Chemical Abundance Analysis of Three $\alpha$-Poor, Metal-Poor Stars in the Ultra-Faint Dwarf Galaxy Horologium I

Abstract

We present chemical abundance measurements of three stars in the ultra-faint dwarf galaxy Horologium I, a Milky Way satellite discovered by the Dark Energy Survey. Using high resolution spectroscopic observations we measure the metallicity of the three stars as well as abundance ratios of several $\alpha$-elements, iron-peak elements, and neutron-capture elements. The abundance pattern is relatively consistent among all three stars, which have a low average metallicity of [Fe/H] $\sim -2.6$ and are not $\alpha$-enhanced ([$\alpha$/Fe] $\sim 0.0$). This result is unexpected when compared to other low-metallicity stars in the Galactic halo and other ultra-faint dwarfs and hints at an entirely different mechanism for the enrichment of Hor I compared to other satellites. We discuss possible scenarios that could lead to this observed nucleosynthetic signature including extended star formation, a Population III supernova, and a possible association with the Large Magellanic Cloud.

References in corpus (84)

• The chemical composition of the Sun
• Where are the missing galactic satellites?
• The observed properties of dwarf galaxies in and around the Local Group
• The Dartmouth Stellar Evolution Database
• The Nucleosynthetic Signature of Population III
• Too big to fail? The puzzling darkness of massive Milky Way subhaloes
• Tracing Galaxy Formation with Stellar Halos I: Methods
• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• The Field of Streams: Sagittarius and its Siblings
• Stellar Chemical Signatures And Hierarchical Galaxy Formation
• Nucleosynthesis and Evolution of Massive Metal-Free Stars
• Optimal Techniques in Two-dimensional Spectroscopy: Background Subtraction for the 21st Century
• Forming the First Stars in the Universe: The Fragmentation of Primordial Gas
• Eight New Milky Way Companions Discovered in First-Year Dark Energy Survey Data
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• Near-Field Cosmology with Metal-Poor Stars
• Eight Ultra-faint Galaxy Candidates Discovered in Year Two of the Dark Energy Survey
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• Tracing Galaxy Formation with Stellar Halos II: Relating Substructure in Phase- and Abundance-Space to Accretion Histories
• R-process enrichment from a single event in an ancient dwarf galaxy
• Non-LTE calculations for neutral Na in late-type stars using improved atomic data
• The Most Metal-Poor Stars. II. Chemical Abundances of 190 Metal-Poor Stars Including 10 New Stars With [Fe/H] < -3.5
• The Quenching of the Ultra-Faint Dwarf Galaxies in the Reionization Era
• The Abundances of Neutron Capture Species in the Very Metal-Poor Globular Cluster M15: An Uniform Analysis of RGB and RHB Stars
• CH in stellar atmospheres: an extensive linelist
• High-Resolution Spectroscopy of Extremely Metal-Poor Stars in the Least Evolved Galaxies: Ursa Major II and Coma Berenices
• Lambda-Cold Dark Matter, Stellar Feedback, and the Galactic Halo Abundance Pattern
• Segue 1: An Unevolved Fossil Galaxy from the Early Universe
• "Galaxy," Defined
• New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars
• The Highly Unusual Chemical Composition of the Hercules Dwarf Spheroidal Galaxy
• Complete element abundances of nine stars in the r-process galaxy Reticulum II
• Improved Laboratory Transition Probabilities for Neutral Chromium and Re-determination of the Chromium Abundance for the Sun and Three Stars
• Line lists for the A2PI-X2Sigma+ (red) and {B2Sigma+-X2Sigma} (violet) Systems of CN, 13C14N, and 12C15N, and Application to Astronomical Spectra
• Chemical Enrichment in the Faintest Galaxies: the Carbon and Iron Abundance Spreads in the Boötes I Dwarf Spheroidal Galaxy and the Segue 1 System
• Complexity on Small Scales III: Iron and alpha Element Abundances in the Carina Dwarf Spheroidal Galaxy
• Detailed Chemical Abundances in the r-Process-Rich Ultra-Faint Dwarf Galaxy Reticulum 2
• A Magellanic Origin of the DES Dwarfs
• Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II
• Farthest Neighbor: The Distant Milky Way Satellite Eridanus II
• Multi-Element Abundance Measurements from Medium-Resolution Spectra. I. The Sculptor Dwarf Spheroidal Galaxy
• Multi-Element Abundance Measurements from Medium-Resolution Spectra. IV. Alpha Element Distributions in Milky Way Dwarf Satellite Galaxies
• 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
• Chemical abundances in LMC stellar populations I. The Inner disk sample Based on observations collected at the VLT UT2 telescope
• New Extremely Metal-Poor Stars in the Galactic Halo
• Stellar Archaeology -- Exploring the Universe with Metal-Poor Stars
• Kinematics and chemistry of recently discovered Reticulum 2 and Horologium 1 dwarf galaxies
• Horologium II: a Second Ultra-faint Milky Way Satellite in the Horologium Constellation
• An R-process enhanced star in the dwarf galaxy Tucana III
• Connecting the first galaxies with ultra faint dwarfs in the Local Group: chemical signatures of Population~III stars
• Chemical abundances in LMC stellar populations. II. The bar sample
• The NACRE Thermonuclear Reaction Compilation and Big Bang Nucleosynthesis
• High-Resolution Spectroscopy of Extremely Metal-Poor Stars in the Least Evolved Galaxies: Leo IV
• Deriving Stellar Effective Temperatures of Metal-Poor Stars with the Excitation Potential Method
• Uncovering the Chemical Signature of the First Stars in the Universe
• Elemental Abundances and their Implications for the Chemical Enrichment of the Boötes~I Ultra-Faint Galaxy
• Chemical Signatures of the First Galaxies: Criteria for One-Shot Enrichment
• Magellan/M2FS Spectroscopy of Tucana 2 and Grus 1
• Fe I Oscillator Strengths for the Gaia-ESO Survey
• Nearest Neighbor: The Low-Mass Milky Way Satellite Tucana III
• Satellites of LMC-Mass Dwarfs: Close Friendships Ruined by Milky Way Mass Halos
• Triangulum II: Not Especially Dense After All
• Improved Ni I log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937
• Iron-Group Abundances in the Metal-Poor Main Sequence Turnoff Star HD~84937
• Galactic Archaeology. The dwarfs that survived and perished
• The Distribution of Alpha Elements in Ultra-Faint Dwarf Galaxies
• Improved Laboratory Transition Probabilities for Er II and Applications to the Erbium Abundances of the Sun and Five r-Process Rich, Metal-Poor Stars
• Identifying true satellites of the Magellanic Clouds
• Discovery of a Faint Outer Halo Milky Way Star Cluster in the Southern Sky
• Preserving chemical signatures of primordial star formation in the first low-mass stars
• High-resolution spectroscopy of extremely metal-poor stars in the least evolved galaxies: Bootes II
• Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy
• The chemical evolution of the Bootes I ultra-faint dwarf galaxy
• The metal-poor Knee in the Fornax Dwarf Spheroidal Galaxy
• Chemical Signatures of the First Supernovae in the Sculptor Dwarf Spheroidal Galaxy
• Chemical Diversity in the Ultra-faint Dwarf Galaxy Tucana II
• Abundance ratios of red giants in low mass ultra faint dwarf spheroidal galaxies
• Digging deeper into the Southern skies: a compact Milky-Way companion discovered in first-year Dark Energy Survey data
• The barium isotopic mixture for the metal-poor subgiant star HD140283
• X-Shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars
• Detailed Abundance Analysis of the Brightest Star in Segue 2, the Least Massive Galaxy
• Gemini/GRACES Spectroscopy of Stars in Triangulum II
• Tagging the Chemical Evolution History of the Large Magellanic Cloud Disk
• Chemical abundances of metal-poor RR Lyrae stars in the Magellanic Clouds

