6 research outputs found
S Coronae Australis -- a T Tauri Twin
The star S CrA is a tight visual binary consisting of two classical T Tauri
stars, both with outstanding spectral characteristics and brightness
variations. High-resolution spectra were collected at ESO and photometric
observations with the SMARTS telescope.
Both stars undergo large variation in brightness caused mainly by variable
foreground extinction. From the stellar parameters we conclude that the two
stars are remarkably similar, and that S CrA can be regarded as a T Tauri twin.
Rotational periods and inclinations are also similar. The stars differ,
however, in terms of degree of veiling and emission line profiles.
We compared observed Balmer emission line profiles with models including
magnetospheric accretion and a disk wind. We found a good match between
observed signatures of accreting gas, wind features, and rotational velocities
with those resulting from our modelling for inclinations of around 65 degrees.
At this orientation the trajectories of infalling gas just above the stellar
surfaces are parallel to the line-of-sight, and accordingly we observe extended
red-shifted absorption components extending to + 380 km/s, the estimated
free-fall velocity at the surface. However, our so derived inclinations differ
from those derived from interferometric near-infrared spectroscopy, and we
discuss possible causes for this puzzling discrepancy.Comment: 11 pages, 12 figure
Clumpy accretion in pre-main-sequence stars as a source of perturbations in circumstellar disks
The development of perturbations in the circumstellar disks of
pre-main-sequence stars caused by clumpy accretion was investigated. Here we
perform 3D hydrodynamical smoothed particle hydrodynamics simulations of disks
perturbed by a recent clump accretion event. These simulations are further
explored by radiative transfer calculations to quantify the observational
appearance of such disks. It was shown that the density waves in the disks were
formed at the fall of the clump. After several revolutions they can transform
into spirals and ring structures. Their images in millimeter wavelengths are
very similar to those observed with Atacama Large Millimeter/submillimeter
Array in some protoplanetary disks. We assume that clumpy accretion may be the
source of such structures.Comment: 14 pages, 18 figures, 1 tabl
Scattered Radiation of Protoplanetary Disks
Scattered radiation of circumstellar (CS) dust plays an important role in the physics of young stars. Its observational manifestations are various but more often they are connected with the appearance of intrinsic polarization in young stars and their CS disks. In our brief review we consider two classes of astrophysical objects in which the participation of scattered radiation is key for understanding their nature. First of all, these are irregular variables (UX Ori type stars). The modern idea of their nature and the mechanism of their variability has been formed thanks to synchronous observations of their linear polarization and brightness. The second class of objects is the CS disks themselves. Their detailed investigation became possible due to observations in polarized light using a coronographic technique and large telescopes
Conditioned suppression or facilitation as a function of the behavioral baseline
Rats were exposed to a multiple schedule of reinforcement. During one component, a bar-press was followed by reinforcement only if it occurred between 15 and 20 sec after the previous response. This differential-reinforcement-of-low-rate (DRL) schedule produced a typical slow rate of responding. During the other component, reinforcement followed the first response to be emitted during limited periods of time which occurred at fixed intervals. These fixed-interval schedules with a limited hold produced higher response rates, described as `interval' or `ratio-like' behavior. Responding during the DRL component increased in frequency during a tone which ended with an unavoidable shock of low intensity, but decreased during the tone when the shock intensity was raised. The `interval' and `ratio-like' responding decreased in frequency during the tone at all shock intensities. Initial acceleration of the DRL responding appeared to be due to adventitious punishment of collateral behavior which was observed between the bar-presses. The more severe conditioned suppression during the fixed-interval components might be the result of the lower probability of reinforcement after any single response