Non-LTE models of the accretion disks of UX Ori stars     

L. V. Tambovtseva  V. P. Grinin  O. V. Kozlova 《Astrophysics》1999,42(1):54-63

The results of a non-LTE analysis of a number of spectral lines formed in the accreting envelopes of UX Ori stars are given. The accretion rate is estimated from an analysis of the first three lines of the Balmer series: M _a = 10^?8 ?10^?9 M _⊙ The gas temperature in this region is about 10,000 K. In the immediate vicinity of the star there is a hotter region, with T > 15,000 K, in which the 5876 Å line of neutral helium, observed in the spectra of these stars, is formed. The region of formation of this line has a small geometrical thickness, covers a small fraction of the star’s visible disk, and evidently consists of the site of contact of the accreting gas with the stellar surface. The low gas rotation rates in this region (150–200 km/sec) may mean that rapid rotation of the accreting gas is damped by the star’s magnetic field, which is strong enough to affect the gas stream. We estimate the magnetic field strength in this region to be about 150 G.  相似文献   

The accretion activity of the Ae Herbig star CQ Tau     

O. V. Kozlova  V. P. Grinin  A. N. Rostopchina 《Astronomy Reports》2000,44(1):36-44

Results of spectral observations of the isolated Ae Herbig star CQ Tau obtained in 1995–1998 in the H_α line and near the sodium resonance doublet are presented, together with simultaneous photometric monitoring of the star. CQ Tau is a member of the family of young UX Ori stars with nonperiodic Algol-like brightness decreases. The star is surrounded by an accretion disk, in which its emission-line spectrum and part of its absorption-line spectrum are formed. The strong variability of the H_α, D NaI, and HeI 5876 Å lines testifies that the gaseous disk is appreciably inhomogeneous in both the radial and azimuthal directions. This inhomogeneity probably results from uneven feeding by the circumstellar material from the peripheral regions of the circumstellar disk. Over the four years of observations, we observed the star in deep minima three times (ΔV～2). On these nights, an increase in the H_α equivalent width followed the decrease in radiation flux. In the two deepest minima, the normally two-component line profile had only a single component with a nearly symmetrical profile. This behavior of the H_α line is in good agreement with the results of numerical modeling of Algol-like minima and can be used to estimate the parameters of the dust clouds eclipsing the star and inner accretion disk. These estimates suggest that the circumstellar dust clouds can approach very close to the star and be sublimated there.  相似文献   

Modeling of Hydrogen Emission Lines in the Spectrum of UX Ori in Its Bright State and during Eclipses     

Tambovtseva  L. V.  Grinin  V. P.  Dmitriev  D. V. 《Astronomy Reports》2020,64(12):1026-1041

Astronomy Reports - The hydrogen spectrum of the UX Ori-type star is modeled in a bright state and during an eclipse by an opaque dusty fragment of its own protoplanetary disk. The disk wind is...  相似文献   

SPH simulations of structures in protoplanetary disks     

T. V. Demidova  V. P. Grinin 《Astronomy Letters》2017,43(2):106-119

Using the GADGET-2 code modified by us, we have computed hydrodynamic models of a protoplanetary disk perturbed by a low-mass companion. We have considered the cases of circular and eccentric orbits coplanar with the disk and inclined relative to its midplane. During our simulations we computed the column density of test particles on the line of sight between the central star and observer. On this basis we computed the column density of circumstellar dust by assuming the dust and gas to be well mixed with a mass ratio of 1: 100. To study the influence of the disk orientation relative to the observer on the interstellar extinction, we performed our computations for four inclinations of the line of sight to the disk plane and eight azimuthal directions. The column densities in the circumstellar disk of the central star and the circumbinary disk were computed separately. Our computations have shown that periodic column density oscillations can arise in both inner and circumbinary disks. The amplitude and shape of these oscillations depend on the system’s parameters (the orbital eccentricity and inclination, the component mass ratio) and its orientation in space. The results of our simulations can be used to explain the cyclic brightness variations of young UX Ori stars.  相似文献   

Brightness oscillations in models of young binary systems with low-mass secondary components     

T. V. Demidova  V. P. Grinin  N. Ya. Sotnikova 《Astronomy Letters》2010,36(7):498-505

We consider a model for the cyclic brightness variations of a young star with a low-mass companion that accretes matter from the remnants of a protostellar cloud. At small inclinations of the binary orbit to the line of sight, the streams of matter and the density waves excited in the circumbinary disk can screen the primary component of the binary from the observer. To study these phenomena, we have computed grids of hydrodynamic models for binary systems by the SPH method based on which we have calculated the phase light curves for the different orientations of the orbit. The model parameters were varied within the following ranges: the component mass ratio q = 0.01–0.1 and the eccentricity e = 0–0.5. We adopted optical grain characteristics typical of circumstellar dust. Our computations have shown that the brightness oscillations with orbital phase can have a complex structure. The amplitudes and shapes of the light curves depend strongly on the inclination of the binary orbit and its orientation relative to the observer and on the accretion rate. The results of our computations are used to analyze the cyclic activity of UX Ori stars.  相似文献   

