EDP Sciences
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Volume 399, Number 1, February III 2003
Page(s) 105 - 112
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20021777

A&A 399, 105-112 (2003)
DOI: 10.1051/0004-6361:20021777

Red giants in open clusters

X. NGC 1817
J.-C. Mermilliod1, D. W. Latham2, E. V. Glushkova3, M. A. Ibrahimov4, V. M. Batirshinova4, R. P. Stefanik2 and D. J. James1, 5

1  Institut d'Astronomie de l'Université de Lausanne, 1290 Chavannes-des-Bois, Switzerland
2  Harvard-Smithsonian Center for Astrophysics, 60 Graden Street, Cambridge, Massachusetts 02138, USA
3  Sternberg Astronomical Institute, Universitetskii pr. 13, Moscow 119899, Russia
4  Ulugh Beg Astronomical Institute, Academy of Sciences of Uzbekistan, Astronomicheskaya str. 33, Tashkent 700052, Uzbekistan
5  School of physics and Astronomy, University of St Andrews, St Andrews, Fife, KY169SS, UK

(Received 13 June 2002 / Accepted 12 November 2002 )

Radial-velocity and BV CCD observations of 29 red-giant candidates in the central part of the intermediate-age open cluster NGC 1817 have confirmed the membership of 21 stars. In addition, we have used radial velocities and new  UBVR photoelectric photometry to investigate the membership of 59 new candidates located in an outer corona surrounding NGC 1817, identified from the POSS plates. We have confirmed 18 new members out to a distance of 27 $\arcmin$ from the centre, thus doubling the previous cluster radius. Ten definite spectroscopic-binary members have been discovered, corresponding to a binary frequency of 25.6% and four orbits have been determined so far. Three additional stars have been identified as possible spectroscopic-binary members. We derive a cluster mean velocity of +65.33 $\pm$ 0.09 (0.52 s.e.) km s -1 based on 29 members with no detected velocity variations plus the 3 binary members with orbital solutions. The radial distribution of the 39 red-giant members shows a strong concentration of spectroscopic binaries in the inner part of the cluster, similar to that observed in M 67, although NGC 1817 is much younger.

Key words: open clusters and associations: individual: NGC 1817 -- stars: binaries: spectroscopic -- techniques: radial velocities -- stars: AGB and post-AGB

Offprint request: J.-C. Mermilliod, Jean-Claude.Mermilliod@obs.unige.ch

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