Star-forming protoclusters associated with methanol masers

Minier, V., Burton, M.G., Hill, T., Pestalozzi, M.R., Purcell, C.R., Garay, G., walsh, A.J., and Longmore, S. (2005) Star-forming protoclusters associated with methanol masers. Astronomy & Astrophysics, 429. pp. 945-960.

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Abstract

We present a multiwavelength study of five methanol maser sites which are not directly associated with a strong (>100 mJy) radio continuum source: G 31.28+0.06, G 59.78+0.06, G 173.49+2.42 (S231, S233IR), G 188.95+0.89 (S252, AFGL5180) and G 192.60-0.05 (S255IR). These radio-quiet methanol maser sites are often interpreted as precursors of ultra-compact H II regions or massive protostar sites. In this work, the environment of methanol masers is probed from mid-IR to millimetre wavelengths at angular resolutions of 8''-34''. Spectral energy distribution (SED) diagrams for each site are presented, together with mass and luminosity estimates. Each radio-quiet maser site is always associated with a massive (>50 Mȯ), deeply embedded (Av>40 mag) and very luminous (>104 Lȯ) molecular clump, with Ltotal∝ Mgas0.75. These physical properties characterise massive star-forming clumps in earlier evolutionary phases than H II regions. In addition, colder gas clumps seen only at mm-wavelengths are also found near the methanol maser sites. These colder clumps may represent an even earlier phase of massive star formation. These results suggest an evolutionary sequence for massive star formation from a cold clump, seen only at mm wavelengths, evolving to a hot molecular core with a two-component SED with peaks at far-IR and mid-IR wavelengths, to an (ultra-compact) H II region. Alternatively, the cold clumps might be clusters of low-mass YSOs, in formation near the massive star-forming clusters. Finally, the values of the dust grain emissivity index (β) range between 1.6 and 1.9.

Item ID: 9051
Item Type: Article (Refereed Research - C1)
Keywords: masers; stars: formation; ISM: dust; extinction
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Reproduced with permission from Astronomy & Astrophysics. © ESO

ISSN: 1432-0746
Date Deposited: 15 Mar 2010 05:44
FoR Codes: 02 PHYSICAL SCIENCES > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970102 Expanding Knowledge in the Physical Sciences @ 100%
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