An Inventory of Interstellar Ices toward the Embedded Protostar W33A
| Autor: | E. F. van Dishoeck, Erika L. Gibb, Jacqueline V. Keane, Jean Chiar, Adwin Boogert, O. Kerkhof, Perry A. Gerakines, Pascale Ehrenfreund, Douglas C. B. Whittet, Alexander G. G. M. Tielens, W. A. Schutte |
|---|---|
| Rok vydání: | 2000 |
| Předmět: | |
| Zdroj: | Astrophys. J. |
| ISSN: | 1538-4357 0004-637X |
| DOI: | 10.1086/308940 |
| Popis: | This paper presents, for the —rst time, a complete 2.4¨25 km spectrum of the dust-embedded young stellar object W33A. The spectrum was obtained with the Short Wavelength Spectrometer of the Infrared Space Observatory at a mean resolving power of D750. The spectrum displays deep ice and silicate H 2 O absorptions centered at 3.0 and 9.7 km, respectively, together with absorption features identi—ed with various other molecules in the solid phase. The 2.4¨5.0 km region of the spectrum is used to investigate the long-standing problem of the ice column density toward W33A, by means of the stretching and H 2 O combination mode features at 3.0 and 4.5 km. Although no —ux is seen at the center of the 3.0 km feature, its central depth may be constrained by —tting assumed pro—les to the short- and long- wavelength wings in our spectrum. We deduce that a value of cm~2 is con- N(H 2 O) \ (1.1 ^ 0.3) ) 1019 sistent with these features, a factor of at least 3 less than predicted by the bending mode at 6.0 km; H 2 O the reason for this discrepancy is unclear. We report new results on the abundances of nitrogen-bearing species in the ices toward W33A. Solid is detected for the —rst time in this line of sight, by means NH 3 of the inversion-mode feature at 9.0 km. The column density is cm~2, N(NH 3 ) \ (1.7 ^ 0.4) ) 1018 implying an abundance of D15% relative to comparable to that recently reported toward the H 2 O, young star NGC 7538 IRS 9. However, we —nd no convincing evidence for absorptions associated with the C"N stretching mode of nitriles in the 4.4¨4.6 km region of the spectrum. If nitriles are present in the ices along this line of sight, they must have column density no more than D1017 cm~2 or D1% relative to This argues against identi—cation of the deep 4.62 km iXCNfeature with isonitriles, as |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|