Abundance Patterns of $\alpha$ and Neutron-capture Elements in the Helmi Stream

Abstract

We identified 8 additional stars as members of the Helmi stream (HStr) in the combined GALAH+ DR3 and $Gaia$ EDR3 catalog. By consistently reevaluating claimed members from the literature, we consolidate a sample of 22 HStr stars with parameters determined from high-resolution spectroscopy and spanning a considerably wider (by $\sim$0.5 dex) metallicity interval ($-2.5\lesssim [Fe/H]<-1.0$) than previously reported. Our study focuses on $\alpha$ (Mg and Ca) and neutron-capture (Ba and Eu) elements. We find that the chemistry of HStr is typical of dwarf spheroidal (dSph) galaxies, in good agreement with previous $N$-body simulations of this merging event. Stars of HStr constitute a clear declining sequence in $[\alpha /Fe]$ for increasing metallicity up to $[Fe/H]\sim -1.0$. Moreover, stars of HStr show a median value of $+$0.5 dex for $[Eu/Fe]$ with a small dispersion ($\pm$0.1 dex). Every star analyzed with $[Fe/H]<-1.2$ belong to the $r$-process enhanced ($[Eu/Fe]>+0.3$ and $[Ba/Eu]<0.0$) metal-poor category, providing remarkable evidence that, at such low-metallicity regime, stars of HStr experienced enrichment in neutron-capture elements predominantly via $r$-process nucleosynthesis. Finally, the extended metallicity range also suggests an increase in $[Ba/Eu]$ for higher $[Fe/H]$, in conformity with other surviving dwarf satellite galaxies of the Milky Way.

arXiv comment9 pages (+2 appendix), 4 figures. Accepted for publication in ApJ Letters

References in corpus (44)

• The Sloan Digital Sky Survey: Technical Summary
• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• Multi-messenger Observations of a Binary Neutron Star Merger
• Local Kinematics and the Local Standard of Rest
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• Gaia Early Data Release 3: The astrometric solution
• Star Formation Histories, Abundances and Kinematics of Dwarf Galaxies in the Local Group
• SEGUE: A Spectroscopic Survey of 240,000 stars with g=14-20
• The mass distribution and gravitational potential of the Milky Way
• Co-formation of the Galactic disc and the stellar halo
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• The GALAH+ Survey: Third Data Release
• Debris streams in the solar neighbourhood as relicts from the formation of the Milky Way
• AGAMA: Action-based galaxy modelling architecture
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• VLT/UVES Abundances in Four Nearby Dwarf Spheroidal Galaxies: I. Nucleosynthesis and Abundance Ratios
• Abundances and Kinematics of Field Halo and Disk Stars I: Observational Data and Abundance Analysis
• The Stellar Abundances for Galactic Archeology (SAGA) Database - Compilation of the Characteristics of Known Extremely Metal-Poor Stars
• Streams, substructures and the early history of the Milky Way
• The stellar halo of the Galaxy
• StarHorse: A Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars
• A high resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy
• Complete element abundances of nine stars in the r-process galaxy Reticulum II
• From Nuclei to the Cosmos: Tracing Heavy-Element Production with the Oldest Stars
• From the bulge to the outer disc: StarHorse stellar parameters, distances, and extinctions for stars in APOGEE DR16 and other spectroscopic surveys
• The $R$-Process Alliance: First Release from the Southern Search for $r$-Process-Enhanced Stars in the Galactic Halo
• Dynamical Relics of the Ancient Galactic Halo
• Characterization and history of the Helmi streams with Gaia DR2
• Characterizing the Chemistry of the Milky Way Stellar Halo: Detailed Chemical Analysis of a Metal-Poor Stellar Stream
• VLT/FLAMES high-resolution chemical abundances in Sculptor: a textbook dwarf spheroidal galaxy
• Halo Substructure in the SDSS-Gaia Catalogue : Streams and Clumps
• VLT/FLAMES spectroscopy of red giant branch stars in the Fornax dwarf spheroidal galaxy
• Stellar Abundances for Galactic Archaeology Database IV - Compilation of Stars in Dwarf Galaxies
• The R-process Alliance: First Magellan/MIKE Release from the Southern Search for R-Process-enhanced Stars
• Elevated r-process enrichment in Gaia Sausage and Sequoia
• Chemo-dynamics of outer halo dwarf stars, including \textit{Gaia}-Sausage and \textit{Gaia}-Sequoia candidates
• Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys
• The R-Process Alliance: Chemo-Dynamically Tagged Groups of Halo $r$-Process-Enhanced Stars Reveal a Shared Chemical-Evolution History
• The S2 Stream: the shreds of a primitive dwarf galaxy
• The Hamburg/ESO R-process Enhanced Star survey (HERES) IX. Constraining pure r-process Ba/Eu abundance ratio from observations of r-II stars
• R-process-rich stellar streams in the Milky Way
• Targeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy

Cited by in corpus (20)

• Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G=18.5
• StarHorse results for spectroscopic surveys + Gaia DR3: Chrono-chemical populations in the solar vicinity, the genuine thick disk, and young-alpha rich stars
• The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3
• Reconstructing the Disrupted Dwarf Galaxy $Gaia$-Sausage/Enceladus Using its Stars and Globular Clusters
• Dynamically Tagged Groups of Metal-Poor Stars from the Best \& Brightest Survey
• High-precision chemical abundances of Galactic building blocks. II. Revisiting the chemical distinctness of the Helmi streams
• Origin of highly $r$-process-enhanced stars in a cosmological zoom-in simulation of a Milky Way-like galaxy
• Dynamically Tagged Groups of Metal-Poor Stars II. The Radial Velocity Experiment Data Release 6
• Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ($[Fe/H]\lesssim -3$) Regime
• The observable properties of galaxy accretion events in Milky Way-like galaxies in the FIRE-2 cosmological simulations
• Extending the Chemical Reach of the H3 Survey: Detailed Abundances of the Dwarf-galaxy Stellar Stream Wukong/LMS-1
• Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. III. Dynamically Tagged Groups and Chemodynamical Properties
• Unveiling the past evolution of the progenitor of the Helmi streams
• Exploring the chemodynamics of metal-poor stellar populations
• Chemical Abundances of the Typhon Stellar Stream
• Chemodynamical Properties and Ages of Metal-Poor Stars in S-PLUS
• Nearby stellar substructures in the Galactic halo from DESI Milky Way Survey Year 1 Data Release
• The Chemodynamical Nature of the Triangulum-Andromeda Overdensity
• The neutron-capture and alpha-elements abundance ratios scatter in old stellar populations. Cosmological simulations of the stellar halo
• HE0144-4657: A Carbon-Enhanced Ultra Metal-Poor Star ([Fe/H] ~ -4.1) from the Helmi Stream Disrupted Dwarf Galaxy