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
.