J/ApJS/252/3 High-velocity stars in the Gal. halo from LAMOST & Gaia (Li+, 2021)
591 high-velocity stars in the Galactic halo selected from LAMOST DR7 and Gaia
DR2.
Li Y.-B., Luo A.-L., Lu Y.-J., Zhang X.-S., Li J., Wang R., Zuo F.,
Xiang M., Ting Y.-S., Marchetti T., Li S., Wang Y.-F., Zhang S., Hattori K.,
Zhao Y.-H., Zhang H.-W., Zhao G.
<Astrophys. J. Suppl. Ser., 252, 3 (2021)>
=2021ApJS..252....3L 2021ApJS..252....3L
ADC_Keywords: Radial velocities; Proper motions; Stars, distances;
Abundances, [Fe/H]; Milky Way; Stars, halo; Photometry, UBVRI
Keywords: High-velocity stars
Abstract:
In this paper, we report 591 high-velocity star candidates (HiVelSCs)
selected from over 10 million spectra of Data Release 7 (DR7) of the
Large Sky Area Multi-object Fiber Spectroscopic Telescope and the
second Gaia data release, with three-dimensional velocities in the
Galactic rest frame larger than 445km/s. We show that at least
43 HiVelSCs are unbound to the Galaxy with escape probabilities larger
than 50%, and this number decreases to eight if the possible parallax
zero-point error is corrected. Most of these HiVelSCs are metal-poor
and slightly α-enhanced inner halo stars. Only 14% of them have
[Fe/H]>-1, which may be the metal-rich "in situ" stars in the halo
formed in the initial collapse of the Milky Way or metal-rich stars
formed in the disk or bulge but kinematically heated. The low ratio of
14% implies that the bulk of the stellar halo was formed from the
accretion and tidal disruption of satellite galaxies. In addition,
HiVelSCs on retrograde orbits have slightly lower metallicities on
average compared with those on prograde orbits; meanwhile, metal-poor
HiVelSCs with [Fe/H]<-1 have an even faster mean retrograde velocity
compared with metal-rich HiVelSCs. To investigate the origins of
HiVelSCs, we perform orbit integrations and divide them into four
types, i.e., hypervelocity stars, hyper-runaway stars, runaway stars
and fast halo stars.
Description:
The Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST)
is a 4m quasi-meridian reflective Schmidt telescope, which is equipped
with 4000 fibers and can observe up to 4000 targets per exposure
simultaneously.
In 2020 March, LAMOST DR7 provided 10,608,416 low-resolution spectra
in the wavelength range of 3690-9100Å with a resolution of R∼1800.
The LAMOST Stellar Parameter Pipeline (LASP) estimates atmospheric
parameters and RV, and it has an accuracy of about 150K, 0.25dex,
0.15dex, and 5.0km/s for the effective temperature (Teff), surface
gravity (logg), metallicity ([Fe/H]), and RV, respectively, for
spectra of signal-to-noise ratios (S/Ns) higher than 10.
See Section 2.1.
In this paper, we cross-match LAMOST DR7 with Gaia DR2 to find
high-velocity stars.
