From: LARRY KLAES (ljk4_at_msn.com)
Date: Fri Dec 23 2005 - 09:20:21 PST
Paper: astro-ph/0512561
Date: Thu, 22 Dec 2005 13:45:36 GMT (241kb)
Title: Photodissociation of organic molecules in star-forming regions II:
Acetic acid
Authors: S. Pilling (1 and 2), A. C. F. Santos (3) and H. M. Boechat-Roberty
(1) ((1) OV-UFRJ, (2) IQ-UFRJ, (3) IF-UFRJ)
Comments: Comments: 8 pages, 5 figures, 3 tables. Accepted to be printed in
A&A
\\
Fragments from organic molecule dissociation (such as reactive ions and
radicals) can form interstellar complex molecules like amino acids. The goal
of
this work is to experimentally study photoionization and photodissociation
processes of acetic acid (CH$_3$COOH), a glycine (NH$_2$CH$_2$COOH)
precursor
molecule, by soft X-ray photons. The measurements were taken at the
Brazilian
Synchrotron Light Laboratory (LNLS), employing soft X-ray photons from a
toroidal grating monochromator (TGM) beamline (100 - 310 eV). Mass spectra
were
obtained using the photoelectron photoion coincidence (PEPICO) method.
Kinetic
energy distribution and abundances for each ionic fragment have been
obtained
from the analysis of the corresponding peak shapes in the mass spectra.
Absolute photoionization and photodissociation cross sections were also
determined. We have found, among the channels leading to ionization, that
only
4-6% of CH$_3$COOH survive the strong ionization field. CH$_3$CO$^+$,
COOH$^+$
and CH$_3^+$ ions are the main fragments, and the presence of the former may
indicate that the production-destruction process of acetic acid in hot
molecular cores (HMCs) could decrease the H$_2$O abundance since the net
result
of this process converts H$_2$O into OH + H$^+$. The COOH$^+$ ion plays an
important role in ion-molecule reactions to form large biomolecules like
glycine.
\\ ( http://arXiv.org/abs/astro-ph/0512561 , 241kb)
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Paper: astro-ph/0512563
Date: Thu, 22 Dec 2005 14:11:29 GMT (946kb)
Title: Molecular gas in the Andromeda galaxy
Authors: Ch. Nieten (1), N. Neininger (1,2,3), M. Guelin (3), H. Ungerechts
(4), R. Lucas (3), E. M. Berkhuijsen (1), R. Beck (1), R. Wielebinski (1)
((1) MPI fuer Radioastronomie, Bonn, Germany, (2) Radioastronomisches
Institut, Univ. Bonn, Germany, (3) IRAM, Grenoble, France, (4) IRAM,
Granada,
Spain)
Comments: 21 pages, 16 figures. Accepted for publication in A&A
\\
We present a new 12CO(J=1-0)-line survey of the Andromeda galaxy, M31,
covering the bright disk with the highest resolution to date (85 pc along
the
major axis), observed On-the-Fly (in italics) with the IRAM 30-m telescope.
We
discuss the distribution of the CO emission and compare it with the
distributions of HI and emission from cold dust traced at 175mum. Our main
results are: 1. Most of the CO emission comes from the radial range R=3-16
kpc,
but peaks near R=10 kpc. The emission is con- centrated in narrow, arm-like
filaments defining two spiral arms with pitch angles of 7d-8d. The average
arm-interarm brightness ratio along the western arms reaches 20 compared to
4
for HI. 2. For a constant conversion factor Xco, the molecular fraction of
the
neutral gas is enhanced in the arms and decreases radially. The apparent
gas-to-dust ratios N(HI)/I175 and (N(HI)+2N(H2))/I175 increase by a factor
of
20 between the centre and R=14 kpc, whereas the ratio 2N(H2)/I175 only
increases by a factor of 4. Implications of these gradients are discussed.
In
the range R=8-14 kpc total gas and cold dust are well correlated; molecular
gas
is better correlated with cold dust than atomic gas.
\\ ( http://arXiv.org/abs/astro-ph/0512563 , 946kb)
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