Hypervelocity runaways from the Large Magellanic Cloud

Boubert, Douglas; Erkal, Denis; Evans, N. W.; Izzard, Robert G.

doi:10.1093/mnras/stx848

Cited by 67 publications

(70 citation statements)

References 83 publications

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“…Another intriguing origin for these stars not originating from the GC is that they come from the Large Magellanic Cloud (LMC), either as runaway stars (Boubert et al 2017), or by the extension of the Hills mechanism to a hypothetical MBH at the centre of the LMC (Boubert & Evans 2016). Uncertainties are at the moment too large to pinpoint their ejection location, and we dot not further expand on this possibility in this paper.…”

Section: Runaway Star Candidatesmentioning

confidence: 91%

An artificial neural network to discover hypervelocity stars: candidates in Gaia DR1/TGAS

Marchetti

Rossi

Kordopatis

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The paucity of hypervelocity stars (HVSs) known to date has severely hampered their potential to investigate the stellar population of the Galactic Centre and the Galactic Potential. The first Gaia data release (DR1, 2016 September 14) gives an opportunity to increase the current sample. The challenge is the disparity between the expected number of hypervelocity stars and that of bound background stars. We have applied a novel data mining algorithm based on machine learning techniques, an artificial neural network, to the Tycho-Gaia astrometric solution (TGAS) catalogue. With no pre-selection of data, we could exclude immediately ∼ 99% of the stars in the catalogue and find 80 candidates with more than 90% predicted probability to be HVSs, based only on their position, proper motions, and parallax. We have cross-checked our findings with other spectroscopic surveys, determining radial velocities for 30 and spectroscopic distances for 5 candidates. In addition, follow-up observations have been carried out at the Isaac Newton Telescope for 22 stars, for which we obtained radial velocities and distance estimates. We discover 14 stars with a total velocity in the Galactic rest frame > 400 km s −1 , and 5 of these have a probability > 50% of being unbound from the Milky Way. Tracing back their orbits in different Galactic potential models we find one possible unbound HVS with v ∼ 520 km s −1 , 5 bound HVSs, and, notably, 5 runaway stars with median velocity between 400 and 780 km s −1 . At the moment, uncertainties in the distance estimates and ages are too large to confirm the nature of our candidates by narrowing down their ejection location, and we wait for future Gaia releases to validate the quality of our sample. This test successfully demonstrates the feasibility of our new data mining routine.

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Section: Runaway Star Candidatesmentioning

confidence: 91%

An artificial neural network to discover hypervelocity stars: candidates in Gaia DR1/TGAS

Marchetti

Rossi

Kordopatis

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…S5-HVS1 is at least 1200 km s −1 , one of the key questions we are interested in is whether the star has been ejected from the Galactic Centre, the MW disk, or some other system such as a globular cluster or satellite galaxy. While some fast moving stars have been tentatively associated with other galaxies like the Large Magellanic Cloud (Edelmann et al 2005;Gualandris & Portegies Zwart 2007;Boubert & Evans 2016;Boubert et al 2017;Erkal et al 2019), in this paper we will focus only on ejection from the MW disk and the Galactic Centre.…”

Section: Kinematics Of S5-hvs1mentioning

confidence: 99%

Discovery of a nearby 1700 km s−1 star ejected from the Milky Way by Sgr A*

Koposov

Boubert

et al. 2019

Monthly Notices of the Royal Astronomical Society

119

123

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We present the serendipitous discovery of the fastest Main Sequence hyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey (S 5 ). The star S5-HVS1 is a ∼ 2.35 M A-type star located at a distance of ∼ 9 kpc from the Sun and has a heliocentric radial velocity of 1017 ± 2.7 km s −1 without any signature of velocity variability. The current 3-D velocity of the star in the Galactic frame is 1755 ± 50 km s −1 . When integrated backwards in time, the orbit of the star points unambiguously to the Galactic Centre, implying that S5-HVS1 was kicked away from Sgr A* with a velocity of ∼ 1800 km s −1 and travelled for 4.8 Myr to the current location. This is so far the only HVS confidently associated with the Galactic Centre. S5-HVS1 is also the first hyper-velocity star to provide constraints on the geometry and kinematics of the Galaxy, such as the Solar motion V y, = 246.1 ± 5.3 km s −1 or position R 0 = 8.12 ± 0.23 kpc. The ejection trajectory and transit time of S5-HVS1 coincide with the orbital plane and age of the annular disk of young stars at the Galactic centre, and thus may be linked to its formation. With the S5-HVS1 ejection velocity being almost twice the velocity of other hyper-velocity stars previously associated with the Galactic Centre, we question whether they have been generated by the same mechanism or whether the ejection velocity distribution has been constant over time.

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“…The origin of HVSs may, however, be extragalactic as well. The Large Magellanic Cloud has been proposed as a potential source of HVSs (Boubert & Evans 2016;Boubert et al 2017). Indeed, the unique object HVS 3 has been suggested to originate from the Large Magellanic Cloud (Edelmann et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Hypervelocity stars in theGaiaera

Kreuzer

Irrgang

Heber

2020

A&A

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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 km s −1 . In order to unravel the nature and origin of those highvelocity 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 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. HVS 22 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 +690 −560 km s −1 .

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Hypervelocity runaways from the Large Magellanic Cloud

Cited by 67 publications

References 83 publications

An artificial neural network to discover hypervelocity stars: candidates in Gaia DR1/TGAS

An artificial neural network to discover hypervelocity stars: candidates in Gaia DR1/TGAS

Discovery of a nearby 1700 km s−1 star ejected from the Milky Way by Sgr A*

Hypervelocity stars in theGaiaera

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