm 0.1) dex. The measured Balmer decrements result in the upper limit MW extinction in this direction of (A_{B}=3overset{textrm{m}}{.}06pm 0overset{textrm{m}}{.}14). This is smaller by (0overset{textrm{m}}{.}63) than (A_{B}), used in the previous estimates of the distance to Cas 1. This reduces the original EDD distance to (4.1pm 0.36) Mpc. We use the LV galaxies relationship between their (12+log(textrm{O/H})) and blue absolute magnitude, (M_{B}), published by Berg et al. in 2012, to restrict (M_{B}) for Cas 1. The related distance estimate to Cas 1 is 1.64 Mpc with the 1 (sigma) uncertainty of a factor of 2.17. From obtained here (Z({textrm{gas}})sim Z_{odot}/10), we conclude that Cas 1 is not an XMP dwarf. Its newly derived distances are consistent with each other within 1 (sigma) errors, with the likely distance of about 3.73 Mpc. This distance favors Cas 1 to reside in the environs of IC 342, but not in the field.

In this paper, we study the fractal properties of the stellar medium in the solar vicinity based on the Gaia DR2 data for 200 000 stars of all spectral types at distances from 1 to 100 pc from the Sun. We consider the main stages of the development of ideas about the fractal structure in the stellar medium of galaxies. Analysis of the spatial distribution of stars is performed using by the ‘‘mass–radius’’ method. Numerical calculations show that the mean conditional local stellar density in spheres with the increasing radius (r) with the center in the (i)-th star is approximated by power laws, which confirms the de Vaucouleurs–Mandelbrot conclusions for fractal structures in gravitating media and indicates the presence of fractal structures in the stellar medium in the solar neighborhood with the fractal dimension (Dsimeq 2.41). The characteristics of the fractal properties of the medium, determined from a sample of 200 000 stars, are discussed and compared with an earlier result obtained for 13 000 F and G dwarfs in the solar neighborhood according to the Geneva–Copenhagen survey.

The kinematics of the young stellar association near the Sun TW Hya is studied. Kinematic estimates of the age of this association were obtained in two ways. The first method—the analysis of stellar trajectories integrated back in time—gave an estimate of the age (t=4.9pm 1.2) Myr. The second was to analyze the instantaneous velocities of the stars; it showed that there was a volume expansion of the stellar system with the angular velocity coefficient (K_{xyz}=103pm 12) km s({}^{-1}) kpc({}^{-1}). Based on this effect, the time that passed from the beginning of the expansion of the TW Hya association to the present moment was found, (t=9.5pm 1.1) Myr. The following principal semi-axes of the residual velocity ellipsoid were determined: (sigma_{1,2,3}=(5.25,1.84,0.35)pm(0.34,0.63,0.26)) km s({}^{-1}).

The stellar and integral photometry of 30 irregular dwarf galaxies was performed in the (F606W) ((V)) and (F814W) ((I)) filters based on archival images from the Hubble Space Telescope. Distances were determined for 12 galaxies using the TRGB method. Branches of blue supergiants were identified on the plotted Hertzsprung–Russell diagrams, and the average luminosities of the three brightest stars were calculated. The color indices ((V-I)) and luminosities of galaxies in the (V) and (I) filters were determined in circular apertures with the maximum radius (textrm{Rad}=50^{primeprime}). A diagram of the dependence between the luminosities of galaxies and their brightest stars was developed, which shows that the luminosity of the brightest stars increases with increasing luminosity of the parent galaxies. A comparison of the dependence for 30 irregular galaxies with a similar one for 150 spiral and irregular galaxies, published by Tikhonov et al. in 2021, shows their similarity. This result confirms the hypothesis that the absence of bright massive stars in dwarf irregular galaxies cannot be explained by the small number of stars in these galaxies. Using the results of Hunter et al. (2019 and 2021), we developed a dependence between the luminosity of galaxies and the mass of the third-largest H I cloud of these galaxies. The presented correlation, as well as the well-known Larson correlation proposed in 1982, between the mass of molecular hydrogen clouds and the mass of stars born in them, give us reason to conclude that the dependence between the luminosity of galaxies and the brightest stars is a consequence of the correlation between the luminosity (mass) of galaxies and the average mass of the gaseous clouds of these galaxies.

The linear polarization observations of S5 0716(+)714 carried out by the author in 2019–2021 were continued from December 8, 2021 to March 12, 2022. These observations confirm the author’s statment made in 2022 about a periodic dependence of the degree of linear polarization of S5 0716(+)714 on its optical flux. The harmonic period varies from 3 to 8 mJy in the 3 to 55 mJy interval.

We present the results of a spectral survey towards a dense molecular condensation and young stellar objects (YSOs) projected on the border of the H II region RCW 120 and discuss the emission of the 20 molecules that produce the brightest lines. The survey is performed with the APEX telescope in the 200–260 GHz frequency range. We provide evidences for two outflows in the dense gas. The first one is powered by the RCW 120 S2 YSO and oriented along the line of sight. The second outflow around RCW 120 S1 is aligned almost perpendicular to the line of sight. We show that the areas with bright emission of CH({}_{3})OH, CH({}_{3})CCH and CH({}_{3})CN are organised into an onion-like structure, where CH({}_{3})CN traces warmer regions around the YSOs than the other molecules. Methanol seems to be released into the gas phase by shock waves in the vicinity of the outflows while thermal evaporation still does not work towards the YSOs. We find only a single manifestation of the UV radiation in the molecules, namely, enhanced abundances of small hydrocarbons CCH and c-C({}_{3})H({}_{2}) in the photo-dissociation region.

Using stellar evolution models, empirical atlases of stellar spectra, the ATLAS9 stellar model library, and published relations between observational and astrophysical characteristics of stars of different luminosity classes, we investigate the possibilities of their separation in the space of atmospheric and photometric parameters (T_{textrm{eff}}{-}log g), (T_{textrm{eff}}{-}(B-R)_{0}) (Johnson), (T_{textrm{eff}}{-}(BP-RP)_{0}) (Gaia). We propose an approximation of the zero age (ZAMS) and terminal age (TAMS) main sequence lines in the (T_{textrm{eff}}{-}log g) coordinates, and show that more than (90%) of stars of luminosity class III from empirical atlases of stellar spectra are shifted toward smaller values of (log g) relative to TAMS and, as a rule, have values of (log g<3.2). It is shown that the (T_{textrm{eff}}{-}(B-R)_{0}) dependence in the Johnson photometric system is sensitive to the luminosity class in certain ranges of effective temperatures. At the same time, the (T_{textrm{eff}}{-}(BP-RP)_{0}) dependence for main-sequence stars in the Gaia photometric system is found to be valid with an accuracy better than (0overset{textrm{m}}{.}15) for stars of all luminosity classes and all spectral types earlier than M2.