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 \(\log \mathrm{g}\) estimates are obtained using parallax estimates from the Gaia DR3 database whenever possible. Microturbulent velocity (\(\zeta \)) was derived using calibration equation of \(\log \mathrm{g}\) & \({\zeta }\). 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.