The chemical composition of the high velocity POST AGB star HD 56126(F5I)

Abstract

From an analysis of high-resolution spectra of the IRAS source HD 56126 (F5I), it is found that its photospheric abundances of C, O, S are nearly solar and N is overabundant by about -0.2 dex. The abundance of Fe and related elements suggest that HD 56126 is metal-poor (Fe/H is not greater than -1.0). The atmospheric parameters of HD 56126 are found to be T(eff) = 6500 K, log g = 0.5, Fe/H = 1.0, and zeta = 4 km/s. The radial velocity measurements yield Vr = +105 km/s and VLSR = +52.3 km/s, and show that HD 56126 is a high-velocity star belonging to the old disk population. The large abundance ratios of CNO and S elements with respect to Fe are due to depletions of Fe and related elements but not of CNO and S elements. It is suggested that in the recent past, during the AGB stage of the evolution of these star, they extended cool denser outer envelopes in which the temperature reached to the limit of condensation temperature of refractory elements, resulting in the formation of dust grains close to the star