Interstellar 12C/13C ratios through CH+ ll 3957,4232 absorption in local clouds: incomplete mixing in the ISM

Abstract

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+ ll3957.7,4232.3 and 13CH+ ll3958.2,4232.0 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 zeta 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 6.9 sigma scatter. Thus we report on a 6.9 sigma 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 zetaOph cloud, while R = 88.6 +- 3.0 toward HD152235 in the Lupus clouds, R = 62.2 +- 5.3 towards HD110432 in the Coalsack, and R = 98.9 +- 10.1 toward HD170740. The observed variations in 13C/12C are the first significant detection of chemical heterogeneity in the local ISM.

18 pages, 12 figures, accepted for publication in A&A

References in corpus (8)

• Interstellar Turbulence II: Implications and Effects
• Abundances of Deuterium, Oxygen, and Nitrogen in the Local Interstellar Medium: Overview of First Results from the Far Ultraviolet Spectroscopic Explorer Mission
• Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. I. Observations toward delta Orionis by the Interstellar Medium Absorption Profile Spectrograph
• Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. II. Observations toward Gamma2 Velorum and Zeta Puppis by the Interstellar Medium Absorption Profile Spectrograph
• Further Evidence for Chemical Fractionation from Ultraviolet Observations of Carbon Monoxide
• Detection of the ^3P_2 - ^3P_1 Submillimeter Transition of 13CI in the Interstellar Medium: Implication for Chemical Fractionation
• The Chemical Evolution of the Milky Way
• The Galactic Disk Distribution of Planetary Nebulae with Warm Dust Emission Features: II

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