Journal Article

Metallicities and radial velocities of five open clusters including a new candidate member of the Monoceros stream*

Steven R. Warren and Andrew A. Cole

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 393, issue 1, pages 272-296
Published in print February 2009 | ISSN: 0035-8711
Published online January 2009 | e-ISSN: 1365-2966 | DOI:
Metallicities and radial velocities of five open clusters including a new candidate member of the Monoceros stream*

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Near-infrared spectra of 133 red giant stars from 10 Galactic open clusters and two Galactic globular clusters spanning 2.2 dex in metallicity and 11 Gyr in age are presented. We combine this sample with 10 clusters from Cole and collaborators to investigate the Ca ii triplet line strengths and their relation to cluster metallicity and position along the red giant branch. We show that characterizing the stellar surface gravity using Ks-band photometry (relative to the horizontal branch) taken from the Two Micron All-Sky Survey allows for metallicity measurements at least as precise as those derived using V- or I-band data. This has the great advantage that uniform photometry and reliable astrometry are available for a large number of clusters. Using Ks-band photometry also reduces the effect of differential reddening within a given cluster. We find no significant evidence for age or metallicity effects to the linear Ca ii triplet–metallicity relationship over the small range in magnitudes studied when homogeneous reference metallicities are used. We derive the first spectroscopic metallicity and new radial velocity estimates for five open clusters: Berkeley 81, Berkeley 99, IC 1311, King 2 and NGC 7044. King 2 has an anomalous radial velocity compared with the local disc population. We discuss the possibility that it is part of the Monoceros tidal stream.

Keywords: techniques: spectroscopic; stars: abundances; stars: late-type; globular clusters: general; open clusters and associations: general

Journal Article.  12555 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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