Very Large Telescope Spectra of Carbon Stars in the Large Magellanic Cloud and Their Metallicity Dependence

Details Very Large Telescope Spectra of Carbon Stars in the Large Magellanic Cloud and Their Metallicity Dependence Very Large Telescope Spectra of Carbon Stars in the Large Magellanic Cloud and Their Metallicity Dependence

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apj...580l.133m&link_type=abstract

The Astrophysical Journal, Volume 580, Issue 2, pp. L133-L136.

Astronomy and Astrophysics

Astronomy

30

Infrared: Stars, Galaxies: Magellanic Clouds, Stars: Abundances, Stars: Agb And Post-Agb, Stars: Atmospheres, Stars: Carbon

Scientific paper

Very Large Telescope (VLT) L-band spectra of six carbon stars in the Large Magellanic Cloud are presented. The stars show absorption bands at 3.1 μm (HCN and C2H2), and 3.8 μm, which is probably due to C2H2. Two LMC stars show strong 3.5 μm HCN absorption. The equivalent widths of the 3.1 μm and 3.8 μm bands are systematically larger in LMC carbon stars than in carbon stars in the solar neighborhood. Moreover, the ratio of the equivalent widths of the 3.8 and 3.1 μm bands is much larger in the LMC, suggesting a higher ratio of n(C2H2)/n(HCN). The stronger absorption bands are in contrast to the assumption that if the elemental abundances are scaled from the carbon star's abundances in the solar neighbor, the abundances of these molecules are less at lower metallicity. We argue for a systematically larger C/O ratio in LMC carbon stars. In the Galactic carbon stars n(C)/n(O)~1.05-1.1 on average; our chemical model shows that the stronger molecular bands in the LMC carbon stars could be explained with n(C)/n(O)>1.2. The higher C/O ratio can also explain the higher ratio of n(C2H2)/n(HCN) in LMC stars than in the solar neighborhood. Based on observations obtained at the European Southern Observatory, Chile (proposal 68.D-0660).

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