Showing papers in "Astronomy Letters in 2013"

Constraints on dark matter in the solar system

Abstract: We have searched for and estimated the possible gravitational influence of dark matter in the Solar system based on the EPM2011 planetary ephemerides using about 677 thousand positional observations of planets and spacecraft. Most of the observations belong to present-day ranging measurements. Our estimates of the dark matter density and mass at various distances from the Sun are generally overridden by their errors (σ). This suggests that the density of dark matter ρ dm, if present, is very low and is much less than the currently achieved error of these parameters. We have found that ρ dm is less than 1.1 × 10−20 g cm−3 at the orbital distance of Saturn, ρ dm < 1.4 × 10−20 g cm−3 at the orbital distance of Mars, and ρ dm < 1.4 × 10−19 g cm−3 at the orbital distance of the Earth. We also have considered the case of a possible concentration of dark matter to the Solar system center. The dark matter mass in the sphere within Saturn’s orbit should be less than 1.7 × 10−10 M ⊙ even if its possible concentration is taken into account.

On timing and spectral characteristics of the X-ray pulsar 4U 0115+63: Evolution of the pulsation period and the cyclotron line energy

Abstract: An overview of the results of observations for the transient X-ray pulsar 4U 0115+63, amember of a binary system with a Be star, since its discovery to the present day (∼40 years) based on data from more than dozen observatories and instruments is presented. An overall light curve and the history of change in the spin frequency of the neutron star over the entire history of its observations, which also includes the results of recent measurements made by the INTEGRAL observatory during the 2004, 2008, and 2011 outbursts, are provided. The source’s energy spectra have also been constructed from the INTEGRAL data obtained during the 2011 outburst for a dynamic range of its luminosities 1037−7 × 1037 erg s−1. We show that apart from the fundamental harmonic of the cyclotron absorption line at energy∼11 keV, its four higher harmonics at energies ≃24, 35.6, 48.8, and 60.7 keV are detected in the spectrum. We have performed a detailed analysis of the source’s spectra in the 4–28 keV energy band based on all of the available RXTE archival data obtained during bright outbursts in 1995–2011. We have confirmed that modifying the source’s continuum model can lead to the disappearance of the observed anticorrelation between the energy of the fundamental harmonic of the cyclotron absorption line and the source’s luminosity. Thus, the question about the evolution of the cyclotron absorption line energy with the luminosity of the X-ray pulsar 4U 0115+63 remains open and a physically justified radiation model for X-ray pulsars is needed to answer it.

Influence of departures from LTE on oxygen abundance determination in the atmospheres of A-K stars

Abstract: We have performed non-LTE calculations for O I with a multilevel model atom using currently available atomic data for a set of parameters corresponding to stars of spectral types from A to K. Departures from LTE lead to a strengthening of O I lines, and the difference between the non-LTE and LTE abundances (non-LTE correction) is negative. The non-LTE correction does not exceed 0.05 dex in absolute value for visible O I lines for main-sequence stars in the entire temperature range. For the infrared O I 7771 A line, the non-LTE correction can reach −1.9 dex. The departures from LTE are enhanced with increasing temperature and decreasing surface gravity. We have derived the oxygen abundance for three A-type mainsequence stars with reliably determined parameters (Vega, Sirius, HD 32115). For each of the stars, allowance for the departures from LTE leads to a decrease in the difference between the abundances from infrared and visible lines, for example, for Vega from 1.17 dex in LTE to 0.14 dex when abandoning LTE. In the case of Procyon and the Sun, inelastic collisions with HI affect the statistical equilibrium of OI, and agreement between the abundances from different lines is achieved when using Drawin’s classical formalism. Based on the O I 6300, 6158, 7771-5, and 8446 A lines of the solar spectrum, we have derived the mean oxygen abundance log ɛ = 8.74 ± 0.05 using a classical plane-parallel model solar atmosphere and log ɛ +3D = 8.78 ± 0.03 by applying the 3D corrections taken from the literature.

