Paper: astro-ph/0512291
Date: Mon, 12 Dec 2005 19:19:49 GMT (74kb)

Title: Ultraviolet Radiation Constraints around the Circumstellar Habitable
Zones

Authors: Andrea P. Buccino, Guillermo A. Lemarchand, Pablo J. D. Mauas

Comments: 29 pages, 8 figures
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Ultraviolet radiation is known to inhibit photosynthesis, induce DNA
destruction and cause damage to a wide variety of proteins and lipids. In
particular, UV radiation between 200-300 nm becomes energetically very damaging
to most of the terrestrial biological systems. On the other hand, UV radiation
is usually considered one of the most important energy source on the primitive
Earth for the synthesis of many biochemical compounds and, therefore, essential
for several biogenesis processes. In this work, we use these properties of the
UV radiation to define the bounderies of an ultraviolet habitable zone. We also
analyze the evolution of the UV habitable zone during the main sequence stage
of the star. We apply these criteria to study the UV habitable zone for those
extrasolar planetary systems that were observed by the International
Ultraviolet Explorer (IUE). We analyze the possibility that extrasolar planets
and moons could be suitable for life, according to the UV constrains presented
in this work and other accepted criteria of habitability (liquid water, orbital
stability, etc.).

\\ ( http://arXiv.org/abs/astro-ph/0512291 , 74kb)

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Paper: astro-ph/0512292
Date: Mon, 12 Dec 2005 14:46:55 GMT (56kb)

Title: Gas Flow Across Gaps in Protoplanetary Disks

Authors: Steve H. Lubow and Gennaro D'Angelo

Comments: 10 pages, 3 figures, 1 table. To appear in The Astrophysical Journal
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We analyze the gas accretion flow through a planet-produced gap in a
protoplanetary disk. We adopt the alpha disk model and ignore effects of
planetary migration. We develop a semi-analytic, one-dimensional model that
accounts for the effects of the planet as a mass sink and also carry out
two-dimensional hydrodynamical simulations of a planet embedded in a disk. The
predictions of the mass flow rate through the gap based on the semi-analytic
model generally agree with the hydrodynamical simulations at the 25% level.
Through these models, we are able to explore steady state disk structures and
over large spatial ranges. The presence of an accreting Jupiter-mass planet
significantly lowers the density of the disk within a region of several times
the planet's orbital radius. The mass flow rate across the gap (and onto the
central star) is typically 10% to 25% of the mass accretion rate outside the
orbit of the planet, for planet-to-star mass ratios that range from 5e-5 to
1e-3.

\\ ( http://arXiv.org/abs/astro-ph/0512292 , 56kb)