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

The high-resolution (⁠|$R\sim 48\, 000$|⁠) 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, ξt = 10 ± 4 km s−1, and v sin  i  = 37 ± 6 km s−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. [ABSTRACT FROM AUTHOR]