Abstract
Aims. We study in this paper the ice composition in the envelope around intermediate-mass class I Young Stellar Objects (YSOs).
Methods. We performed a spectroscopic survey toward five intermediate-mass class I YSOs located in the Southern Vela molecular cloud in the L (2.85-4.0 m) and M (4.55-4.8 m) bands at resolving powers -800 up to 10 000, using the Infrared Spectrometer and Array Camera mounted on the Very Large Telescope-ANTU. Lower mass companion objects were observed simultaneously in both bands.
Results. Solid H 2O at 3 m is detected in all sources, including the companion objects. CO ice at 4.67 m is detected in a few main targets and one companion object. One object ( LLN 19 ) shows little CO ice but strong gas-phase CO ro-vibrational lines in absorption. The CO ice profiles are different from source to source. The amount of water ice and CO ice trapped in a water-rich mantle may correlate with the flux ratio at 12 and 25 m. The abundance of H2O-rich CO likely correlates with that of water ice. A weak feature at 3.54 m attributed to solid CH 3OH and a broad feature near 4.62 m are observed toward , but not toward the other sources. The derived abundances of solid CH 3OH and OCN- are ~% and ~% of the H 2O ice abundance respectively. The H 2O optical depths do not show an increase with envelope mass, nor do they show lower values for the companion objects compared with the main protostar. The line-of-sight CO ice abundance does not correlate with the source bolometric luminosity.
Conclusions. Comparison of the solid CO profile toward LLN 17 , which shows an extremely broad CO ice feature, and that of its lower mass companion at a few thousand AU, which exhibits a narrow profile, together with the detection of OCN- toward LLN 17 provide direct evidences for local thermal processing of the ice.
Methods. We performed a spectroscopic survey toward five intermediate-mass class I YSOs located in the Southern Vela molecular cloud in the L (2.85-4.0 m) and M (4.55-4.8 m) bands at resolving powers -800 up to 10 000, using the Infrared Spectrometer and Array Camera mounted on the Very Large Telescope-ANTU. Lower mass companion objects were observed simultaneously in both bands.
Results. Solid H 2O at 3 m is detected in all sources, including the companion objects. CO ice at 4.67 m is detected in a few main targets and one companion object. One object ( LLN 19 ) shows little CO ice but strong gas-phase CO ro-vibrational lines in absorption. The CO ice profiles are different from source to source. The amount of water ice and CO ice trapped in a water-rich mantle may correlate with the flux ratio at 12 and 25 m. The abundance of H2O-rich CO likely correlates with that of water ice. A weak feature at 3.54 m attributed to solid CH 3OH and a broad feature near 4.62 m are observed toward , but not toward the other sources. The derived abundances of solid CH 3OH and OCN- are ~% and ~% of the H 2O ice abundance respectively. The H 2O optical depths do not show an increase with envelope mass, nor do they show lower values for the companion objects compared with the main protostar. The line-of-sight CO ice abundance does not correlate with the source bolometric luminosity.
Conclusions. Comparison of the solid CO profile toward LLN 17 , which shows an extremely broad CO ice feature, and that of its lower mass companion at a few thousand AU, which exhibits a narrow profile, together with the detection of OCN- toward LLN 17 provide direct evidences for local thermal processing of the ice.
| Original language | English |
|---|---|
| Pages (from-to) | 251-265 |
| Number of pages | 14 |
| Journal | Astronomy and Astrophysics |
| Volume | 449 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - Apr 2006 |
Keywords
- astrophysics
- interstellar ice
- stars
- young stellar objects