From: LARRY KLAES (ljk4_at_msn.com)
Date: Thu Sep 22 2005 - 14:56:06 UTC
Paper: astro-ph/0509613
Date: Tue, 20 Sep 2005 23:55:33 GMT (353kb)
Title: S Ori J053825.4-024241: A Classical T Tauri-like object at the
substellar boundary
Authors: J. A. Caballero, E. L. Mart\'{\i}n, M. R. Zapatero Osorio, V. J. S.
B\'ejar, R. Rebolo, Ya. Pavlenko, R. Wainscoat
Categories: astro-ph
Comments: 12 pages, 15 figures. Accepted for publication in Astronomy &
Astrophysics, section 5. Galactic structure, stellar clusters and
populations.
The official date of acceptance is 24/08/2005. Acknowledgements of the use
of
telescopes, instruments, catalogues and software are also given
\\
We present a spectrophotometric analysis of S Ori J053825.4-024241, a
candidate member close to the substellar boundary of the young (1-8 Myr),
nearby (~360 pc) sigma Orionis star cluster. Our optical and near-infrared
photometry and low-resolution spectroscopy indicate that S Ori
J053825.4-024241
is a likely cluster member with a mass estimated from evolutionary models at
0.06+0.07-0.02 Msol, which makes the object a probable brown dwarf. The
radial
velocity of S Ori J053825.4-024241 is similar to the cluster systemic
velocity.
This target, which we have classified as an M 6.0+-1.0 low-gravity object,
shows excessemission in the near-infrared and anomalously strong photometric
variability for its type (from the blue to the J band), suggesting the
presence
of a surrounding disc. The optical spectroscopic observations show a
continuum
excess at short wavelengths and a persistent and resolved Halpha emission
(pseudo-equivalent width of ~-250 AA) in addition to the presence of other
forbidden and permitted emission lines, which we interpret as indicating
accretion from the disc and possibly mass loss. We conclude that despite the
low mass of S Ori J053825.4-024241, this object exhibits some of the
properties
typical of active classical T Tauri stars.
\\ ( http://arXiv.org/abs/astro-ph/0509613 , 353kb)
Paper: astro-ph/0509643
Date: Wed, 21 Sep 2005 18:15:30 GMT (309kb)
Title: Chemistry and line emission of outer protoplanetary disks
Authors: Inga Kamp, Cornelis P. Dullemond, Michiel Hogerheijde, Jesus Emilio
Enriquez
Categories: astro-ph
Comments: 10 pages, 6 figures, to be published in the conferences
proceedings
of the IAU Symposium 231 on Astrochemistry
\\
The structure and chemistry of protoplanetary disks depends strongly on the
nature of the central star around which it has formed. The dust temperature
is
mainly set by the stellar luminosity, while the chemistry of the upper disk
layers depends on the amount of intercepted UV and X-ray flux. We will study
the differences in chemistry, thermal sturcture and line emission around
Herbig
Ae/Be, T Tauri stars and low mass M dwarfs. Predictions will be made for
future
observations with SOFIA and Herschel.
\\ ( http://arXiv.org/abs/astro-ph/0509643 , 309kb)
Paper: astro-ph/0509637
Date: Wed, 21 Sep 2005 15:36:06 GMT (53kb)
Title: A disk of dust and molecular gas around a high-mass protostar
Authors: Nimesh A. Patel, Salvador Curiel, T. K. Sridharan, Qizhou Zhang,
Todd
R. Hunter, Paul T. P. Ho, Jose M. Torrelles, James M. Moran, Jose F. Gomez &
Guillem Anglada
Categories: astro-ph
Journal-ref: Nature 437, 109, (2005)
\\
The processes leading to the birth of low-mass stars such as our Sun have
been well studied, but the formation of high-mass (> 8 x Sun's mass) stars
has
heretofore remained poorly understood. Recent observational studies suggest
that high-mass stars may form in essentially the same way as low-mass stars,
namely via an accretion process, instead of via merging of several low-mass
(<
8 Msun) stars. However, there is as yet no conclusive evidence. Here, we
report
the discovery of a flattened disk-like structure observed at submillimeter
wavelengths, centered on a massive 15 Msun protostar in the Cepheus-A
region.
The disk, with a radius of about 330 astronomical units (AU) and a mass of 1
to
8 Msun, is detected in dust continuum as well as in molecular line emission.
Its perpendicular orientation to, and spatial coincidence with the central
embedded powerful bipolar radio jet, provides the best evidence yet that
massive stars form via disk accretion in direct analogy to the formation of
low-mass stars.
\\ ( http://arXiv.org/abs/astro-ph/0509637 , 53kb)
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