Analysis of the Historical Light Curve of the UX Ori Star CQ Tau     

D. N. Shakhovskoj  V. P. Grinin  A. N. Rostopchina 《Astrophysics》2005,48(2):135-142

An historical light curve for the UX Ori star CQ Tau is constructed for the period from 1939 through 2003. The star’s photometric behavior includes a cyclical component with a period of about 21 years. An analysis of the periodogram reveals a shorter cycle with a duration of about 1020 days after this cycle is subtracted. Since the photometric activity of UX Ori type stars is caused by variations in the circumstellar extinction, both of these cycles indicate the existence of large-scale deviations from axial symmetry in the distribution of matter in the circumstellar disk of CQ Tau. The orbiting of these inhomogeneities about the star also causes oscillatory variations in its brightness. An analysis of the color-magnitude diagrams reveals differences in the optical parameters of the circumstellar dust along the line of sight in various phases of the 21-year cycle: absorption by larger particles predominates near the brightness maximum of CQ Tau. This means that the reduced circumstellar extinction in this part of the circumstellar disk is the result of a smaller contribution from small particles; this may be evidence of the onset of a process of coagulation of the dust particles and their conversion into large-scale bodies and planetesimals.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 165–174 (May 2005).  相似文献   

Disk wind in young binaries with low-mass secondary components: Optical observational manifestations     

V. P. Grinin  L. V. Tambovtseva 《Astronomy Letters》2002,28(9):601-616

We consider a model of a young binary with a low-mass secondary component. Mass accretion from the remnants of the protostellar cloud onto the binary components is assumed to take place in accordance with current models; i.e., it proceeds mainly onto the low-mass component. The accretion is accompanied by mass outflow (disk wind), whose low-velocity component can be partially captured by the primary component. As a result, an asymmetric common envelope is formed. Its densest part is involved in the orbital motion of the secondary and can periodically shield the primary component of the binary from the observer. Assuming a standard dust-to-gas ratio for the disk wind (1: 100), we calculated the possible photometric effects from such eclipses and showed that they could be observed even at moderate accretion rates onto the low-mass binary component, ∼10⁻⁸–10⁻⁹ M _⊙ per year. In this case, the parameters of the minima depend on the model of the disk wind, on the ratio of its characteristic velocity to the orbital velocity of the secondary, and on its orbital inclination to the line of sight. These results can form the basis for interpreting a wide range of phenomena observed in young stars, such as the activity cycles in UX Ori stars, the unusually broad minima in some young eclipsing systems, etc., and for searching for substellar objects and massive protoplanets. In addition, the peripheral parts of the gas and dust disk around a young binary can fall within the shadow zone produced by the opaque part of the common envelope. In such cases, a shadow from the common envelope must be observed on the disk; this shadow must move over the disk following the orbital motion of the low-mass component. Detection and investigation of such structures in the images of protoplanetary disks may become a method of searching for protoplanets and studying binaries at early stages of their evolution.  相似文献   

On the origin of the azimuthal asymmetry in pole-on protoplanetary disks: The case of LkHα 101     

T. V. Demidova  V. P. Grinin 《Astronomy Letters》2014,40(6):334-342

The model of a protoplanetary disk around a star with a low-mass companion (M ₂: M ₁ ≤ 0.1) moving in a circular orbit inclined at a small angle to the disk plane (≤10°) is considered. The SPH method is used to calculate the hydrodynamic flows. The orbital motion of the companion leads to a nonuniform distribution of matter in the disk: a matter-free gap, density waves, and gas flows are formed in it. As a result of perturbations, the inner part of the disk is inclined relative to its periphery and does not coincide with the orbital plane of the companion either. This leads to an anisotropic illumination of the disk by the star and, as a consequence, to the appearance of a large-scale inhomogeneity in the disk image: it has a bright horseshoe-shaped region and a small shadow zone located asymmetrically relative to the line of nodes. An asymmetry of the disk image is clearly seen even when it is viewed pole-on. The orbital motion of the companion does not lead to any synchronous motion of the dark (shadow) and bright regions: they only execute small oscillations relative to some preferential direction. The asymmetric image of the disk around the star LkHα 101 seen nearly pole-on can be reproduced rather accurately within the proposed model. A study of such asymmetric disks opens up new opportunities for the search of massive bodies in the neighborhoods of young stars.  相似文献   

Rossiter-mclaughlin effect in emission from UX Ori stars     

V. P. Grinin  I. S. Potravnov 《Astrophysics》2013,56(1):1-7

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Variability of the hydrogen and calcium emission in the spectrum of SU Aur     

V. P. Grinin  A. S. Mitskevich  L. V. Timoshenko 《Astrophysics》1985,22(1):24-28

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