Optical high-resolution spectroscopy of 14 young $\alpha$-rich stars

Abstract

We report chemical abundances of 14 young $\alpha$-rich stars including neutron-capture elements based on high-quality optical spectra from HIRES/Keck I and differential line-by-line analysis. From the comparison of the abundance patterns of young $\alpha$-rich stars to those of nearby bright red giants with a similar metallicity range ($-0.7<[Fe/H]<-0.2$), we confirm their high $\alpha$-element abundances reported by previous studies based on near-infrared spectroscopy. We reveal for the first time low abundances of $s$-process elements and high abundances of $r$-process elements. All the abundances are consistent with those seen in typical $\alpha$-rich population of the Galactic disk, and no abundance anomalies are found except for Li-enhancement in one object previously reported and mild enhancement of Na in two stars. In particular, the lack of $s$-process enhancement excludes the hypothesis that mass transfer from asymptotic giant branch stars plays an important role in the formation of young $\alpha$-rich stars. The high frequency of radial velocity variation (more than $50\%$) is also confirmed. We argue that mass transfer from low-mass red giants is the likely dominant formation mechanism for young $\alpha$-rich stars.

arXiv commentAccepted for publication in ApJ

References in corpus (43)

• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The NumPy array: a structure for efficient numerical computation
• The Sloan Digital Sky Survey: Technical Summary
• The chemical composition of the Sun
• The Gaia mission
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood
• Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis
• Production of all the r-process nuclides in the dynamical ejecta of neutron star mergers
• The Ages of Stars
• A Three-Dimensional Map of Milky-Way Dust
• Neutron star mergers versus core-collapse supernovae as dominant r-process sites in the early Galaxy
• Stellar yields from metal-rich asymptotic giant branch models
• Ensemble Asteroseismology of Solar-Type Stars with the NASA Kepler Mission
• Synthetic Stellar Photometry - I. General considerations and new transformations for broad-band systems
• Near-UV Observations of HD221170: New Insights into the Nature of r-Process-Rich Stars
• Galactic archaeology: mapping and dating stellar populations with asteroseismology of red-giant stars
• Both accurate and precise gf-values for FeII lines
• The Solar Twin Planet Search. I. Fundamental parameters of the stellar sample
• Young [$\alpha$/Fe]-enhanced stars discovered by CoRoT and APOGEE: What is their origin?
• The intermediate r-process in core-collapse supernovae driven by the magneto-rotational instability
• Lithium Abundances of Extremely Metal-Poor Turn-off Stars
• Improved Laboratory Transition Probabilities for Neutral Chromium and Re-determination of the Chromium Abundance for the Sun and Three 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 origin and evolution of r- and s-process elements in the Milky Way stellar disk
• Improved Ti II log(gf) Values and Abundance Determinations in the Photospheres of the Metal-Poor Star HD 84937
• Fe I Oscillator Strengths for the Gaia-ESO Survey
• Enrichment of r-process elements in dwarf spheroidal galaxies in chemo-dynamical evolution model
• An accurate and self-consistent chemical abundance catalogue for the APOGEE/Kepler sample
• The temporal evolution of neutron-capture elements in the Galactic discs
• Neutron Star Mergers as the Origin of r-Process Elements in the Galactic Halo Based on the Sub-halo Clustering Scenario
• Improved Ni I log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937
• Binary stars in the Galactic thick disc
• Cannibals in the thick disk: the young $\alpha -$rich stars as evolved blue stragglers
• Wavelength Accuracy of the Keck HIRES Spectrograph and Measuring Changes in the Fine Structure Constant
• Experimental and theoretical oscillator strengths of Mg I for accurate abundance analysis
• Determining Ages of APOGEE Giants with Known Distances
• GRACES observations of young [alpha/Fe]-rich stars
• KIC 9821622: An interesting lithium-rich giant in the Kepler field
• Transition properties of potassium atom
• On the observational characteristics of lithium-enhanced giant stars in comparison with normal red giants

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• Cannibals in the thick disk II -- Radial-velocity monitoring of the young alpha-rich stars
• The Flattening Metallicity Gradient in the Milky Way's Thin Disk
• Star Formation Timescales of the Halo Populations from Asteroseismology and Chemical Abundances
• Stragglers of the thick disc
• The Gaia-ESO Survey: Spectroscopic-asteroseismic analysis of K2 stars in Gaia-ESO
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data II. Chrono-chemo-kinematics of the disc
• J01020100-7122208: an accreted evolved blue straggler that wasn't ejected from a supermassive black hole
• Concerning Li-rich status of KIC~9821622: A Kepler field RGB star reported as Li-rich Giant
• Exploring the History of Stellar Mergers with Chemistry: Examining the Origins of Massive $\alpha$-Enriched Stars using Carbon Isotope Ratios
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