Segue-2 Limits on Metal-Rich Old-Population Hypervelocity Stars in the Galactic Halo

Kollmeier, Juna A.; Gould, Andrew; Rockosi, Constance M.; Knapp, G. R.; Johnson, Jennifer A.; Morrison, Heather; Harding, Paul; Weaver, B. A.

doi:10.1088/0004-637x/723/1/812

Cited by 38 publications

(45 citation statements)

References 48 publications

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“…hypervelocity trajectories in this small region (e.g., Hills 1988;Yu & Tremaine 2003;Bromley et al 2006;Kenyon et al 2014;Hamers & Perets 2017); observations support this assessment (e.g., Brown et al 2006a;Kollmeier & Gould 2007;Kollmeier et al 2009Kollmeier et al , 2010Brown et al 2014). On the basis of the relatively short lifetimes of giants compared to these main sequence stars, the likelihood of observing an evolved star in this region is even lower.…”

Section: Comparison With Theorymentioning

confidence: 88%

Nearby High-speed Stars in Gaia DR2

Bromley

Kenyon

Brown

et al. 2018

ApJ

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We investigate the nature of nearby (10-15 kpc) high-speed stars in the Gaia DR2 archive identified on the basis of parallax, proper motion and radial velocity. Together with a consideration of their kinematic, orbital, and photometric properties, we develop a novel strategy for evaluating whether high speed stars are statistical outliers of the bound population or unbound stars capable of escaping the Galaxy. Out of roughly 1.5 million stars with radial velocities, proper motions, and 5-σ parallaxes, we identify just over 100 high-speed stars. Of these, only two have a nearly 100% chance of being unbound, with indication that they are not just bound outliers; both are likely hyperrunaway stars. The rest of the high speed stars are likely statistical outliers. We use the sample of high-speed stars to demonstrate that radial velocity alone provides a poor discriminant of nearby, unbound stars. However, these stars are efficiently identified from the tangential velocity, using just parallax and proper motion. Within the full Gaia DR2 archive of stars with 5-σ parallax and proper motion but no radial velocity, we identify a sample of 19 with speeds significantly larger than the local escape speed of the Milky Way based on tangential motion alone.

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Section: Comparison With Theorymentioning

confidence: 88%

Nearby High-speed Stars in Gaia DR2

Bromley

Kenyon

Brown

et al. 2018

ApJ

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“…Previously, most of the high-to-hyper-velocity stars were thought to be young (relatively massive) hot stars originating from the Galactic center (e.g., Hills 1988;Brown 2015, and references therein). However, the recent SEGUE study by Palladino et al (2014) used a combination of radial velocities and proper motions to show that lowmass F and G stars could be traveling with high enough speed to allow them to escape the Galaxy, and that these stars did not originate in the Galactic center (see also Kollmeier et al 2010;Nidever et al 2012). Geier et al (2015) confirmed these findings by conducting a kinematic and spectroscopic follow-up of the fastest known HVS star, which travels at ∼1200 km s −1 through the Galaxy.…”

Section: Introductionmentioning

confidence: 99%

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Hansen¹,

Rich

Koch

et al. 2016

A&A

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Low-mass variable high-velocity stars are interesting study cases for many aspects of Galactic structure and evolution. Until recently, the only known high-or hyper-velocity stars were young stars thought to originate from the Galactic center. Wide-area surveys such as APOGEE and BRAVA have found several low-mass stars in the bulge with Galactic rest-frame velocities higher than 350 km s −1 . In this study we present the first abundance analysis of a low-mass RR Lyrae star that is located close to the Galactic bulge, with a space motion of ∼-400 km s −1 . Using medium-resolution spectra, we derived abundances (including upper limits) of 11 elements. These allowed us to chemically tag the star and discuss its origin, although our derived abundances and metallicity, at [Fe/H] = −0.9 dex, do not point toward one unambiguous answer. Based on the chemical tagging, we cannot exclude that it originated in the bulge. However, its retrograde orbit and the derived abundances combined suggest that the star was accelerated from the outskirts of the inner (or even outer) halo during many-body interactions. Other possible origins include the bulge itself, or the star might have been stripped from a stellar cluster or the Sagittarius dwarf galaxy when it merged with the Milky Way.

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“…parent population is possibly consistent with the disk origination (Bartko et al 2010;Zhang et al 2013;Kollmeier et al 2010). In order to distinguish the ejection mechanisms of HVSs and put constraints on the origin of the parent population of HVSs, it is quite necessary to search for the low-mass HVSs.…”

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confidence: 99%

19 low mass hypervelocity star candidates from the first data release of the LAMOST survey

Luo

Zhao

et al. 2015

Res. Astron. Astrophys.

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Hyper-velocity stars are believed to be ejected out from the Galactic center through dynamical interactions between (binary) stars and the central massive black hole(s). In this paper, we report 19 low mass F/G/K type hyper-velocity star candidates from over one million stars of the first data release of the LAMOST general survey. We determine the unbound probability for each candidate using a Monte-Carlo simulation by assuming a non-Gaussian proper-motion error distribution, Gaussian heliocentric distance and radial velocity error distributions. The simulation results show that all the candidates have unbound possibilities over 50% as expected, and one of them may even exceed escape velocity with over 90%probability. In addition, we compare the metallicities of our candidates with the metallicity distribution functions of the Galactic bulge, disk, halo and globular cluster, and conclude that the Galactic bulge or disk is likely the birth place for our candidates.

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Segue-2 Limits on Metal-Rich Old-Population Hypervelocity Stars in the Galactic Halo

Cited by 38 publications

References 48 publications

Nearby High-speed Stars in Gaia DR2

Nearby High-speed Stars in Gaia DR2

Chemical abundances in a high-velocity RR Lyrae star near the bulge

19 low mass hypervelocity star candidates from the first data release of the LAMOST survey

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