HETEROGENEITY IN {sup 12}CO/{sup 13}CO ABUNDANCE RATIOS TOWARD SOLAR-TYPE YOUNG STELLAR OBJECTS
- North Carolina Museum of Natural Sciences, 121 West Jones Street, Raleigh, NC 27603 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Department of Earth, Planetary, and Space Sciences, University of California Los Angeles, 595 Charles E. Young Drive East, Geology Building, Los Angeles, CA 90095-1567 (United States)
This study reports an unusual heterogeneity in [{sup 12}C{sup 16}O]/[{sup 13}C{sup 16}O] abundance ratios of carbon monoxide observed in the gas phase toward seven ∼solar-mass young stellar objects (YSOs) and three dense foreground clouds in the nearby star-forming regions, Ophiuchus, Corona Australis, Orion, and Vela, and an isolated core, L43. Robust isotope ratios were derived using infrared absorption spectroscopy of the 4.7 μm fundamental and 2.3 μm overtone rovibrational bands of CO at very high spectral resolution (λ/Δλ ≈ 95,000), observed with the Cryogenic Infrared Echelle Spectrograph (CRIRES) on the Very Large Telescope. We find [{sup 12}C{sup 16}O]/[{sup 13}C{sup 16}O] values ranging from ∼85 to 165, significantly higher than those of the local interstellar medium (ISM) (∼65–69). These observations are evidence for isotopic heterogeneity in carbon reservoirs in solar-type YSO environments, and encourage the need for refined galactic chemical evolution models to explain the {sup 12}C/{sup 13}C discrepancy between the solar system and local ISM. The oxygen isotope ratios are consistent with isotopologue-specific photodissociation by CO self-shielding toward the disks, VV CrA N and HL Tau, further substantiating models predicting CO self-shielding on disk surfaces. However, we find that CO self-shielding is an unlikely general explanation for the high [{sup 12}C{sup 16}O]/[{sup 13}C{sup 16}O] ratios observed in this study. Comparison of the solid CO against gas-phase [{sup 12}C{sup 16}O]/[{sup 13}C{sup 16}O] suggests that interactions between CO ice and gas reservoirs need to be further investigated as at least a partial explanation for the unusually high [{sup 12}C{sup 16}O]/[{sup 13}C{sup 16}O] observed.
- OSTI ID:
- 22521918
- Journal Information:
- Astrophysical Journal, Vol. 813, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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