An inefficient dwarf: Chemical abundances and the evolution of the Ursa Minor dwarf spheroidal galaxy

Abstract

We present detailed chemical element abundance ratios of 17 elements in three metal poor stars in the Ursa Minor dwarf spheroidal galaxy, which we combine with extant data from the literature to assess the predictions of a novel suite of galaxy chemical evolution models. The spectroscopic data were obtained with the Keck/HIRES instrument and revealed low metallicities of [Fe/H]=-2.12, -2.13 and -2.67 dex. While the most metal poor star in our sample shows an overabundance of [Mn/Fe] and other Fe-peak elements, our overall findings are in agreement with previous studies of this galaxy: elevated values of the [alpha/Fe] ratios that are similar to, or only slightly lower than, the halo values but with SN Ia enrichment at very low metallicity, as well as an enhancement of the ratio of first to second peak neutron capture elements [Y/Ba] with decreasing metallicity. The chemical evolution models which were tailored to reproduce the metallicity distribution function of the dSph, indicate that UMi had an extended star formation which lasted nearly 5 Gyr with low efficiency and are able to explain the [Y/Ba] enhancement at low metallicity for the first time. In particular, we show that the present day lack of gas is probably due to continuous loss of gas from the system, which we model as winds.

10 pages, 7 figures, tables

References in corpus (8)

• New Grids of ATLAS9 Model Atmospheres
• Stellar Velocities in the Carina, Fornax, Sculptor and Sextans dSph Galaxies: Data from the Magellan/MMFS Survey
• NLTE abundances of Mn in a sample of metal-poor stars
• The Highly Unusual Chemical Composition of the Hercules Dwarf Spheroidal Galaxy
• Explaining the Ba, Y, Sr, and Eu abundance scatter in metal-poor halo stars: constraints to the r-process
• The chemical evolution of Manganese in different stellar systems
• Detailed Abundances of Two Very Metal-Poor Stars in Dwarf Galaxies
• A comparison of the s- and r-process element evolution in local dwarf spheroidal galaxies and in the Milky Way

Cited by in corpus (13)

• TOPoS: II. On the bimodality of carbon abundance in CEMP stars. Implications on the early chemical evolution of galaxies
• The Southern Stellar Stream Spectroscopic Survey (S5): Chemical Abundances of Seven Stellar Streams
• The formation of the Milky Way halo and its dwarf satellites; a NLTE-1D abundance analysis. II. Early chemical enrichment
• Zinc in the Sculptor dwarf spheroidal galaxy
• Simultaneous Constraints on the Star Formation History and Nucleosynthesis of Sculptor dSph
• Manganese spread in Ursa Minor as a proof of sub-classes of type Ia supernovae
• The SAMI-Fornax Dwarfs Survey III: Evolution of [$\alpha$/Fe] in dwarfs, from Galaxy Clusters to the Local Group
• Discovery of 18 stars with -3.10 < [Fe/H] < -1.45 in the Sagittarius dwarf galaxy
• The Pristine Inner Galaxy Survey (PIGS) IX. The largest detailed chemical analysis of very metal-poor stars in the Sagittarius dwarf galaxy
• Does the chemical signature of TYC 8442-1036-1 originate from a rotating massive star that died in a faint explosion?
• Too small to succeed: the difficulty of sustaining star formation in low-mass haloes
• An ancient system hidden in the Galactic plane?
• A relic from a past merger event in the Large Magellanic Cloud