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D. E. Welty (Chicago), S. R. Federman (Toledo), R. Gredel (CAHA), D. L. Lambert (Texas), J. A. Thorburn (Chicago)
We report some initial results on the abundances of interstellar CH, CH+, and CN in the Magellanic Clouds, derived from high S/N spectra of 5 SMC and 9 LMC stars obtained with the VLT/UVES. We detect CH and/or CH+ toward 2 SMC and 8 LMC stars, and detect CN toward one of the LMC stars. To our knowledge, these are the first reported detections of these molecular species in the ISM of the Magellanic Clouds, apart from those of CH and CH+ toward SN 1987A. The column densities now available for CH, H2, K I, and Na I indicate that all those species are typically less abundant in the Magellanic Clouds than in our Galaxy, presumably due to the lower metallicities and generally stronger ambient radiation fields there. The relationships among those four species, however, appear to be similar to those observed in the Galactic ISM, except that Na I/H2, K I/H2, and CH/H2 are generally lower in the SMC.
Toward most of our targets, the UVES spectra also reveal absorption at velocities corresponding to the Magellanic Clouds ISM from several of the typically strongest of the enigmatic diffuse interstellar bands (e.g., those at 5780, 5797, and 6284 A). In most cases, the Magellanic Clouds DIBs are weaker, for a given N(H), than those typically observed in our Galaxy (again presumably due to the lower metallicities and stronger radiation fields) --- but they are also weaker, relative to Na I, than in the Milky Way.
We comment briefly on the implications of these data for models of diffuse cloud chemistry in low-metallicity systems and for the properties of the (still unidentified) carriers of the DIBs.
This work has been supported by NASA LTSA grant NAG5-11413 to the University of Chicago.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.