A quantitative spectral analysis of 14 hypervelocity stars from the MMT survey

Abstract

Hypervelocity stars (HVSs) travel so fast that they may leave the Galaxy. The tidal disruption of a binary system by the supermassive black hole in the Galactic center is widely assumed to be their ejection mechanism. To test the hypothesis of an origin in the Galactic center using kinematic investigations, the current space velocities of the HVSs need to be determined. With the advent of Gaia's second data release, accurate radial velocities from spectroscopy are complemented by proper motion measurements of unprecedented quality. Based on a new spectroscopic analysis method, we provide revised distances and stellar ages, both of which are crucial to unravel the nature of the HVSs. We reanalyzed low-resolution optical spectra of 14 HVSs from the MMT HVS survey using a new grid of synthetic spectra, which account for deviations from local thermodynamic equilibrium, to derive effective temperatures, surface gravities, radial velocities, and projected rotational velocities. Stellar masses, radii, and ages were then determined by comparison with stellar evolutionary models that account for rotation. Finally, these results were combined with photometric measurements to obtain spectroscopic distances. The resulting atmospheric parameters are consistent with those of main sequence stars with masses in the range 2.5 - 5.0 $M_{\odot }$. The majority of the stars rotate at fast speeds, providing further evidence for their main sequence nature. Stellar ages range from 90 to 400 Myr and distances (with typical $1\sigma$-uncertainties of about 10-15%) from 30 to 100 kpc. Except for one object (B711), which we reclassify as A-type star, all stars are of spectral type B. The spectroscopic distances and stellar ages derived here are key ingredients for upcoming kinematic studies of HVSs based on Gaia proper motions.

arXiv commentAccepted for publication in A&A (Astronomy and Astrophysics)

References in corpus (21)

• Correcting for the Effects of Interstellar Extinction
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
• 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
• HE 0437-5439 -- an unbound hyper-velocity main-sequence B-type star
• US 708 - An unbound hyper-velocity subluminous O star
• MMT Hypervelocity Star Survey III: A Complete Survey of Faint B-type Stars in the Northern Milky Way Halo
• Populations of rotating stars. - I. Models from 1.7 to 15 Msun at Z = 0.014, 0.006, and 0.002 with Ω/Ωcrit between 0 and 1
• Testing common classical LTE and NLTE model atmosphere and line-formation codes for quantitative spectroscopy of early-type stars
• Ejection velocities of high Galactic latitude runaway stars
• Predicted Space Motions for Hypervelocity and Runaway Stars: Proper Motions and Radial Velocities for the GAIA Era
• LMC origin of the hyper-velocity star HE 0437-5439. Beyond the supermassive black hole paradigm
• 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
• The Nature of the Hyper-Runaway Candidate HIP 60350
• Runaway Stars, Hypervelocity Stars, and Radial Velocity Surveys
• Predicting the hypervelocity star population in Gaia
• HVS7: a chemically peculiar hyper-velocity star
• 'Slow' and Fast Rotators among Hypervelocity Stars
• The Nature of Hypervelocity Stars and the Time Between Their Formation and Ejection

Cited by in corpus (25)

• A hot subdwarf-white dwarf super-Chandrasekhar candidate supernova Ia progenitor
• A stripped helium star in the potential black hole binary LB-1
• Hypervelocity stars in the Gaia era: Runaway B stars beyond the velocity limit of classical ejection mechanisms
• A new class of Roche lobe-filling hot subdwarf binaries
• 591 high velocity stars in the Galactic halo selected from LAMOST DR7 and Gaia DR2
• A quantitative in-depth analysis of the prototype sdB+BD system SDSS J08205+0008 revisited in the Gaia era
• A proto-helium white dwarf stripped by a substellar companion via common-envelope ejection -- Uncovering the true nature of a candidate hypervelocity B-type star
• Radial velocity variability and evolution of hot subdwarf stars
• Neutron stars colliding with binary companions: formation of hypervelocity stars, pulsar planets, bumpy superluminous supernovae and Thorne-Żytkow objects
• Hypervelocity Stars in the Gaia era. Revisiting the most extreme stars from the MMT survey
• PG 1610$+$062: a runaway B star challenging classical ejection mechanisms
• $\gamma$ Columbae: the recently stripped, pulsating core of a massive star
• The OmegaWhite Survey for Short-Period Variable Stars VII: High amplitude, short period blue variables
• Blue extreme disk-runaway stars with Gaia EDR3
• SHOTGLAS II. MUSE spectroscopy of blue horizontal branch stars in the core of $\omega$ Centauri and NGC 6752
• A spectroscopic and kinematic survey of fast hot subdwarfs
• EPIC 216747137: a new HW Vir eclipsing binary with a massive sdOB primary and a low-mass M-dwarf companion
• The first massive compact companion in a wide orbit around a hot subdwarf star
• A 500 pc volume-limited sample of hot subluminous stars II. Atmospheric parameters, mass distribution, and kinematics
• Eclipsing Binaries Found by the EREBOS Project: Gaia DR2 6097540197980557440 -- A Deeply Eclipsing sdB+dM System
• Where are the binaries? -- Searching for blue horizontal-branch stars in binary systems in the inner Galactic Halo
• On Stellar Migration from Andromeda to the Milky Way
• Hot subdwarf stars from the Hamburg Quasar Survey
• Runaway blue main-sequence stars at high Galactic latitudes. Target selection with Gaia and spectroscopic identification
• Discovery of a double white dwarf in the Galactic globular cluster NGC 6397