SPECTROSCOPIC INVESTIGATIONS OF GALACTIC CLUSTERS WITH ASSOCIATED CEPHEID VARIABLES. III. COLLINDER 394 AND BB SGR

Анотація

We present the results of a spectro-
scopic and photometric investigation of 20 objects
from the open cluster Collinder 394, which contains
the Cepheid BB Sgr. Besides the Cepheid, we studied
tree K-giants, four B-giants, and twelve B-A-F main
sequence stars. Radial velocities (RV), vsini, T eff ,
logg, were determined using spectroscopic model
fitting and atmosphere models. We have derived the
color-excesses, reddenings, and intrinsic colors for
these stars using their T eff and logg from compar-
ison to the atmosphere models, especially for hot
stars. Proper motions, RV and GAIA DR2 2018
parallax/distance values for these stars allowed us
to determine their membership in the cluster and
absolute magnitudes. We found that seven stars
do not belong to the cluster. The parallaxes and
reddenings of 13 confidently cluster members led to
the distances in a range of 630–800 pc, although
the majority of them (8 objects) are located at a
mean distance of 657.7±66.7 pc, and 5 objects with
the Cepheid could probably belong to the cluster’s
corona. All the members have [Fe/H] near 0.1 dex.
The main sequence B-star No. 76 (HD 174307) has a
low rotational velocity projection, and this fact allows
us to determine its chemical composition to compare
with that of the Cepheid BB Sgr. Its CNO and
Na abundances are close to the solar one, while the
Cepheid show a deficit of carbon, an overabundance of
nitrogen, nearly solar oxygen, and an overabundance
of sodium. Three foreground K-giants have different C
abundances (from a deficit to the solar), and Na (from
the solar to an overabundance) as well as a solar-like
O content. The foreground F7-8 V star No. 75 (CPD
−20 ◦ 7218) was revealed to be a Li-rich star, while the
A7 V star No. 69 (BD −20 ◦ 5290) has an anomalous
deficit of CNO with overabundances of some α, r- and
s-process elements.