Hypervelocity Stars in the Gaia era. Revisiting the most extreme stars from the MMT survey

Abstract

The hypervelocity star (HVS) survey conducted at the Multiple Mirror Telescope (MMT) identified 42 B-type stars in the Galactic halo whose radial velocity in the Galactic rest-frame exceeds $+275$kms${}^{-1}$. In order to unravel the nature and origin of those high-velocity outliers, their complete six-dimensional phase space information is needed. To this end, we complemented positions and proper motions from the second data release of {\it Gaia} with revised radial velocities and spectrophotometric distances that are based on a reanalysis of the available MMT spectra of 40 objects using state-of-the-art model spectra and a tailored analysis strategy. The resulting position and velocity vectors for 37 stars were then used as input for a subsequent kinematic investigation to obtain as complete a picture as possible. The combination of projected rotational velocity, position in the Kiel diagram, and kinematic properties suggests that all objects in the sample except two (B576, B598) are very likely to be main sequence stars. While the available data are still not precise enough to constrain the place of origin for 19 program stars, we identified eight objects that either come from the outer rim of the Galactic disk or not from the disk at all, along with ten that presumably stem from the Galactic disk. For almost all of those 18 targets with more or less well-constrained spatial origin, the Galactic center (GC) is disqualified as a possible place of origin. The most notable exception is B576, the origin of which coincides extremely well with the GC when assuming a blue horizontal branch (BHB) nature for it. HVS22 is by far the most extreme object in the sample. Although its origin is completely unconstrained, an ejection from the GC by the Hills mechanism is the most plausible explanation for its current Galactic rest-frame velocity of $1530_{-560}^{+690}$kms${}^{-1}$.

References in corpus (64)

• The Sloan Digital Sky Survey: Technical Summary
• Gaia Data Release 2. Summary of the contents and survey properties
• Correcting for the Effects of Interstellar Extinction
• The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III
• Gaia Data Release 2: The astrometric solution
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very Large Telescope
• Gaia Data Release 2: Photometric content and validation
• Estimating distances from parallaxes
• Ultraviolet Radiation from Evolved Stellar Populations -- I. Models
• Hot subluminous stars
• The Present and Future Mass of the Milky Way Halo
• Discovery of an Unbound Hyper-Velocity Star in the Milky Way Halo
• Spectroscopic Analysis of DA White Dwarfs: Stark Broadening of Hydrogen Lines Including Non-Ideal Effects
• Three Hypervelocity White Dwarfs in Gaia DR2: Evidence for Dynamically Driven Double-Degenerate Double-Detonation Type Ia Supernovae
• The third data release of the Kilo-Degree Survey and associated data products
• The VISTA Science Archive
• Milky Way Mass Models for Orbit Calculations
• HE 0437-5439 -- an unbound hyper-velocity main-sequence B-type star
• US 708 - An unbound hyper-velocity subluminous O star
• A stellar census in globular clusters with MUSE: Binaries in NGC 3201
• Estimating distances from parallaxes. II. Performance of Bayesian distance estimators on a Gaia-like catalogue
• The properties of dynamically ejected runaway and hyper-runaway stars
• MMT Hypervelocity Star Survey III: A Complete Survey of Faint B-type Stars in the Northern Milky Way Halo
• Dynamical ejections of massive stars from young star clusters under diverse initial conditions
• A reanalysis of the Gaia Data Release 2 photometric sensitivity curves using HST/STIS spectrophotometry
• The characteristics of high velocity O and B stars which are ejected from supernovae in binary systems
• The Great Escape: Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*
• Optical atmospheric extinction over Cerro Paranal
• The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
• The Southern Stellar Stream Spectroscopic Survey ($S^5$): Overview, Target Selection, Data Reduction, Validation, and Early Science
• The ELM Survey. VII. Orbital Properties of Low Mass White Dwarf Binaries
• On the origin of high-velocity runaway stars
• An Alternative Origin for Hypervelocity Stars
• Rotation Velocities of Red and Blue Field Horizontal-Branch Stars
• MMT Hypervelocity Star Survey
• A Successful Targeted Search for Hypervelocity Stars
• Flux calibration of medium-resolution spectra from 300 nm to 2500 nm: Model reference spectra and telluric correction
• Gaia DR2 in 6D: Searching for the fastest stars in the Galaxy
• An unusual white dwarf star may be a surviving remnant of a subluminous Type Ia supernova
• Maximum speed of hypervelocity stars ejected from binaries
• Revisiting hypervelocity stars after Gaia DR2
• Testing common classical LTE and NLTE model atmosphere and line-formation codes for quantitative spectroscopy of early-type stars
• A hypervelocity star with a Magellanic origin
• Gaia and the Galactic Center Origin of Hypervelocity Stars
• The First Hypervelocity Star from the LAMOST Survey
• Ejection velocities of high Galactic latitude runaway stars
• Hypervelocity runaways from the Large Magellanic Cloud
• Partly burnt runaway stellar remnants from peculiar thermonuclear supernovae
• LMC origin of the hyper-velocity star HE 0437-5439. Beyond the supermassive black hole paradigm
• Lessons from the curious case of the `fastest' star in Gaia DR2
• Hypervelocity stars in the Gaia era: Runaway B stars beyond the velocity limit of classical ejection mechanisms
• Proper Motions and Trajectories for 16 Extreme Runaway and Hypervelocity Stars
• A new method for an objective, ${\chi }^2$-based spectroscopic analysis of early-type stars
• A Dipole on the Sky: Predictions for Hypervelocity Stars from the Large Magellanic Cloud
• Discovery of two new hypervelocity stars from the LAMOST spectroscopic surveys
• Nearby high-speed stars in Gaia DR2
• A quantitative spectral analysis of 14 hypervelocity stars from the MMT survey
• New nearby hypervelocity stars and their spatial distribution from Gaia DR2
• GALEX Absolute Calibration and Extinction Coefficients Based on White Dwarfs
• The Nature of Hypervelocity Stars and the Time Between Their Formation and Ejection
• A new Hyper-Runaway star discovered from LAMOST and GAIA: ejected almost in the galactic rotation direction
• PG 1610$+$062: a runaway B star challenging classical ejection mechanisms
• Kinematics in galactic tidal tails - A source for Hypervelocity stars?

