Detailed Chemical Abundances in the r-Process-Rich Ultra-Faint Dwarf Galaxy Reticulum 2

Abstract

The ultra-faint dwarf galaxy Reticulum 2 (Ret 2) was recently discovered in images obtained by the Dark Energy Survey. We have observed the four brightest red giants in Ret 2 at high spectral resolution using the Michigan/Magellan Fiber System. We present detailed abundances for as many as 20 elements per star, including 12 elements heavier than the Fe group. We confirm previous detection of high levels of r-process material in Ret 2 (mean [Eu/Fe]=+1.69+/-0.05) found in three of these stars (mean [Fe/H]=-2.88+/-0.10). The abundances closely match the r-process pattern found in the well-studied metal-poor halo star CS22892-052. Such r-process-enhanced stars have not been found in any other ultra-faint dwarf galaxy, though their existence has been predicted by at least one model. The fourth star in Ret 2 ([Fe/H]=-3.42+/-0.20) contains only trace amounts of Sr ([Sr/Fe]=-1.73+/-0.43) and no detectable heavier elements. One r-process enhanced star is also enhanced in C (natal [C/Fe]=+1.1). This is only the third such star known, which suggests that the nucleosynthesis sites leading to C and r-process enhancements are decoupled. The r-process-deficient star is enhanced in Mg ([Mg/Fe]=+0.81+/-0.14), and the other three stars show normal levels of alpha-enhancement (mean [Mg/Fe]=+0.34+/-0.03). The abundances of other alpha and Fe-group elements closely resemble those in ultra-faint dwarf galaxies and metal-poor halo stars, suggesting that the nucleosynthesis that led to the large r-process enhancements either produced no light elements or produced light-element abundance signatures indistinguishable from normal supernovae.

Accepted for publication in the Astronomical Journal. 12 pages, 6 figures, 8 tables

References in corpus (35)

• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• Kilonova Light Curves from the Disk Wind Outflows of Compact Object Mergers
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• Discovery of HE 1523-0901, a Strongly r-Process Enhanced Metal-Poor Star with Detected Uranium
• Near-UV Observations of HD221170: New Insights into the Nature of r-Process-Rich Stars
• Segue 1: An Unevolved Fossil Galaxy from the Early Universe
• New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars
• The s process in massive stars at low metallicity. Effect of primary N14 from fast rotating stars
• Bright Metal-Poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields
• The Highly Unusual Chemical Composition of the Hercules Dwarf Spheroidal Galaxy
• Binarity in Carbon-Enhanced Metal-Poor stars
• Improved Laboratory Transition Probabilities for Neutral Chromium and Re-determination of the Chromium Abundance for the Sun and Three Stars
• Galactic r-process enrichment by neutron star mergers in cosmological simulations of a Milky Way-mass galaxy
• The History of R-Process Enrichment in the Milky Way
• Detection of Elements at All Three r-process Peaks in the Metal-Poor Star HD 160617
• An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars
• Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data
• The role of neutron star mergers in the chemical evolution of the Galactic halo
• Stellar Chemical Abundances: In Pursuit of the Highest Achievable Precision
• Fe I Oscillator Strengths for the Gaia-ESO Survey
• Neutron Star Mergers as the Origin of r-Process Elements in the Galactic Halo Based on the Sub-halo Clustering Scenario
• Carbon-Enhanced Metal-Poor Stars: Relics from the Dark Ages
• Faint Population III supernovae as the origin of the most iron-poor stars
• Nucleosynthesis in Magnetically Driven Jets from Collapsars
• Nine New Metal-Poor Stars on the Subgiant and Red Horizontal Branches with High Levels of r-process Enhancement
• Enrichment history of r-process elements shaped by a merger of neutron star pairs
• Fundamental properties of the Population II fiducial stars HD 122563 and Gmb 1830 from CHARA interferometric observations
• Chemical Inhomogeneities in the Milky Way Stellar Halo
• Compact Stellar Binary Assembly in the First Nuclear Star Clusters and r-Process Synthesis in the Early Universe
• Experimental Mg I oscillator strengths and radiative lifetimes for astrophysical applications on metal-poor stars - New data for the Mg I b triplet
• Detailed Abundance Analysis of the Brightest Star in Segue 2, the Least Massive Galaxy
• A chemical confirmation of the faint Bootes II dwarf Spheroidal Galaxy
• Chemical Feature of Eu abundance in the Draco dwarf spheroidal galaxy

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