From: LARRY KLAES (ljk4_at_msn.com)
Date: Thu Nov 10 2005 - 10:15:37 PST
Paper: astro-ph/0511250
Date: Wed, 9 Nov 2005 00:30:14 GMT (346kb)
Title: Formation and Evolution of Planetary Systems (FEPS): Primordial Warm
Dust Evolution From 3-30 Myr around Sun-like Stars
Authors: M.D. Silverstone (1), M.R. Meyer (1), E.E. Mamajek (2), D.C. Hines
(3), L.A. Hillenbrand (4), J. Najita (5), I. Pascucci (1), J. Bouwman (6),
J.S. Kim (1), J.M. Carpenter (4), J.R. Stauffer (7), D.E. Backman (8) A.
Moro-Martin (9), T. Henning (6), S. Wolf (6), T.Y. Brooke (7), D.L. Padgett
(7) ((1) Steward Obs., U. of AZ, (2) Harvard-Smithsonian CfA (3) Space
Science Institute, (4) Dept. of Astron., CalTech, (5) NOAO, (6)
Max-Plank-Institut fur Astronomie, (7) Spitzer Science Cntr., (8) NASA-Ames
Research Cntr., (9) Dept. of Astrophys. Sci., Princeton U.)
Comments: 16 pages, includes 2 figures and 2 tables
\\
We present data obtained with the Infrared Array Camera (IRAC) aboard the
Spitzer Space Telescope (Spitzer) for a sample of 74 young (t < 30 Myr old)
Sun-like (0.7 < M(star)/M(Sun) < 1.5) stars. These are a sub-set of the
observations that comprise the Spitzer Legacy science program entitled the
Formation and Evolution of Planetary Systems (FEPS). Using IRAC we study the
fraction of young stars that exhibit 3.6-8.0 micron infrared emission in
excess
of that expected from the stellar photosphere, as a function of age from
3-30
Myr. The most straightforward interpretation of such excess emission is the
presence of hot (300-1000K) dust in the inner regions (< 3 AU) of a
circumstellar disk. Five out of the 74 young stars show a strong infrared
excess, four of which have estimated ages of 3-10 Myr. While we detect
excesses
from 5 optically thick disks, and photospheric emission from the remainder
of
our sample, we do not detect any excess emission from optically thin disks
at
these wavelengths. We compare our results with accretion disk fractions
detected in previous studies, and use the ensemble results to place
additional
constraints on the dissipation timescales for optically-thick, primordial
disks.
\\ ( http://arXiv.org/abs/astro-ph/0511250 , 346kb)
Paper: astro-ph/0511261
Date: Wed, 9 Nov 2005 12:52:02 GMT (37kb)
Title: The circumstellar disc around the Herbig AeBe star HD169142
Authors: W. R. F. Dent (1), J. M. Torrelles (2 and 3), M. Osorio (4), N.
Calvet
(5), G. Anglada (4) ((1) UK Astronomy Technology Centre, Royal Observatory
Edinburgh, UK, (2) Instituto de Ciencias del Espacio (CSIC)-IEEC Barcelona,
Spain, (3) On sabbatical leave at the UK Astronomy Technology Centre, Royal
Observatory Edinburgh, UK, (4) Instituto de Astrof\'{\i}sica de
Andaluc\'{\i}a (CSIC), Granada, Spain, (5) Dept. of Astronomy, University of
Michigan, St., Ann Arbor, MI, USA)
Comments: 13 pages, 2 figures. Accepted by MNRAS
\\
We present 7 mm and 3.5 cm wavelength continuum observations toward the
Herbig AeBe star HD169142 performed with the Very Large Array (VLA) with an
angular resolution of ~1". We find that this object exhibits strong (~4.4
mJy),
unresolved (~1") 7 mm continuum emission, being one of the brightest
isolated
Herbig AeBe stars ever detected with the VLA at this wavelength. No emission
is
detected at 3.5 cm continuum, with a 3 sigma upper limit of ~0.08 mJy. From
these values, we obtain a spectral index of ~2.5 in the 3.5 cm to 7 mm
wavelength range, indicating that the observed flux density at 7mm is most
likely dominated by thermal dust emission coming from a circumstellar disc.
We
use available photometric data from the literature to model the spectral
energy
distribution (SED) of this object from radio to near-ultraviolet
frequencies.
The observed SED can be understood in terms of an irradiated accretion disc
with low mass accretion rate, 10^{-8} solar masses per year, surrounding a
star
with an age of ~10 Myr. We infer that the mass of the disc is ~0.04 solar
masses, and is populated by dust grains that have grown to a maximum size of
1
mm everywhere, consistent with the lack of silicate emission at 10 microns.
These features, as well as indications of settling in the wall at the dust
destruction radius, led us to speculate the disc of HD169142 is in an
advanced
stage of dust evolution, particularly in its inner regions.
\\ ( http://arXiv.org/abs/astro-ph/0511261 , 37kb)
Paper: astro-ph/0511278
Date: Wed, 9 Nov 2005 18:09:45 GMT (23kb)
Title: Proper motion Pleiades candidate L-type brown dwarfs
Authors: G. Bihain, R. Rebolo, V. J. S. Bejar, J. A. Caballero, C. A. L.
Bailer-Jones, R. Mundt
Comments: 2 pages, 2 figures, ULMSF Workshop, accepted for publication in
Astron. Nachrichten
\\
We present results of an optical and near-infrared (IR) 1.8 deg^2 survey in
the Pleiades open cluster to search for substellar objects. From optical
I-band
images from the CFHT and J-band images from the 3.5 m CAHA Telescope, we
identify 18 faint and very red L brown dwarf candidates, with I> 20.9 and
I-J>
3.2. The follow-up observations of nine objects in the H- and Ks-bands
confirm
that eight belong to the IR sequence of the cluster and the proper motion
measurements of seven candidates confirm that they are Pleiades members. A
preliminary estimation of the substellar mass spectrum dN/dM in the form of
a
power law M^-alpha provides alpha=0.57+-0.14. We extrapolate this function
to
estimate the number of very low-mass brown dwarfs and planetary mass objects
that could be present in the cluster down to 1 M_Jup. Sensitive searches
combining far red and near infrared observations may unveal these objects in
a
near future.
\\ ( http://arXiv.org/abs/astro-ph/0511278 , 23kb)
This archive was generated by hypermail 2.1.6 : Thu Nov 10 2005 - 10:20:13 PST