Issue |
A&A
Volume 447, Number 2, February IV 2006
|
|
---|---|---|
Page(s) | L9 - L12 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:200500230 | |
Published online | 07 February 2006 |
Letter to the Editor
Evidence supporting the kinematic interpretation of water maser proper motions
1
INAF, Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Str. 54, 09012 Capoterra (CA), Italy e-mail: cgoddi@ca.astro.it
2
Instituto de Ciencias del Espacio (CSIC)–IEEC, Gran Capitá 2, 08034 Barcelona, Spain
3
Instituto de Astronomía, UNAM, Apdo. Postal 70-264, 04510 México, D.F., México
4
INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
Received:
7
December
2005
Accepted:
21
December
2005
We have analyzed multi-epoch 22 GHz water maser observations
performed with the Very Long Baseline Array (VLBA) towards the high-mass star
forming region (SFR) G24.78+0.08.
The spatial structure of the water maser integrated intensity has been
obtained at three different epochs and found to maintain a very remarkable
persistent morphology over the three epochs. Evidence of systematic
(expanding) motions for the whole structure traced by the maser
emission is
also reported. In addition, we have obtained, from previously reported
data, the integrated emission
of a cluster of water masers spread over 10 mas within the
expanding shell of
0.16'' size around the young stellar object W75 N (B)-VLA 2. As in
G24.78+0.8, we also find that the morphology
of the integrated intensity of the water masers of this cluster
persists over different
observed
epochs.
These results strongly support the interpretation that the measured
proper
motions of the water masers are due to real physical motions of
distinct blobs of maser-emitting gas, rather than to other
effects, such as a travelling background illuminating wave or
turbulence in the
circumstellar medium. This result is crucial in
astrophysical
applications of maser proper-motion measurements, including distance
determinations and studies of circumstellar gas kinematics in SFRs and
late-type stars.
Key words: masers / stars: formation / ISM: kinematics and dynamics
© ESO, 2006
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