Blue straggler stars in the globular cluster NGC 5466

Abstract

Twenty-four blue straggler stars have been identified in the low central concentration globular cluster NGC 5053. New deep color-magnitude (C-M) diagrams to 23 mag, constructed from photometry of over 6000 stars on 4-shooter CCD frames, show that they form a well-defined sequence in the CM diagram, extending up to ~2.2 mag brighter than the main-sequence turnoff point. The 12 most luminous blue stragglers are found to be significantly more centrally concentrated than the cluster subgiants with magnitudes in the same interval (a similar result is known for the blue stragglers in the globular cluster NGC 5466). Furthermore, they are also found to be more centrally concentrated than the 12 lower luminosity blue stragglers. Comparisons of the projected radial distributions of the bright and faint blue stragglers, with the radial distributions that are expected for stars of mass 0.8, 1.6, and 2.4 M 0 (calculated using multimass King models) suggests that the brightest blue stragglers have an average mass of <^M) = 1.3 + 0.3 M 0 , which is less than or comparable to twice the mean mass of a main-sequence turnoff star, and the lower luminosity blue stragglers have a mean mass similar to that of the main-sequence turnoff stars (i.e., M ~ 0.8 M 0)-By fitting theoretical isochrones computed by Bell and VandenBerg to the observed main-sequence turnoff and subgiant branch regions of NGC 5053, a distance modulus of (m-M) 0 = 16.05 ± 0.14 mag, and an age of 18 ± 3 Gyr are derived for NGC 5053. The main-sequence luminosity function shows no sign of " turning over " for stars brighter than M g ~ 5 mag.

Photometric catalog of nearby globular clusters

“…6) NGC 5466 has one of the lowest central densities among the GGCs. Previous CMDs are not very recent; Nemec & Harris (1987) present photographic and CCD data, with the CCD CMD extending from V ∼ 21, to just below the HB (not present). We have not found more recent CMDs for this cluster.…”

The Abundance Spread Among Giants and Subgiants in the Globular Cluster Omega Centauri

“…There are, however, small differences in the two sample distributions. If we pare the BG sample to only include stars at cluster radii greater than 8 ′ to be consistent with the SG sample, we find that a two-sided Kolmogorov-Smirnov (K-S) test (Nemec & Harris 1987, Press, et al 1992 gives a probability of the rejection of the hypothesis that the two samples are drawn from the same parent population at 80%, independent of which metallicity scale is chosen. The sense of the difference is that the BG sample has a small number of metal-rich stars that are much more metal-rich than the SG sample.…”

SX Phoenicis Stars in the Globular Cluster NGC 5466

“…Instrumental magnitudes were obtained using the point-spread function ( PSF) fitting photometry routine in the IRAF/ DAOPHOT package (Stetson 1987;Massey & Davis 1992). Nemec & Harris (1987) presented photoelectric photometry of 36 stars in the outer region of NGC 5466, of which we select 10 stars located in our observing fields for the standardization of the instrumental magnitudes. For standardization, we selected nine and five frames for V and B bands, respectively, taken under good seeing conditions on 2002 March 12.…”

“…Nemec & Harris (1987) found 48 blue straggler stars, which are mostly concentrated within r ¼ 3 0 from the center of the cluster. Several kinds of variable stars are known to exist in this cluster: six SX Phoenicis stars Chen & Corwin 1999), three eclipsing binaries Kallrath et al 1992;McKinley & Corwin 1998), a Cepheid, and more than 20 RR Lyrae stars (Clement et al 2001).…”