The Hyper-MUCHFUSS project: probing the Galactic halo with sdB stars

Abstract

High-velocity stars in the Galactic halo, e.g. the so-called hyper-velocity stars (HVS), are important tracers of the properties of the dark matter halo, in particular its mass. Based on the SDSS DR6 spectral database a search for the fastest stars among hot subdwarfs (sdB) in the halo is carried out to identify HVS, unbound to the Galaxy, and bound population II stars in order to derive a lower limit to the halo mass. The radial velocity measurements were verified at several telescopes to exclude radial velocity variable stars. Out of 88 stars observed in the follow-up campaign 39 stars were found to have constant radial velocities. For twelve of them we measured a proper motion significantly different from zero and obtained spectroscopic distances from quantitative spectral analysis to construct the full 6D phase space information for a kinematical study. The programme sdBs can be distinguished into two kinematical groups, one (G1) with low Galactic rotation typical of halo stars and a second one (G2) with rapid retrograde motion. The G1 objects crossed the Galactic plane in the central bulge, whereas the G2 stars did in the outer Galactic disc. J1211+1437 (G2) is a HVS candidate, as it is unbound to the Galaxy if the standard Galactic potential is adopted. We conclude that in the ejection scenario G1 stars might have been formed via the slingshot mechanism that invokes acceleration by tidal interaction of a binary with the central supermassive black hole. The G2 stars, however, would originate in the outskirts of the Galactic disc and not in the central bulge. J1211+1437 is the first unbound subdwarf B star, for which we can rule out the slingshot mechanism. Alternatively, we may assume that the stars are old population II stars and therefore have to be bound. Then the kinematics of J1211+1437 set a lower limit of 2 x 10^12 Msun to the mass of the Galactic dark matter halo.

12 pages, 11 figures, accepted for publication in A&A

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Cited by in corpus (34)

• Hot subluminous stars
• Milky Way Mass Models for Orbit Calculations
• MMT Hypervelocity Star Survey III: A Complete Survey of Faint B-type Stars in the Northern Milky Way Halo
• The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
• Mass-accreting white dwarfs and type Ia supernovae
• Hot subdwarf binaries from the MUCHFUSS project - Analysis of 12 new systems and a study of the short-period binary population
• The MUCHFUSS project - Searching for hot subdwarf binaries with massive unseen companions: Survey, target selection and atmospheric parameters
• The population of hot subdwarf stars studied with Gaia -- IV. Catalogues of hot subluminous stars based on Gaia EDR3
• He-accreting carbon-oxygen white dwarfs and type Ia supernovae
• The catalogue of radial velocity variable hot subluminous stars from the MUCHFUSS project
• Binaries discovered by the MUCHFUSS project SDSS J08205+0008 - An eclipsing subdwarf B binary with brown dwarf companion
• Alone but not lonely: Observational evidence that binary interaction is always required to form hot subdwarf stars
• Ejection and Capture Dynamics in Restricted Three-Body Encounters
• 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
• CD-62\degree1346: an extreme halo or hypervelocity CH~star?
• The Nature of Hypervelocity Stars and the Time Between Their Formation and Ejection
• Orbital solutions of eight close sdB binaries and constraints on the nature of the unseen companions
• The fast rotating, low gravity subdwarf B star EC 22081-1916 - Remnant of a common envelope merger event
• Tidal breakup of triple stars in the Galactic Centre
• Spectroscopic twin to the hypervelocity sdO star US 708 and three fast sdB stars from the Hyper-MUCHFUSS project
• Hyper-runaway and hypervelocity white dwarf candidates in \textit{Gaia} Data Release 3: possible remnants from Ia/Iax supernova explosions or dynamical encounters
• An extremely fast halo hot subdwarf star in a wide binary system
• Discovery of a second pulsating intermediate helium-enriched sdOB star
• Candidate hypervelocity stars of spectral type G and K revisited
• The Unseen Population of F to K-type Companions to Hot Subdwarf Stars
• Predicted spatial and velocity distributions of ejected companion stars of helium accretion-induced thermonuclear supernovae
• Hypervelocity star candidates from Gaia DR2 and DR3 proper motions and parallaxes
• An ancient F-type subdwarf from the halo crossing the Galactic plane
• The Origin of HVS17, an Unbound Main Sequence B Star at 50 kpc
• A spectroscopic and kinematic survey of fast hot subdwarfs
• 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
• Probing modified Newtonian dynamics with hypervelocity stars
• MUCHFUSS - Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS