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

Abstract

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 constructed the phase light curves as a function of the rotation angle of the apsidal line relative to the observer. 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.

Reverse rotation of the accretion disk in RW Aur A: Observations and a physical model

“…The flow of matter in binary systems accreting material from protoplanetary disks has been simulated numerically in many studies [7][8][9][10][11][12][13][14][15][16][17]. The simulation results indicate the following major flow elements in these systems: circumstellar accretion disks around the system components, a rarefied area in the central parts of the protoplanetary disk adjoining the binary, and a complex system of gas-dynamical flows.…”

“…For reverse rotation to occur, the angular momentum delivered to the disk by the falling matter must be opposite to the angular momentum of the system. Numerical simulations of these systems have been performed in various studies [7][8][9][10][11][12][13][14][15][16][17], have not indicated the appearance of reversed accretion disks in binary systems for a wide range of parameters. In addition, analysis of the flow structure that forms in the vicinity of a young binary indicates that flows directed opposite to the motion of the components can exist [15].…”

Modulation of circumstellar extinction in a young binary system with a low-mass companion in a noncoplanar orbit

“…This problem was initiated by the observations of large-scale activity cycles in UX Ori stars (Grinin et al 1998) and by the observations of anomalously long eclipses in some young stars (Cohen et al 2003; Barsunova et al 2005; Nordhagen et al 2006; Grinin et al 2008), which cannot be explained in terms of classical models of eclipsing binary systems. Sotnikova and and Demidova et al (2010aDemidova et al ( , 2010b showed that the streams of matter and density waves produced in young binary systems by the orbital motion of their companions can cause (at low inclinations of the orbital plane to the line of sight) various (in shape and duration) periodic fadings of the primary component. One of the main conditions in the computations was coplanarity of the orbital plane and the circumbinary (CB) disk.…”

“…In the previous papers of this series (Sotnikova and Grinin 2007; Demidova et al 2010aDemidova et al , 2010b, we studied the behavior of the circumstellar extinction and brightness in young binary systems accreting matter from the remnants of a protostellar cloud. This problem was initiated by the observations of large-scale activity cycles in UX Ori stars (Grinin et al 1998) and by the observations of anomalously long eclipses in some young stars (Cohen et al 2003; Barsunova et al 2005; Nordhagen et al 2006; Grinin et al 2008), which cannot be explained in terms of classical models of eclipsing binary systems.…”

Hydrodynamics of Young Binaries with Low-Mass Secondaries

“…We used the input parameters to transform the column density of SPH particles to optical depth. Then, we calculated the theoretical brightness curves (see Demidova et al (2010) for more details).…”