Astronomy and Astrophysics, volume 449, 251-265 (2006/4-1)
VLT-ISAAC 3-5 µm spectroscopy of embedded young low-mass stars. III. Intermediate-mass sources in Vela.
THI W.-F., VAN DISHOECK E.F., DARTOIS E., PONTOPPIDAN K.M., SCHUTTE W.A., EHRENFREUND P., D'HENDECOURT L. and FRASER H.J.
Abstract (from CDS):
We study in this paper the ice composition in the envelope around intermediate-mass class I Young Stellar Objects (YSOs). We performed a spectroscopic survey toward five intermediate-mass class I YSOs located in the Southern Vela molecular cloud in the L (2.85-4.0µm) and M (4.55-4.8µm) bands at resolving powers λ/Δλ=600-800 up to 10000, using the Infrared Spectrometer and Array Camera mounted on the Very Large Telescope-ANTU. Lower mass companion objects were observed simultaneously in both bands. Solid H2
O at 3µm is detected in all sources, including the companion objects. CO ice at 4.67µm 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 25µm. The abundance of H2
O-rich CO likely correlates with that of water ice. A weak feature at 3.54µm attributed to solid CH3O
H and a broad feature near 4.62µm are observed toward LLN 17
, but not toward the other sources. The derived abundances of solid CH3
OH and OCN–
are ∼10±2% and ∼1±0.2% of the H2
O ice abundance respectively. The H2
O 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. 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.
stars: circumstellar matter - astrochemistry - ISM: molecules
Table 2: [TVD2006] NNb (Nos 8b, 13b, 17b, 41b) = [TVD2006] IRAS HHMMm+DDMMb N=4.
Fig.8 Cham Irn not identified.
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