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Том 62, № 9 (2018)

Article

Is Dark Matter Needed in Galaxies?

Rozgacheva I., Agapov A.

Аннотация

Arguments indicating that galaxies and galaxy clusters should be considered open, forming systems are presented. Galaxies interact with the intergalactic medium, and are not in virial equilibrium (determined by gravitation and rotation). The usual interpretation of the rotation curves of the outer regions of galaxies beyond the visible stellar disk—that they imply the presence of a massive dark-matter halo— could be erroneous in this case: if the intergalactic medium is being accreted in these regions, the orbital speeds of clouds of neutral hydrogen will not be determined purely by the gravitation of the mass inside their orbits. Galaxy clusters accrete matter (intergalactic gas and galaxies) from the filaments of the large-scale structure at whose intersections they are located. Only their inner regions can approach virial equilibrium. Therefore, the high speeds of galaxies and the high temperature of the intergalactic gas in clusters does not necessarily imply the presence of a high mass of dark matter in galaxy clusters.

Astronomy Reports. 2018;62(9):551-556
pages 551-556 views

A Search for a Globular Cluster whose Passage Through the Galactic Disk Could Induce the Formation of the Gould Belt

Bobylev V., Bajkova A.

Аннотация

The distribution of sites where globular clusters have crossed the Galactic disk during the last 100 million years has been analyzed using the most recent kinematic data for 133 globular clusters (GCs). ThreeGCs (NGC 6341, NGC 7078, and ω Cen) whose distances between the positions where they crossed the Galactic disk and trajectories of the Gould Belt are less than 20% of their heliocentric distances at the crossing time (82, 98, and 96 million years ago, respectively) have been identified. For each of the clusters, this was their next to last, rather than their last, crossing of the Galactic disk. The passage of any one of these three GCs through the disk could potentially have initiated the formation of the Gould Belt.

Astronomy Reports. 2018;62(9):557-566
pages 557-566 views

WR + OB Binary Systems: Observational Evidence of Their Formation as a Result of Mass Exchange

Cherepashchuk A.

Аннотация

An analysis of observational data shows that, in most cases,Wolf–Rayet (WR) stars in known WR+ OB binary systems were formed as a result of mass transfer in initial OB + OB systems, rather than through radial mass loss by the more massive OB star via its stellar wind.

Astronomy Reports. 2018;62(9):567-573
pages 567-573 views

Spectra of Standard Radio Sources at the Current Epoch

Ivanov V., Ipatov A., Rakhimov I., Grenkov S., Andreeva T.

Аннотация

The results of observations aimed at determining the spectra of standard radio sources in an “artificial-Moon” absolute flux scale at epoch 2015.5 at wavelengths of 3.5–18 cm are presented. The sample includes sources with small angular sizes, used as flux-density standards for the calibration of various types of antennas, including large synthesized apertures, over a wide range of frequencies. The artificial-Moon flux scale is constructed in a way that makes it the most accurate of existing scales, and the only scale for which source spectra are not deformed. The methods used to construct the articial-Moon flux scale are briefly described. Repeat measurements of the spectra of standard sources, required to preserve the accuracy of the flux scale, were carried out in 2014–2017 (at a mean epoch of 2015.5) on the 32-m telescope of the Svetloe Observatory of the Institute of Applied Astronomy at four wavelengths: 18, 13, 6.2, and 3.5 cm. The characteristic properties of the measurement methods are discussed, and the data obtained are compared with data from earlier epochs.

Astronomy Reports. 2018;62(9):574-583
pages 574-583 views

Search for H2O Maser Flares in Regions of Formation of Massive Stars

Shakhvorostova N., Vol’vach L., Vol’vach A., Dmitrotsa A., Bayandina O., Val’tts I., Alakoz A., Ashimbaeva N., Rudnitskii G.