Galactic rotation curve and spiral density wave parameters from 73 masers

Abstract: Based on kinematic data on masers with known trigonometric parallaxes and measurements of the velocities of HI clouds at tangential points in the inner Galaxy, we have refined the parameters of the Allen-Santillan model Galactic potential and constructed the Galactic rotation curve in a wide range of Galactocentric distances, from 0 to 20 kpc. The circular rotation velocity of the Sun for the adopted Galactocentric distance R 0 = 8 kpc is V 0 = 239 ± 16 km s−1. We have obtained the series of residual tangential, ΔV θ , and radial, V R , velocities for 73 masers. Based on these series, we have determined the parameters of the Galactic spiral density wave satisfying the linear Lin-Shu model using the method of periodogram analysis that we proposed previously. The tangential and radial perturbation amplitudes are f θ = 7.0±1.2 km s−1 and f R = 7.8±0.7 km s−1, respectively, the perturbation wave length is λ = 2.3±0.4 kpc, and the pitch angle of the spiral pattern in a two-armed model is i = −5.2° ±0.7°. The phase of the Sun ζ ⊙ in the spiral density wave is −50° ± 15° and −160° ± 15° from the residual tangential and radial velocities, respectively.

Galactic kinematics from a sample of young massive stars

Abstract: Based on published sources, we have created a kinematic database on 220 massive (> 10 M ⊙) young Galactic star systems located within ≤3 kpc of the Sun. Out of them, ≈100 objects are spectroscopic binary and multiple star systems whose components are massive OB stars; the remaining objects are massive Hipparcos B stars with parallax errors of no more than 10%. Based on the entire sample, we have constructed the Galactic rotation curve, determined the circular rotation velocity of the solar neighborhood around the Galactic center at R 0 = 8kpc, V 0 = 259±16 km s−1, and obtained the following spiral density wave parameters: the amplitudes of the radial and azimuthal velocity perturbations f R = −10.8 ± 1.2 km s−1 and f θ = 7.9 ± 1.3 km s−1, respectively; the pitch angle for a two-armed spiral pattern i = −6.0° ± 0.4°, with the wavelength of the spiral density wave near the Sun being λ = 2.6 ± 0.2 kpc; and the radial phase of the Sun in χ ⊙ = −120° ± 4°. We show that such peculiarities of the Gould Belt as the local expansion of the system, the velocity ellipsoid vertex deviation, and the significant additional rotation can be explained in terms of the density wave theory. All these effects decrease noticeably once the influence of the spiral density wave on the velocities of nearby stars has been taken into account. The influence of Gould Belt stars on the Galactic parameter estimates has also been revealed. Eliminating them from the kinematic equations has led to the following new values of the spiral density wave parameters: f θ = 2.9 ± 2.1 km s−1 and χ ⊙ = −104° ± 6°.

Possible indication for non-zero neutrino mass and additional neutrino species from cosmological observations

Abstract: The constraints on total neutrino mass and effective number of neutrino species based on CMB anisotropy power spectrum, Hubble constant, baryon acoustic oscillations and galaxy cluster mass function data are presented. It is shown that discrepancies between various cosmological data in Hubble constant and density fluctuation amplitude, measured in standard ΛCDM cosmological model, can be eliminated if more than standard effective number of neutrino species and non-zero total neutrino mass are considered. This extension of ΛCDM model appears to be ≈3σ significant when all cosmological data are used. The model with approximately one additional neutrino type, Neff ≈ 4, and with non-zero total neutrino mass, Σmν ≈ 0.5 eV, provide the best fit to the data. In the model with only one massive neutrino the upper limits on neutrino mass are slightly relaxed. It is shown that these deviations from ΛCDM model appearmainly due to the usage of recent data on the observations of baryon acoustic oscillations. The larger than standard number of neutrino species is measured mainly due to the comparison of the BAO data with direct measurements of Hubble constant, which was already noticed earlier. As it is shown below, the data on galaxy cluster mass function in this case give the measurement of non-zero neutrino mass.

Influence of spontaneous fission rates on the yields of superheavy elements in the r-process

Abstract: The formation of heavy elements in the neutron star merger scenario is considered. In such a scenario, the duration of the r-process is long and when the nucleosynthesis wave passes through the region of actinides, beta-delayed, neutron-induced, and spontaneous fission are added to the main r-process reaction channels. The dependence of the formation of superheavy elements on spontaneous fission model is investigated numerically. The formation of nuclei lighter than the cadmium-peak elements and cosmochronometer nuclei is shown to depend on strongly on the spontaneous fission model used in nucleosynthesis calculations. The regions of nuclei with short spontaneous fission half-lives prevent the formation of superheavy elements in the r-process, but the prediction of their yields is so far inaccurate because of an insufficient accuracy of calculating a number of transactinide parameters. The relative contributions from neutron-induced, beta-delayed, and spontaneous fission have been determined for various spontaneous fission models in the nucleosynthesis scenario considered.

