Elemental abundances of the supergiant stars σ Cygnus and η Leonis

Abstract

This study aims to analyse the elemental abundances for the late B type supergiant star $\sigma$ Cyg and the early A-type supergiant $\eta$ Leo using ATLAS9 (Kurucz, 1995; Sbordone et al., 2004), assuming local thermodynamic equilibrium (LTE). The spectra used in this study are obtained from Dominion Astrophysical Observatory and have high resolution and signal-to-noise ratios. The effective temperature and the surface gravity of $\sigma$ Cyg are determined from the ionisation equilibria of Al I/II, Mg I/II, Fe I/II, Fe II/III , and by fitting to the wings of H${}_{\gamma }$ and H${}_{\beta }$ profiles as $\text{T}$${}_{eff}$ = 10388 K and log $\text{g}$ = 1.80. The elemental abundances of $\eta$ Leo} are determined using $\text{T}$${}_{eff}$ = 9600 K and log $\text{g}$ = 2.00, as reported by Przybilla et al. (2006). The ionisation equilibria of C I/II, N I/II, Mg I/II, Ca I/II, Cr I/II and Fe I/II/III are also satisfied in the atmosphere of $\eta$ Leo. The radial velocities of $\sigma$ Cyg and $\eta$ Leo are -7.25$\pm$7.57 km s${}^{-1}$ and 10.40 $\pm$ 13.37 km s${}^{-1}$, respectively. The derived projected rotational velocities \textit{vsini} from synthetic spectra are 27 and 2 km s${}^{-1}$ for both stars, respectively. The macroturbulent velocities ($\zeta$) are 24 $\pm$ 2 km s${}^{-1}$ and 14.5 $\pm$ 1.5 km s${}^{-1}$. Also, the microturbulent velocities ($\xi$) have been determined for both of stars as 3.5 km s${}^{-1}$. The CNO abundance results of $\sigma$ Cyg and $\eta$ Leo show C deficiency, N overabundance and O in excess.

8 tables, 6 figures, and 45 pages, Published in New Astronomy

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