New cluster members and halo stars of the Galactic globular cluster NGC 1851

Abstract

NGC 1851 is an intriguing Galactic globular cluster, with multiple stellar evolutionary sequences, light and heavy element abundance variations and indications of a surrounding stellar halo. We present the first results of a spectroscopic study of red giant stars within and outside of the tidal radius of this cluster. Our results identify nine probable new cluster members (inside the tidal radius) with heliocentric radial velocities consistent with that of NGC 1851. We also identify, based on their radial velocities, four probable extratidal cluster halo stars at distances up to ~3.1 times the tidal radius, which are supportive of previous findings that NGC 1851 is surrounded by an extended stellar halo. Proper motions were available for 12 of these 13 stars and all are consistent with that of NGC 1851. Apart from the cluster members and cluster halo stars, our observed radial velocity distribution agrees with the expected distribution from a Besancon disk/N-body stellar halo Milky Way model generated by the Galaxia code, suggesting that no other structures at different radial velocities are present in our field. The metallicities of these stars are estimated using equivalent width measurements of the near infrared calcium triplet absorption lines and are found, within the limitations of this method, to be consistent with that of NGC 1851. In addition we recover 110 red giant cluster members from previous studies based on their radial velocities and identify three stars with unusually high radial velocities.

10 pages, 8 figures. Accepted for publication in MNRAS

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• The GALAH Survey: Observational Overview and Gaia DR1 companion
• The Outer Envelopes of Globular Clusters. II. NGC 1851, NGC 5824 and NGC 1261
• Tails and streams around the Galactic globular clusters NGC1851, NGC1904, NGC2298 and NGC2808
• Detailed Chemical Abundances in NGC 5824: Another Metal-Poor Globular Cluster with Internal Heavy Element Abundance Variations
• A Chemical Composition Survey of the Iron-Complex Globular Cluster NGC 6273 (M 19)
• Stellar envelopes of globular clusters embedded in dark mini-haloes
• A broad perspective on multiple abundance populations in the globular cluster NGC 1851
• The most metal-poor Galactic globular cluster: the first spectroscopic observations of ESO280-SC06
• Confirming the intrinsic abundance spread in the globular cluster NGC 6273 (M 19) with calcium triplet spectroscopy
• New halo stars of the Galactic globular clusters M3 and M13 in the LAMOST DR1 Catalog
• Gaia-ESO Survey: Detailed elemental abundances in red giants of the peculiar globular cluster NGC 1851
• CAPOS: The bulge Cluster APOGEE Survey VI. Characterizing multiple stellar populations and chemical abundances in the bulge globular cluster NGC 6569
• Rediscovering the origins of the stellar halo with chemical tagging