Fine structure of the sources of quasi-periodic pulsations in “single-loop” solar flares

Abstract: Analysis of the observational data obtained with a high angular resolution in the ranges of vacuum ultraviolet (1″, TRACE) and hard X-ray (4″, RHESSI) emissions in some solar flares previously considered “single-loop” ones shows that they are not such flares. The thick single loops with a diameter of 13″–21″ observed in these flares in the microwave range with an angular resolution of 5″–10″ (NoRH) are actually arcades of thinner loops with a diameter of less than 3″. In this case, the observed quasi-periodic pulsations of microwave emission are not a consequence of the oscillations of an isolated thick loop, as is usually assumed, but a result of the successive involvement of many relatively thinner loops in the process of flare energy release. The established facts impose significant constraints on the generation models of pulsations in flares.

Gamma-ray bursts and the production of cosmogenic radionuclides in the Earth’s atmosphere

Abstract: An explanation is offered for the impulsive increase in the concentration of cosmogenic radiocarbon in annual tree rings (Δ14C ∼ 12‰) from AD ≃775. A possible cause of such an increase could be the high-energy emission from a Galactic gamma-ray burst. It is shown that such an event should not lead to an increase in the total production of 10Be in the atmosphere, as distinct from the effect of cosmic-ray fluxes on the atmosphere. At the same time, the production of an appreciable amount of 36Cl, which can be detected in Greenland and Antarctica ice samples of the corresponding age, should be expected. This allows the effects caused by a gamma-ray burst and anomalously powerful proton events to be distinguished.

Estimation of the solar galactocentric distance and galactic rotation velocity from near-solar-circle objects

Abstract: We have tested the method of determining the solar Galactocentric distance R 0 and Galactic rotation velocity V 0 modified by Sofue et al. using near-solar-circle objects. The motion of objects relative to the local standard of rest has been properly taken into account. We show that when such young objects as star-forming regions or Cepheids are analyzed, allowance for the perturbations produced by the Galactic spiral density wave improves the statistical significance of the estimates. The estimate of R 0 = 7.25 ± 0.32 kpc has been obtained from 19 star-forming regions. The following estimates have been obtained from a sample of 14 Cepheids (with pulsation periods P > 5 d ): R 0 = 7.66 ± 0.36 kpc and V 0 = 267 ± 17 km s−1. We consider the influence of the adopted Oort constant A and the character of stellar proper motions (Hipparcos or UCAC4). The following estimates have been obtained from a sample of 18 Cepheids with stellar proper motions from the UCAC4 catalog: R 0 = 7.64 ± 0.32 kpc and V 0 = 217 ± 11 km s−1.

Shock acceleration of solar cosmic rays

Abstract: We investigated the acceleration of solar cosmic rays (SCRs) by the shock waves produced by coronal mass ejections. We performed detailed numerical calculations of the SCR spectra produced during the shock propagation in the solar corona in terms of a model based on the diffusive transport equation using a realistic set of physical parameters for the corona. The resulting SCR energy spectrum N(e) ∝ e−γ exp [− (e/emax)α] is shown to include a power-law portion with an index γ≃2 that ends with an exponential tail with α ≃ 2.5 − β, where β is the spectral index of the background Alfven turbulence. The maximum SCR energy lies within the range emax = 1–300 MeV, depending on the shock velocity. Because of the steep spectrum of the SCRs, their backreaction on the shock structure is negligible. The decrease in the Alfven Mach number of the shock due to the increase in the Alfven velocity with heliocentric distance r causes the efficient SCR acceleration to terminate when the shock reaches a distance of r = 2–3R ⊙. Since the diffusive SCR propagation in this case is faster than the shock expansion, SCR particles intensively escape from the shock vicinity. A comparison of the calculated SCR fluxes expected near the Earth’s orbit with available experimental data indicates that the theory satisfactorily explains all of the main observed features.

