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Том 63, № 3 (2019)

Article

Masses of RR Lyrae Stars with Different Chemical Abundances in the Galactic Field

Marsakov V., Gozha M., Koval’ V.

Аннотация

The surface gravities and effective temperatures have been added to a compilative catalog published earlier, which includes the relative abundances of several chemical elements for 100 field RR Lyrae stars. These atmoshperic parameters and evolutionary tracks from the Dartmouth database are used to determine the masses of the stars and perform a comparative analysis of the properties of RR Lyrae stars with different chemical compositions. The masses of metal-rich ([Fe/H] > −0.5) RR Lyrae stars with thin disk kinematics are in the range (0.51−0.60)M. Only stars with initial masses exceeding 1M can reach the horizontal branch during the lifetime of this subsystem. To become an RR Lyrae variable, a star must have lost approximately half of its mass during the red-giant phase. The appearance of such young, metal-rich RR Lyrae stars is possibly due to high initial helium abundances of their progenitors. According to the Dartmouth evolutionary tracks for Y = 0.4, a star with an initial mass as low as 0.8 M could evolve to become an RR Lyrae variable during this time. Such stars should have lost (0.2−0.3)M in the red-giant phase, which seems quite realistic. Populations of red giants and RR Lyrae stars with such high helium abundances have already been discovered in the bulge; some of these could easily be transported to the solar neighborhood as a consequence of perturbations due to inhomogeneities of the Galaxy’s gravitational potential.

Astronomy Reports. 2019;63(3):203-211
pages 203-211 views

Radio Sources in the Central Section of the RZF Catalog. Search for Objects with Ultra-Steep Spectra

Pariiskii Y., Semenova T., Temirova A., Bursov N.

Аннотация

Results of reducing and selecting data from the Ratan Zenith Field (RZF) are presented. A deep survey in the region 0h ≤ R.A. ≤ 24h, 40.5° ≤ DEC ≤ 42.5° carried out on the RATAN-600 radio telescope was used. Within +2′ of the center of the survey region, 448 objects were detected, 69 of them with ultra-steep spectra (USS). The SDSS digital optical survey (DR12), NVSS radio maps, and the FIRST catalogs have been used to cross-identify 208 radio sources from the RZF catalog, obtained as part of the “Genetic Code of the Universe” project. The characteristics of these objects are studied, and the distribution of the SDSS galaxies in a two-color diagram is obtained. Photometric redshifts and radio luminosities at 3940 and 1400 MHz are determined for 27 objects with spectral indices α < −1.1 (Sνα) for which magnitudes in various filters are presented in the SDSS. In the sample of USS objects, 12 galaxies have redshifts z < 0.5, are detected at wavelength λ = 7.6 cm, and have relatively high radio luminosities (type FR II or intermediate type FR I–FR II). Only one radio galaxy proved to be a rare nearby galaxy with relatively low radio luminosity L1400 MHz = 1.51 × 1024 W/Hz (type FR I). Two objects are candidate GHz-Peaked Spectrum objects.

Astronomy Reports. 2019;63(3):212-223
pages 212-223 views

A Putative Planet Orbiting the Pulsar PSR B0525+21

Rodin A.

Аннотация

Using the example of the pulsar B0525+21, a fundamentally new explanation has been proposed for the abrupt period changes observed in many pulsars, namely the presence of a companion orbiting the pulsar in a highly eccentric orbit. A model is presented describing the behavior of the barycentric timing residuals of B0525+21 in observations with the DSS 13 and DSS 14 radio telescopes of the Jet Propulsion Laboratory and the Jodrell Bank Lovell radio telescope. The proposed model describes the motion of PSR B0525+21 in a binary system with a planetary secondary moving in an elliptical orbit with period P = 27.74 years, semi-major axis a = 10.35 AU, eccentricity e = 0.96, and mass mc = 0.39M. The angular velocity of the pericenter motion \(\dot{\omega}=0.67\) rad/period has been measured; the presence of this motion provides evidence for a gas–dust disk or asteroid belt around the pulsar.

Astronomy Reports. 2019;63(3):224-228
pages 224-228 views

Profile of the 9.85-GHz Neutral Hydrogen Line Taking into Account the Zeeman Effect (Computations and Solar Observations)

Dravskikh A., Peterova N., Topchilo N.

Аннотация

The 9.85-GHz (3.04 cm) line of atomic hydrogen due to the 22P3/2–22S1/2 transition between levels of the hyperfine structure occupies a special place in the complex spectrum of the Sun. This is essentially the only hydrogen line that is expected in the solar radio spectrum. The promising nature of solar observations in the H3.04 line was first noted in 1952 by Wild, who calculated the line profile using a model for the “quiet” Sun characterized by a weak magnetic field (several Gauss). Computations of this line profile taking into account the strong magnetic fields in solar active regions (hundreds Gauss) are considered here. It is shown that the Zeeman effect leads to appreciable changes in the appearance of the line profile. This may help explain why searches for the H3.04 line have not led to any detections earlier. New observations of the Sun on the RATAN-600 telescope are analyzed with allowance for the Zeeman effect.

