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Том 43, № 10 (2017)
- Год: 2017
- Статей: 7
- URL: https://ogarev-online.ru/1063-7737/issue/view/11933
Article
Improvements on a unified dark matter model
Аннотация
We study, by means of a spherical collapse model, the effect of shear, rotation, and baryons on a generalized Chaplygin gas (gCg) dominated universes. We show that shear, rotation, and the baryon presence slow down the collapse with respect to the simple spherical collapse model. The slowing down in the growth of density perturbation is able to solve the instability of the unified dark matter (UDM) models described in previous papers (e.g., Sandvik et al. 2004) at the linear perturbation level, as also shown by a direct comparison of our model with previous results.
635-643
A model of the cosmic infrared background produced by distant galaxies
Аннотация
The extragalactic background radiation produced by distant galaxies emitting in the far infrared limits the sensitivity of telescopes operating in this range due to confusion. We have constructed a model of the infrared background based on numerical simulations of the large-scale structure of the Universe and the evolution of dark matter halos. The predictions of this model agree well with the existing data on source counts. We have constructed maps of a sky field with an area of 1 deg2 directly from our simulated observations and measured the confusion limit. At wavelengths 100–300 μm the confusion limit for a 10-m telescope has been shown to be at least an order of magnitude lower than that for a 3.5-m one. A spectral analysis of the simulated infrared background maps clearly reveals the large-scale structure of the Universe. The two-dimensional power spectrum of these maps has turned out to be close to that measured by space observatories in the infrared. However, the fluctuations in the number of intensity peaks observed in the simulated field show no clear correlation with superclusters of galaxies; the large-scale structure has virtually no effect on the confusion limit.
644-655
IGR J17445-2747—Yet another X-ray burster in the galactic bulge
Аннотация
The discovery of a type I X-ray burst from the faint unidentified transient source IGR J17445-2747 in the Galactic bulge by the JEM-X telescope onboard the INTEGRAL observatory is reported. Type I bursts are believed to be associated with thermonuclear explosions of accreted matter on the surface of a neutron star with a weak magnetic field in a low-mass X-ray binary. Thus, this observation allows the nature of this source to be established.
656-663
Spectroscopic study of the optical counterpart to the fast X-ray transient IGR J17544-2619 based on observations at the 1.5-m RTT-150 telescope
Аннотация
We present the results of our long-term photometric and spectroscopic observations at the Russian–Turkish RTT-150 telescope for the optical counterpart to one of the best-known sources, representatives of the class of fast X-ray transients, IGR J17544-2619. Based on our optical data, we have determined for the first time the orbital and physical parameters of the binary system by the methods of Doppler spectroscopy.We have calculated theoretical spectra of the optical counterpart by applying non- LTE corrections for selected lines and obtained the parameters of the stellar atmosphere (Teff = 33 000 K, log g = 3.85, R = 9.5 R⊙, and M = 23 M⊙). The latter suggest that the optical star is not a supergiant as has been thought previously.
664-676
Modeling of high-frequency variability in X-ray binaries with black holes
Аннотация
The properties of the aperiodic variability in X-ray binaries with black holes are considered. The power spectra of the luminosity variability for a flat accretion disk that is an emission source with a powerlaw energy spectrum have been modeled. At low frequencies the derived power spectrum has the form of a power law with a slope ϱ ≈ −1 and a cutoff at a frequency corresponding to the characteristic frequency of fluctuations at the inner disk edge; at higher frequencies the power spectrum has a complex form. The high-frequency variability is suppressed due to the arrival time delays of photons emerged in different parts of the disk. The presence of azimuthal accretion rate fluctuations in the disk and the disk surface brightness nonuniformity in the observer’s imaginary plane caused by the relativistic effects give rise to an additional variability component at frequencies ∼ 200 Hz.
677-689
Radial pulsations of red giant branch stars
Аннотация
We performed hydrodynamic computations of nonlinear stellar pulsations of population I stars at the evolutionary stages of the ascending red giant branch and the following luminosity drop due to the core helium flash. Red giants populating this region of the Hertzsprung–Russel diagram were found to be the fundamental mode pulsators. The pulsation period is the largest at the tip of the red giant branch and for stars with initial masses from 1.1 M⊙ to 1.9 M⊙ ranges from ∏ ≈ 254 day to ∏ ≈ 33 day , respectively. The rate of period change during the core helium flash is comparable with rates of secular period change in Mira type variables during the thermal pulse in the helium shell source. The period change rate is largest (∏̇/∏ ≈ −10−2 yr−1) in stars with initial mass MZAMS = 1.1 M⊙ and decreases to ∏̇/∏ ∼ −10−3 yr−1 for stars of the evolutionary sequence MZAMS = 1.9 M⊙. Theoretical light curves of red giants pulsating with periods ∏ > 200 day show the presence of the secondary maximum similar to that observed in many Miras.
690-696
Meridional component of the large-scale magnetic field at minimum and characteristics of the subsequent solar activity cycle
Аннотация
The polar magnetic field near the cycle minimum is known to correlate with the height of the next sunspot maximum. There is reason to believe that the hemispheric coupling can play an important role in forming the next cycle. The meridional component of the large-scale magnetic field can be one of the hemispheric coupling indices. For our analysis we have used the reconstructed data on the large-scale magnetic field over 1915–1986. We show that in several cycles not only the height but also the general course of the cycle can be described in this way about 6 years in advance. This coupling has been confirmed by the currently available data from 1976 to 2016, but the ratio of the meridional field to the total absolute value of the field vector has turned out to be a more promising parameter. In this paper it was calculated at a height of ∼70 Mm above the photosphere. The date of the forthcoming minimum is estimated using this parameter to be mid-2018; using the global field as a forecast parameter gives a later date of the minimum, early 2020.
697-702