UBVRI photometry and polarimetry of the spotted red dwarf MS Ser

UBVRI photometry of the poorly studied spotted star HD 143313 (MS Ser) was carried out in 1991–1997, supplemented with polarization observations in 1996–1997. These observations confirmed the presence of BY Dra-type variability and reliably detected the star’s intrinsic polarization, which is variable in the U band. A model for the star’s spottedness that is consistent with the polarimetry data was constructed based on the collected photometric data. The model calculations suggest that the spotted areas cover up to 15% of the total stellar surface and are about 1500 K cooler than the surrounding photosphere.     

A method for determining stellar parameters from multicolor photometry

Amethod for determining the most probable spectral types, color excesses E _B-V , and distances of stars from multicolor photometry is described. The main idea of the method is modeling the photometric data using various models for the stellar spectra and the interstellar extinction law, and applying the maximum likelihood method. The reliability of the method is estimated using stars with known spectral types and WBVR photometry, based on the empirical library of stellar spectra of Pickles and the model for the interstellar extinction law developed by Fluks et al.     

IR photometry and dust-shell models for two carbon stars

We present JHKLM photometry of the carbon stars ST And and T Lyn acquired in 2000–2010. Along with brightness variations due to pulsations, changes on timescales of 2000–3000 days are also observed. Our combined light curves can be satisfactorily represented with light elements derived from visual observations, but the maxima are delayed relative to the calculated times. A color-index analysis demonstrates that the dust shell of ST And is fairly weak, and is manifest only episodically, while the presence of hot dust was always detected for T Lyn. These results confirm models of spherically symmetric stellar dust shells based on mean-flux data, supplemented with observations in the intermediate IR from the IRAS and AKARI satellites. The visual optical depth of the relatively cool dust shell of ST And assuming a dust temperature at the inner edge of T ₁ = 510 K is very low: τ _V = 0.047. The dust shell of T Lyn is considerably hotter (T ₁ = 940 K), with τ _V = 0.95. We estimate the mass-loss rate to be 1.8 × 10⁻⁷ M _⊙/year for ST And and 3.7 × 10⁻⁷ M _⊙/year for T Lyn.     

IR photometry and models of dust shells for two RCB stars

We present JHKLM photometry obtained in 1984–2009 for the RCB stars UV Cas and SU Tau. No major fadings characteristic of RCB stars were detected during the observations of UV Cas, while two events of this kind occurred for SU Tau. The observed flux and color-index variations can be explained with a changing dust concentration in the line of sight, and possibly variations of the stellar temperature. We use the measured fluxes, supplemented with observations in the intermediate IR, to compute spherically symmetric dust-shell models for the stars. The mass-loss rate is estimated to be 1.7 × 10⁻⁶ M _⊙ yr⁻¹ for UV Cas and 4.1 × 10⁻⁶ M _⊙ yr⁻¹ for SU Tau.     

IR photometry and models for the dust envelopes of two carbon stars

The results of JHKLM photometry of two carbon stars are presented: the irregular variable NQ Cas and the Mira star BD Vul. Data on the mean fluxes supplemented with mid-IR observations with the IRAS, AKARI, andWISE satellites are used to compute spherically symmetrical model dust envelopes for the stars, consisting of particles of amorphous carbon and silicon carbide. The optical depth in the visible for the comparatively cool dust envelope of BD Vul, with a dust temperature at its inner boundary T₁ = 610 K, is fairly low: τ_V = 0.13. The dust envelope of NQ Cas is appreciably hotter (T₁ = 1550 K), and has τ_V = 0.32. The estimated mass-loss rates are 1.5 × 10^?7M_⊙/yr for NQ Cas and 5.9 × 10^?7M_⊙/yr for BD Vul.     

Rapid UBVRI photometry of the active flare stars EV Lac and AD Leo

Regular photometric observations of the two active flare stars EV Lac and AD Leo were carried out in 1996–1999. We have compared the location of the intrinsic radiation of the strongest flares in UBVRI two-color diagrams with those predicted by various models for the radiation sources. Our statistical analysis of flares in EV Lac confirms the 7.5-year activity cycle reported earlier.     