Magnetically active stars in Taurus-Auriga: Photometric variability and basic physical parameters

Abstract: We have analyzed homogeneous long-term photometric observations of 28 well-known weakline T Tauri stars (WTTS) and 60 WTTS candidates detected by the ROSAT observatory toward the Taurus-Auriga star-forming region. We show that 22 known WTTS and 39 WTTS candidates exhibit periodic light variations that are attributable to the phenomenon of spotted rotational modulation. The rotation periods of these spotted stars lie within the range from 0.5 to 10 days. Significant differences between the long-term photometric behaviors of known WTTS and WTTS candidates have been found. We have calculated accurate luminosities, radii, masses, and ages for 74 stars. About 33% of the sample of WTTS candidates have ages younger than 10 Myr. The mean distance to 24 WTTS candidates with reliable estimates of their radii is shown to be 143 ± 26 pc. This is in excellent agreement with the adopted distance to the Taurus-Auriga star-forming region.

On the structure of the magnetic field near a black hole in active galactic nuclei

Abstract: Using the Grad-Shafranov equation, we consider a new analytical model of the black hole magnetosphere based on the assumption that the magnetic field is radial near the horizon and uniform (cylindrical) in the jet region. Within this model, we have managed to show that the angular velocity of particles ΩF near the rotation axis of the black hole can be smaller than ΩH/2. This result is consistent with the latest numerical simulations.

Sub-terahertz emission from solar flares: The plasma mechanism of chromospheric emission

Abstract: We consider the plasma mechanism of sub-terahertz emission from solar flares and determine the conditions for its realization in the solar atmosphere. The source is assumed to be localized at the chromospheric footpoints of coronal magnetic loops, where the electron density should reach n ≈ 1015 cm−3. This requires chromospheric heating at heights h ⩾ 500 km to coronal temperatures, which provides a high degree of ionization needed for Langmuir frequencies ν p ≈ 200–400 GHz and reduces the bremsstrahlung absorption of the sub-THz emission as it escapes from the source. The plasma wave excitation threshold for electron-ion collisions imposes a constraint on the lower density limit for energetic electrons in the source, n 1 > 4 × 109 cm−3. The generation of emission at the plasma frequency harmonic ν ≈ 2ν p rather than the fundamental tone turns out to be preferred. We show that the electron acceleration and plasma heating in the sub-THz emission source can be realized when the ballooning mode of the flute instability develops at the chromospheric footpoints of a flare loop. The flute instability leads to the penetration of external chromospheric plasma into the loop and causes the generation of an inductive electric field that efficiently accelerates the electrons and heats the chromosphere in situ. We show that the ultraviolet radiation from the heated chromosphere emerging in this case does not exceed the level observed during flares.

High-latitude supergiant V5112 Sgr: Enrichment of the envelope with heavy s-process metals

Abstract: High-resolution (R = 60 000) echelle spectroscopy of the post-AGB supergiant V5112 Sgr performed in 1996–2012 with the 6-m BTA telescope has revealed peculiarities of the star’s optical spectrum and has allowed the variability of the velocity field in the stellar atmosphere and envelope to be studied in detail. An asymmetry and splitting of strong absorption lines with a low lower-level excitation potential have been detected for the first time. The effect is maximal in Ba II lines whose profile is split into three components. The profile shape and positions of the split lines change with time. The short-wavelength components of the split absorption lines are shown to be formed in a structured circumstellar envelope, suggesting an efficient dredge-up of the heavy metals produced during the preceding evolution of this star into the envelope. The envelope expansion velocities have been estimated to be V exp ≈ 20 and 30 km s−1. The mean radial velocity from diffuse bands in the spectrum of V5112 Sgr coincides with that from the short-wavelength shell component of the Na I D lines, which leads to the conclusion about their formation in the circumstellar envelope. Analysis of the set of radial velocities V r based on symmetric absorption lines has confirmed the presence of pulsations in the stellar atmosphere with an amplitude ΔV r ≤ 8 km s−1.

