we propose to study far-infrared line and continuum emission from hii regions with unusually narrow radio recombination lines. compared with most star forming regions, these objects require both very low electron temperature (t_e<virgul4600 k) and small nonthermal line broadening in the ionized gas. the low temperatures could be the result of high abundances, low electron density, and/or low effective stellar temperature. the origin of the lack of nonthermal broadening is more speculative, but may be produced by low density and the absence of density gradients and stellar winds. by probing both the ionized gas and the adjacent photodissociated material, the proposed fir line measurements ([siii] (33 microns), [siv] (10.5 microns), and [siii] (35 microns)) together with measurements already obtained during calibration of the lws ([oiii] (52 and 88 microns), [niii] 57 microns), [oi] (63 and 146 microns), [nii] (122 microns), and [cii] (158 microns), and the 43-173 micron continuum) on the same objects will determine the physical conditions which are responsible for the low temperature and the lack of nonthermal line broadening.
Instrument
LWS01 , LWS02 , SWS02 , SWS07
Temporal Coverage
1997-03-23T09:16:12Z/1997-04-05T21:00:56Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the world's first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
