The molecular ion H_3(+) , which has long been considered the cornerstone of gas-phase chemistry in the interstellar medium, has now been detected in both dense and diffuse clouds. The nu_2 vibrational band of H_3(+) near 3.67 mu m has been detected using the facility spectrometer CGS4 at the United Kingdom Infrared Telescope and the Phoenix high-resolution spectrometer at Kitt Peak National Observatory. H_3(+) column densities of a few x 10(14) cm(-2) have been observed along the lines of sight to several embedded young stellar objects such as AFGL 2136. Simple chemical models of H_3(+) chemistry predict number densities of about 10(-4) cm(-3) , independent of total number density. Using this calculation, the observations yield estimates of effective path length and total number densities toward these sources. An unexpectedly large column density of H_3(+) (3.8 x 10(14) cm(-2) ) has also been detected towards the visible star Cygnus OB2 No. 12. Current models of diffuse cloud chemistry predict H_3(+) number densities two to three orders of magnitude lower than in diffuse clouds, implying much longer path lengths. Recent observations of other diffuse cloud sources will also be discussed. H_3(+) has also been detected with column density greater than 10(15) cm(-2) towards the two galactic center sources IRS 3 and GCS 3-2. These observations are interpreted as arising from a combination of both dense and diffuse material.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1998