HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: URSA MAJOR II and COMA BERENICES

Journal Article · Fri Jan 01 00:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/708/1/560· OSTI ID:21392457

Frebel, Anna ^[1]; Simon, Joshua D ^[2]; Geha, Maria ^[3]; Willman, Beth ^[4]

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1. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
2. Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101 (United States)
3. Astronomy Department, Yale University, New Haven, CT 06520 (United States)
4. Haverford College, Haverford, PA 19041 (United States)

We present spectra of six metal-poor stars in two of the ultra-faint dwarf galaxies orbiting the Milky Way (MW), Ursa Major II, and Coma Berenices obtained with the Keck/High Resolution Echelle Spectrometer (HIRES). These observations include the first high-resolution spectroscopic observations of extremely metal-poor ([Fe/H] < -3.0) stars not belonging to the MW halo field star population. We obtain abundance measurements and upper limits for 26 elements between carbon and europium. The entire sample of stars spans a range of -3.2 < [Fe/H] < -2.3, and we confirm that each galaxy contains a large intrinsic spread of Fe abundances. A comparison with MW halo stars of similar metallicities reveals substantial agreement between the abundance patterns of the ultra-faint dwarf galaxies and the MW halo for the light, alpha, and iron-peak elements (C to Zn). This agreement contrasts with the results of earlier studies of more metal-rich stars (-2.5 approx< [Fe/H] approx< -1.0) in more luminous dwarf spheroidal galaxies, which found significant abundance discrepancies with respect to the MW halo data. The abundances of neutron-capture elements (Sr to Eu) in the ultra-faint dwarf galaxies are extremely low, consistent with the most metal-poor halo stars, but not with the typical halo abundance pattern at [Fe/H] approx> -3.0. Not only are our results broadly consistent with a galaxy formation model that predicts that massive dwarf galaxies are the source of the metal-rich component ([Fe/H]> - 2.5) of the MW halo, but they also suggest that the faintest known dwarfs may be the primary contributors to the metal-poor end of the MW halo metallicity distribution.

• OSTI ID: 21392457
• Journal Information: Astrophysical Journal, Vol. 708, Issue 1; Other Information: DOI: 10.1088/0004-637X/708/1/560; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABUNDANCE
CAPTURE
CARBON
EUROPIUM
IRON
MILKY WAY
NEUTRON REACTIONS
SPECTROMETERS
SPECTROSCOPY
STARS
UNIVERSE
BARYON REACTIONS
ELEMENTS
GALAXIES
HADRON REACTIONS
MEASURING INSTRUMENTS
METALS
NONMETALS
NUCLEAR REACTIONS
NUCLEON REACTIONS
RARE EARTHS
TRANSITION ELEMENTS