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Title: BOO-1137-AN EXTREMELY METAL-POOR STAR IN THE ULTRA-FAINT DWARF SPHEROIDAL GALAXY BOOeTES I

Abstract

We present high-resolution (R {approx} 40,000), high-signal-to-noise ratio (20-90) spectra of an extremely metal-poor giant star Boo-1137 in the 'ultra-faint' dwarf spheroidal galaxy (dSph) Booetes I, absolute magnitude M{sub V} {approx} -6.3. We derive an iron abundance of [Fe/H] = -3.7, making this the most metal-poor star as yet identified in an ultra-faint dSph. Our derived effective temperature and gravity are consistent with its identification as a red giant in Booetes I. Abundances for a further 15 elements have also been determined. Comparison of the relative abundances, [X/Fe], with those of the extremely metal-poor red giants of the Galactic halo shows that Boo-1137 is 'normal' with respect to C and N, the odd-Z elements Na and Al, the iron-peak elements, and the neutron-capture elements Sr and Ba, in comparison with the bulk of the Milky Way halo population having [Fe/H] {approx}<-3.0. The alpha-elements Mg, Si, Ca, and Ti are all higher by DELTA[X/Fe] {approx} 0.2 than the average halo values. Monte Carlo analysis indicates that DELTA[alpha/Fe] values this large are expected with a probability {approx}0.02. The elemental abundance pattern in Boo-1137 suggests inhomogeneous chemical evolution, consistent with the wide internal spread in iron abundances we previously reported. The similarity ofmore » most of the Boo-1137 relative abundances with respect to halo values, and the fact that the alpha-elements are all offset by a similar small amount from the halo averages, points to the same underlying galaxy-scale stellar initial mass function, but that Boo-1137 likely originated in a star-forming region where the abundances reflect either poor mixing of supernova (SN) ejecta, or poor sampling of the SN progenitor mass range, or both.« less

Authors:
;  [1];  [2];  [3]
  1. Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia)
  2. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
  3. Department of Physics and Astronomy, Johns Hopkins University, 3900 North Charles Street, Baltimore, MD 21218 (United States)
Publication Date:
OSTI Identifier:
21394364
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 711; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/711/1/350; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; CALCIUM; GALACTIC EVOLUTION; GIANT STARS; GRAVITATION; IRON; MAGNESIUM; MASS; MILKY WAY; MONTE CARLO METHOD; NEUTRON REACTIONS; SAMPLING; SIGNAL-TO-NOISE RATIO; SILICON; TITANIUM; ALKALINE EARTH METALS; BARYON REACTIONS; CALCULATION METHODS; DIMENSIONLESS NUMBERS; ELEMENTS; EVOLUTION; GALAXIES; HADRON REACTIONS; METALS; NUCLEAR REACTIONS; NUCLEON REACTIONS; SEMIMETALS; STARS; TRANSITION ELEMENTS

Citation Formats

Norris, John E, Yong, David, Gilmore, Gerard, and Wyse, Rosemary F. G.,. BOO-1137-AN EXTREMELY METAL-POOR STAR IN THE ULTRA-FAINT DWARF SPHEROIDAL GALAXY BOOeTES I. United States: N. p., 2010. Web. doi:10.1088/0004-637X/711/1/350.
Norris, John E, Yong, David, Gilmore, Gerard, & Wyse, Rosemary F. G.,. BOO-1137-AN EXTREMELY METAL-POOR STAR IN THE ULTRA-FAINT DWARF SPHEROIDAL GALAXY BOOeTES I. United States. https://doi.org/10.1088/0004-637X/711/1/350
Norris, John E, Yong, David, Gilmore, Gerard, and Wyse, Rosemary F. G.,. 2010. "BOO-1137-AN EXTREMELY METAL-POOR STAR IN THE ULTRA-FAINT DWARF SPHEROIDAL GALAXY BOOeTES I". United States. https://doi.org/10.1088/0004-637X/711/1/350.
@article{osti_21394364,
title = {BOO-1137-AN EXTREMELY METAL-POOR STAR IN THE ULTRA-FAINT DWARF SPHEROIDAL GALAXY BOOeTES I},
author = {Norris, John E and Yong, David and Gilmore, Gerard and Wyse, Rosemary F. G.,},
abstractNote = {We present high-resolution (R {approx} 40,000), high-signal-to-noise ratio (20-90) spectra of an extremely metal-poor giant star Boo-1137 in the 'ultra-faint' dwarf spheroidal galaxy (dSph) Booetes I, absolute magnitude M{sub V} {approx} -6.3. We derive an iron abundance of [Fe/H] = -3.7, making this the most metal-poor star as yet identified in an ultra-faint dSph. Our derived effective temperature and gravity are consistent with its identification as a red giant in Booetes I. Abundances for a further 15 elements have also been determined. Comparison of the relative abundances, [X/Fe], with those of the extremely metal-poor red giants of the Galactic halo shows that Boo-1137 is 'normal' with respect to C and N, the odd-Z elements Na and Al, the iron-peak elements, and the neutron-capture elements Sr and Ba, in comparison with the bulk of the Milky Way halo population having [Fe/H] {approx}<-3.0. The alpha-elements Mg, Si, Ca, and Ti are all higher by DELTA[X/Fe] {approx} 0.2 than the average halo values. Monte Carlo analysis indicates that DELTA[alpha/Fe] values this large are expected with a probability {approx}0.02. The elemental abundance pattern in Boo-1137 suggests inhomogeneous chemical evolution, consistent with the wide internal spread in iron abundances we previously reported. The similarity of most of the Boo-1137 relative abundances with respect to halo values, and the fact that the alpha-elements are all offset by a similar small amount from the halo averages, points to the same underlying galaxy-scale stellar initial mass function, but that Boo-1137 likely originated in a star-forming region where the abundances reflect either poor mixing of supernova (SN) ejecta, or poor sampling of the SN progenitor mass range, or both.},
doi = {10.1088/0004-637X/711/1/350},
url = {https://www.osti.gov/biblio/21394364}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 711,
place = {United States},
year = {Mon Mar 01 00:00:00 EST 2010},
month = {Mon Mar 01 00:00:00 EST 2010}
}