Discovery of an Unbound Hypervelocity Star in the Milky Way Halo

Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J.

doi:10.1086/429378

Cited by 355 publications

(439 citation statements)

References 33 publications

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“…If we select only stars within the overdensity region defined by Abadi et al (2009) the spread reduces to ∼250 km s −1 resulting in a minimum progenitor mass still higher than 10 10 M . Concerning the known satellite galaxies the respective authors of the HVS discovery papers have already excluded a kinematical connection to them (Brown et al 2005(Brown et al , 2006a(Brown et al , 2009aEdelmann et al 2005;Hirsch et al 2005). Since we do not expect such a system to have escaped observations to date, we conclude that a satellite origin for the subsample to be unlikely.…”

Section: Discussionmentioning

confidence: 99%

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Kinematics in galactic tidal tails

Piffl¹,

Williams²,

Steinmetz³

2011

A&A

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Context. Recent observations of stars with unusually high radial velocities in the Galactic stellar halo have raised new interest in so-called hypervelocity stars. Traditionally, it is assumed that the velocities of these stars could only come from an interaction with the supermassive black hole in the Galactic center. It was suggested that stars stripped off a disrupted satellite galaxy could reach similar velocities and leave the Galaxy. Aims. In this work we study the kinematics of tidal debris stars in detail to investigate the implications of the new scenario and the probability that the observed sample of hypervelocity stars could partly develop out of such a galaxy collision. Methods. We used a suite of N-body simulations following the encounter of a satellite galaxy with its Milky Way-type host galaxy to gather statistics on the properties of stripped-off stars. We study especially the orbital energy distribution of this population. Results. We quantify the typical pattern in angular and phase space formed by the debris stars. We further develop a simple stripping model to predict the kinematics of stripped-off stars. We show that the distribution of orbital energies in the tidal debris takes a typical form that can be described quite accurately by a simple function. Based on this we develop a method predicting the energy distribution that allows us to evaluate the significance and the implications of highvelocity stars in satellite tidal debris. Conclusions. Generally the tidal collisions of satellite galaxy produce stars that escape into intragalactic space even if the satellite itself is on a bound orbit. The main parameters determining the maximum energy kick a tidal debris star can get is the initial mass of the satellite and only to a lower extent its orbit. Main contributors to an unbound stellar population created in this way are massive satellites (M sat > 10 9 M ). We thus expect intragalactic stars to have a metallicity higher than the surviving satellite population of the Milky Way. However, the probability that the observed HVS population is significantly contaminated by tidal debris stars appears low in light of our results.

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Section: Discussionmentioning

confidence: 99%

“…Recent observations of 17 stars in the Galactic halo with unusually high velocities (Brown et al 2005;Hirsch et al 2005;Edelmann et al 2005;Brown et al 2006aBrown et al ,b, 2007aBrown et al ,b, 2009aTillich et al 2009) have raised new interest in the topic. By the design of the search strategy, these stars typically have blue colors.…”

Section: Introductionmentioning

confidence: 99%

Kinematics in galactic tidal tails

Piffl¹,

Williams²,

Steinmetz³

2011

A&A

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“…The hypervelocity star HE 0437-5439 (Edelmann et al 2005) is analyzed as a first and very interesting application because the spatial origin of this star is still under debate. When hypervelocity stars were first discovered in 2005 (Brown et al 2005), dynamical ejection from the supermassive black hole at the GC (Hills 1988) was supposed to be their only origin because these stars move so fast that they are unbound to the Galaxy. This scenario was challenged by the discovery of the third hypervelocity star HE 0437-5439 (Edelmann et al 2005), a massive B star, because the travel time from the GC to its present position would exceed its lifetime by a factor of 4.…”

Section: The Hypervelocity Star He 0437-5439 Revisitedmentioning

confidence: 99%

Milky Way mass models for orbit calculations

Irrgang

Wilcox

Tucker

et al. 2013

A&A

227

339

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Context. Studying the trajectories of objects like stars, globular clusters, or satellite galaxies in the Milky Way allows the dark matter halo to be traced but requires reliable models of its gravitational potential. Aims. Realistic, yet simple and fully analytical, models have already been presented in the past. However, improved, as well as new, observational constraints have become available in the meantime, calling for a recalibration of the respective model parameters. Methods. Three widely used model potentials are revisited. By a simultaneous least-squares fit to the observed rotation curve, in-plane proper motion of Sgr A*, local mass/surface density, and the velocity dispersion in Baade's window, parameters of the potentials are brought up-to-date. The mass at large radii -in particular, that of the dark matter halo -is hereby constrained by requiring that the most extreme known halo, blue horizontal-branch star has to be bound to the Milky Way. Results. The Galactic mass models are tuned to yield a very good match to recent observations. The mass of the dark matter halo is -within the limitations of the applied models -estimated in a fully consistent way. As a first application, the trajectory of the hypervelocity star HE 0437-5439 is investigated again to check its suggested origin in the Large Magellanic Cloud (LMC). Conclusions. Despite their simplicity, the presented Milky Way mass models are very able to reproduce all observational constraints. Their analytical and simple form makes them ideally suited for fast and accurate orbit calculations. The LMC cannot be ruled out as HE 0437-5439's birthplace.

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“…Its escape velocity according to the Galactic potential of Ortega et al (2002) is 658 km s −1 . These two stars are the first cool, chemically peculiar stars to join the restricted group of hypervelocity B stars first identified by Brown et al (2005). Figure 9 shows the position of CD-62 • 1346, SDSS J130005.62 + 042201.6 ) and SDSS 121150.27 + 143762.2 (Tillich et al 2011) and the F and G dwarf stars from Holmberg et al (2009) in the e − J z diagram.…”

Section: The V − U and E − J Z Diagramsmentioning

confidence: 80%

CD-62°1346: an extreme halo or hypervelocity CH star?

Pereira

Jilinski

Драке

et al. 2012

A&A

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Context. High-velocity halo stars provide important information about the properties of the extreme Galactic halo. The study of unbound and bound Population II stars permits us to better estimate the mass of the halo. Aims. We carried out a detailed spectroscopic and kinematic study and have significantly refined the distance and the evolutionary state of the star. Methods. Its atmospheric parameters, chemical abundances and kinematical properties were determined using high-resolution optical spectroscopy and employing the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code moog. Results. We found that CD-62 • 1346 is a metal-poor ([Fe/H] = −1.6) evolved giant star with T eff = 5300 K and log g = 1.7. The star exhibits high carbon and s-element abundances typical of CH stars. It is also a lead star. Our kinematic analysis of its 3D space motions shows that this star has a highly eccentric (e = 0.91) retrograde orbit with an apogalactic distance of ∼100 kpc, exceeding by a factor of two the distance of the Magellanic Clouds. The star travels with very high velocity relative to the Galactocentric reference frame (V GRF = 570 km s −1 ). Conclusions. CD-62• 1346 is an evolved giant star and not a subgiant star, as was considered earlier. Whether it is bound or unbound to the Galaxy depends on the assumed mass and on the adopted Galactic potential. We also show that the star HD 5223 is another example of a high-velocity CH star that exceeds the Galactic escape velocity. Possible origins of these two high-velocity stars are briefly discussed. CD-62 • 1346 and HD 5223 are the first red giant stars to join the restricted group of hypervelocity stars.

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Discovery of an Unbound Hypervelocity Star in the Milky Way Halo

Cited by 355 publications

References 33 publications

Kinematics in galactic tidal tails

Kinematics in galactic tidal tails

Milky Way mass models for orbit calculations

CD-62°1346: an extreme halo or hypervelocity CH star?

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