Investigation of properties of galaxy clusters in the Hercules supercluster region

Abstract: We investigated the properties of galaxy clusters in the region of the Hercules supercluster using observational data from the SDSS and 2MASS catalogs and the NED. We have selected 13 galaxy clusters with a total dynamical mass of 4.82 × 1015 M ⊙ in a 100 × 45 Mpc supercluster region in the plane of the sky (0.030 < z < 0.041). In addition, our sample includes eight clusters from the immediate neighborhoods of the superclusters and ten field clusters at the same z. The derived properties of the rich Hercules supercluster are shown in comparison with the data for the poor Leo supercluster. The main parameters of the virialized galaxy cluster regions in the near infrared (K s ) for the Hercules supercluster differ from those for the Leo supercluster: the number of galaxies and the total luminosity (to a limiting magnitude of −21 · 5) increase with cluster mass (L K,200 ∝ M 200 0.91±0.07 and N 200 ∝ M 200 0.94±0.07 ), but the dependences are steeper by 0.28 and 0.22. In the virialized cluster regions, the fraction of early-type galaxies selected by the bulge contribution, concentration index, and u t= r color is, on average, 66% (60% in Leo, 70% in the field) among the galaxies brighter than −23 · 3 and 54% (51% in Leo, 61% in the field) among the galaxies brighter than −22 · 3. The fraction of early-type galaxies in the superclusters does not change with galaxy cluster mass and luminosity. The composite luminosity function of the rich Hercules supercluster is described by a Schechter function and does not differ from the luminosity function of the poor Leo supercluster for the luminosity interval [−26 m , −21 · 5] but differs from the field luminosity function at the same z determined from ten galaxy clusters.

Long-duration plasma heating in solar microflares of X-ray class A1.0 and lower

Abstract: Three solar microflares of X-ray class ∼A1.0 and lower observed at solar activity minimum in 2009 have been studied: the April 19, 2009 flare (A0.38), the June 24, 2009 flare (A0.47), and the July 18, 2009 flare (A2.2). A distinguishing feature of these events from other microflares of low X-ray classes was the maintenance of a high plasma temperature (T 4 MK) at the decay phase well after the flare peak. The lifetimes of the high-temperature emission source in the corona in all three cases exceed considerably its conductive and radiative cooling times, while the thermal energy released at the decay phase of the flare exceeds the energy liberated during its impulsive phase by an order of magnitude. It is hypothesized that a high plasma temperature in microflares of low X-ray classes can be maintained for a long time through magnetic reconnection associated with mass ejections from the flare region. The lifetime of the hot plasma in the corona in this case can exceed appreciably the plasma cooling time. The study has shown that the eruption of material actually occurred in all three investigated microflares.

Evolution and pulsation period change in the Large Magellanic Cloud Cepheids

Abstract: Theoretical estimates of the pulsation period change rates in LMC Cepheids are obtained from consistent calculation of stellar evolution and nonlinear stellar pulsation for stars with initial chemical composition X = 0.7, Z = 0.008, initial masses 5M⊙ ≤ MZAMS ≤ 9M⊙ and pulsation periods ranged from 2.2 to 29 day. The Cepheid hydrodynamical models correspond to the evolutionary stage of thermonuclear core helium burning. During evolution across the instability strip in the HR diagram the pulsation period Π of Cepheids is the quadratic function of the evolution time for the both fundamental mode and first overtone. Cepheids with initial masses MZAMS ≥ 7M⊙ pulsate in the fundamental mode and the period change rate \(\dot \Pi\) varies nearly by a factor of two for both crossings of the instability strip. In the period-period change rate diagram the values of Π and \(\dot \Pi\) concentrate within the strips, their slope and half-width depending on both the direction of the movement in the HR-diagram and the pulsation mode. For oscillations in the fundamental mode the half-widths of the strip are \(\delta log\dot \Pi = 0.35\) and \(\delta log\dot \Pi = 0.2\) for the first and the secon crossings of the instability strip, respectively. Results of computations are comparedwith observations of nearly 700 LMC Cepheids. Within existing observational uncertainties of \(\dot \Pi\) the theoretical dependences of the period change rate on the pulsation period are in a good agreement with observations.

Cepheid Kinematics and the Galactic Warp

Abstract: The space velocities of 200 long-period (P>5 days) classical Cepheids with known proper motions and line-of-sight velocities whose distances were estimated from the period-luminosity relation have been analyzed. The linear Ogorodnikov-Milne model has been applied, with the Galactic rotation having been excluded from the observed velocities in advance. Two significant gradients have been found in the Cepheid velocities, ∂W/∂Y = −2.1 ± 0.7 km s−1 kpc−1 and ∂V/∂Z = 27 ± 10 km s−1 kpc−1. In such a case, the angular velocity of solid-body rotation around the Galactic X axis directed to the Galactic center is −15 ± 5 km s−1 kpc−1.

