Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004ans...325...13s&link_type=abstract
Astronomische Nachrichten, Vol. 325, Supplement 1, Short Contributions Presented at the Annual Scientific Meeting of the Astrono
Astronomy and Astrophysics
Astronomy
Scientific paper
The formation of massive stars is one of the unresolved mysteries of present research. Whether the dominant formation process for massive stars is disk accretion or coalescence is still an open question. In this respect, we studied the object AFGL 490 in much more detail. This object is a key target of the class of deeply embedded young stellar objects with a mass of 8-10 Msun (spectral type B2-B3, D=1kpc) being in a transition stage to Herbig Be stars. Our new observational data confirm our previous suggestion of the presence of a massive gas torus or disk around this object. Thus, our optically thin C17O 2-1 data point to a clumpy gas ring inclined to our line of sight with an angle of 50-80 deg; in which the 230GHz-continuum point source is centered. The velocity distribution of this gas exhibits the signature of rotation. In addition, our VLA 7mm data show an extension of the "continuum point" source in the same direction as the elongated gas ring. Based on our previous Plateau de Bure data in CS 2-1, we estimated a gas mass inside a radius of 4000 AU of about 8 M which is similar to the mass of the central star. In addition, the variability of the source extension in the NIR and in the VLA-2cm continuum (Hoare et al., Campbell et al.) in the same orientation as the disk is interpreted as a variability in the accretion onto the star which supports well the idea that such a massive disk cannot exist for a very long time without disrupting due to its own self-gravity. Thus, we can speculate that the outer gas torus feeds the inner gravitationally unstable gas disk until the torus is depleted. Then, the gas torus and the disk disappear in 10^3 to 10^4 years. This would be in a good agreement with the observations that Herbig Be stars (and more massive stars) have no disks anymore, and this would be a possible procedure to build up stars with masses -- maybe -- until 15 to 20Msun. Here, more theoretical work and high-resolution observations are needed.
P. H. acknowledges partial support from the Research Corporation grant No CC4996, as well as from NSF grant AST-0098524.
Araya Esteban
Henning Thomas
Hofner Peter
Linz Hendrik
Schreyer Katharina
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