On the reconstruction of the surface structure of the spotted stars

We have developed and tested a light-curve inversion technique for photometric mapping of spotted stars. The surface of a spotted star is partitioned into small area elements, over which a search is carried out for the intensity distribution providing the best agreement between the observed and model light curves within a specified uncertainty. We have tested mapping techniques based on the use of both a single light curve and several light curves obtained in different photometric bands. Surface reconstruction artifacts due to the ill-posed nature of the problem have been identified.     

Galaxies and stars

The distribution of galaxies in the vicinity of stars brighter than V=7.25^m is analyzed. The number density of galaxies is slightly decreased in such regions. This result is statistically significant and cannot be explained as a direct effect of the extended photographic images of these stars. The result is apparently associated with the presence of clouds near the stars, which absorb or scatter light.     

Age and interstellar absorption in young star-formation regions in the galaxies NGC 1068, NGC 4449, NGC 4490, NGC 4631, and NGC 4656/57 derived from multicolor photometry

We have compared the results of multicolor U BV R and Hα photometry for 169 young star-formation complexes in five galaxies using a grid of evolutionary models for young star clusters. The ages and interstellar absorptions are estimated for 102 star-formation complexes with the standard uncertainties σ _t = 0.30 dex and $ \sigma _{A_V } = 0.45^m We have compared the results of multicolor U BV R and Hα photometry for 169 young star-formation complexes in five galaxies using a grid of evolutionary models for young star clusters. The ages and interstellar absorptions are estimated for 102 star-formation complexes with the standard uncertainties σ _t = 0.30 dex and . The accuracies of these parameters were verified using numerical simulations. Original Russian Text ? A.S. Gusev, V.I. Myakutin, A.E. Piskunov, F.K. Sakhibov, M.S. Khramtsova, 2008, published in Astronomicheskiĭ Zhurnal, 2008, Vol. 85, No. 9, pp. 794–809.     

Photometry and polarimetry of the classical Herbig Ae star VV Ser

We present the results of our long-term photometric and polarimetric observations of the classical Herbig Ae star VV Ser, performed at the Crimean Astrophysical Observatory as part of a program of photometric and polarimetric monitoring of UX Ori stars. We recorded an unusually deep minimum of VV Ser (ΔV≈3^m), with a turn of the color tracks in the V-(U-B) and V-(B-V) diagrams (“the blueing effect”) observed for the first time for this star. The increase of the linear polarization during the minimum brightness was consistent with expectations for variable circumstellar extinction models, and the maximum polarization in the B band reached a record value for UX Ori stars in the deepest part of the minimum (12.8±1.4%). Our results cannot be explained by models with an axially symmetrical circumstellar dust disk consisting of silicate grains. They point to the existence of a large-scale nonuniformity in the azimuthal dust distribution near VV Ser attributable to the presence of a second component or protoplanet.     

穿越冈底斯地体的宽频地震探测研究

青藏高原是大约60 Ma以来印度次大陆与欧亚大陆直接碰撞形成的,是研究大陆碰撞过程和发展板块构造理论的最佳场所。冈底斯构造带位于印度次大陆与欧亚大陆碰撞的前沿地带,对冈底斯构造带的探测结果将直接影响到对大陆碰撞过程和整个青藏高原地壳变形过程的认识。2011年9月至2012年9月一条穿越冈底斯(GDS)地体的地震深部探测剖面始于班公怒江断裂带北缘,向南穿越了崩错—嘉黎断裂带、冈底斯地体、雅鲁藏布缝合线并跨过藏南拆离断层系(STD),终止于喜马拉雅山南坡。本文作者利用天然地震体波完成了该条剖面的二维走时残差反演,展现出了该地段深部构造格局。首先验证了冈底斯地体浅部存在大面积部分熔融层的研究结论;支持甲玛大型斑岩铜矿为大陆碰撞挤压条件下岩浆上侵的成矿模式;PKP曲线描绘出了本次研究区间内Moho界面的形态,确定地壳最厚处在雅江缝合线南北两侧约50 km区间。这些推论和发现为青藏高原深部的结构研究提供了重要信息。     

