9-13 September 2019
University of Geneva A100 Sciences II
Europe/Zurich timezone

CNO abundances in the early Galaxy


Dr Susmitha Rani Antony (Tata Institute of Fundamental Research Mumbai)


Carbon-enhanced metal-poor (CEMP) stars contribute to about 20% of the metal-poor stars below [Fe/H] < -2.0. The origin of carbon in these stars could be due to AGB mass transfer in a binary system. These class of objects (CEMP-s) also show enhancement of s-process elements, and most of them show radial velocity variations indicating the presence of a companion. However, the class of CEMP stars that do not show s-process enhancements, that are more dominant at much lower metallicities ([Fe/H] < -3.5), are thought to be true first low mass stars that received contributions from winds of rotating very massive star (spinars) or faint supernovae. C, N, O abundances of these objects are crucial to understand the contributions of C, N, O from these massive stars. Carbon and nitrogen abundances can be derived from the $C_{2}$, CH, CN and NH bands. However, obtaining oxygen abundance is very time-consuming and difficult in CEMP stars due to the weak 6300 [OI] line and crowded C2 and CN lines in cool-CEMP stars that require high resolution, high S/N optical spectra. Hence, we use NIR CO rovibrational bands in the NIR region, to derive oxygen abundances. For a carbon-enhanced star, the CO lines are sensitive to change in oxygen abundances. We also derived C, N, O abundances from optical wavelengths to calibrate the C, N, O abundances from NIR CO lines for a subset of CEMP stars. Here, we report CNO measurements of 10 CEMP stars from high-resolution optical spectra and low-resolution NIR spectra and compare them. This is the first time such comparison of CNO abundance over optical and NIR wavelength done in CEMP stars. We also present a detailed abundance of alpha, Fe-peak, and n-capture elements as well to understand the origin of CNO.

Primary authors

Dr Susmitha Rani Antony (Tata Institute of Fundamental Research Mumbai) Prof. Sivarani Thirupathi (Indian Institute of Astrophysics Bengaluru) Prof. Devendra K Ojha (Tata Insitute of Fundamental Research Mumbai) Mr Avrajit Bandhyopadhyay (Indian Institute of Astrophysics Bengaluru) Dr Joe Philip Ninan (Pennsylvania State University) Dr Arun Surya (UCSD Center for Astrophysics and Space Sciences ) Ms Athira Unni (Indian Institute of Astrophysics)

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