THE DISCOVERY OF AN ULTRA-FAINT STAR CLUSTER IN THE CONSTELLATION OF URSA MINOR

Journal Article · Sun Jul 01 00:00:00 EDT 2012 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/753/1/L15· OSTI ID:22047703

Munoz, R R; Geha, M; Vargas, L C ^[1]; Cote, P; Stetson, P ^[2]; Santana, F A ^[3]; Simon, J D ^[4]

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1. Astronomy Department, Yale University, New Haven, CT 06520 (United States)
2. Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7 (Canada)
3. Departamento de Astronomia, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago (Chile)
4. Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

We report the discovery of a new ultra-faint globular cluster in the constellation of Ursa Minor, based on stellar photometry from the MegaCam imager at the Canada-France-Hawaii Telescope. We find that this cluster, Munoz 1, is located at a distance of 45 {+-} 5 kpc and at a projected distance of only 45' from the center of the Ursa Minor dwarf spheroidal galaxy. Using a maximum-likelihood technique we measure a half-light radius of 0.'5, or equivalently 7 pc, and an ellipticity consistent with being zero. We estimate its absolute magnitude to be M{sub V} -0.4 {+-} 0.9, which corresponds to L{sub V} = 120{sup +160}{sub -65} L{sub Sun} and we measure a heliocentric radial velocity of -137 {+-} 4 km s{sup -1} based on Keck/DEIMOS spectroscopy. This new satellite is separate from Ursa Minor by {approx}30 kpc and 110 km s{sup -1} suggesting the cluster is not obviously associated with the dSph, despite the very close angular separation. Based on its photometric properties and structural parameters we conclude that Munoz 1 is a new ultra-faint stellar cluster. Along with Segue 3 this is one of the faintest stellar clusters known to date.

• OSTI ID: 22047703
• Journal Information: Astrophysical Journal Letters, Vol. 753, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTRONOMY
ASTROPHYSICS
DISTANCE
EMISSION SPECTROSCOPY
GALAXIES
MAXIMUM-LIKELIHOOD FIT
PHOTOMETRY
RADIAL VELOCITY
SATELLITES
STAR CLUSTERS
TELESCOPES
VISIBLE RADIATION