in the bow shock model for cometary ultracompact hii regions, a stellar wind from a fast moving star interacts with the surrounding molecular cloud. the wind shocks against the ism and pushes it out of the way. since the shock velocity is hundreds to thousands of kilometers per second, the immediate postshock temperatures are in excess of 10^7 k. this extremely hot gas is in direct thermal contact with the very much cooler and denser hii region bounding the wind cavity. a mixing zone or conductive interface exists between the two phases. in either case there is likely to be a substantial column density of material whose temperature is near the peak of the cooling curve, of order 5x10^5 k. at this temperature the important coronal lines of fevii at 7.81 and 9.51 microns arise and we propose attempting their detection with sws02. we expect line strengths as weak as about 1% of the continuum. this is a difficult measurement, but we have planned the experiment with the view of a 5-sigma detection of a line of this strength, paying careful attention to possible systematics in the spectral baseline which otherwise would limit us. if these lines are found, it will validate the bow shock model for cometary ultracompact hii regions. additionally it will point to these objects as potential laboratories for the study of thermal energy transport in extreme conditions where temperature scale lengths are small compared to the electron mean free path.
Instrument
SWS02
Temporal Coverage
1996-09-20T03:27:47Z/1996-09-20T05:24:53Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds 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.
European Space Agency, VAN BUREN et al., 1999, 'INFRARED CORONAL LINES IN ULTRACOMPACT HII REGIONS', 1.0, European Space Agency, https://doi.org/10.5270/esa-cy72f9p
