From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Jun 22 2005 - 13:37:47 PDT
Paper: astro-ph/0506474
Date: Mon, 20 Jun 2005 20:56:38 GMT (304kb)
Title: Investigating the Nature of the Dust Emission around Massive
Protostar
NGC 7538 IRS 1: Circumstellar Disk and Outflow?
Authors: James M. De Buizer (1) and Vincent Minier (2) ((1) Gemini
Observatory,
(2) DAPNIA/DSM/CEA Centre d'Etudes de Saclay)
Comments: 8 pages; 4 figures; Accepted for publication by ApJ; Version with
full resolution images available at http://www.ctio.noao.edu/~debuizer/
\\
We have obtained high resolution mid-infrared images of the high mass
protostar NGC 7538 IRS 1 using Michelle on Gemini North and find that the
circumstellar dust associated with this source is extended on both large and
small scales. The large-scale mid-infrared emission is asymmetric about the
peak of IRS 1, being more extended to the northwest than the southeast. The
position angle of the mid-infrared emission is similar to the position angle
of
the linearly distributed methanol masers at this location which are thought
to
trace a circumstellar disk. However, this position angle is also very
similar
to that of the CO outflow in this region which appears to be centered on IRS
1.
We suggest that the large-scale extended mid-infrared emission is coming
from
dust heated on the walls of the outflow cavities near the source. IRS 1 is
also
elongated in the mid-infrared on a smaller scale, and this elongation is
near
PERPENDICULAR to the axis of the CO outflow (and the linearly distributed
methanol masers). Because of its orientation with respect to the outflow and
its estimated size (R_disk~450AU at 11.7um), we propose that the small-scale
elongation seen in the mid-infrared is a circumstellar disk that may be
collimating the outflow from IRS 1.
\\ ( http://arXiv.org/abs/astro-ph/0506474 , 304kb)
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\\
Paper: astro-ph/0506496
Date: Tue, 21 Jun 2005 15:16:19 GMT (395kb)
Title: Evolution of protoplanetary disks: Constraints from DM Tauri and GM
Aurigae
Authors: Ricardo Hueso and Tristan Guillot
Comments: 24 pages, 22 figures, paper accepted for publication in A&A
\\
We present a one-dimensional model of the formation and viscous evolution of
protoplanetary disks. The formation of the early disk is modeled as the
result
of the gravitational collapse of an isothermal molecular cloud. The disk's
viscous evolution is integrated according to two parameterizations of
turbulence: The classical $\alpha$ representation and a $\beta$
parameterization, representative of non-linear turbulence driven by the
keplerian shear. We apply the model to DM Tau and GM Aur, two classical
T-Tauri
stars with relatively well-characterized disks, retrieving the evolution of
their surface density with time. We perform a systematic Monte-Carlo
exploration of the parameter space (i.e. values of the $\alpha$-$\beta$
parameters, and of the temperature and rotation rate in the molecular cloud)
to
find the values that are compatible with the observed disk surface density
distribution, star and disk mass, age and present accretion rate. We find
that
the observations for DM Tau require $0.001<\alpha<0.1$ or $2\times
10^{-5}<\beta<5\times 10^{-4}$. For GM Aur, we find that the turbulent
viscosity is such that $4\times 10^{-4}<\alpha<0.01$ or $2\times
10^{-6}<\beta<8\times 10^{-5}$. These relatively large values show that an
efficient turbulent diffusion mechanism is present at distances larger than
$\sim 10 $AU. This is to be compared to studies of the variations of
accretion
rates of T-Tauri stars versus age that mostly probe the inner disks, but
also
yield values of $\alpha\sim 0.01$. We show that the mechanism responsible
for
turbulent diffusion at large orbital distances most probably cannot be
convection because of its suppression at low optical depths.
\\ ( http://arXiv.org/abs/astro-ph/0506496 , 395kb)
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