SETI public: 4 papers

• Previous message: LARRY KLAES: "SETI public: Planetary catastrophe risks cannot generally be inferred from the Earth's format"

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
\\
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
\\
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)

Paper: astro-ph/0512404
Date: Thu, 15 Dec 2005 16:47:10 GMT (47kb)

Title: The PAH Emission Deficit In Low-Metallicity Galaxies - A Spitzer View

Authors: B. O'Halloran, S. Satyapal and R. P. Dudik

Comments: 19 pages, 4 figures, accepted for publication in ApJ
\\
Archival observations of 18 starburst galaxies that span a wide range in
metallicity reveal for the first time a correlation between the ratio of
emission line fluxes of [FeII] at 26 microns and [NeII] at 12.8 microns and
the
7.7 micron PAH strength, with the [FeII]/[NeII] flux ratio decreasing with
increasing PAH strength. We also find a strong correlation between the
[FeII]/[NeII] flux ratio and the host galaxy metallicity, with the flux
ratio
decreasing with increasing metallicity.

Since [FeII] emission has been linked primarily to supernova shocks, we
attribute the high [FeII]/[NeII] ratios in low-metallicity galaxies to
enhanced
supernova activity. We consider this to be a dominant mechanism for PAH
destruction, rather than grain destruction in photoionized regions
surrounding
young massive stars. We also consider whether the extreme youth of the
low-metallicity galaxies is responsible for the lack of PAH emission.

\\ ( http://arXiv.org/abs/astro-ph/0512404 , 47kb)

Paper: astro-ph/0512421
Date: Thu, 15 Dec 2005 22:32:50 GMT (191kb)

Title: Exoplanet Imaging with a Phase-induced Amplitude Apodization
Coronagraph
III. Hybrid Approach: Optical Design and Diffraction Analysis

Authors: E.A. Pluzhnik, O. Guyon, S.T. Ridgway, F. Martinache, R.A.
Woodruff,
C. Blain, R. Galicher

Comments: Submitted to ApJ
\\
Properly apodized pupils can deliver point spread functions (PSFs) free of
Airy rings, and are suitable for high dynamical range imaging of extrasolar
terrestrial planets (ETPs). To reach this goal, classical pupil apodization
(CPA) unfortunately requires most of the light gathered by the telescope to
be
absorbed, resulting in poor throughput and low angular resolution.
Phase-induced amplitude apodization (PIAA) of the telescope pupil (Guyon
2003)
combines the advantages of classical pupil apodization (particularly low
sensitivity to low order aberrations) with full throughput, no loss of
angular
resolution and little chromaticity, which makes it, theoretically, an
extremely
attractive coronagraph for direct imaging of ETPs. The two most challenging
aspects of this technique are (1) the difficulty to polish the required
optics
shapes and (2) diffraction propagation effects which, because of their
chromaticity, can decrease the spectral bandwidth of the coronagraph. We
show
that a properly designed hybrid system combining classical apodization with
the
PIAA technique can solve both problems simultaneously. For such a system,
the
optics shapes can be well within today's optics manufacturing capabilities,
and
the $10^{-10}$ PSF contrast at $\approx 1.5 \lambda/D$ required for
efficient
imaging of ETPs can be maintained over the whole visible spectrum. This
updated
design of the PIAA coronagraph maintains the high performance of the earlier
design, since only a small part of the light is lost in the classical
apodizer(s).

\\ ( http://arXiv.org/abs/astro-ph/0512421 , 191kb)

• Previous message: LARRY KLAES: "SETI public: Planetary catastrophe risks cannot generally be inferred from the Earth's format"

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