AAS 205th Meeting, 9-13 January 2005
Session 74 ISM II
Oral, Tuesday, January 11, 2005, 10:00-11:30am, California

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[74.01] Interstellar 12C/13C ratios from CH+ VLT data

T. L. Wilson (ESO & MPIfR, Bonn), S. Casassus (Dept. de Astronomia, Univ. de Chile), O. Stahl (Landessternwarte Koenigsuhl, Heidelberg)

The 12C/13C isotope ratio is a tracer of stellar yields and the efficiency of mixing in the ISM. 12CH+/13CH+ is not affected by interstellar chemistry, and is the most secure way of measuring 12C/13C in the diffuse ISM. R=12C/13C is 89 in the solar system. Previous measurements of 12CH+ lines (at 3957.7 and 4232.3 Angstroms) and 13CH+ lines (at 3958.2 and 4232.0 Angstroms) in absorption toward nearby stars indicate some variations in 12C/13C, with values ranging from 40 to 90. These results suggested inefficient mixing, but were strongly affected by noise. With UVES on the VLT we have greatly improved on previous interstellar 12C/13C measurements. We report on a 5 sigma detection of 10% variations in the carbon isotopic ratio on scales of ~100 pc: R= 77.0 ±2.0 in the \zetaOph cloud, while R = 95.3 ±2.8 toward HD152235 in the Lupus cloud and R =125 ±11 toward HD170740. The weighted 12C/13C ratio in the local ISM is R = 83.1 ±1.5, while the weighted dispersion of our measurements is 5.4, giving a 3.6 sigma scatter. The observed variations in 13C/12C are the first significant detection of incomplete mixing in the local ISM.

S.C. acknowledges support from Fondecyt grant 1030805 and from the Chilean Center for Astrophysics FONDAP 15010003. Based on observations obtained with UVES at the ESO Very Large Telescope, Paranal, Chile (proposal No. 71.C-0367(A))

The author(s) of this abstract have provided an email address for comments about the abstract: twilson@eso.org

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