SETI public: The latest papers on exoplanets and other relevant goodies

• Previous message: LARRY KLAES: "SETI public: Do Telescopes Need Astronomers?"

Paper: astro-ph/0507115
Date: Tue, 5 Jul 2005 23:07:21 GMT (420kb)

Title: Astrometric Methods and Instrumentation to Identify and Characterize
Extrasolar Planets: A Review

Authors: A. Sozzetti (Harvard-Smithsonian Center for Astrophysics)
Comments: 61 pages, 8 figures, PASP, accepted (October 2005 issue)
\\
I present a review of astrometric techniques and instrumentation utilized to
search for, detect, and characterize extra-solar planets. First, I briefly
summarize the properties of the present-day sample of extrasolar planets, in
connection with predictions from theoretical models of planet formation and
evolution. Next, the generic approach to planet detection with astrometry is
described, with significant discussion of a variety of technical,
statistical,
and astrophysical issues to be faced by future ground-based as well as
space-borne efforts in order to achieve the required degree of measurement
precision. After a brief summary of past and present efforts to detect
planets
via milli-arcsecond astrometry, I then discuss the planet-finding
capabilities
of future astrometric observatories aiming at micro-arcsecond precision.
Lastly, I outline a number experiments that can be conducted by means of
high-precision astrometry during the next decade, to illustrate its
potential
for important contributions to planetary science, in comparison with other
indirect and direct methods for the detection and characterization of
planetary
systems.

\\ ( http://arXiv.org/abs/astro-ph/0507115 , 420kb)

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Paper: astro-ph/0507122
Date: Wed, 6 Jul 2005 07:14:23 GMT (64kb)

Title: Whims of an Accreting Young Brown Dwarf: Exploring Emission Line
Variability of 2MASSW J1207334-393254

Authors: Alexander Scholz, Ray Jayawardhana, Alexis Brandeker (University of
Toronto)
Comments: 12 pages, 2 figures, ApJL, accepted
\\
We report the first comprehensive study of emission line variability in an
accreting young brown dwarf. We have collected 14 high-resolution optical
spectra of 2MASSW J1207334-393254 (M8), a likely member of the nearby
8-million-year-old TW Hydrae association. These spectra show a variety of
emission lines that are commonly seen in classical T Tauri stars. Halpha
line
in particular shows dramatic changes in shape and intensity in our dataset,
both on timescales of several weeks and several hours. In spectra from
late-January, the line is relatively weak and only slightly asymmetric.
Spectra
from mid- and late-March show intense, broad and asymmetric Halpha emission,
indicative of on-going disk accretion. We estimate that the accretion rate
could have changed by a factor of 5-10 over ~6 weeks in this brown dwarf.
March
spectra also reveal significant `quasi-periodic' changes in the Halpha line
profile over the course of a night, from clearly double-peaked to nearly
symmetric. These nightly profile changes, roughly consistent with the brown
dwarf's rotation period, could be the result of a redshifted absorption
feature
coming into and out of our line of sight; when the profile is double-peaked
we
may be looking into an accretion column, flowing from the inner disk edge on
to
the central object, indicating that the accretion is probably channelled
along
the magnetic field lines. Our findings provide strong support for the
magnetospheric accretion scenario, and thus for the existence of large-scale
magnetic fields, in the sub-stellar regime (abridged).

\\ ( http://arXiv.org/abs/astro-ph/0507122 , 64kb)

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Paper: astro-ph/0507136
Date: Wed, 6 Jul 2005 16:00:26 GMT (436kb)

Title: Phase-Dependent Properties of Extrasolar Planet Atmospheres

Authors: Travis S. Barman, Peter H. Hauschildt and France Allard
Comments: 8 pages, 7 figures, accepted for publication in the Astrophysical
Journal
\\
Recently the Spitzer Space Telescope observed the transiting extrasolar
planets, TrES-1 and HD209458b. These observations have provided the first
estimates of the day side thermal flux from two extrasolar planets orbiting
Sun-like stars. In this paper, synthetic spectra from atmospheric models are
compared to these observations. The day-night temperature difference is
explored and phase-dependent flux densities are predicted for both planets.
For
HD209458b and TrES-1, models with significant day-to-night energy
redistribution are required to reproduce the observations. However, the
observational error bars are large and a range of models remains viable.

\\ ( http://arXiv.org/abs/astro-ph/0507136 , 449kb)

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Paper: astro-ph/0507137
Date: Wed, 6 Jul 2005 16:32:06 GMT (60kb)

Title: On water ice formation in interstellar clouds

Authors: Renaud Papoular
Comments: 9 pages, 6 figures. MNRAS, in press
\\
A model is proposed for the formation of water ice mantles on grains in
interstellar clouds. This occurs by direct accretion of monomers from the
gas,
be they formed by gas or surface reactions. The model predicts the existence
of
a threshold in interstellar light extinction, A(v), which is mainly
determined
by the adsorption energy of water molecules on the grain material; for
hydrocarbon material, chemical simulation places this energy between 0.5 and
2
kcal/mole, which sets the visible exctinction threshold at a few magnitudes,
as
observed. Once the threshold is crossed, all available water molecules in
the
gas are quickly adsorbed, forming an ice mantle, because the grain cools
down
and the adsorption energy on ice is higher than on bare grain. The model
also
predicts that the thickness of the mantle, and, hence, the optical thickness
at
3 mu, grow linearly with A(v), as observed, with a slope which depends upon
the
total amount of water in the gas. Chemical simulation was also used to
determine the adsorption sites and energies of O and OH on hydrocarbons, and
study the dynamics of formation of water molecules by surface reactions with
gaseous H atoms, as well as their chances of sticking in situ.

\\ ( http://arXiv.org/abs/astro-ph/0507137 , 60kb)
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