WFPC2 observations of the globular cluster M30

Brian Yanny, Puragra Guhathakurta, Donald P. Schneider, John N. Bahcall

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Abstract

We describe images of the center of the dense globular cluster M30 (NGC 7099) obtained with the Hubble Space Telescope Wide Field/Planetary Camera 2. Data taken in the F336W, F439W, and F555W filters (approximately U, B, and K) yield a color-magnitude diagram with photometric errors of 1 σ = 0.05 mag for stars with V < 17.5, and 1 σ ∼ 0.1 mag at V = 20, which is 1.5 mag fainter than the main-sequence turnoff. Simulations show that the star identifications are essentially complete for stars with V < 19.5, even in the densest regions of the cluster. The projected radial distribution of stars can be represented by a power law distribution: N(r) ∼ rα, with slope α = -0.4 ± 0.15, into radii less than 0″.4 (0.015 pc). The radial profile is also consistent with a flat core of any radius smaller than ∼ 1″.5 (0.05 pc), but inconsistent with any core radius larger than 2″.5 (0.09 pc). A total of 30 blue straggler candidates within 20″ of the cluster center have been identified from the three-color data. Their radial distribution is strongly centrally concentrated when compared to the horizontal branch, red giant branch, or main-sequence stars in the cluster. The abundance of blue stragglers (relative to red giants and subgiants) within r ≲ 20″ of the center of M30 is fBS = 0.19 ± 0.04, about twice as high as in other dense clusters.

Original languageEnglish (US)
Pages (from-to)L59-L62
JournalAstrophysical Journal
Volume435
Issue number1 PART 2
DOIs
StatePublished - Nov 1 1994

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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