The first high-resolution ( R \sim 50,000 ) optical spectrum of the B - type star , LS III +52 ^ { \circ } 24 , identified as the optical counterpart of the hot post - AGB candidate IRAS 22023+5249 ( I22023 ) is presented .
We report the detailed identifications of the observed absorption and emission features in the full wavelength range ( 4290 - 9015 Å ) as well as the atmospheric parameters and photospheric abundances ( under the Local Thermodinamic Equilibrium approximation ) for the first time .
The nebular parameters ( T _ { e } , N _ { e } ) are also derived .
We estimate T _ { eff } =24,000 K , log g=3.0 , \xi _ { t } =7 kms ^ { -1 } and the derived abundances indicate a slightly metal-deficient evolved star with C/O < 1 .
The observed P - Cygni profiles of hydrogen and helium clearly indicate on-going post - AGB mass loss .
The presence of [ N II ] and [ S II ] lines and the non - detection of [ O III ] indicate that photoionisation has just started .
The observed spectral features , large heliocentric radial velocity , atmospheric parameters , and chemical composition indicate that I22023 is an evolved post - AGB star belonging to the old disk population .
The derived nebular parameters ( T _ { e } =7000 K , N _ { e } =1.2 \times 10 ^ { 4 } cm ^ { -3 } ) also suggest that I22023 may be evolving into a compact , young low-excitation Planetary Nebula .
Our optical spectroscopic analysis together with the recent Spitzer detection of double-dust chemistry ( the simultaneous presence of carbonaceous molecules and amorphous silicates ) in I22023 and other B-type post-AGB candidates may point to a binary system with a dusty disk as the stellar origin common to the hot post-AGB stars with O-rich central stars .