A Hubble Space Telescope Study of the Enigmatic Milky Way Halo Globular Cluster Crater

Daniel R. Weisz, Sergey E. Koposov, Andrew E. Dolphin, Vasily Belokurov, Mark Gieles, Mario L. Mateo, Edward W. Olszewski, Alison Sills, Matthew G. Walker

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We analyze the resolved stellar populations of the faint stellar system, Crater, based on deep optical imaging takenwith the Advanced Camera for Surveys on theHubble Space Telescope. Crater’s color–magnitude diagram(CMD)extends∼4 mag below the oldest main-sequence(MS)turnoff. Structurally, wefind that Crater has a half-lightradius of∼20 pc and no evidence for tidal distortions. We model Crater’s CMD as a simple stellar population(SSP) and alternatively by solving for its full star formation history. In both cases, Crater is well described by anSSP with an age of∼7.5 Gyr, a metallicity of[M/H]∼−1.65, a total stellar mass of M∗~1e4 M, and a luminosity of Mν~-5.3, located at a distance of d∼145 kpc, with modest uncertainties due to differences in theunderlying stellar evolution models. We argue that the sparse sampling of stars above the turnoff and subgiantbranch are likely to be 1.0–1.4M blue stragglers and their evolved descendants, as opposed to intermediate-ageMS stars. We find that Crater is an unusually young cluster given its location in the Galaxy’s outer halo. Wediscuss scenarios for Crater’s origin, including the possibility of being stripped from the SMC or the accretion fromlower-mass dwarfs such as Leo I or Carina. Despite uncertainty over its progenitor system, Crater appears to havebeen incorporated into the Galaxy more recently thanz∼1(8 Gyr ago), providing an important new constraint on the accretion history of the Galaxy.
Original languageEnglish
JournalAstrophysical Journal
Publication statusPublished - 2 May 2016

Keywords / Materials (for Non-textual outputs)

  • astro-ph.GA


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