Astronomy Reports. 2019;63(3):229-237
pages 229-237 views

Long-Period Variations in Oscillations of the Earth’s Pole due to Lunar Perturbations

Perepelkin V., Rykhlova L., Filippova A.

Аннотация

A numerical–analytical approach is used to investigate irregular effects in oscillations of the Earth’s pole related to variations in the Chandler and annual components. An approach to studying oscillations in the motion of the Earth’s pole based on a joint analysis of the Chandler and annual components of this motion is proposed. A transformation to a new coordinate system in which the motion of the pole is synchronous with the precession of the lunar orbit can be found in this approach. Estimates of the precision of predictions of the coordinates of the Earth’s pole taking into account additional terms due to lunar perturbations are presented.

Astronomy Reports. 2019;63(3):238-247
pages 238-247 views

Method for Estimating the Doppler Factors of Relativistic Radio Jets

Artyukh V.

Аннотация

An expression for the intensity of synchrotron emission from a radio source (in the optically thin regime) in terms of the energy densities in the magnetic field and particles is obtained, based on a definition of a relativistic electron related to its rest energy. A relationship is obtained between the energy densities in particles Ee and the magnetic field EH for a physical system containing a magnetic field and relativistic electrons in a minimum-energy state. A method for estimating the Doppler factors of the relativistic electrons has been developed. This method does not requires that all radio sources have the same radiation energies (brightness temperatures): it is sufficient that the energies of the magnetic fields and relativistic particles in the source be approximately equal. The method yields Doppler-factor estimates with reasonably good accuracy, even when there are modest deviations from energy equipartition in the radio source,making it applicable to many radio sources. The method is used to estimate the Doppler factor of the radio jet in CTA 21.

Astronomy Reports. 2019;63(3):167-173
pages 167-173 views

Solar Wind Magnetic Field Turbulence over the Solar Activity Cycle Inferred from Coronal Sounding Experiments with Helios Linear-Polarized Signals

Efimov A., Lukanina L., Chashei I., Bird M., Pätzold M.

Аннотация

Results of experiments on polarized radio sounding of the outer solar corona using the Helios spacecraft from 1975 to 1984 are presented. The characteristic parameters of the temporal spectra of fluctuations in the Faraday rotation of the plane of polarization for heliocentric distances from 3.5 to 5.5 solar radii are obtained. The absolute level of these fluctuations and, consequently, the level of fluctuations of the magnetic field, is almost independent of the solar activity. It is well known that the global structure of the solar wind varies with the solar cycle such that there is slow solar wind at low latitudes and fast solar wind at high latitudes during solar minima. In contrast, a slow solar wind dominates at all latitudes during solar maxima. One explanation for the invariance of the fluctuations observed by sounding the circumsolar plasma is that the mean magnetohydrodynamic turbulence of the low-latitude, slow solar wind depends weakly on the phase of the solar cycle.

Astronomy Reports. 2019;63(3):174-181
pages 174-181 views

A Double Wave in the Orbital-period Variations of the Eclipsing Binary RT Per

Khaliullina A.

Аннотация

Orbital-period variations of the low-mass, semi-detached eclipsing binary RT Per are analyzed. In addition to the secular variation of the orbital period determined by the mass transfer between the components, cyclic variations are also present. Both the light-time effect and magnetic oscillations can describe the cyclic orbital-period variations of RT Per. The secular period increase can be explained by a uniform flow of matter from the lower-mass to the higher-mass component at a rate of 0.60 × 10−8M-/year, with the total angular momentum being conserved. The period variations can be represented equally accurately by either a superposition of two cyclic variations or a superposition of a secular period increase and two cyclic variations. Approximately the same parameters are derived for the lower-period (36.8 year) variations when the times of minima are fitted with a linear or a quadratic formula. For the longer-period variation, a period of 275 years and amplitude of 0.104 days are found using the linear formula, or 89 years and 0.045 days using the quadratic formula.

Astronomy Reports. 2019;63(3):182-189
pages 182-189 views

Surface Photometry of Proplyds in the Vicinity of θ1 Ori C

Mamedkhanova G., Ismailov N.

Аннотация

Results of studies of the surface-brightness distributions of a group of young stellar objects located within 16″ of the star θ1 Ori C are presented. Isophotes around each proplyd are constructed using violet, red, and near-infrared images. No regularity in the sizes of the diametral cross sections of the proplyds in the various photometric bands is observed. The measured relative intensities are converted to absolute fluxes, and the absolute luminosities of the brightest parts of the disks and of the disk peripheries are estimated. The ratio of the semi-major to the semi-minor axes of the objects range from 1.5 to 2.5. The maximum lengths of the proplyd tails in various filters range from 300 to 700 AU. They become shorter with decreasing distance from the illuminating star, possibly due to enhanced dissipation of the disk, due to the growth in the role of photovaporization.

Astronomy Reports. 2019;63(3):190-202
pages 190-202 views