NATURE OF W51e2: MASSIVE CORES AT DIFFERENT PHASES OF STAR FORMATION

Journal Article · Wed Feb 10 00:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/710/1/843· OSTI ID:21394474

Hui, Shi; Han, J L ^[1]

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1. National Astronomical Observatories, Chinese Academy of Sciences, Jia20 Datun Road, Chaoyang District, Beijing 100012 (China)

We present high-resolution continuum images of the W51e2 complex processed from archival data of the Submillimeter Array (SMA) at 0.85 and 1.3 mm and the Very Large Array at 7 and 13 mm. We also made line images and profiles of W51e2 for three hydrogen radio recombination lines (RRLs; H26alpha, H53alpha, and H66alpha) and absorption of two molecular lines of HCN(4-3) and CO(2-1). At least four distinct continuum components have been detected in the 3'' region of W51e2 from the SMA continuum images at 0.85 and 1.3 mm with resolutions of 0.''3 x 0.''2 and 1.''4 x 0.''7, respectively. The west component, W51e2-W, coincides with the ultracompact H II region reported from previous radio observations. The H26alpha line observation reveals an unresolved hyper-compact ionized core (<0.''06 or <310 AU) with a high electron temperature of 1.2 x 10{sup 4} K, with the corresponding emission measure EM>7 x 10{sup 10} pc cm{sup -6} and the electron density N{sub e} >7 x 10{sup 6} cm{sup -3}. The inferred Lyman continuum flux implies that the H II region W51e2-W requires a newly formed massive star, an O8 star or a cluster of B-type stars, to maintain the ionization. W51e2-E, the brightest component at 0.85 mm, is located 0.''9 east from the hyper-compact ionized core. It has a total mass of {approx}140 M{sub sun} according to our spectral energy distribution analysis and a large infall rate of >1.3 x 10{sup -3} M{sub sun} yr{sup -1} inferred from the absorption of HCN. W51e2-E appears to be the accretion center in W51e2. Given the fact that no free-free emission and no RRLs have been detected, the massive core of W51e2-E appears to host one or more growing massive proto-stars. Located 2'' northwest from W51e2-E, W51e2-NW is detected in the continuum emission at 0.85 and 1.3 mm. No continuum emission has been detected at lambda>= 7 mm. Along with the maser activities previously observed, our analysis suggests that W51e2-NW is at an earlier phase of star formation. W51e2-N is located 2'' north of W51e2-E and has only been detected at 1.3 mm with a lower angular resolution ({approx}1''), suggesting that it is a primordial, massive gas clump in the W51e2 complex.

• OSTI ID: 21394474
• Journal Information: Astrophysical Journal, Vol. 710, Issue 1; Other Information: DOI: 10.1088/0004-637X/710/1/843; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION
ELECTRON DENSITY
ELECTRON TEMPERATURE
EMISSION
ENERGY SPECTRA
HYDROCYANIC ACID
HYDROGEN
IONIZATION
LYMAN LINES
MASERS
MASS
RECOMBINATION
STARS
AMPLIFIERS
ELECTRONIC EQUIPMENT
ELEMENTS
EQUIPMENT
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
MICROWAVE AMPLIFIERS
MICROWAVE EQUIPMENT
NONMETALS
SORPTION
SPECTRA