Classification and characterization using HCT/HFOSC spectra of carbon stars selected from the HES survey

Abstract

We present results from the analysis of 88 carbon stars selected from Hamburg/ESO (HES) survey using low-resolution spectra (R ∼1330 & 2190). The spectra were obtained with the Himalayan Faint Object Spectrograph Camera (HFOSC) attached to the 2-m Himalayan Chandra Telescope (HCT). Using well-defined spectral criteria based on the strength of carbon molecular bands, the stars are classified into different groups. In our sample, we have identified 53 CH stars, four C-R stars, and two C-N type stars. Twenty-nine stars could not be classified due to the absence of prominent C2 molecular bands in their spectra. We could derive the atmospheric parameters for 36 stars. The surface temperature was determined using photometric calibrations and synthesis of the H-alpha line profile. The surface gravity log g estimates are obtained using parallax estimates from the Gaia DR3 database whenever possible. Microturbulent velocity (ζ ) was derived using calibration equation of log g & ζ . We could determine metallicity for 48 objects from near-infrared Ca II triplet features using calibration equations. The derived metallicity ranges from −0.43 ≤ [Fe/H] ≤ −3.49. Nineteen objects were found to be metal-poor ([Fe/H] ≤ −1), 14 very metal-poor ([Fe/H] ≤ −2), and five extremely metal-poor ([Fe/H] ≤ −3.0) stars. Eleven objects were found to have a metallicity in the range −0.43 ≤ [Fe/H] ≤ −0.97. We could derive the carbon abundance for 25 objects using the spectrum synthesis calculation of the C2 band around 5165 Å. The most metal-poor objects found will make important targets for follow-up detailed chemical composition studies based on high-resolution spectroscopy, and are likely to provide insight into the Galactic chemical evolution.