3,810 research outputs found
Integral formula for elliptic SOS models with domain walls and a reflecting end
In this paper we extend previous work of Galleas and the author to elliptic
SOS models. We demonstrate that the dynamical reflection algebra can be
exploited to obtain a functional equation characterizing the partition function
of an elliptic SOS model with domain-wall boundaries and one reflecting end.
Special attention is paid to the structure of the functional equation. Through
this approach we find a novel multiple-integral formula for that partition
function.Comment: 31 pages, 3 figures; v2: minor improvements, reference adde
N-body simulations of star clusters
Two aspects of our recent N-body studies of star clusters are presented: (1)
What impact does mass segregation and selective mass loss have on integrated
photometry? (2) How well compare results from N-body simulations using NBODY4
and STARLAB/KIRA?Comment: 2 pages, 1 figure with 4 panels (in colour, not well visible in
black-and-white; figures screwed in PDF version, ok in postscript; to see
further details get the paper source). Conference proceedings for IAUS246
'Dynamical Evolution of Dense Stellar Systems', ed. E. Vesperini (Chief
Editor), M. Giersz, A. Sills, Capri, Sept. 2007; v2: references correcte
New insight into the physics of atmospheres of early type stars
The phenomenon of mass loss and stellar winds from hot stars are discussed. The mass loss rate of early type stars increases by about a factor of 100 to 1000 during their evolution. This seems incompatible with the radiation driven wind models and may require another explanation for the mass loss from early type stars. The winds of early type stars are strongly variable and the stars may go through active phases. Eclipses in binary systems by the stellar winds can be used to probe the winds. A few future IUE studies are suggested
Stagnation and Infall of Dense Clumps in the Stellar Wind of tau Scorpii
Observations of the B0.2V star tau Scorpii have revealed unusual stellar wind
characteristics: red-shifted absorption in the far-ultraviolet O VI resonance
doublet up to +250 km/s, and extremely hard X-ray emission implying gas at
temperatures in excess of 10^7 K. We describe a phenomenological model to
explain these properties. We assume the wind of tau Sco consists of two
components: ambient gas in which denser clumps are embedded. The clumps are
optically thick in the UV resonance lines primarily responsible for
accelerating the ambient wind. The reduced acceleration causes the clumps to
slow and even infall, all the while being confined by the ram pressure of the
outflowing ambient wind. We calculate detailed trajectories of the clumps in
the ambient stellar wind, accounting for a line radiation driving force and the
momentum deposited by the ambient wind in the form of drag. We show these
clumps will fall back towards the star with velocities of several hundred
km/sec for a broad range of initial conditions. The infalling clumps produce
X-ray emitting plasmas with temperatures in excess of (1-6)x10^7 K in bow
shocks at their leading edge. The infalling material explains the peculiar
red-shifted absorption wings seen in the O VI doublet. The required mass loss
in clumps is 3% - 30% ofthe total mass loss rate. The model developed here can
be generally applied to line-driven outflows with clumps or density
irregularities. (Abstract Abridged)Comment: To appear in the ApJ (1 May 2000). 24 pages, including 6 embedded
figure
Towards Understanding The B[e] Phenomenon: IV. Modeling of IRAS 00470+6429
FS CMa type stars are a recently described group of objects with the B[e]
phenomenon that exhibit strong emission-line spectra and strong IR excesses. In
this paper we report the first attempt for a detailed modeling of IRAS
00470+6429, for which we have the best set of observations. Our modeling is
based on two key assumptions: the star has a main-sequence luminosity for its
spectral type (B2) and the circumstellar envelope is bimodal, composed of a
slowly outflowing disk-like wind and a fast polar wind. Both outflows are
assumed to be purely radial. We adopt a novel approach to describe the dust
formation site in the wind that employs timescale arguments for grain
condensation and a self-consistent solution for the dust destruction surface.
With the above assumptions we were able to reproduce satisfactorily many
observational properties of IRAS 00470+6429, including the H line profiles and
the overall shape of the spectral energy distribution. Our adopted recipe for
dust formation proved successful in reproducing the correct amount of dust
formed in the circumstellar envelope. Possible shortcomings of our model, as
well as suggestions for future improvements, are discussed.Comment: 11 pages, 7 figures, accepted for publication in The Astrophysical
Journa
The Star Cluster Population of M51
We present the age and mass distribution of star clusters in M51. The
structural parameters are found by fitting cluster evolution models to the
spectral energy distribution consisting of 8 HST-WFPC2 pass bands. There is
evidence for a burst of cluster formation at the moment of the second encounter
with the companion NGC5195 (50-100 Myr ago) and a hint for an earlier burst
(400-500 Myr ago). The cluster
IMF has a power law slope of -2.1. The disruption time of clusters is
extremely short (< 100 Myr for a 10^4 Msun cluster).Comment: 2 pages, to appear in "The Formation and Evolution of Massive Young
Star Clusters", 17-21 November 2003, Cancun (Mexico
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