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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 225945.0, MPI für Astronomie / Publikationen_mpia
Constraints in the circumstellar density
distribution of massive young stellar objects
Authors:Alvarez, C.; Hoare, M.; Lucas, P.
Date of Publication (YYYY-MM-DD):2004
Title of Journal:Astronomy and Astrophysics
Start Page:203
End Page:213
Review Status:not specified
Audience:Not Specified
Abstract / Description:We use a Monte Carlo code to generate
synthetic near-IR reflection nebulae that
resemble those (normally associated with a
bipolar outflow cavity) seen towards massive
young stellar objects (YSOs). The 2D
axi-symmetric calculations use an analytic
expression for a flattened infalling rotating
envelope with a bipolar cavity representing an
outflow. We are interested in which aspects of
the circumstellar density distribution can be
constrained by observations of these reflection
nebulae. We therefore keep the line of sight
optical depth constant in the model grid, as
this is often constrained independently by
observations. It is found that envelopes with
density distributions corresponding to mass
infall rates of ‚‚sim;10-4
M‚‚odot; yr-1 (for an
envelope radius of 4700 AU) seen at an
inclination angle of ‚‚sim; deg 45 approximately
reproduce the morphology and extension of the
sub-arcsecond nebulae observed in massive YSOs.
Based on the flux ratio between the approaching
and receding lobe of the nebula, we can
constrain the system inclination angle. The
cavity opening angle is well constrained from the
nebula opening angle. Our simulations indicate
that to constrain the outflow cavity shape and
the degree of flattening in the envelope, near-IR
imaging with higher resolution and dynamic range
than speckle imaging in 4 m-class telescopes is
needed. The radiative transfer code is also used
to simulate the near-IR sub-arcsecond nebula seen
in <ASTROBJ>Mon R2 IRS3</ASTROBJ>. We find
indications of a shallower opacity law in this
massive YSO than in the interstellar medium, or
possibly a sharp drop in the envelope density
distribution at distances of ‚‚sim;1000 AU from
the illuminating source.
Free Keywords:scattering; stars: formation; techniques:
; high angular resolution; radiative transfer;
; stars: winds; outflow
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
External Affiliations:University of Leeds, Leeds LS2 9JT, UK; Kapteyn
Astronomical Institute, Postbus 800, 9700 AV Groningen,
The Netherlands; Max-Planck-Institut f‚‚uuml;r
Astronomie, K‚‚ouml;nigstuhl 17, 69117
Heidelberg, Germany), AB(Physics and Astronomy
Department, University of Leeds, Leeds LS2 9JT,
UK), AC(Dept. of Physical Sciences, University of
Hertfordshire, College Lane, Hatfield AL10 9AB,
Identifiers:URL: [ID No:1]
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