Cited by in corpus (19)

• 591 high velocity stars in the Galactic halo selected from LAMOST DR7 and Gaia DR2
• Gaia DR3 in 6D: The search for fast hypervelocity stars and constraints on the Galactic Centre environment
• Core-Collapse Supernovae in Binaries as the Origin of Galactic Hyper-Runaway Stars
• Constraints on the Galactic Centre environment from Gaia hypervelocity stars
• On the origins of extreme velocity stars as revealed by large-scale Galactic surveys
• Comparing hypervelocity star populations from the Large Magellanic Cloud and the Milky Way
• Constraints on the Galactic Centre environment from Gaia hypervelocity stars II: The evolved population
• Blue extreme disk-runaway stars with Gaia EDR3
• High Velocity Stars in SDSS/APOGEE DR17
• SHOTGLAS II. MUSE spectroscopy of blue horizontal branch stars in the core of $\omega$ Centauri and NGC 6752
• Constraints on the origins of hypervelocity stars: velocity distribution, mergers and star-formation history
• Probing the shape of the Milky Way dark matter halo with hypervelocity stars: a new method
• Non-thermal emission in hyper-velocity and semi-relativistic stars
• Constraints on the abundance of $0.01c$ stellar engines in the Milky Way
• Runaway blue main-sequence stars at high Galactic latitudes. Target selection with Gaia and spectroscopic identification
• Searching for new Hypervelocity Stars with Gaia DR3 and VLT/FORS2 Spectroscopy
• On Stellar Migration from Andromeda to the Milky Way
• A Recent Supermassive Black Hole Binary in the Galactic Center Unveiled by the Hypervelocity Stars
• Discovery of Galactic center ejected star in DESI DR1