Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...417..645g&link_type=abstract
Astrophysical Journal v.417, p.645
Astronomy and Astrophysics
Astronomy
47
Ism: H Ii Regions, Ism: Individual Alphanumeric: W51, Ism: Molecules, Ism: Structure, Masers, Radio Continuum: Interstellar
Scientific paper
High angular resolution and high-sensitivity observations at wavelengths of 1.3 and 3.6 cm have detected three new ultracompact emission regions in the core of the W51 (regions d and e). In total, five ultracompact continuum objects of diameter less than 300 to 3000 AU are located in W51 d and e. These sources may best be explained as photoionized stellar winds. This suggests that there may exist a quasi-stable point in early stellar evolution where observable H II regions are formed by stellar winds around massive stars.
These observations demonstrate that the taxonomy of H II region classification may be heavily affected by sensitivity, and a lack of complete spatial sampling by interferometric mapping. For example, the W51 d region, previously classified as cometary, is shown by our higher resolution and sensitivity observations also to have the properties normally associated with shell-like regions. These new observations suggest that the bow shock model, which is suggested to explain the morphology of cometary H II regions, but cannot explain shell sources, does not fully explain the W51 d H II region.
The J, K = (9, 8) NH3 maser associated with W51 d has been shown to have a minimum brightness temperature of 2.7 × 106 K. This maser is most probably saturated.
Gaume Ralph A.
Johnston Ken J.
Wilson Thomas L.
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