Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...518..733d&link_type=abstract
The Astrophysical Journal, Volume 518, Issue 2, pp. 733-739.
Astronomy and Astrophysics
Astronomy
25
Ism: Abundances, Ism: Clouds, Ism: Molecules
Scientific paper
We present measurements of the H_2CO ortho-para ratio toward four star-forming cores, L723, L1228, L1527, and L43, and one quiescent core, L1498. Combining these data with earlier results by Minh et al., three quiescent cores are found to have ortho-para ratios near 3, the ratio of statistical weights expected for gas-phase formation processes. In contrast, ortho-para ratios are 1.5-2.1 in five star-forming cores, suggesting thermalization at a kinetic temperature of 10 K. We attribute modification of the ortho-para ratio in the latter cores to formation and-or equilibration of H_2CO on grains with subsequent release back into the gas phase due to the increased energy inputs from the forming star and outflow. We see accompanying enhancements in the H_2CO abundance relative to H_2 to support this idea. The results suggest that the formaldehyde ortho-para ratio can differentiate between quiescent cores and those in which low-mass star formation has occurred.
Dickens James E. Jr.
Irvine William M.
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