The chemical evolution of the boÖtes I ultra-faint dwarf galaxy

Journal Article · Mon Aug 01 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/826/2/110· OSTI ID:22868864

Frebel, Anna ^[1]; Norris, John E. ^[2]; Gilmore, Gerard ^[3]; Wyse, Rosemary F. G. ^[4]

---

1. Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
2. Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT, 2611 (Australia)
3. Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA (United Kingdom)
4. The Johns Hopkins University, Department of Physics and Astronomy, Baltimore, MD 21218 (United States)

We present chemical abundance measurements of two metal-poor red giant stars in the ultra-faint dwarf galaxy Boötes I, based on Magellan/MIKE high-resolution spectra. For Boo-980, with [Fe/H]=−3.1, we present the first elemental abundance measurements, while Boo-127, with [Fe/H]=−2.0, shows abundances in good agreement with previous measurements. Light and iron-peak element abundance ratios in the two Boötes I stars, as well as those of most other Boötes I members, collected from the literature, closely resemble those of regular metal-poor halo stars. Neutron-capture element abundances Sr and Ba are systematically lower than the main halo trend and also show a significant abundance spread. Overall, this is similar to what has been found for other ultra-faint dwarf galaxies. We apply corrections to the carbon abundances (commensurate with stellar evolutionary status) of the entire sample and find 21% of stars to be carbon-enhanced metal-poor (CEMP) stars, compared to 13% without using the carbon correction. We reassess the metallicity distribution functions for the CEMP stars and non-CEMP stars, and confirm earlier claims that CEMP stars might belong to a different, earlier population. Applying a set of abundance criteria to test to what extent Boötes I could be a surviving first galaxy suggests that it is one of the earliest assembled systems that perhaps received gas from accretion from other clouds in the system, or from swallowing a first galaxy or building block type object. This resulted in the two stellar populations observable today.

• OSTI ID: 22868864
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 826; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON
COMPARATIVE EVALUATIONS
CORRECTIONS
DISTRIBUTION FUNCTIONS
DWARF STARS
ELEMENT ABUNDANCE
GALACTIC EVOLUTION
GALAXIES
IRON
METALLICITY
NEUTRON REACTIONS
RED GIANT STARS
SPECTRA
UNIVERSE