Nonstationarity of hot post-AGB objects: Variations of the brightness and spectrum of IRAS 01005+7910, IRAS 22023+5249, and IRAS 22495+5134

Abstract: UBV photometry for two hot protoplanetary nebula candidates, early B supergiants with emission lines in the spectrum, IRAS 01005+7910 and IRAS 22023+5249, as well as for IRAS 22495+5134, the central star of the young compact planetary nebula M 2–54, is presented for the first time. Fast irregular brightness variations of the stars with maximum amplitudes up to and color-brightness correlations have been found: the B - V colors tend to become redder with increasing brightness, while U - B more likely decrease with brightening. The color excesses E(B - V) have been determined. The equivalent widths and absolute intensities of emission lines have been derived from low-resolution spectroscopy. Spectral variability has been revealed in all objects. The parameters of the gaseous nebula have been calculated for M 2–54: N e ∼ 104 cm−3and T e = 7700 ± 200 K. A joint analysis of the photometric and spectroscopic data suggests that stellar wind variations can be one of the causes of the stellar variability. The luminosities and distances of all three objects have been estimated.

Galactic bar: Normal mode of the stellar disk or a superposition of transient spirals?

Abstract: Several mechanisms of bar mode formation in stellar galactic disks, including the Toomre swing amplification mechanism and modal approaches, are considered. Using the well-known Kuzmin-Toomre stellar disk model as an example, it has been shown through numerical simulations that the stellar bar results from the development of an unstable normal mode. The pattern speed and the spiral wave growth rate found from a numerical experiment agree well with the linear perturbation theory. The nonlinear evolution of the bar is traced. The possible role of growing transient spirals in the formation of bars is discussed.

The quasi-biennial cycle of solar activity and dynamo theory

Abstract: We have investigated the behavior of dynamo waves within the framework of a nonlinear αω-dynamo by taking into account the thickness of the convective zone, turbulent diffusivity, and meridional circulation. We show that there exists a regime in the model where short and longer patterns are simultaneously observed in the butterfly diagrams for the magnetic field. This regime is similar to the mixed cycle of the Sun, when fast quasi-biennial oscillations are observed against the background of the 22-year cycle.

Estimation of the pitch angle of the Galactic spiral pattern

Abstract: To estimate the pitch angle i of the Galactic spiral arms, we have used data on Galactic masers with known trigonometric parallaxes. These masers are associated with very young objects located in active star-forming regions. The well-knownmethod of analyzing the “position angle-distance logarithm” diagram has been applied. Our estimates of the angle i obtained from four segments of different arms belonging to the grand-design structure are in satisfactory agreement between themselves and are close to i = −13°. The segment of the outer arm is of greatest interest. It contains only three masers, but we have additionally invoked data on 12 very young star clusters with their distances estimated by Camargo et al. from infrared photometry. Using such a combination of data, we have found i = −13.3° ± 1.3°. Comparison of this value with other spiral density wave parameters obtained from a kinematic analysis of masers leads us to conclude that the model of a four-armed spiral pattern is most likely realized in our Galaxy.

On the kinematic age of RZ Psc

Abstract: RZ Psc belongs to the family of young UX Ori stars whose photometric activity is due to strong extinction variations in the circumstellar disks surrounding them. However, in contrast to all the remaining stars of this type, no evidence of youth has been detected for RZ Psc until recently. A rough estimate of the star’s kinematic age was made for the first time in our previous paper (Grinin et al. 2010). It shows that RZ Psc is intermediate in its evolutionary status between young stars in Orion and stars with debris disks. In this paper, we provide a refined estimate of the kinematic age for the star confirming this conclusion. According to this estimate, the age of RZ Psc is approximately 25 ± 5 Myr at M * = 1M ⊙.

