Galactic H II Regions.IV. 1.95-CM Observations with High Angular Resolution and High Positional Accuracy

Abstract

view Abstract Citations (477) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galactic H II Regions.IV. 1.95-CM Observations with High Angular Resolution and High Positional Accuracy Schraml, J. ; Mezger, P. G. Abstract Compact 1111 regions of high electron density but small linear dimensions are believed to be the ionized remnants of recently formed 0 stars or clusters of 0 stars. In this survey, H ii regions of high surface brightness in the radio continuum are mapped at the wavelength of 1.95 cm with an angular resolution of about 2'. Compact 1111 regions are found to be superimposed on an extended background of lower surface brightness. After separation from the background, the physical parameters of the compact components are determined. Their electron temperatures, rms velocities of internal turbulence, and kinematic dis- tances are obtained from observations of the H109a line. Where possible, radio contours are compared with the optical picture of the H ii region as determined by its Ha radiation. Although there is a general agreement between radio and optical features, marked differences are found in a detailed comparison. It seems that for most of the investigated H ii regions the variation in optical surface brightness is to a large extent determined by obscuration by dust rather than by the emission measure. With a few exceptions, the exciting stars of compact H ii regions could not be found, a fact that implies these stars are hidden behind a dense cocoon of dust, which seems to be capable of prevailing in the ultraviolet radiation field of an 0 star for a relatively long period. The radio center of a compact component in M8 coincides with the "hourglass" nebula, which might be part of the ionized cocoon of the 07 star Herschel 36. Centers of non-thermal emission of the two central OH lines are found to be closely associated with nearby compact H ii regions. Velocity dispersions range between 1.2 and 16 km sec'; the projected distances range from 0.08 to 1.4 pc. Recent observations are consistent with the hypothesis that centers of non-thermal OH emission are protostars, i.e., dense condensations of neutral matter which are im- bedded in H it regions of low electron density Publication: The Astrophysical Journal Pub Date: April 1969 DOI: 10.1086/149964 Bibcode: 1969ApJ...156..269S full text sources ADS | data products SIMBAD (3) Related Materials (3) Part 1: 1967ApJ...147..471M Part 2: 1967ApJ...147..490M Part 3: 1967ApJ...150..807M