Globular cluster photometry with the Hubble Space Telescope. 3: Blue stragglers and variable stars in the core of M3

Details Globular cluster photometry with the Hubble Space Telescope. 3: Blue stragglers and variable stars in the core of M3 Globular cluster photometry with the Hubble Space Telescope. 3: Blue stragglers and variable stars in the core of M3

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aj....108.1786g&link_type=abstract

The Astronomical Journal (ISSN 0004-6256), vol. 108, no. 5, p. 1786-1809

Astronomy and Astrophysics

Astronomy

30

Blue Stars, Color-Magnitude Diagram, Globular Clusters, Horizontal Branch Stars, Radial Distribution, Red Giant Stars, Spaceborne Astronomy, Star Distribution, Stellar Spectrophotometry, Ultraviolet Astronomy, Variable Stars, Astrometry, Astronomical Photography, Cameras, Charge Coupled Devices, Hubble Space Telescope, Light Curve, Stellar Color, Stellar Luminosity, Ultraviolet Spectra, Ultraviolet Spectroscopy

Scientific paper

This paper describes Hubble Space Telescope (HST)/Planetary Camera-I images of the core of the dense globular cluster M3 (NGC 5272). Stellar photometry in the F555W (V) and F785LP (I) bands, with a 1-sigma photometric accuracy of about 0.1 mag, has been used to construct color-magnitude diagrams of about 4700 stars above the main-sequence turnoff within r less than or approximately equal to 1 min of the cluster center. We have also analyzed archival HST F336W (U) images of M3 obtained by the Wide Field/Planetary Camera-I Instrument Definition Team. The UVI data are used to identify 28 blue straggler (BS) stars within the central 0.29 sq. arcmin. The specific frequency of BSs in this region of M3, NBS/NV less than (V(HB+2)) = 0.094 +/- 0.019, is about a factor of 2 - 3 higher than that found by Bolte et al. in a recent ground-based study of the same region, but comparable to that seen in the sparse outer parts of the same cluster and in HST observations of the core of the higher density cluster 47 Tuc. The BSs in M3 are slightly more centrally concentrated than red giant branch stars while horizontal branch stars are somewhat less concentrated red giants. The radial distribution of V-selected subgiant and turnoff stars is well fit by a King model with a core radius rcore = 28 arcmin +/- 2 arcmin (90% confidence limits), which corresponds to 1.4 pc. Red giant and horizontal branch stars selected in the ultraviolet data (U less than 18) have a somewhat more compact distribution (rcore = 22.5 arcmin). The HST U data consist of 17 exposures acquired over a span of three days. We have used these data to isolate 40 variable stars for which relative astrometry, brightnesses, colors, and light curves are presented. A Kolmogorov-Smirnov test indicates that, typically, the variability for each star is significant at the 95% level. We identify two variable BS candidates (probably of the SX Phe type), out of a sample of approximately 25 BSs in which variability could have been detected. Most of the variables are RR Lyrae stars on the horizontal branch. All of them have periods P greater than or approximately equal 8 h.

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