Spectroscopic investigations of classical Cepheids and main-sequence stars in galactic open clusters and associations

I. A. Usenko; V. V. Kovtyukh; V. G. Klochkova; V. E. Panchuk

doi:doi:10.1051/0004-6361:20011076

Free access

Issue		A&A Volume 376, Number 3, September IV 2001


Page(s)		885 - 891
Section		Stellar clusters and associations
DOI		http://dx.doi.org/10.1051/0004-6361:20011076

A&A 376, 885-891 (2001)
DOI: 10.1051/0004-6361:20011076

II. Open cluster Platais 1 (C2128+488) and small-amplitude Cepheid V1726 Cygni

I. A. Usenko^{1, 2}, V. V. Kovtyukh^{1, 2}, V. G. Klochkova^{3, 4} and V. E. Panchuk^{3, 4}

¹ Astronomical Observatory of Odessa State University, Odessa 65014, Ukraine
e-mail: val@deneb.odessa.ua
² Isaac Newton Institute of Chile, Odessa Branch, Ukraine
³ Special Astrophysical Observatory, Russian Academy of Sciences, Nizhny Arkhyz, Stavropol Territory 369167, Russia
e-mail: valenta@sao.ru; panchuk@sao.ru
⁴ Isaac Newton Institute of Chile, SAO RAS Branch, Russia

(Received 27 February 2001 / Accepted 24 July 2001 )

Abstract
The small-amplitude Cepheid V1726 Cyg and two members of open cluster Platais 1 ( Platais 1 star No. 1 (1921) and Platais 1 star No. 111 (1600) ) were investigated, using high-resolution CCD spectra. The following results were obtained: 1) All objects have the same metallicities, close to that of the Sun (for V1726 Cyg weighted average [ Fe/H]=+0.05, for Platais 1 star No. 1 (1921) [ Fe/H]=+0.13); 2) values of $T_{\rm eff}$ and $\log g$ for the B-stars are in excellent agreement with those determined from (B-V) colour indices using a $(B-V)\sim(T_{\rm eff}$ , $\log g$ ) calibration; 3) the elemental abundances indicate that V1726 Cyg is in the post first dredge-up stage with an age near $1.5 \times 10^{8}$ , and is crossing the Cepheid instability strip for the third time. Mean values of $T_{\rm eff}=6100$ K and $\log g=2.35 \pm 0.05$ permit us to refine its colour excess to $E_{B-V}=0\fm 33$ , which for a distance of $d = 1568\pm 13$ pc corresponds to $M_{V}=-2\fm 99$ . The Cepheid could therefore be pulsating in the fundamental tone, although pulsation in the first overtone is not excluded; 4) Platais 1 Star No. 1 (1921) is a slowly rotating HgMn-star with a high helium content, while Platais 1 star No. 111 (1600) is a rapidly rotating main-sequence star with a helium content comparable to that of the Sun; 5) the age of the open cluster is estimated to be about $2.5 \times 10^{8}$ yr.

Key words: galaxy: open clusters: and associations -- stars: abundances -- stars: Cepheids -- stars: general

Offprint request: I. A. Usenko, igus@deneb.odessa.ua

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