High-resolution spectroscopy of the high-velocity hot post-AGB star IRAS 18379–1707 (LS 5112)

Abstract

The high-resolution ( R ∼ 48 000) optical spectrum of the B-type supergiant LS 5112, identified as the optical counterpart of the post-AGB candidate IRAS 18379–1707 is analysed. We report the detailed identifications of the observed absorption and emission features in the wavelength range 3700–9200 Å for the first time. The absorption line spectrum has been analysed using non-LTE model atmosphere techniques to determine stellar atmospheric parameters and chemical composition. We estimate T eff = 18 000 ± 1000 K, log g = 2.25 ± 0.08, ξ t = 10 ± 4kms − 1 , and v sin i = 37 ± 6kms − 1 , and the derived abundances indicate a metal-deficient ([M/H] ≈− 0.6) post-AGB star. Chemical abundances of eight different elements were obtained. The estimates of the CNO abundances in IRAS 18379– 1707 indicate that these elements are overabundant with [(C + N + O)/S] =+ 0.5 ± 0.2 suggesting that the products of helium burning have been brought to the surface as a result of third dredge-up on the AGB. From the absorption lines, we derived heliocentric radial velocity of V r =− 124.0 ± 0.4 km s − 1 . We have identified permitted emission lines of O I ,N I ,Na I , S II ,Si II ,C II ,Mg II , and Fe III . The nebula forbidden lines of [N I ], [O I ], [Fe II ], [N II ], [S II ], [Ni II ], and [Cr II ] have also been identified. The Balmer lines H α ,H β , and H γ show P-Cygni behaviour clearly indicating post-AGB mass-loss process in the object with the wind velocity up to 170 km s − 1 .