Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010mwac.meet..p16w&link_type=abstract
"Midwest Astrochemistry Meeting 2010, held 5-6 November at the University of Illinois at Urbana-Champaign. http://midwest.astroc
Astronomy and Astrophysics
Astronomy
Scientific paper
In general, sight lines in the Magellanic Clouds probe environmental conditions somewhat different from those in the ISM of our Galaxy - lower metallicities, lower dust-to-gas ratios, stronger UV radiation fields, and differences in UV extinction (especially in the SMC). Those differences are predicted to significantly affect the structure and composition of diffuse molecular clouds there. The sight line toward the O9.5 Ib star Sk 143, located in the near "wing" region of the SMC, is somewhat unusual (for the SMC), however - exhibiting a high fraction of hydrogen in molecular form; a Milky Way-like UV extinction curve (with 2175 Å bump) and dust-to-gas ratio; and relative abundances of CH, CN, and the (unidentified) carriers of certain of the diffuse interstellar bands more similar to those seen in the local Galactic ISM. In this poster, we report the detection of absorption from interstellar C2 and C3 toward Sk 143, in optical spectra obtained with the ESO VLT/UVES (FWHM ~ 4 km s-1; S/N ~ 130-270). These detections of C2 (rotational levels J=0-8) and C3 (J=0-12) absorption in the SMC are the first beyond our Galaxy. The total abundances of C2 and C3 (relative to H2) are similar to those found in diffuse Galactic molecular clouds - despite the lower metallicity of the SMC. Analysis of the rotational excitation of C2 yields an estimated kinetic temperature Tk ~ 25 K and a (moderately high) total hydrogen density nH ~ 800 cm-3 compared to the T01 ~ 45 K and nH ~ 85 cm-3 obtained from H2. The populations of the lower rotational levels of C3 are consistent with an excitation temperature of about 35 K.
Black John Harry
Howk C. Lehner N. J.
McCall Benhamin J.
Welty Daniel E.
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