Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...284..233c&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 284, no. 1, p. 233-240
Astronomy and Astrophysics
Astronomy
26
Astronomical Catalogs, Color-Color Diagram, Far Infrared Radiation, H Ii Regions, Infrared Astronomy, Point Sources, Cross Correlation, Line Spectra, Star Formation, Stellar Luminosity
Scientific paper
The IRAS Point Source Catalogue (PSC) has been compared with a catalog of 462 (diffuse) H II regions detected in hydrogen radio recombination lines. To distinguish the true IRAS counterpart of the H II region from chance coincidences the distribution of offset and the position in color-color plots as a function of F(60 micrometers) are investigated. It is found that sources with F(60 micrometers) less than 100 Jy have a high probability of being chance coincidences. The far infrared properties of the H II regions are investigated for a subsample of 252 IRAS PSC sources which have a high (greater than 80%) probability of being true coincidences. The majority satisfy the Wood and Churchwell color criteria which identify ultracompact H II regions; therefore, these criteria select ultracompact as well as more diffuse H II regions, or, alternatively, diffuse H II and ultracompact H II regions may often be mixed, as predicted by the sequential star formation theory. The luminosity of a single star required to produce the observed H II line emission correlates very well with the far infrared luminosity and is, on the average, higher than the observed value. Consequently, the stars ionizing the extended H II regions can account for the bulk of the observed FIR emission and no contribution from lower mass stars of the cluster is necessary.
Codella Claudio
Felli Marcello
Natale Vincenzo
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