Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.307p&link_type=abstract
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole
Astronomy and Astrophysics
Astronomy
Scientific paper
The total H2 column density is a fundamental quantity used to determine a variety of properties such as chemical abundances, the importance self-shielding from radiation fields, cloud mass, etc. Since H2 is a homonuclear molecule without a dipole moment, CO is often used as a proxy for the H2 abundance. However, since CO is often optically thick, especially towards the highest column density regions in molecular clouds, the total H2 column density is often poorly constrained. The large number of high-J lines of C18O, available to us via the Herschel Space Observatory, provide an unprecedented ability to model the total molecular column density. Using the emission from all the observed lines (up to J = 17 - 16) we can simply sum up the column densities in the individual levels to obtain the total column. With additional knowledge of source size we can even include the source filling factor, and so can get the true total column. We will present results of Herschel/HIFI observations of C18O and C17O in Orion KL (from the HEXOS Key Project). LTE modeling of the known sizes, VLSR, and line widths allow us to determine the total column densities in the extended ridge, outflow, hot core, and compact ridge components.
Bergin Edwin A.
Herschel Hexos Team
Lis Darek C.
Phillips Thomas G.
Plume Rene
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