On the Origin of a Sample of Suspected CH Stars in the Large Magellanic Cloud

We present (R— I)KC photometry based on optical spectrophotometry, and JHK photometry for the carbon stars suspected of being CH stars discovered by Hartwick and Cowley (1988) in the field of the LMC. These carbon stars are shown to be more luminous than the red giant branch tip of the Galactic Population II giants and CH stars, and therefore are not members of the old stellar population in the LMC. The mean bolometric magnitude for this sample is Mbol=— 5.3 while the brightest members reach Mbol= — 6.2. These carbon stars are significantly bluer and somewhat brighter in the mean than the LMC carbon stars discovered by Blanco et al. (1980). We argue that the luminosity and color distributions presented in this paper, as well as the kinematical properties presented by Cowley and Hartwick (1991), are consistent with the association of this sample of carbon stars with a younger population of AGB stars compared to the Blanco et al. (1980) carbon stars, possibly with ages near 10ɸ years. The enhancement of resonance lines of s-processed elements as reported by Hartwick and Cowley (1988) are reminiscent of the possible enhancements of these elements in Galactic N stars, and are consistent with the prediction of the "third dredge-up" phase in the evolution of intermediate-mass AGB giants.