Disk wind in young binaries and the origin of the cyclic activity of young stars

We present the results of our numerical simulations of the cyclic brightness modulation in young binary systems with eccentric orbits and low-mass secondary components. We suggest that the binary components accrete matter from the remnants of the protostellar cloud, with the main accretor (according to current models) being the low-mass component. The brightness variations of the primary are attributable to the periodic extinction variations on the line of sight caused by the disk wind from the secondary and by the common envelope produced by this wind. The distribution of matter in the envelope was calculated in the ballistic approximation. When calculating the optical effects produced by the dust component of the disk wind, we adopted the dust-to-gas mass ratio of 1:100 characteristic of the interstellar medium and the optical parameters of the circumstellar dust typical of young stars. Our calculations show that the theoretical light curves for binaries with elliptical orbits exhibit a wider variety of shapes than those for binaries with circular orbits. In this case, the parameters of the photometric minima (their depth, duration, and shape of the light curve) depend not only on the disk-wind parameters and the orbital inclination of the binary to the line of sight, but also on the longitude of the periastron. We investigate the modulation of the scattered radiation from the common envelope with orbital phase in the single-scattering approximation. The modulation amplitude is shown to be at a maximum when the system is seen edge-on and to be also nonzero in binaries seen pole-on. We discuss possible applications of the theory to young stellar objects. In particular, several model light curves have been found to be similar to those of candidate FU Orionis stars (FUORs).     

Mechanisms for eclipsing in exotic eclipsing systems

The stars ε Aur, KH 15D, and H 187 are utterly different in their fundamental characteristics. However, they share two important features: (1) prolonged eclipses are observed in all three and (2) there are no spectroscopic signs of a second component. The light curves of these objects are substantially similar, which may indicate a uniform mechanism for the eclipses. This article analyzes models for eclipsing in these objects proposed by different authors and discusses the problems associated with their application. __________ Translated from Astrofizika, Vol. 49, No. 4, pp. 553–571 (November 2006).     

Formation of emission spectra in movin media

Conclusions It can be seen from the above review that the theory of radiative transfer in moving media in its classical field of applications is a well-developed branch of theoretical astrophysics. Studies i n recent years have clarified important questions such as the asymptotic behavior of the kernel functions and the characteristic lengths of the theory. It has been established that there are two types of radiative coupling, and the influence of nonlocal radiative coupling on the formation of spectral lines and radiation pressure has been investigated. The theory now has at its disposal a large selection of asymptotic, approximate, and numerical methods for solving different applied problems.Despite the competition from numerical methods, the overwhelming majority of calculations of emission spectra in the region of supersonic motions has been made on the basis of the escape-probability method and its generalization to the case of nonlocal radiative coupling. This is explained not only by the simplicity and economy of the method but even more by the fact that the greater accuracy of the calculations that can be achieved by using numerical methods is frequently spurious, since it certainly exceeds the accuracy of the basic assumptions. The real way to increase the reliability in the diagnosis of a radiating gas is, first, to solve simultaneously many-level problems for the group of elements whose lines are observed in the spectrum of the object. Second, where possible, one must solve simultaneously the stationary equations and the heat balance equations.Crimean Astrophysical Observatory. Translated from Astrofizika, Vol. 20, No. 2, pp. 365–417, March–April, 1984.     

Disk wind and magnetospheric accretion in emission from the Herbig Ae star MWC 480

The young Herbig Ae star MWC 480 (HD 31648) is one of the comprehensively spectroscopically studied stars in the ultraviolet, optical, and infrared spectral ranges. Using non-LTE modeling of its hydrogen spectrum, we have calculated the contribution to the hydrogen emission from such important regions of the circumstellar environment as the disk wind and the magnetosphere. We have used our own observations of the stellar spectrum performed with the 2.4-m telescope at the Thai National Observatory to quantitatively check our theoretical calculations. In addition, all of the visible and infrared spectra available in the literature have been used for a qualitative comparison. The modeling results have revealed a significant role of the magneto-centrifugal disk wind in the formation of atomic hydrogen emission. The cause of the emission line variability in the spectrum ofMWC 480 is discussed.     

Unusual Photometric Activity of the Weak-line T Tauti Star V715 Per

The results of many-year photometric observations of the weak-line T Tauri star V715 Per in the optical (V RI) and infrared (JHK) photometric bands are presented. The period of the star’s lowamplitude brightness variations in the V RI bands detected earlier, 5.23d, is confirmed. This period persists during the entire 14-year time interval of the observations, but its amplitude varies with time. The same period was found in the variations of JHK infrared fluxes, with the brightness variations in the two ranges being almost synchronous. The most probable origin of these variations is periodic eclipses of the star by its own disk, perturbed by its interaction with the magnetosphere (AA Tau-type variations). In addition to the periodic brightness variations, the star also displayed sporadic Algol-like minima characteristic of UX Ori stars during several years (2005–2011). The amplitude of these variations increasedmonotonically, reaching approximately 1^m in the V band by the end of 2010, after which the deep fadings ended. During this entire time interval, the amplitude of the periodic variations was observed to decrease. After 2011, the periodic component began to become stronger again. These changes of the photometric activity of V715 Per can be explained by an increasing rate of gas accretion onto the star, decreasing the radius of warped regions of the disk and leading to accompanying Algol-like fadings. This model assumes a low inclination of the circumstellar disk in V715 Per to the line of sight.     

Disc wind in the HH 30 binary models

Recent interferometric observations of the young stellar object (YSO) HH 30 have revealed a low-velocity outflow in the¹²CO J =1–2 molecule line. We present here two models of the low-velocity disc winds with the aim of investigating the origin of this molecular outflow. Following Andlada et al., we treated HH 30 as a binary system. Two cases have been considered: (i) the orbital period   P = 53 yr  and (ii)   P ≤ 1 yr  . Calculations showed that in the first case the outflow cone had a spiral-like structure due to summing the velocities of the orbital motion and the disc wind. Such a structure contradicts the observations. In the second case, the outflow cone demonstrates a symmetry relatively to the system axis and agrees well with the observations.