DISCOVERY OF A FAINT OUTER HALO MILKY WAY STAR CLUSTER IN THE SOUTHERN SKY

作者：Kim Dongwon^*; Jerjen Helmut; Milone Antonino P; Mackey Dougal; Da Costa Gary S

来源：Astrophysical Journal, 2015, 803(2): 63.

DOI：10.1088/0004-637X/803/2/63

• Galaxy: formation
• Galaxy: halo
• galaxies: dwarf
• globular clusters: general
• Local Group

We report the discovery of a new, low-luminosity star cluster in the outer halo of the Milky Way. High-quality gr photometry is presented, from which a color-magnitude diagram is constructed, and estimates of age, [Fe/H], [alpha/Fe], and distance are derived. The star cluster, which we designate as Kim 2, lies at a heliocentric distance of similar to 105 kpc. With a half-light radius of similar to 12.8 pc and ellipticity of epsilon similar to 0.12, it shares the properties of outer halo globular clusters, except for at higher metallicity ([Fe/H] similar to -1.0) and lower luminosity (M-V similar to -1.5). These parameters are similar to those for the globular cluster AM 4, which is considered to be associated with the Sagittarius dwarf spheroidal galaxy. We find evidence of dynamical mass segregation and the presence of extra-tidal stars that suggests that Kim 2 is most likely a star cluster. Spectroscopic observations for radial-velocity membership and chemical abundance measurements are needed to further understand the nature of the object.

• 出版日期2015-4-20