Near-infrared spectra of 29 carbon stars: Simple estimates of effective temperature

Abstract

Near-infrared spectra of 29 carbon stars in the 0.9-2.4 μm range were obtained by using a cross-dispersed echelle spectrograph. The target stars, which were classified into C-H, C-R, C-J, and C-N types, were selected from an atlas of Barnbaum, Stone, and Keenan (1996, ApJS, 105,419). Because the stars are non long-period variables, the phase differences of the light curves do not strongly affect the spectra. The effective temperatures (Teff) of the carbon stars were estimated with errors of ±200 K by fitting our spectra at wavelengths of 1.35,1.74, and 2.29 μm, with simple model spectra, while considering the H- opacity minimum to be around 1.6 μm. At these wavelengths, molecular absorption due to CO, CN, and C2 is not strong. The derived effective temperatures are distributed between 5100K and 2600 K, and highly correlate with the temperature sequence in Barnbaum, Stone, and Keenan (ibid.), although the stars with temperature sequences beyond 4 have similar temperatures near ∼ 3000 K. We also compared our results with values derived by other methods in the literature: the aperture diameter method, the infrared flux method, and some model calculations. © 2007. Astronomical Society of Japan.