Astronomy and Astrophysics, volume 441, 181 (2005/10-1)
Interstellar 12C/13C ratios through CH+λλ3957,4232 absorption in local clouds: incomplete mixing in the ISM.
CASASSUS S., STAHL O. and WILSON T.L.
Abstract (from CDS):
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 12CH+λλ3957.7,4232.3 and 13CH+λλ3958.2,4232.0 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 ζ Oph, 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 78.27±1.83, 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: R=74.7±2.3 in the ζ Oph cloud, while R=88.6±3.0 toward HD 152235 in the Lupus clouds, R=62.2±5.3 towards HD 110432 in the Coalsack, and R=98.9±10.1 toward HD 170740. The observed variations in 13C/12C are the first significant detection of chemical heterogeneity in the local ISM.ME ZET OPH CLOUD
ISM: abundances - ISM: clouds - ISM: molecules - ISM: individual objects: Coalsack - ISM: individual objects: Lupus cloud - ISM: individual objects: ζ Oph cloud
VizieR on-line data:
<*** spectra not received at CDS *** >
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