Near-Infrared Spectra of 29 Carbon Stars: Simple Estimates of Effective Temperature

• Published in: Publications of the Astronomical Society of Japan Vol. 59; no. 5; pp. 939 - 953
• Main Authors: Tanaka, Masuo, Letip, Ahmatjan, Nishimaki, Yuichirou, Yamamuro, Tomoyasu, Motohara, Kentaro, Miyata, Takashi, Aoki, Wako
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford Universtiy Press 25.10.2007
• Subjects: stars: carbon; infrared: stars; techniques: spectroscopic
• ISSN: 0004-6264; 2053-051X
• DOI: 10.1093/pasj/59.5.939

Near-infrared spectra of 29 carbon stars in the 0.9–2.4 $\mu$ m 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 ( $T_{\mathrm{eff}}$ ) of the carbon stars were estimated with errors of $\pm\;$ 200 K by fitting our spectra at wavelengths of 1.35, 1.74, and 2.29 $\mu$ m, with simple model spectra, while considering the H $^{-}$ opacity minimum to be around 1.6 $\mu$ m. At these wavelengths, molecular absorption due to CO, CN, and C $_{2}$ is not strong. The derived effective temperatures are distributed between 5100 K 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 $\sim$ 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.