153 research outputs found
A.I.R. Guest Recital
Program listing performers and works performe
The Formation and Role of Vortices in Protoplanetary Disks
We carry out a two-dimensional, compressible, simulation of a disk, including
dust particles, to study the formation and role of vortices in protoplanetary
disks. We find that anticyclonic vortices can form out of an initial random
perturbation of the vorticity field. Vortices have a typical decay time of the
order of 50 orbital periods (for a viscosity parameter alpha=0.0001 and a disk
aspect ratio of H/r = 0.15). If vorticity is continuously generated at a
constant rate in the flow (e.g. by convection), then a large vortex can form
and be sustained (due to the merger of vortices).
We find that dust concentrates in the cores of vortices within a few orbital
periods, when the drag parameter is of the order of the orbital frequency.
Also, the radial drift of the dust induces a significant increase in the
surface density of dust particles in the inner region of the disk. Thus,
vortices may represent the preferred location for planetesimal formation in
protoplanetary disks.
We show that it is very difficult for vortex mergers to sustain a relatively
coherent outward flux of angular momentum.Comment: Sumitted to the Astrophysical Journal, October 20, 199
The anomalous accretion disk of the Cataclysmic Variable RW Sextantis
Synthetic spectra covering the wavelength range 900\AA~to 3000\AA~provide an
accurate fit, established by a analysis, to a combined
observed spectrum of RW Sextantis. Two separately calibrated distances to the
system establish the synthetic spectrum comparison on an absolute flux basis
but with two alternative scaling factors, requiring alternative values of
for final models. Based on comparisons for a range of
values, the observed spectrum does not follow the standard model. Rather than
the exponent 0.25 in the expression for the radial temperature profile, a value
close to 0.125 produces a synthetic spectrum with an accurate fit to the
combined spectrum. A study of time-series spectra shows that a proposed
warped or tilted disk is not supported by the data; an alternative proposal is
that an observed non-axisymmetric wind results from an interaction with the
mass transfer stream debris.Comment: 56 pages, 15 figures, 11 tables. Accepted for The Astrophysical
Journa
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