Volume 441, Number 1, October I 2005
|Page(s)||181 - 194|
|Section||Interstellar and circumstellar matter|
|Published online||13 September 2005|
Interstellar C/C ratios through CH3957,4232 absorption in local clouds: incomplete mixing in the ISM
Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile e-mail: firstname.lastname@example.org
2 Landessternwarte Königstuhl, 69117 Heidelberg, Germany e-mail: O.Stahl@lsw.uni-heidelberg.de
3 ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany e-mail: email@example.com
4 Max-Planck-Institut für Radioastronomie, Postfach 2024, 53010 Bonn, Germany
Accepted: 2 June 2005
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 90 in the solar system. Previous measurements of 12CH3957.7,4232.3 and 13CH3958.2,4232.0 absorption toward nearby stars indicate some variations in 12C/13C, with values ranging from 40 to 90 suggesting inefficient mixing. Except for the cloud toward ζOph, these R values are strongly affected by noise. With UVES on the VLT we have improved on the previous interstellar 12C/13C measurements. The weighted 12C/13C ratio in the local ISM is , while the weighted dispersion of our measurements is 12.7, giving a 6.9σ scatter. Thus we report on a 6.9σ detection of 16.2% root-mean-square variations in the carbon isotopic ratio on scales of ~100 pc: in the ζOph cloud, while toward HD 152235 in the Lupus clouds, towards HD 110432 in the Coalsack, and toward HD 170740. The observed variations in 13C/12C are the first significant detection of chemical heterogeneity in the local ISM.
Key words: ISM: abundances / ISM: clouds / ISM: molecules / ISM: individual objects: Coalsack / ISM: individual objects: Lupus cloud / ISM: individual objects: ζOph cloud
© ESO, 2005
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