Astrophysical Bulletin

Chúng tôi đã tìm kiếm một gradient hướng tâm (theo chiều dọc) của trường từ dài hạn của ngôi sao hóa học đặc biệt $$\alpha^{2}$$ CVn. Chúng tôi đã xem xét lịch sử các nghiên cứu từ trường của đối tượng này cho thấy sự khác biệt lớn trong dữ liệu thu được bằng các phương pháp khác nhau. Những khác biệt như vậy có thể được giải thích bởi thực tế rằng trường từ giảm mạnh (mạnh hơn 2 bậc so với trường hợp cấu trúc lưỡng cực) theo độ cao trong bầu khí quyển. Dữ liệu quang phổ, quang phổ phân cực và quang phổ quang học cho thấy rằng cấu trúc quy mô lớn và quy mô nhỏ của bầu khí quyển $$\alpha^{2}$$ CVn không thay đổi trong hơn 90 năm quan sát.

The paper presents the results of determination of fundamental parameters (effective temperature, surface gravity, luminosity, mass, radius, rotation velocity, and radial velocity) for 146 stars observed at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the Main Stellar Spectrograph during 2009–2011; 124 of the stars are magnetic or potentially magnetic objects. We obtained and analyzed at least 500 pairs of circularly-polarized-emission spectra. Various methods and approaches were used in estimating the fundamental parameters.

We determined the spatial structure of the scattered concentration of galaxies in the Canes Venatici constellation. We redefined the distances for 30 galaxies of this region using the deep images from the Hubble Space Telescope archive with the WFPC2 and ACS cameras.We carried out a high-precision stellar photometry of the resolved stars in these galaxies, and determined the photometric distances by the tip of the red giant branch (TRGB) using an advanced technique and modern calibrations. High accuracy of the results allows us to distinguish the zone of chaotic motions around the center of the system. A group of galaxies around M94 is characterized by the median velocity V LG = 287 km/s, distance D = 4.28 Mpc, internal velocity dispersion σ = 51 km/s and total luminosity L B = 1.61 × 1010 L ⊗. The projection mass of the system amounts to M p = 2.56 × 1012 M ⊗, which corresponds to the mass-luminosity ratio of (M/L) p = 159 (M/L)⊗. The estimate of the mass-luminosity ratio is significantly higher than the typical ratio M/L B ∼ 30 for the nearby groups of galaxies. The CVn I cloud of galaxies contains 4–5 times less luminous matter compared with the well-known nearby groups, like the Local Group, M81 and CentaurusA. The central galaxy M94 is at least 1m fainter than any other central galaxy of these groups. However, the concentration of galaxies in the Canes Venatici may have a comparable total mass.

We list the principal stages of astroclimatic studies concerned with choosing the sites for astrophysical observatories in Caucasus and Crimea. We chow that the sites for three observatories in Northern Caucasus (Kislovodsk Mountain Astronomical Station of Pulkovo Main Astronomical Observatory of the Russian Academy of Sciences, Special Astrophysical Observatory of the Russian Academy of Sciences, Terskol Observatory) were chosen without obtaining representative statistical data in terms of the number of clear night hours and seeing. We report the data on the number of clear night hours and seeing for the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences based on results of long-term observations. We discuss the possible causes of the discrepancies between experimental and forecast data and conclude that currently none of the three observatories in the North Caucasus can be preferred because of the great variety of the methods employed and limited statistics in terms of astroclimatic and meteorological parameters for some sites.

Global magnetic fields of flare stars evolve very fast—at times of tens–hundreds of days. In our opinion, this is due to mutual addition of local magnetic fields generated by the differential rotation of these objects.With the example of two flare stars,OT Ser and YZCMi, we consider possiblemechanisms of generation and disspation of local and global magnetic fields and the mechanism of “magnetic deceleration” of these stars according to the scheme “differential rotation–generation of local magnetic fields–fluorescence of energy accumulated by local magnetic fields during flares.” We also estimated the rotation energy and global magnetic field for OT Ser and YZCMi. It is shown that even strong dissipation of the accumulated local magnetic energy in the flare on February 9, 2008 (UT 20:22:00) in YZCMi has not had any impact on the global magnetic field.

We report the results of three-year long observations of OH masers at 1665 MHz in the W3(OH) source carried out with the 32-m antenna of Svetloe Radio Astronomical Observatory.We found that the strongest activity during the period from December 2011 through March 2012 was exhibited by the region at radial velocity −46.2km s−1. The region showed no activity in the ensuing time. The most striking outburst was the event that occurred on January 23, 2013 at UT 03:27. At that time the flux of the region increased by a factor of seven in 90 s, and then decreased down to the initial level. Such a time scale yields the upper estimate of 0.18 AU (2.7 × 1012 cm) for the linear size of the maser dot. In 2013–2014 intensity variations were found the −47.6 and −45.1km s−1 components with time scales on the order of 10 hours and anticorrelated behavior of the left- and right-hand polarization fluxes. This is the first time that such phenomena have been found in the behavior of OH maser emission, and they cannot be explained by any existing models of maser variability.

We present the results of the study of a red nova from the observations carried out with the Russian 6-m telescope (BTA) along with other telescopes of SAO RAS and SAI MSU. To investigate the nova progenitor,we used the data from the Digital Sky Survey and amateur photos available on the Internet. In the period between April 1993 and July 2014, the brightness of the progenitor gradually increased by $$2_ \cdot ^m 2$$ in the V-band. At the peak of the first outburst in mid-November 2014, the star reached an absolute visual magnitude of $$- 12_ \cdot ^m 75$$ but was discovered later, in February 2015, in a repeated outburst at the magnitude of $$- 11_ \cdot ^m 65$$ . The amplitude of the outburst was minimum among the red novae, only $$5_ \cdot ^m 6$$ in V-band. The Hα emission line and the background of a cool supergiant continuum with gradually decreasing surface temperature were observed in the spectra. Such process is typical for red novae, although the object under study showed extreme parameters: maximum luminosity, maximum outburst duration, minimum outburst amplitude, unusual shape of the light curve. This event is interpreted as a massive OB star system components’merging accompanied by formation of a common envelope and then the expansion of this envelope with minimal energy losses.

With the 6-m telescope we performed the magnetic field B e measurements for the chemically peculiar star HD 965. During 2000–2015 we obtained over 30 spectra with a Zeeman circular polarization analyzer. The longitudinal field reaches +600 G at the positive extremum and goes below −1300 G at the negative one. The magnetic monitoring of the star shows that the period of B e variability, i.e., the rotation period, exceeds 15 years. Thus, HD 965 belongs to the five slowest rotators among magnetic stars.