Some properties of dust outside the galactic disk

Abstract: The joint use of accurate near- and mid-infrared photometry from the 2MASS and WISE catalogues has allowed the variations of the extinction law and the dust grain size distribution in high Galactic latitudes (|b| > 50°) at distances up to 3 kpc from the Galactic midplane to be analyzed. The modified method of extrapolation of the extinction law applied to clump giants has turned out to be efficient for separating the spatial variations of the sample composition, metallicity, reddening, and properties of the medium. The detected spatial variations of the coefficientsE(H − W1)/E(H − Ks), E(H − W2)/E(H − Ks), and E(H − W3)/E(H − Ks) are similar for all high latitudes and depend only on the distance from the Galactic midplane. The ratio of short-wavelength extinction to long-wavelength one everywhere outside the Galactic disk has been found to be smaller than that in the disk and, accordingly, the mean dust grain size is larger, while the grain size distribution in the range 0.5–11 µm is shifted toward coarse dust. Specifically, the mean grain size initially increases sharply with distance from the Galactic midplane, then decreases gradually, approaching a value typical of the disk at |Z| ≈ 2.4 kpc, and, further out, stabilizes or may increase again. The coefficients under consideration change with coordinate Z with a period of about 1312 ± 40 pc, coinciding every 656 ± 20 pc to the south and the north and showing a significant anticorrelation between their values in the southern and northern hemispheres at intermediate Z. Thus, there exists a unified large-scale periodic structure of the interstellar medium at high latitudes within at least 5 kpc. The same periodic variations have also been found for the extinction coefficient R V within 600 pc of the Galactic midplane through the reduction of different photometric data for stars of different classes.

Systematic variations of interstellar linear polarization and growth of dust grains

Abstract: The observed relation between the interstellar linear polarization curve parameters K and λ max characterizing the width and the wavelength of the polarization maximum, respectively, is interpreted quantitatively. We have considered 57 stars located in four dark clouds with evidence of star formation: in Taurus, Chamaeleon, around the stars ρ Oph and R CrA. In our modeling we have used the spheroidal dust grain model applied previously to simultaneously interpret the interstellar extinction and polarization curves in a wide wavelength range. The observed trend K ≈ 1.7λ max is shown to be most likely related to the growth of dust grains due to coagulation rather than accretion. The relationship of the interstellar polarization curve parameters K and λ max to the mean dust grain size is discussed.

Spatial Variations of the Extinction Law in the Galactic Disk from Infrared Observations

Abstract: Infrared photometry in the J (1.2 µm), H (1.7 µm), Ks (2.2 µm) bands from the 2MASS catalogue and in the W1 (3.4 µm), W2 (4.6 µm), W3 (12 µm), W4 (22 µm) bands from the WISE catalogue is used to reveal the spatial variations of the interstellar extinction law in the infrared near the midplane of the Galaxy by the method of extrapolation of the extinction law applied to clump giants. The variations of the coefficients E(H − W1)/E(H − Ks), E(H − W2)/E(H − Ks), E(H − W3)/E(H − Ks), and E(H − W4)/E(H − Ks) along the line of sight in 2° × 2° squares of the sky centered at b = 0° and l = 20°, 30°, ..., 330°, 340° as well as in several 4° × 4° squares with |b| = 10° are considered. The results obtained here agree with those obtained by Zasowski et al. in 2009 using 2MASS and Spitzer-IRAC photometry for the same longitudes and similar photometric bands, confirming their main result: in the inner (relative to the Sun) Galactic disk, the fraction of fine dust increases with Galactocentric distance (or the mean dust grain size decreases). However, in the outer Galactic disk that was not considered by Zasowski et al., this trend is reversed: at the disk edge, the fraction of coarse dust is larger than that in the solar neighborhood. This general Galactic trend seems to be explained by the influence of the spiral pattern: its processes sort the dust by size and fragment it so that coarse and fine dust tend to accumulate, respectively, at the outer and inner (relative to the Galactic center) edges of the spiral arms. As a result, fine dust may exist only in the part of the Galactic disk far from both the Galactic center and the edge, while coarse dust dominates at the Galactic center, at the disk edge, and outside the disk.

