Paper: astro-ph/0512402
Date: Thu, 15 Dec 2005 15:55:14 GMT (472kb)

Title: Two-dimensional models of layered protoplanetary discs - II. The effect
of a residual viscosity in the dead zone

Authors: R. Wunsch, A. Gawryszczak, H. Klahr, M. Rozyczka

Comments: 9 pages, 5 figures, accepted for publication in MNRAS
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We study axisymmetric models of layered protoplanetary discs taking radiative
transfer effects into account, and allowing for a residual viscosity in the
dead zone. We also explore the effect of different viscosity prescriptions. In
addition to the ring instability reported in the first paper of the series we
find an oscillatory instability of the dead zone, accompanied by variations of
the accretion rate onto the central star. We provide a simplified analytical
description explaining the mechanism of the oscillations. Finally, we find that
the residual viscosity enables stationary accretion in large regions of layered
discs. Based on results obtained with the help of a simple 1-D hydrocode we
identify these regions, and discuss conditions in which layered discs can give
rise to FU~Orionis phenomena.
\\ ( http://arXiv.org/abs/astro-ph/0512402 , 472kb)
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Paper: astro-ph/0512403
Date: Thu, 15 Dec 2005 16:00:08 GMT (19kb)

Title: The Infrared Glow of First Stars
Authors: R. Salvaterra, M. Magliocchetti, A. Ferrara, R. Schneider
Comments: 4 pages, 2 figures, submitted to MNRAS
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Kashlinsky et al. (2005) find a significant cosmic infrared background
fluctuation excess on angular scales >50 arcsec that cannot be explained by
instrumental noise or local foregrounds. The excess has been tentatively
attributed to emission from primordial very massive (PopIII) stars formed <200
Myr after the Big Bang. Using an evolutionary model motivated by independent
observations and including various feedback processes, we find that PopIII
stars can contribute <40% of the total background intensity, \nu J_\nu ~ 1-2 nW
m^-2 sr^-1 in the 0.8-8 \mum range, produced by all galaxies at z>5. The
clustering of these high redshift sources accounts very precisely for the
infrared fluctuation excess. We conclude that the origin of such fluctuations
can be attributed to galaxies at redshift z>5 predominantly hosting stars with
masses and properties similar to the present ones.

\\ ( http://arXiv.org/abs/astro-ph/0512403 , 19kb)