Issue |
A&A
Volume 471, Number 1, August III 2007
|
|
---|---|---|
Page(s) | L13 - L16 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20077974 | |
Published online | 26 June 2007 |
Letter to the Editor
The hyperyoung H ii region in G24.78+0.08 A1*
1
Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Catalunya, Spain e-mail: mbeltran@am.ub.es
2
INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
3
INAF, Istituto di Radioastronomia, Sezione di Firenze, Largo E. Fermi 5, 50125 Firenze, Italy
Received:
30
May
2007
Accepted:
15
June
2007
Context.G24.78+0.08 A1 is a 20 star surrounded by a hypercompact (HC) Hii
region, driving a CO bipolar outflow, and located at the center of a
massive rotating toroid undergoing infall towards the HC Hii region. Recent water maser
observations suggest that the HC Hii region is expanding and accretion onto
the star is halted.
Aims.To confirm the expansion scenario proposed for the HC Hii region on the basis of recent H2O maser observations.
Methods.We carried out continuum VLA observations at 1.3 cm and 7 mm with the A array plus Pie Town configuration to map the HC Hii region towards G24.78+0.08 A1.
Results.The emission of the HC Hii region has been resolved and shows a ring-shape structure.
The profiles of the emission obtained by taking slices at different angles
passing through the barycenter of the HC Hii region confirm the shell
structure of the emission. The ratio between the inner and the outer radius
of the shell, , derived by fitting the normalized
brightness temperature profile passing through the peak of the 7 mm emission,
is 0.9, which indicates that the shell is thin. The deconvolved outer radius
estimated from the fit is 590 AU. These results imply that the HC Hii region in
G24 A1 cannot be described in terms of a classical, homogeneous Hii region but is instead an ionized
shell. This gives support to the model of an expanding wind-driven, ionized
shell suggested by the kinematics and distribution of the H2O masers
associated with the HC Hii region. According to this model, the HC Hii
region is expanding on very short times scales, 21–66 yr.
Key words: ISM: individual objects: G24.78+0.08 A1 / ISM: Hii regions / stars: circumstellar matter / stars: formation
© ESO, 2007
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.