Issue |
A&A
Volume 437, Number 3, July III 2005
|
|
---|---|---|
Page(s) | 947 - 956 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20052872 | |
Published online | 30 June 2005 |
Very compact radio emission from high-mass protostars
II. Dust disks and ionized accretion flows
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: [vdtak;kmenten]@mpifr-bonn.mpg.de
Received:
12
February
2005
Accepted:
22
March
2005
This paper reports 43 GHz imaging of the high-mass
protostars W 33A, AFGL 2591 and NGC 7538 IRS9 at ~ and
~
resolution. In each case, weak (~mJy-level),
compact (Ø ~ 100 AU) emission is detected, which has an
elongated shape (axis ratio ~3).
However, for AFGL 2591 and NGC 7538 IRS9, the emission is
single-peaked, while for the highest-luminosity source,
W 33A, a “mini-cluster” of three sources is detected.
The derived sizes, flux densities, and broad-band radio spectra
of the sources
support recent models where the initial expansion of H ii regions
around very young O-type stars is prevented by stellar gravity. In
these models, accretion flows onto high-mass stars originate in
large-scale molecular envelopes and become ionized close to the
star. These models reproduce our observations of ionized gas as
well as the structure of the molecular envelopes of these sources on
10
AU scales derived previously from single-dish sub-millimeter continuum and line mapping.
For AFGL 2591, the 43 GHz flux density is also consistent with dust
emission from a disk recently seen in near-infrared “speckle”
images. However, the alignment of the 43 GHz emission with the
large-scale molecular outflow argues against an origin in a disk for
AFGL 2591 and NGC 7538 IRS9. In contrast, the outflow from W 33A
does not appear to be collimated.
Together with previously presented case studies of W 3 IRS5 and AFGL 2136, our results indicate that the
formation of stars and stellar clusters with luminosities up to
~105
proceeds through accretion and
produces collimated outflows as in the solar-type case,
with the “additional feature” that the accretion flow
becomes ionized close to the star. Above ~105
, clusters of H ii regions appear, and
outflows are no longer collimated, possibly as the result
of mergers of protostars or pre-stellar cores.
Key words: accretion, accretion disks / stars: formation / instrumentation: high angular resolution / ISM: H ii regions
© ESO, 2005
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