Observations Of Unusual Carbon Isotope Fractionation In Protostars Using VLT/CRIRES

Details Observations Of Unusual Carbon Isotope Fractionation In Protostars Using VLT/CRIRES Observations Of Unusual Carbon Isotope Fractionation In Protostars Using VLT/CRIRES

Jan 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21536906s&link_type=abstract

American Astronomical Society, AAS Meeting #215, #369.06; Bulletin of the American Astronomical Society, Vol. 42, p.560

Astronomy and Astrophysics

Astronomy

Scientific paper

We present high-resolution K- and M-band spectra of CO isotopologues toward several young stellar objects and one background source in the ρ Ophiuchus star-forming cloud, obtained using the CRIRES spectrograph (R 95,000) at the VLT. The rovibrational absorption data yield highly precise quantitative measurements of isotope ratios for both carbon and oxygen in objects with primordial disk geometry as well as in those surrounded by a molecular envelope. Our calculations indicate large 12CO/13CO ratios for all sources as compared to their parent clouds and/or the local interstellar medium, suggesting that there may be significant fractionation and/or chemical inheritance in YSOs from their parent clouds.
Derived 12C/13C ratios for the YSOs are significantly higher than the assumed ambient value ( 65): 150 ± 7 for the partially embedded object, IRS 63; 112 ± 7 for the embedded object, IRS 43; and 158 ± 9 for IRS 51, a disk reddened by the ρ Oph ridge, results for which likely trace chemistry in the foreground cloud. These unusually high carbon isotope ratios are consistent with several ρ Oph cores reported in the literature, including previously derived high ratios for the embedded YSO RE 50 in Orion (12C/13C = 110 ± 7) and the VV CrA disk in Corona Australis (12C/13C = 100 ± 10). Our YSO data also show cold ( 20 K) and warm (150 - 250 K) regimes, with temperatures showing a systematic trend with optical depth. Initial modeling results from the 2D ray-tracing code, RADLite, argue that the derived ratios are not likely due to systematic radiative transfer effects, but reflect real local fractionation due to chemical and/or photochemical phenomena. Additional high-resolution observations of local YSOs in various evolutionary stages will help further our understanding of solar system chemical evolution and possible chemical inheritance from cloud to disk.

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