HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: BOÖTES II

We present high-resolution Magellan/MIKE spectra of the four brightest confirmed red giant stars in the ultra-faint dwarf galaxy Bootes II (Boo II). These stars all inhabit the metal-poor tail of the Boo II metallicity distribution function. The chemical abundance pattern of all detectable elements...

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Bibliographic Details
Published inThe Astrophysical journal Vol. 817; no. 1; p. 41
Main Authors Ji, Alexander P, Frebel, Anna, Simon, Joshua D, Geha, Marla
Format Journal Article
LanguageEnglish
Published United States 20.01.2016
Subjects
Abundance
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BINARY STARS
CAPTURE
Capture (nuclear)
COMPARATIVE EVALUATIONS
DISTRIBUTION FUNCTIONS
Dwarf galaxies
ELEMENT ABUNDANCE
Enrichment
EV RANGE
Galactic halos
GALAXIES
METALLICITY
NEUTRON REACTIONS
RADIAL VELOCITY
RED GIANT STARS
RESOLUTION
Stars
VARIATIONS
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Summary:We present high-resolution Magellan/MIKE spectra of the four brightest confirmed red giant stars in the ultra-faint dwarf galaxy Bootes II (Boo II). These stars all inhabit the metal-poor tail of the Boo II metallicity distribution function. The chemical abundance pattern of all detectable elements in these stars is consistent with that of the Galactic halo. However, all four stars have undetectable amounts of neutron-capture elements Sr and Ba, with upper limits comparable to the lowest ever detected in the halo or in other dwarf galaxies. One star exhibits significant radial velocity variations over time, suggesting it to be in a binary system. Its variable velocity has likely increased past determinations of the Boo II velocity dispersion. Our four stars span a limited metallicity range, but their enhanced [alpha]-abundances and low neutron-capture abundances are consistent with the interpretation that Boo II has been enriched by very few generations of stars. The chemical abundance pattern in Boo II confirms the emerging trend that the faintest dwarf galaxies have neutron-capture abundances distinct from the halo, suggesting the dominant source of neutron-capture elements in halo stars may be different than in ultra-faint dwarfs.
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ISSN:0004-637X
1538-4357
DOI:10.3847/0004-637X/817/1/41