26 research outputs found

### An active asteroid belt causing the UX Ori phenomenon in RZ Psc

We report the discovery of mid-infrared excess emission in the young object
RZ Psc. The excess constitutes ~8% of its Lbol, and is well fit by a single
500K black-body implying a dust free region within 0.7AU for optically thick
dust. The object displays dust obscuration events (UXOR behaviour) with a
time-scale that suggests dusty material on orbits of 0.5AU. We also report a
12.4 year cyclical photometric variability which can be interpreted as due to
perturbations in the dust distribution. The system is characterized by a high
inclination, marginal extinction (during bright photometric states), a single
temperature for the warm dust, and an age estimate which puts the star beyond
the formation stage. We propose that the dust occultation events present a
dynamical view of an active asteroid belt whose collisional products
sporadically obscure the central star.Comment: Accepted for A&A letter

### Hydrodynamic Processes in Young Binary Systems as a Source of Cyclic Variations of Circumstellar Extinction

Hydrodynamic models of a young binary system accreting matter from the
remnants of a protostellar cloud have been calculated by the SPH method. It is
shown that periodic variations in column density in projection onto the primary
component take place at low inclinations of the binary plane to the line of
sight. They can result in periodic extinction variations. Three periodic
components can exist in general case. The first component has a period equal to
the orbital one and is attributable to the streams of matter penetrating into
the inner regions of the binary. The second component has a period that is a
factor of 5-8 longer than the orbital one and is related to the density waves
generated in a circumbinary (CB) disk. The third, longest period is
attributable to the precession of the inner asymmetric region of CB disk. The
relationship between the amplitudes of these cycles depends on the model
parameters as well as on the inclination and orientation of the binary in
space. We show that at a dust-to-gas ratio of 1:100 and and a mass extinction
coefficient of 250 cm$^2$ g$^{-1}$, the amplitude of the brightness variations
of the primary component in the V-band can reach $1^m$ at a mass accretion rate
onto the binary components of $10^{-8} M_{\odot}$ yr$^{-1}$ and a $10^{\rm o}$
inclination of the binary plane to the line of sight. We discuss possible
applications of the model to pre-main-sequence stars.Comment: 13 pages, 6 figures, published in Astronomy Letters (v.33, 2007

### Bimodal Brightness Oscillations in Models of Young Binary Systems

We consider a model for the cyclic activity of young binary stars that
accrete matter from the remnants of a protostellar cloud. If the orbit of such
a binary system is inclined at a small angle to the line of sight, then 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 by the SPH (smoothed particle hydrodynamics) method, we have computed
grids of hydrodynamic models for binary systems based on which we have
constructed the light curves as a function of the orbital phase.The main
emphasis is on investigating the properties of the brightness oscillations.
Therefore, the model parameters were varied within the following ranges: the
component mass ratio q = M2 : M1 = 0.2 - 0.5 and the eccentricity e = 0 - 0.7.
The parameter that defined the binary viscosity was also varied. We adopted
optical grain characteristics typical of circumstellar dust. Our computations
have shown that bimodal oscillations are excited in binaries with eccentric
orbits, provided that the binary components do not differ too much in mass. In
this case, the ratios of the periods and amplitudes of the bimodal oscillations
and their shape depend strongly on the inclination of the binary plane and its
orientation relative to the observer. Our analysis shows that the computed
light curves can be used in interpreting the cyclic activity of UX Ori stars.Comment: 14 pages, 5 figures, 1 tabl

### Brightness Oscillations in Models of Young Binary Systems with Low-Mass Secondary Components

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.Comment: 13 pages,8 figures, 1 tabl