BVRI surface photometry of the galaxy NGC 3726

We present BVRI surface photometry of the late-type spiral galaxy NGC 3627. The distributions of the color indices and extinction-independent Q indices show that the observed photometric asymmetry in the inner part of the galaxy, including the bar, is due to an asymmetric distribution of absorbing material. The bluest regions of star formation are located in a ring surrounding the bar. The background-subtracted color indices of individual blue knots are used to estimate the ages of young stellar aggregates. In combination with previously published photometric data, our measurements indicate that the R-band profile of the disk is rather flat in its inner part (r<50″) and becomes steeper further from its center. We estimate the mass of the disk and dark halo by decomposing the rotation curve. The mass-to-light ratio M/L _B for the stellar disk is ≈1.4. The galaxy possesses a massive dark halo; however, the mass of the disk exceeds that of the halo in the inner part of the galaxy, which displays a regular spiral structure.     

The activity of late-type stars: the Sun among stars with cyclic activity

The coronal and chromospheric emission of several hundred late-type stars whose activity was recently detected are analyzed. This confirms the previous conclusion for stars of HK project that there exist three groups of objects: active red M dwarfs, G-K stars with cyclic activity, and stars exhibiting high but irregular activity. The X-ray fluxes, EUV-spectra, and X-ray cycles can be used to study the main property of stellar coronas—the gradual increase in the number of high-temperature (T ≥ 10 MK) regions in the transition from the Sun to cyclically active K dwarfs and more rapidly rotating F and G stars with irregular activity. The level of X-ray emission is closely related to the spottedness of the stellar surface. The correlation between the chromospheric and coronal emission is weak when the cycles are well-defined, but becomes strong when the activity is less regular. Unexpectedly, stars whose chromospheric activity is even lower than that of the Sun are fairly numerous. Common and particular features of solar activity among the activity of other cyclically active stars are discussed. Our analysis suggests a new view of the problem of heating stellar coronas: the coronas of stars with pronounced cycles are probably heated by quasistationary processes in loops, while prolonged nonstationary coronal events are responsible for heating the coronas of F and G stars with high but irregular activity.     

Cobalt in stars and the galaxy

An analysis of the abundance of cobalt in atmospheres of red giants, indicates they can be divided into two groups: stars with the normal [Co/Fe] abundance and those with a small [Co/Fe] excess. A comparative analysis of the spectrograms taking into account the effect of superfine splitting provides evidence for a [Co/Fe] excess in some stars. We have also detected physical and kinematical differences between these groups. Stars with a [Co/Fe] excess are related to the thick-disk population of the Galaxy. These stars are older and less massive, display lower metallicities, and have Galactic velocities corresponding to those of thick-disk objects. It is suggested that the observed pattern of a [Co/Fe] excess in the halo and thick disk reflects the chemical composition of the Galaxy at a very early stage of its evolution, when Population III objects existed. The lower abundance excess in the thick disk compared to the halo and the absence of an excess in the thin disk are due to the contributiuon from Type I supernovae at later stages of the Galaxy’s evolution. We have found that the thick disk of the Galaxy displays gradients of its cobalt and iron abundances, possibly providing evidence that the thick disk formed as a result of the collapse of a protogalactic cloud.     

Formation and evolution of Ae and Be stars

Several scenarios for the formation of accretion and decretion disks in single and binary Ae and Be stars are proposed. It is shown that, in order for a rapidly rotating main-sequence Be star to lose mass via a disk, the star’s rotation must be quasi-rigid-body. Estimates show that such rotation can be maintained by the star’s magnetic field, which is probably a relict field. The evolution of single Be main-sequence stars is numerically simulated allowing for mass loss via the stellar wind and rotational mass loss assuming rigid-body rotation. The stellar wind is the factor that determines the maximum mass of Be stars, which is close to 30M _⊙. The evolution of Be stars in close binaries is analyzed in the approximation adopted in our scenario. Long gamma-ray bursts can be obtained as a result of the collapse of rapidly rotating oxygen—neon degenerate dwarfs—the accreting companions of Be stars—into neutron stars.     