Kinematics of the active region of the quasar 3C 345

Abstract: The fine structure of the quasar 3C 345 in polarized emission at 7 mm and 2 cm has been investigated. The kinematics is shown to correspond to an anticentrifuge: the thermal plasma of the surrounding space accretes onto the disk, flows to the center, and is ejected in the form of a rotating bipolar outflow that carries away the excess angular momentum as it accumulates. The bipolar outflow consists of a high-velocity central jet surrounded by a low-velocity component. The low-velocity flows are the rotating hollow tubes ejected from the peripheral part of the disk with a diameter ∼O1 = 2.2 pc and from the region O2 = 1 pc. The high-velocity jet with a diameter O3 = 0.2 pc is ejected from the central part of the disk, while the remnant falls onto the forming central body. The ejection velocity of the high-velocity flow is v ⩾ 0.06c. At a distance up to ∼1 pc, the jet accelerates to an apparent velocity v ∼ 8c. Further out, uniform motion is observed within ∼2 pc following which deceleration occurs. The jet structure corresponding to a conical diverging helix with an increasing pitch is determined by gasdynamic instability. The counterjet structure is a mirror reflection of the nearby part of the jet. The brightness temperature of the fragment of the high-velocity flow at the exit from the counterjet nozzle is Tb ≈ (1012−1013) K. The disk inclined at an angle of 60° to the plane of the sky shadows the jet ejector region. Ring currents observed in the tangential directions as parallel chains of components are excited in the rotating flows. The magnetic fields of the rotating bipolar outflow and the disk are aligned and oriented along the rotation axis. The translational motions of the jet and counterjet are parallel and antiparallel to the magnetic field, which determines their acceleration or deceleration. The quasar core is surrounded by a thermal plasma. The sizes of the HII region reach ∼30 pc. The electron density decreases with increasing distance from the center from Ne ≈ 108 to ≈105 cm−3. The observed emission from the jet fragments at the exit from the nozzle is partially absorbed by the thermal plasma, is refracted with increasing distance—moves with an apparent superluminal velocity, and decelerates as it goes outside the HII region.

Non-LTE modeling of narrow emission components of He and Ca lines in optical spectra of classical T Tauri stars

Abstract: Using LTE calculations of the structure of T Tauri stellar atmospheres heated by radiation from an accretion shock (Dodin and Lamzin 2012), we have calculated the spectrum of the hot spot emerging on the stellar surface by taking into account non-LTE effects for He I, He II, Ca I, and Ca II. Assuming the pre-shock gas density N 0 and velocity V 0 to be the same at all points of the accretion stream cross section, we have calculated the spectrum of the star+circular spot system at various N 0, V 0, and parameters characterizing the star and the spot. Using nine stars as an example, we show that the theoretical optical spectra reproduce well the observed veiling of photospheric absorption lines as well as the profiles and intensities of the so-called narrow components of He II and Ca I emission lines with an appropriate choice of parameters. The accreted gas density in all of the investigated stars except DK Tau has been found to be N 0 > 1012 cm−3. We have managed to choose the parameters for eight stars at a calcium abundance in the accreted gas ξ Ca equal to the solar one, but we have been able to achieve agreement between the calculations and observations for TW Hya only by assuming ξ Ca to be approximately a factor of 3 lower than the solar one. The estimated parameters do not depend on interstellar extinction, because they have been determined from the spectra normalized to the continuum level. The calculated intensity of Ca II lines has turned out to be lower than the observed one, but this contradiction can be eliminated by assuming that, in addition to the accreted gas with a high density N 0, a more rarefied gas also falls onto the star. The theoretical equivalent widths and relative intensities of the subordinate He I lines disagree significantly with the observations. This is apparently because non-LTE effects should be taken into account when calculating the structure of the upper layers of the hot spot, the accuracy of the cross sections for collisional processes from upper levels is insufficient, and the spot inhomogeneity should probably be taken into account.

Galactic dynamo with helicity fluxes

Abstract: We construct an approximation for the magnetic field of galaxies that takes into account the magnetic helicity conservation law. In our calculations, we use the fact that the galactic disk is fairly thin and, therefore, the magnetic field component perpendicular to the galactic disk can be neglected (the so-called no-z approximation). However, an averaging of the magnetic field over the entire galaxy, as was done in previous works, is not performed. Our results are compared both with the approximation that disregards the helicity flux and with the results obtained in models with helicity fluxes but without averaging. We show that, compared to the classical model, there are a number of new effects (for example, magnetic field oscillations) and, compared to the model with averaging, the behavior of the magnetic field “softens”: its stationary value is reached more slowly and the oscillation amplitude decreases. This is because the dissipative processes changing the magnetic field growth rate are taken into account in our model. In contrast to the model with averaging, here it becomes possible to construct the dependence of the magnetic field and helicity on the distance from the galactic center.