The gas/solid methane abundance ratio toward deeply embedded protostars
| Autor: | Boogert, ACA, Helmich, EP, van Dishoeck, EF, Schutte, WA |
|---|---|
| Přispěvatelé: | Kapteyn Astronomical Institute |
| Jazyk: | angličtina |
| Rok vydání: | 1998 |
| Předmět: |
ICE ANALOGS
CH4 Physics::Instrumentation and Detectors abundances LINE stars : individual : NGC 7538 : IRS9 W 33A REGION infrared : ISM : lines and bands GAS CHEMISTRY ISM : dust extinction YOUNG STARS PHASE CO MOLECULAR CLOUDS ABSORPTION molecules Astrophysics::Earth and Planetary Astrophysics Physics::Chemical Physics Astrophysics::Galaxy Astrophysics |
| Zdroj: | Astronomy & astrophysics, 336(1), 352-358. EDP Sciences |
| ISSN: | 0004-6361 |
| Popis: | We present the detection of re-vibrational absorption lines of the deformation mode of gaseous CH4 toward the massive protostars W 33A, and NGC 7538 : IRS9, using the SWS spectrometer an board of the Infrared Space Observatory. The observed lines indicate that the CH4 gas is warm (T similar to N 90 K), and has a low abundance (similar to 4 10(-7)). The CH4 ice in these Lines of sight is embedded in a polar matrix (Boogert et al. 1996), and the gas/solid state abundance ratio is low (similar to 0.5). We discuss models for the formation of interstellar CH4. The observations impose strong limitations on time dependent gas phase models, e.g. a low initial CO/C ratio would be required, the CH4 must have been formed and subsequently condensed on the grains within a narrow time window, and an additional mechanism would be necessary to form polar ice mantles. More likely, interstellar CH4 is formed through grain surface reactions at a high CO/C ratio, which explains the low observed CH4 abundance (similar to 10(-6)) the presence of CH4 in a polar ice, the low gas/solid ratio, and the absence of a strong cold CH4 gas component. The observed warm CH4 gas probably has sublimated from the grains in the 'hot core' region surrounding the protostar. |
| Databáze: | OpenAIRE |
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