HCT/HESP study of two carbon stars from the LAMOST survey

Abstract

Carbon stars, enhanced in carbon and neutron-capture elements, provide a wealth of information about the nucleosynthesis history of the Galaxy. In this work, we present the first ever detailed abundance analysis of the carbon star LAMOSTJ091608.81+230734.6 and a detailed abundance analysis of neutron-capture elements for the object LAMOSTJ151003.74+305407.3. Updates on the abundances of elements C, O, Mg, Ca, Cr, Mn and Ni for LAMOSTJ151003.74+305407.3 are also presented. Our analysis is based on high-resolution spectra obtained using the Hanle Echelle Spectrograph (HESP) attached to the Himalayan Chandra Telescope (HCT) at the Indian Astronomical Observatory, Hanle. The stellar atmospheric parameters (Teff, log g, microturbulance ζ, metallicity [Fe/H]) are found to be (4820, 1.43, 1.62, −0.89) and (4500, 1.55, 1.24, −1.57) for these two objects, respectively. The abundance estimates of several elements, namely C, N, O, Na, α-elements, Fe-peak elements and neutron-capture elements Rb, Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm and Eu, are presented. Our analysis shows the star LAMOSTJ151003.74+305407.3 to be a CEMP-r/s star, and LAMOSTJ091608.81+230734.6 to be a CH giant. We have examined if the i-process model yields ([X/Fe]) of heavy elements could explain the observed abundances of the CEMP-r/s star based on a parametric model-based analysis. The negative values obtained for the neutron-density-dependent [Rb/Zr] ratio confirm former low-mass asymptotic giant branch companions for both stars. Kinematic analysis shows that LAMOSTJ151003.74+305407.3 belongs to the Galactic halo population while LAMOSTJ091608.81+230734.6 belongs to the disc population.