Other
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.341s&link_type=abstract
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole
Other
Scientific paper
High-resolution near-infrared observations of CO isotopologues towards nearby protostars enable us to derive precise abundance ratios of carbon and oxygen isotopologues in young stellar objects (YSOs) and surrounding molecular clouds within 1 kpc of the Sun. These isotopic analyses inform our understanding of the early stages of protoplanetary disk formation and facilitate comparisons between data derived from meteoritic analyses and those from protostellar systems evolving today. Using the CRIRES spectrograph (R=95,000) on the Very Large Telescope, we observed 4.7 μm fundamental and 2.3 μm overtone rovibrational CO absorption spectra towards protostellar disks, envelopes and foreground clouds. Abundance ratios of [12C16O]/[13C16O] range from ˜84-158, values that are significantly higher than those of the ambient parent clouds (˜65). We found a positive correlation between solid [12C16O] column densities and gas-phase [12C16O]/[13C16O], suggesting that ice-gas partitioning of the 12C16O and 13C16O isotopologues may be at least a partial explanation for the unusually high ratios observed towards these objects, may play a significant role in protostellar chemistry, and may have been an important process in determining the solar system carbon isotopic composition. Our findings also suggest that protostars may not be isotopically similar to the clouds in which they form, violating the assumptions in Galactic chemical evolution models for describing the [12C]/[13C] discrepancy between the solar system ([12C]/[13C] ˜87) and local ISM ([12C]/[13C] ˜62-68). We find high ratios in both warm and cold gas, indicating that the signatures of ice-gas partitioning are unlikely due to a simple closed system of ice-gas exchange; rather, they may be preserved through carbon chemistry or other processes. While isotope-specific photodissociation of CO is an unlikely explanation for the high [12CO]/[13CO] in our sample, it may account for the [12C16O] excesses relative to [12C18O] and [12C17O] in several objects observed in this study.
Morris Mark R.
Pontoppidan Klaus Martin
Smith Richard L.
Young Edward D.
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