High-speed stars. II. An unbound star, young stars, bulge metal-poor stars, and Aurora candidates

Abstract

The data from the Gaia satellite led us to revise our conception of the Galaxy structure and history. Hitherto unknown components have been discovered and a deep re-thinking of what the Galactic halo is is in progress. We selected from the Gaia catalogue stars with extreme transverse velocities with respect to the Sun ($|V_T|>500$ and observed them with FORS2 at the ESO VLT, to classify them using both their chemical and dynamical properties. Two apparently young stars, identified in paper\,I, were observed with UVES. We derived abundances for Na, Mg, Ca, Ti, Mn, and Fe, analysing the spectra with while for Ba we used line profile fitting. We computed actions from parallaxes and kinematical data. The stars span the metallicity range $Fe/H-0.5$ with $Fe/H=-1.6$. Star GHS143 has a total speed of about 1440 which is almost three times faster than the local escape velocity of 522 strongly implying this star is unbound to the Galaxy. Remarkably, this star is not escaping from the Galaxy, but it is falling into it. Ten stars are apparently young with masses in excess of 1.3M. Their interpretation as evolved blue stragglers is doubtful. The existence of a young metal-poor population is possible. The two stars observed with UVES show no lithium, suggesting they are blue stragglers. We detected a metal-poor population, confined to the bulge, that we call SpiteF, and argue that it is the result of a recent accretion event. We detect 102 candidates of the Aurora population that should have formed prior to the formation of the disc. Our sample is non-homogeneous and mainly retrograde. The stars are metal poor, and 23<!PCT!> have Fe/H -2.0$. Our selection is efficient at finding very metal-poor stars, but it selects peculiar populations.

Astronomy and Astrophysics - In press

References in corpus (55)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• galpy: A Python Library for Galactic Dynamics
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• Gaia EDR3 view on Galactic globular clusters
• The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• The Dual Origin of Stellar Halos
• NLTE abundances of Mn in a sample of metal-poor stars
• From dawn till disk: Milky Way's turbulent youth revealed by the APOGEE+Gaia data
• The GIRAFFE Inner Bulge Survey (GIBS) III. Metallicity distributions and kinematics of 26 Galactic bulge fields
• NLTE determination of the sodium abundance in a homogeneous sample of extremely metal-poor stars
• The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
• Kinematics at the Edge of the Galactic Bulge: Evidence for Cylindrical Rotation
• Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies
• The Poor Old Heart of the Milky Way
• Selecting accreted populations: metallicity, elemental abundances, and ages of the Gaia-Sausage-Enceladus and Sequoia populations
• galstreams: A Library of Milky Way Stellar Stream Footprints and Tracks
• A Sequoia in the Garden: FSR 1758 - Dwarf Galaxy or Giant Globular Cluster?
• Growth of galactic bulges by mergers. II. Low-density satellites
• The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3
• The Pristine survey X: a large population of low-metallicity stars permeates the Galactic disk
• Maximum speed of hypervelocity stars ejected from binaries
• Reconstructing the Disrupted Dwarf Galaxy $Gaia$-Sausage/Enceladus Using its Stars and Globular Clusters
• On feathers, bifurcations and shells: the dynamics of tidal streams across the mass scale
• The Pristine Inner Galaxy Survey (PIGS) I: Tracing the kinematics of metal-poor stars in the Galactic bulge
• Stellar triples on the edge; Comprehensive overview of the evolution of destabilised triples leading to stellar and binary exotica
• GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos
• Nitrogen enrichment and clustered star formation at the dawn of the Galaxy
• The Bulge Radial Velocity Assay for RR Lyrae stars (BRAVA-RR) DR2: a Bimodal Bulge?
• Kinematics and Metallicities in the Bootes III Stellar Overdensity: a Disrupted Dwarf Galaxy?
• New light on Galactic post-asymptotic giant branch stars. I. First distance catalogue
• A new class of fossil fragments from the hierarchical assembly of the Galactic bulge
• The bimodal [Mg/Fe] versus [Fe/H] bulge sequence as revealed by APOGEE DR14
• The COMBS Survey -- II. Distinguishing the Metal-Poor Bulge from the Halo Interlopers
• Gaia DR3 in 6D: The search for fast hypervelocity stars and constraints on the Galactic Centre environment
• The COMBS survey I: Chemical Origins of Metal-Poor Stars in the Galactic Bulge
• The Pristine Inner Galaxy Survey (PIGS) V: a chemo-dynamical investigation of the early assembly of the Milky Way with the most metal-poor stars in the bulge
• Fast rotating Blue Stragglers prefer loose clusters
• Spectral Energy Distribution of Blue Stragglers in the core of 47 Tucanae
• Exploring the diversity and similarity of radially anisotropic Milky Way-like stellar haloes: implications for disrupted dwarf galaxy searches
• Determining thermal dust emission from Planck HFI data using a sparse, parametric technique
• The Most Metal-poor Stars in the Inner Bulge
• Discovery of A candidate Hypervelocity star originated from the Sagittarius Dwarf Spheroidal galaxy
• Spinning like a Blue Straggler: the population of fast rotating Blue Straggler stars in Omega Centauri
• On the origins of extreme velocity stars as revealed by large-scale Galactic surveys
• Young giants of intermediate mass Evidence of rotation and mixing
• The accretion history of the Milky Way. I. How it shapes globular clusters and dwarf galaxies
• 60 candidate high-velocity stars originating from the Sagittarius dwarf spheroidal galaxy in Gaia EDR3
• The Gaia RVS benchmark stars II. A sample of stars selected for their Gaia high radial velocity

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• SDSS J102915.14+172927.9: Revisiting the chemical pattern
• Discovery of a pair of very metal-poor stars enriched in neutron-capture elements: The proto-disk r-II star BPS CS 29529-0089 and the Gaia-Sausage-Enceladus r-I star TYC 9219-2422-1
• High speed stars: III. Detailed abundances and binary nature of the extreme speed star GHS143
• The Gaia RVS benchmark stars II. A sample of stars selected for their Gaia high radial velocity
• On the Use of Field RR Lyrae as Galactic Probes -- VIII. Early Formation of the Galactic Spheroid
• A Sequoia stellar candidate with very high 7Li and 9Be
• Gaia DR3 high radial velocity stars: Genuine fast-moving objects or outliers?