We define our sample of high-velocity stars as those who can escape
from the Galaxy in at least one of the seven Galactic potential models
adopted in this work, or have total velocities in the Galactic rest
frame larger than 450km/s, and this results in a total of
591 high-velocity star candidates (HiVelSCs) found from the
LAMOST-Gaia catalog.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
hivelscs.dat 580 591 The high-velocity star candidates (HiVelSCs) catalog
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See also:
III/254 : 2nd Cat. of RVel with Astrometric Data (Kharchenko+, 2007)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
V/153 : LAMOST DR4 catalogs (Luo+, 2018)
V/164 : LAMOST DR5 catalogs (Luo+, 2019)
J/AJ/103/514 : High-velocity stars toward South Galactic Cap (Reid+ 1992)
J/BaltA/11/465 : Radial velocities of F5-M stars (Sperauskas+, 2002)
J/A+A/410/527 : Abundances in the Galactic disk (Bensby+, 2003)
J/ApJ/647/303 : Spectroscopic survey of hypervelocity stars (Brown+, 2006)
J/A+A/445/939 : Metal-poor stars uvby-beta photometry. XI. (Schuster+, 2006)
J/ApJ/684/1143 : BHB candidates in the Milky Way (Xue+, 2008)
J/A+A/511/L10 : Abundances and space velocities of 94 stars (Nissen+, 2010)
J/MNRAS/411/2596 : High Galactic latitude runaway stars (Silva+, 2011)
J/ApJ/751/55 : MMT hypervelocity star survey. II. (Brown+, 2012)
J/A+A/555/A12 : Foreground Galactic stars properties (Kordopatis+, 2013)
J/A+A/568/A7 : Model SDSS colors for halo stars (Allende Prieto+, 2014)
J/ApJ/813/26 : Runaway M dwarf candidates from SDSS-DR7 (Favia+, 2015)
J/MNRAS/448/822 : LAMOST candidate members of star clusters (Xiang+, 2015)
J/AJ/156/90 : New cat. of APOGEE RVel standard stars (Huang+, 2018)
J/ApJS/245/34 : Abundances for 6 million stars from LAMOST DR5 (Xiang+, 2019)
J/A+A/638/A122 : High-speed stars. Galactic hitchhikers (Caffau+, 2020)
http://dr7.lamost.org/ : LAMOST DR7 home page
http://faststars.space/ : The open fast stars catalog
Byte-by-byte Description of file: hivelscs.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- --- [Hivel]
6- 8 I3 --- Seq [1/591] High-velocity star number
10- 48 A39 --- spID LAMOST DR7 identifier
50- 57 A8 --- --- [Gaia DR2]
59- 77 I19 --- Gaia Gaia DR2 identifier
79- 89 F11.7 deg RAdeg Gaia DR2 barycentric right ascension (ICRS)
at Epoch=2015.5
91- 96 F6.4 deg e_RAdeg [0.007/0.3] RAdeg uncertainty
98- 108 F11.8 deg DEdeg [-7/72.4] Gaia DR2 barycentric declination
(ICRS) at Epoch=2015.5
110- 115 F6.4 deg e_DEdeg [0.009/0.2] DEdeg uncertainty
117- 119 I3 --- S/N [7/610] r-band signal-to-noise ratio
121- 126 A6 --- SpT Spectral type from LAMOST
128- 131 I4 km/s RV [-593/494] Radial velocity measured by the
LASP from LAMOST
133- 134 I2 km/s e_RV [3/35] RV uncertainty
136- 143 F8.3 mas/yr pmRA [-249/233] Gaia DR2 proper motion in RA
(pmRA*cosDE)
