Time-Series BVI Photometry for the Globular Cluster NGC 6981 (M72)

Abstract

We present new BVI photometry of the globular cluster NGC 6981 (M72), based mostly on ground-based CCD archive images. We present a new color-magnitude diagram (CMD) that reaches almost four magnitudes below the turn-off level. We performed new derivations of metallicity and morphological parameters of the evolved sequences, in good agreement with previous authors, obtaining a value of [Fe/H] ~ -1.50 in the new UVES scale. We also identify the cluster's blue straggler population. Comparing the radial distribution of these stars with the red giant branch population, we find that the blue stragglers are more centrally concentrated, as found in previous studies of blue stragglers in globular clusters. Taking advantage of the large field of view covered by our study, we analyzed the surface density profile of the cluster, finding extratidal main sequence stars out to r ~ 14.1 arcmin or about twice the tidal radius. We speculate that this may be due to tidal disruption in the course of M72's orbit, in which case tidal tails associated with the cluster may exist. We also take a fresh look at the variable stars in the cluster, recovering all previous known variables, including three SX Phoenicis stars, and adding three previously unknown RR Lyrae (1 c-type and 2 ab-type) to the total census. Finally, comparing our CMD with unpublished data for M3 (NGC 5272), a cluster with similar metallicity and horizontal branch morphology, we found that both objects are essentially coeval.

Accepted for publication in AJ

References in corpus (10)

• The fraction of binary systems in the core of thirteen low-density Galactic globular clusters
• Light and Motion in SDSS Stripe 82: The Catalogues
• The radial distribution of blue straggler stars and the nature of their progenitors
• Formation and evolution of clumpy tidal tails around globular clusters
• Are Globular Clusters the Remnant Nuclei of Progenitor Disk Galaxies?
• Variable stars in the Globular Cluster NGC 2808
• The extra-mixing efficiency in very low metallicity RGB stars
• Structure and Evolution of Low-Mass Stars: An Overview and Some Open Problems
• EMCCD photometry reveals two new variable stars in the crowded central region of the globular cluster NGC 6981
• The Globular Cluster NGC 5286. I. A New CCD BV Color-Magnitude Diagram

Cited by in corpus (3)

• The Two-Colour EMCCD Instrument for the Danish 1.54m Telescope and SONG
• Signatures of tidal disruption in the Milky Way globular cluster NGC 6981 (M72)
• RR Lyrae mode switching in globular cluster M 68 (NGC 4590)