Cited by in corpus (35)

• The Faintest Dwarf Galaxies
• The Orbital Histories of Magellanic Satellites Using Gaia DR2 Proper Motions
• Gaia Proper Motions and Orbits of the Ultra-Faint Milky Way Satellites
• Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies
• Chemical Abundances in the Ultra-Faint Dwarf Galaxies Grus I and Triangulum II: Neutron-Capture Elements as a Defining Feature of the Faintest Dwarfs
• Revised and new proper motions for confirmed and candidate Milky Way dwarf galaxies
• Proper motions of Milky Way Ultra-Faint satellites with $Gaia$ DR2 $\times$ DES DR1
• Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III
• Chemical Abundances of new member stars in the Tucana II dwarf galaxy
• Chemical Abundance Analysis of Tucana III, the Second $r$-process Enhanced Ultra-Faint Dwarf Galaxy
• The Origin of r-process Enhanced Metal-Poor Halo Stars In Now-Destroyed Ultra-Faint Dwarf Galaxies
• The R-Process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5-455510
• Chemical Analysis of the Ultra-Faint Dwarf Galaxy Grus~II. Signature of high-mass stellar nucleosynthesis
• Detailed chemical abundances of stars in the outskirts of the Tucana II ultra-faint dwarf galaxy
• Metallicity Distribution Functions of 13 Ultra-Faint Dwarf Galaxy Candidates from Hubble Space Telescope Narrowband Imaging
• Stellar mass segregation as separating classifier between globular clusters and ultra-faint dwarf galaxies
• How much metals did the first stars provide to the ultra-faint dwarfs?
• Simulating Metal Mixing of Both Common and Rare Enrichment Sources in a Low Mass Dwarf Galaxy
• The R-Process Alliance: Discovery of a low-alpha, r-Process-Enhanced Metal-Poor Star in the Galactic Halo
• Ancient Very Metal-Poor Stars Associated With the Galactic Disk in the H3 Survey
• High Resolution Optical Spectroscopy of Stars in the Sylgr Stellar Stream
• The SAMI-Fornax Dwarfs Survey III: Evolution of [$\alpha$/Fe] in dwarfs, from Galaxy Clusters to the Local Group
• Metallicity Distribution Function of the Eridanus~II Ultra-Faint Dwarf Galaxy from Hubble Space Telescope Narrow-band Imaging
• s-process Enirchment of Ultrafaint Dwarf Galaxies
• The impact of carbon and oxygen abundances on the metal-poor initial mass function
• Chemical abundance analysis of extremely metal-poor stars in the Sextans dwarf spheroidal galaxy
• Chemical evolution of ultra-faint dwarf galaxies: testing the IGIMF
• The formation of the Milky Way halo and its dwarf satellites: a NLTE-1D abundance analysis. IV. Segue 1, Triangulum II, and Coma Berenices UFDs
• G112-43/44: A metal-poor binary star with a unique chemical composition and kinematics like the Helmi streams
• Empirical Constraints on Core Collapse Supernova Yields using Very Metal Poor Damped Lyman Alpha Absorbers
• The Challenge to MOND from ultra faint dwarf galaxies
• The oldest stars with low neutron-capture element abundances and origins in ancient dwarf galaxies
• Measuring Resolved Star Formation Histories from High-Precision Color-Magnitude Diagrams with StarFormationHistories.jl
• A second-generation star in a relic dwarf galaxy
• Understanding Stellar Mass-Metallicity and Size Relations in Simulated Ultra-Faint Dwarf Galaxies