145- 149 F5.3 mas/yr e_pmRA [0.016/0.5] pmRA uncertainty
151- 158 F8.3 mas/yr pmDE [-285.2/73.3] Gaia DR2 proper motion in DEC
160- 164 F5.3 mas/yr e_pmDE [0.018/0.4] pmDE uncertainty
166- 170 F5.3 mas plx [0.06/7.8] Gaia DR2 parallax
172- 176 F5.3 mas e_plx [0.012/0.3] plx uncertainty
178- 182 F5.2 mag Gmag [10.63/17.57] Gaia DR2 G-band magnitude
184- 188 F5.2 mag BPmag [9.29/20.3] Gaia DR2 BP-band magnitude
190- 194 F5.2 mag RPmag [6.75/19.43] Gaia DR2 RP-band magnitude
196 I1 --- Astro [0/1] Reliable astrometric parameters?
(1=high-quality; 476 occurrences --
see Section 2.4)
198- 201 I4 km/s RVc [-587/499] LASP radial velocity corrected
the zero-point from LAMOST
203- 206 F4.1 kpc Dist [0.1/15.4] Heliocentric distance
from this work
208- 210 F3.1 kpc e_Dist [0/2.4] Lower uncertainty on Dist
212- 214 F3.1 kpc E_Dist [0/3.3] Upper uncertainty on Dist
216- 220 F5.1 kpc X [-15.5/-0.8] Cartesian Galactocentric
X-coordinate from this work
222- 224 F3.1 kpc e_X [0/1.8] Lower uncertainty on X
226- 228 F3.1 kpc E_X [0/1.9] Upper uncertainty on X
230- 233 F4.1 kpc Y [-3.5/13] Cartesian Galactocentric
Y-coordinate from this work
235- 237 F3.1 kpc e_Y [0/2] Lower uncertainty on Y
239- 241 F3.1 kpc E_Y [0/3] Upper uncertainty on Y
243- 246 F4.1 kpc Z [-5.3/11.2] Cartesian Galactocentric
Z-coordinate from this work
248- 250 F3.1 kpc e_Z [0/1.7] Lower uncertainty on Z
252- 254 F3.1 kpc E_Z [0/3] Upper uncertainty on Z
256- 259 F4.1 kpc rGC [4/17] Galactocentric distance
from this work
261- 263 F3.1 kpc e_rGC [0/2] Lower uncertainty on rGC
265- 267 F3.1 kpc E_rGC [0/2.8] Upper uncertainty on rGC
269- 272 I4 km/s Vx [-612/706] Cartesian Galactocentric
X-velocity from this work
274- 276 I3 km/s e_Vx [1/142] Lower uncertainty on Vx
278- 280 I3 km/s E_Vx [1/179] Upper uncertainty on Vx
282- 285 I4 km/s Vy [-865/439] Cartesian Galactocentric
Y-velocity from this work
287- 289 I3 km/s e_Vy [3/237] Lower uncertainty on Vy
291- 293 I3 km/s E_Vy [3/146] Upper uncertainty on Vy
295- 298 I4 km/s Vz [-461/601] Cartesian Galactocentric
Z-velocity from this work
300- 301 I2 km/s e_Vz [2/95] Lower uncertainty on Vz
303- 305 I3 km/s E_Vz [3/139] Upper uncertainty on Vz
307- 309 I3 km/s Vgc [447/922] Cartesian Galactocentric total
velocity from this work
311- 313 I3 km/s e_Vgc [5/169] Lower uncertainty on Vgc
315- 317 I3 km/s E_Vgc [5/248] Upper uncertainty on Vgc
319- 325 F7.5 --- e [0.89/1] Orbit eccentricity from this work
327- 333 F7.5 --- e_e [0.0003/0.3] Lower uncertainty on e
335- 341 F7.5 --- E_e [9e-05/0.08] Upper uncertainty on e
343- 348 F6.1 kpc Zmax [12/5447] Orbit maximum height above
the Galactic disk from this work
350- 355 F6.1 kpc e_Zmax [3/2465] Lower uncertainty on Zmax
357- 362 F6.1 kpc E_Zmax [2/2516] Upper uncertainty on Zmax
364- 370 F7.1 kpc Rmin [0.1/540.3]?=-9999 Minimum crossing radius
from this work
372- 378 F7.1 kpc e_Rmin [0/535]?=-9999 Lower uncertainty on Rmin
380- 386 F7.1 kpc E_Rmin [0/836]?=-9999 Upper uncertainty on Rmin
388- 394 F7.4 kpc2/Myr2 E-phi [-0.0005/0.004] The difference between
orbit energy E and potential energy at
infinity
396- 401 F6.4 kpc2/Myr2 e_E-phi [0/0.002] Lower uncertainty on E-phi
403- 408 F6.4 kpc2/Myr2 E_E-phi [0/0.003] Upper uncertainty on E-phi
410- 412 I3 km/s VescW [552/670] Escape velocity estimated
by the potential model in W19 (1)
414- 416 I3 km/s VescG [547/642] Escape velocity estimated
by the potential model in G05 (1)
418- 420 I3 km/s VescKe [525/646] Escape velocity estimated
