Other
Scientific paper
Nov 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.247..343h&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. 247, NO.2/NOV15, P. 343, 1990
Other
42
Scientific paper
Cosmic-ray heating and cosmic-ray-induced photodesorption have been suggested as mechanisms for keeping heavy elements in the gas phase in dense interstellar clouds and in the dense cores, in particular. Cosmic-ray heating is efficient at returning CO to the gas phase, but we point out that, because it does not drive CH4 desorption and because reactions of CO with He+ initiate hydrocarbon formation, cosmic-ray heating will not limit the decline of the CO abundance in the gas phase. Concerning photodesorption, we argue for the first time that photodesorption occurs only if the photon is absorbed in the outer couple of monolayers of the mantle and, consequently, that the yield of molecules per photon striking a grain is only about 0.1. Such a low yield implies that desorption by photons emitted in the decay of electronic states excited in collisions of H2 with energetic electrons produced by cosmic-ray ionization is important in dark regions only when the number density is 103 cm-2 or lower. We also note the inability of several other proposed desorption mechanisms to maintain high gas-phase abundances of heavy elements in dense gas. We suggest that no proposed desorption mechanism significantly limits the depletion of heavy molecules in long-lived, dense cores, which typically have number densities of 104-105 cm-3. The absence (which has been attributed to very high depletion, Menten et al.), of evidence of infall in the profiles of NH3 lines in clumps containing infrared sources supports this view. Consequently, dark quiescent dense cores which are normally detected in molecular emission, must evolve on time-scales shorter than those for heavy elements to accrete on to the grains in these regions.
Hartquist Thomas W.
Williams David. A.
No associations
LandOfFree
Cosmic-Ray Induced Desorption and High Depletions in Dense Cores does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Cosmic-Ray Induced Desorption and High Depletions in Dense Cores, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cosmic-Ray Induced Desorption and High Depletions in Dense Cores will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-841703