Аннотация

Results of systematic observations of a sample of bright H2O maser sources with fluxes, on average, exceeding 200 Jy in their main spectral feature during April–September 2017 (G25.65+1.05, G25.825−0.178, G27.184−0.082, G34.403+0.233, G35.20−0.74, G43.8−0.13, G107.30+5.64) are presented. These observations were carried out in preparation for Very Long Baseline Interferometry observations with an array including the Crimean Astrophysical Observatory 22-m radio telescope. All these sources display fairly strong variability during the time interval considered, encompassing fluxes from ∼40 to ∼2300 Jy. A flare reaching ∼17 000 Jy was detected at a velocity of 42.8 km/s in G25.65+1.05 on September 7, 2017, which subsequently grew to 60 000 Jy at the end of September 2017. This suggests the presence of compact maser structures. The velocities covered by various spectral components range from 5 to 20 km/s. In three sources (G25.65+1.05,G25.825−0.178,G35.20−0.74), a general growth in the fluxes of all the spectral features is observed, which may indicate variations in the conditions for pumping by an external source, for example, variations in the infrared flux from a central source or the passage of a shock. Possible evidence for the presence of bipolar outflows or disk structures in G25.65+1.05 is discussed.

Astronomy Reports. 2018;62(9):584-608
pages 584-608 views

Observations of OH and H2O Maser Emission in the Star-Forming Region S128

Ashimbaeva N., Colom P., Lekht E., Pashchenko M., Rudnitskii G., Tolmachev A.

Аннотация

Results of monitoring hydroxyl and water masers in the star-forming region S128 are presented. A large number of emission features in the 1665 MHz OH line have been detected in both circular polarizations. In spite of the strong variability of the flux density in the main 1665 MHz line, the radial velocities of the features remained constant. Zeeman splitting of the 1720MHz line equal to 0.86 km/s was detected, corresponding to a longitudinal magnetic field of 3.6 mG. The variability of the H2O emission has a cyclic character with a quasi-period of 4–14 yrs. The evolution of individual features confirms that the H2O sources A and B are associated with an ionization front between two colliding CO clouds, and shows that the activity was transferred from maser B to maser A in 1999–2001.

Astronomy Reports. 2018;62(9):609-622
pages 609-622 views

Changes of the Optical Spectrum of the Hypergiant ρ Cas due to a Shell Ejection in 2013

Klochkova V., Panchuk V., Tavolzhanskaya N.

Аннотация

Spectral monitoring of the yellow hypergiant ρ Cas with the by 6-m telescope of the Special Astrophysical Observatory with a spectral resolution of R ≥ 60 000 has led to the detection of new features in the kinematic state of its extended atmosphere following the ejection of matter in 2013. Significant changes in the profile of the Hα line were detected: the line had a doubled core for the first time in a 2014 spectrum, an inverse P Cygni profile on February 13, 2017, and the profile was again doubled on August 6, 2017 and September 5, 2017, but was strongly shifted toward longer wavelengths, indicating a rapid infall of matter. Splitting of the profiles of strong, low-excitation absorption lines into three components was first detected in 2017. There is no correlation between the evolution of the profiles of Hα and the splitted absorption lines. Pulsation-like variability with an amplitude of about 10 km/s is characteristic only of symmetric weak and moderate-intensity absorption lines. Shell emission lines of iron-group elements can be identified in the long-wavelength part of a spectrum obtained in 2013, whose intensity decreased until they completely disappeared in 2017. In the absence of emission in the cores of the H and K lines of Ca II, emission lines of shell metals are visible in the wings of these lines.

Astronomy Reports. 2018;62(9):623-635
pages 623-635 views

Erratum

Erratum to: “Relationship between the Elemental Abundances and the Kinematics of Galactic-Field RR Lyrae Stars”

Marsakov V., Gozha M., Koval V.

Аннотация

Several errors concerning the single star V455 Oph have been discovered in the study [1], which, however, do not affect the main conclusions of that study. V455 Oph was mistakenly ascribed the elemental composition of a different star. The spectroscopic elemental abundances of the RR Lyrae star V455 Oph were not determined, making it necessary to use the photometric abundance [Fe/H] = −1.42, and not +0.19, as was indicated in the published paper and in the on-line catalog; any reference to the star should be removed from the abstract and text of the paper. The authors apologize for these errors. In particular, the following text should be removed from Section 3 (p. 56): “However, RR Lyrae stars with the kinematics of the accreted halo also include some very metals-rich objects. For example, V455 Oph”… to the end of that paragraph. The second-to-last paragraph of Section 5, beginning “We also consider the chemical composition of V455 Oph to be unique”… should be removed in its entirety. Finally, the points ascribed to V455 Oph in Figs. 1e, 1f, Figs. 2a–2d, and Figs. 3a–3d should be considered erroneous.

Astronomy Reports. 2018;62(9):636-636
pages 636-636 views

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