EDP Sciences
Free access
Issue
A&A
Volume 414, Number 1, January IV 2004
Page(s) 299 - 315
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20031623


A&A 414, 299-315 (2004)
DOI: 10.1051/0004-6361:20031623

IRAS 23385+6053: A candidate protostellar massive object

F. Fontani1, R. Cesaroni2, L. Testi2, C. M. Walmsley2, S. Molinari3, R. Neri4, D. Shepherd5, J. Brand6, F. Palla2 and Q. Zhang7

1  Dipartimento di Astronomia e Fisica dello spazio, Largo E. Fermi 2, 50125 Firenze, Italy
2  INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
3  IFSI, CNR, via Fosso del Cavaliere, 00133 Roma, Italy
4  Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d'Hères, France
5  National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
6  Istituto di Radioastronomia, CNR, via Gobetti 101, 40129 Bologna, Italy
7  Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

(Received 11 June 2003 / Accepted 14 October 2003)

Abstract
We present the results of a multi-line and continuum study towards the source IRAS 23385+6053 performed with the IRAM-30 m telescope, the Plateau de Bure Interferometer, the Very Large Array Interferometer and the James Clerk Maxwell Telescope. We have obtained single-dish maps in the C 18O (1-0), C 17O (1-0) and (2-1) rotational lines, interferometric maps in the CH 3C 2H (13-12) line, NH 3(1,1) and (2,2) inversion transitions, and single-pointing observations of the CH 3C 2H (6-5), (8-7) and (13-12) rotational lines. The new results confirm our earlier findings, namely that IRAS 23385+6053 is a good candidate high-mass protostellar object, precursor of an ultracompact HII region. The source is roughly composed of two regions: a molecular core ~ $0.03\,\div\,0.04$ pc in size, with a temperature of ~ 40 K and an H 2 volume density of the order of 10 7 cm -3, and an extended halo of diameter $\leq$0.4 pc, with an average kinetic temperature of ~ 15 K and H 2 volume density of the order of 10 5 cm -3. The core temperature is much smaller than what is typically found in molecular cores of the same diameter surrounding massive ZAMS stars. From the continuum spectrum we deduce that the core luminosity is between 150 and 1.6  $\times$ $10^{4}~L_{\odot}$, and we believe that the upper limit is near the "true" source luminosity. Moreover, by comparing the H 2 volume density obtained at different radii from the IRAS source, we find that the halo has a density profile of the type  $n_{\rm H_{2}}\propto r^{-2.3}$. This suggests that the source is gravitationally unstable. The latter hypothesis is also supported by a low virial-to-gas mass ratio ( $M_{\rm VIR}/M_{\rm gas}$  $\leq$ 0.3). Finally, we demonstrate that the temperature at the core surface is consistent with a core luminosity of  $10^3~L_{\odot}$ and conclude that we might be observing a protostar still accreting material from its parental cloud, the mass of which is at present ~ $6~M_{\odot}$.


Key words: stars: formation -- radio lines: ISM -- ISM: molecules -- ISM: individual objects: IRAS 23385+6053

Offprint request: F. Fontani, fontani@arcetri.astro.it

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