by the potential model in K14 (1)
422- 424 I3 km/s VescKo [498/614] Escape velocity estimated
by the potential model in K10 (1)
426- 428 I3 km/s VescP [472/582] Escape velocity estimated
by the potential model in P90 (1)
430- 432 I3 km/s VescM [444/576] Escape velocity estimated
by the potential model in B15 (1)
434- 436 I3 km/s VescX [434/538] Escape velocity estimated
by the potential model in X08 (1)
438- 442 F5.3 --- Pgc [0/0.991] Probability of ejecting from
the GC
444- 448 F5.3 --- Pmw [0/1] Probability of ejecting from
the Galactic disk
450- 454 F5.3 --- PubW [0/1] Unbound probability in the potential
model in W19 (1)
456- 460 F5.3 --- PubG [0/1] Unbound probability in the potential
model in G05 (1)
462- 466 F5.3 --- PubKe [0/1] Unbound probability in the potential
model in K14 (1)
468- 472 F5.3 --- PubKo [0/1] Unbound probability in the potential
model in K10 (1)
474- 478 F5.3 --- PubP [0/1] Unbound probability in the potential
model in P90 (1)
480- 484 F5.3 --- PubM [0/1] Unbound probability in the potential
model in B15 (1)
486- 490 F5.3 --- PubX [0/1] Unbound probability under the
potential model in X08 (1)
492- 494 A3 --- Class Origin classification (2)
496- 500 I5 K Teff [3784/13760] Effective temperature estimated
by the LASP from this work
502- 504 I3 K e_Teff [10/794] Teff uncertainty
506- 509 F4.2 [cm/s2] logg [0.75/5.49] Log of surface gravity estimated
by the LASP from this work
511- 514 F4.2 [cm/s2] e_logg [0.01/1.03] Logg uncertainty
516- 520 F5.2 [Sun] [Fe/H] [-2.5/1] Metallicity estimated by the LASP
from this work
522- 525 F4.2 [Sun] e_[Fe/H] [0/0.61] [Fe/H] uncertainty
527- 530 I4 K TeffDD [4075/8506]?=-999 Effective temperature
estimated by the data-driven Payne method
(see Xiang+ 2019ApJS..245...34X 2019ApJS..245...34X)
from this work
532- 535 I4 K e_TeffDD [16/511]?=-999 TeffDD uncertainty
537- 543 F7.2 [cm/s2] loggDD [1.17/5.04]?=-999 Log of surface gravity
estimated by the data-driven Payne method
from this work
545- 551 F7.2 [cm/s2] e_loggDD [0.03/0.95]?=-999 LoggDD uncertainty
553- 559 F7.2 [-] [Fe/H]DD [-3.5/0.3]?=-999 Metallicity estimated by
the data-driven Payne method from this work
561- 567 F7.2 [-] e_[Fe/H]DD [0.02/0.8]?=-999 [Fe/H]DD uncertainty
569- 573 F5.2 [-] a/Fe [-0.29/0.65] α abundance estimated by
the data-driven Payne method
575- 578 F4.2 [-] e_a/Fe [0.01/0.42] a/Fe uncertainty
580 I1 --- C [0/1] HiVelSCs satisfy all more conservative
criteria in Section 5.2 (1=conservative;
92 occurrences)
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Note (1): The seven potential models come from the following references:
P90 = Paczynski 1990ApJ...348..485P 1990ApJ...348..485P
G05 = Gnedin+ 2005ApJ...634..344G 2005ApJ...634..344G
X08 = Xue+ 2008ApJ...684.1143X 2008ApJ...684.1143X
K10 = Koposov+ 2010ApJ...712..260K 2010ApJ...712..260K
K14 = Kenyon+ 2014ApJ...793..122K 2014ApJ...793..122K
B15 = Bovy 2015ApJS..216...29B 2015ApJS..216...29B
W19 = Watkins+ 2019ApJ...873..118W 2019ApJ...873..118W
Note (2): Four types as follows:
HVS = the fastest hypervelocity stars in the Galaxy (Pgc>0.16);
91 occurrences
HRS = hyper-runaway stars (Pgc<0.16, PMW>0.5 and Pub>0.5);
107 occurrences
RS = runaway stars (Pgc<0.16, PMW>0.5 and Pub<0.5); 221 occurrences
OUT = fast halo stars (Pgc<0.16, PMW<0.5); 172 occurrences
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History:
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(End) Emmanuelle Perret [CDS] 28-Jan-2022