Studies of classical barium stars

Using atmosphere models based on high-resolution spectra, we have derived the abundances of chemical elements in the atmospheres of seven classical barium stars and compared them with the elemental abundances of moderate barium stars and normal red giants. The behavior of elements up to the iron peak is the same in all three groups of giants, providing evidence that they have a common origin. The dependence of the anomalous abundances of s-process elements on stellar mass and metallicity is qualitatively similar for all three groups, probably indicating that a substantial role is played by the evolutionary phase of the stars. We conclude that the barium-star phenomenon and the overabundances of s-process elements in barium stars cannot be explained as a consequence of binarity alone. The extent to which the s-process elements are overabundant is affected by the mass, metallicity, and evolutionary phase of the given star, and any of these parameters may prove to be important in a specific object.     

Dynamical evolution of multiple stars

We have modeled the dynamical evolution of small groups of N=3–18 stars in the framework of the gravitational N-body problem, taking into account possible coalescences of stars and the ejection of single and binary stars from the system. The distribution of states is analyzed for a time equal to 300 initial crossing times of the system. The parameters of the binaries and stable triple systems formed, as well as those of ejected single stars, are studied. In most cases, the evolution of the group results in the formation of a binary or stable triple system. The orbital eccentricities of the binaries formed are distributed according to the law f(e)=2e. As a rule, stable triple systems display pronounced hierarchy (the mean ratio of the semimajor axes of the outer and inner binaries is about 20:1). Stars are ejected with velocities from several km/s to several tens of km/s. The results of the modeling are compared with the parameters of observed wide binaries and triple systems.     

High-velocity stars as a result of encounters between stars and massive binary black holes in galactic nuclei

Numerical simulations of the motions of stars in the gravitational fields of binary black holes with various component mass ratios have been carried out. Two models are considered: (1) the two-body problem with two fixed centers; (2) the general three-body problem. The first model is applicable only over short times Δt ? T, where T is the period of the binary system. The second model is applicable at all times except for during close encounters of stars with one of the binary components, r ≤ 0.00002 pc, where r is the distance from the star to the nearer black hole. In very close passages, relativistic corrections must be taken into account. Estimates of the probability of formation of high-velocity stars as a result of such interactions are obtained. It is shown that this mechanism is not suitable for the nucleus of our Galaxy due to the probable absence of a second massive black hole in the central region of the Galaxy.     

A model for the population of helium stars in the Galaxy: Low-mass stars

We model the Galactic ensemble of helium stars using population synthesis techniques, assuming that all helium stars are formed in binaries. In this picture, single helium stars are produced by mergers of helium remnants of the components of close binaries (mainly, the merging of helium white dwarfs) or in the disruption of binaries with helium components during supernova explosions. The estimated total birthrate of helium stars in the Galaxy is 0.043 yr^?1; the total number is 4 × 10⁶; and the binarity rate is 76%. We construct a subsample of low-mass (M_He ? 2M_⊙) helium stars defined by observational selection effects: the limiting magnitude (V_He ≤ 16), ratio of the magnitudes of the components in binaries (V_He ≤ V_comp), and lower limit for the semiamplitude of the radial velocity required for detecting binarity (K_min = 30 km s^?1). The parameters of this subsample are in satisfactory agreement with observations of helium subdwarfs. In particular, the binarity rate in the selection-limited sample is 58%. We analyze the relations between the orbital periods and masses of helium subdwarfs and their companions in systems with various combinations of components. We predict that the overwhelming majority (～97%) of unobserved companions to helium stars will be white dwarfs, predominantly, carbon-oxygen white dwarfs.