Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aj....106...31r&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 106, no. 1, p. 31-38, 406, 407.
Other
13
Auriga Constellation, H I Regions, H Ii Regions, Molecular Gases, Monatomic Gases, Photodissociation, B Stars, Far Infrared Radiation, Infrared Imagery
Scientific paper
The H II regions Sharpless 217 and 219 have been mapped in H I line and continuum emission at 21 cm wavelength with the wide-field DRAO synthesis telescope. Both regions have prominent H I zones on the peripheries of the ionization indicating direct photodissociation of the surrounding molecular gas by the exciting stars. Although the ionization of each region is principally due to a single exciting star, we identify a minor peak of emission in Sh 217 with a pair of closely spaced B stars. The H I emission from each region extends over about 8 km/s in radial velocity but shows no indication of a shocked component or of other systematic motions. FIR images from IRAS show that the heated dust component in each case is approximately coextensive with the photodissociation region, although there is no detailed correlation between the H I and infrared emissions. A distance-independent parameter, the observed ratio of the radio flux density to the infrared flux, is compared with the predicted ratio for the particular exciting stars to provide estimates in the two cases of the fractions of stellar emission which escape to the general interstellar medium. Parameters, measured and derived, for the two regions are compared to those from models of the development of H I dissociation zones with time. The comparison indicates that Sh 217 and Sh 219 are relatively young regions with ages not more than a few 10,000 yr.
Leahy Denis A.
Roger Robert S.
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