J/MNRAS/490/157 Fastest stars in the Galaxy with Gaia DR2 (Marchetti+, 2019)
Gaia DR2 in 6D: searching for the fastest stars in the Galaxy.
Marchetti T., Rossi E.M., Brown A.G.A.
<Mon. Not. R. Astron. Soc., 490, 157-171 (2019)>
=2019MNRAS.490..157M 2019MNRAS.490..157M (SIMBAD/NED BibCode)
ADC_Keywords: Radial velocities ; Parallaxes, trigonometric ; Proper motions ;
Stars, distances ; Milky Way ; Optical
Keywords: Galaxy: centre - Galaxy: kinematics and dynamics -
Galaxy: stellar content
Abstract:
We search for the fastest stars in the subset of stars with radial
velocity measurements of the second data release (DR2) of the European
Space Agency mission Gaia. Starting from the observed positions,
parallaxes, proper motions, and radial velocities, we construct the
distance and total velocity distribution of more than 7 million stars
in our Milky Way, deriving the full 6D phase space information in
Galactocentric coordinates. These information are shared in a
catalogue, publicly available at
http://home.strw.leidenuniv.nl/~marchetti/research.html. To search for
unbound stars, we then focus on stars with a probability greater than
50 per cent of being unbound from the Milky Way. This cut results in a
clean sample of 125 sources with reliable astrometric parameters and
radial velocities. Of these, 20 stars have probabilities greater than
80 per cent of being unbound from the Galaxy. On this latter
subsample, we perform orbit integration to characterize the stars'
orbital parameter distributions. As expected given the relatively
small sample size of bright stars, we find no hypervelocity star
candidates, stars that are moving on orbits consistent with coming
from the Galactic Centre. Instead, we find seven hyperrunaway star
candidates, coming from the Galactic disc. Surprisingly, the remaining
13 unbound stars cannot be traced back to the Galaxy, including two of
the fastest stars (around 700km/s). If conformed, these may constitute
the tip of the iceberg of a large extragalactic population or the
extreme velocity tail of stellar streams.
Description:
We derived distance and total velocities for all the 7183262 stars
with a full phase space measurement in the Gaia DR2 catalogue (Gaia
Collaboration 2018A&A...616A...1G 2018A&A...616A...1G, Cat. I/345) in order to find
unbound objects and velocity outliers. We defined our sample of
high-velocity stars as those stars with an estimated probability of
being unbound from the Milky Way Pub>50 per cent, resulting in a
total of 125 stars with reliable astrometric parameters and radial
velocities. We traced back the high-velocity stars in the Galactic
potential to derive orbital parameters.
Out of these 125 stars, we found 20 stars with predicted probabilities
Pub>80 per cent. The observed and derived kinematic properties of
these stars are summarized in Table 2, the other 105 stars are
presented in Table C1. In Table D1, we report the updated values of
the distance, total velocity, and Pub for the 20 stars included in
Table 2, after including the -0.029mas global parallax zero-point
mentioned in Lindegren et al. (2018A&A...616A...2L 2018A&A...616A...2L, Cat. I/345).
Finally, in Table E1 we present artificially inflated parallax
uncertainties to keep into account systematic errors and the updated
parameters.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 157 20 Observed and derived properties for the 20
'clean' high-velocity star candidates with a
probability >80% of being unbound from the
Galaxy
tablec1.dat 52 105 Distances and total velocities in the Galactic
rest frame for the 105 'clean' high-velocity
star candidates with 0.5<Pub=<0.8
tabled1.dat 52 20 Distances and total velocities in the Galactic
rest frame for the 20 'clean' high-velocity
star candidates with Pub>0.8 presented in
Table 2, including the -0.029mas global
parallax offset
tablee1.dat 52 20 Distances and total velocities in the Galactic
rest frame for the 20 'clean' high-velocity
star candidates with Pub>0.8 presented in
Table 2, including systematic errors in parallax
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR2 Gaia DR2 object identifier
21 A1 --- f_GaiaDR2 [eg] Flag on GaiaDR2 (1)
23- 31 F9.5 deg RAdeg Right ascension (J2000)
33- 41 F9.5 deg DEdeg Declination (J2000)
43- 48 F6.3 mas plx Gaia DR2 parallax
50- 54 F5.3 mas e_plx Error on plx
56- 62 F7.3 mas/yr pmRA Gaia DR2 proper motion in right ascension
64- 68 F5.3 mas/yr e_pmRA Error on pmRA
70- 76 F7.3 mas/yr pmDE Gaia DR2 proper motion in declination
78- 82 F5.3 mas/yr e_pmDE Error on pmDE
84- 91 F8.3 km/s RV Gaia DR2 radial velocity
93- 97 F5.3 km/s e_RV Error on RV
99-103 F5.2 mag Gmag Gaia DR2 G-band magnitude
105-109 I5 pc d Distance
111-114 I4 pc E_d Upper error on d
116-119 I4 pc e_d Lower error on d
121-125 I5 pc rGC Galactocentric distance
127-130 I4 pc E_rGC Upper error on rGC
132-135 I4 pc e_rGC Lower error on rGC
137-139 I3 km/s vGC Total velocity in the galactic rest frame
141-143 I3 km/s E_vGC Upper error on vGC
145-147 I3 km/s e_vGC Lower error on vGC
149-152 F4.2 --- PMW Probability for a star to come from the
Milky Way (2)
154-157 F4.2 --- Pub Probability of being unbound from the
Galaxy (G1)
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Note (1): Flag as follows:
e = Extragalactic high-velocity star candidate
g = Galactic high-velocity star candidate
Note (2): We define the probability PMW for a star to come from the Milky Way
as the fraction of Monte Carlo realizations resulting in a minimum
crossing radius within the edge of the stellar disc: rmin<rdisc,
where rdisc=25kpc (Xu et al. 2015ApJ...801..105X 2015ApJ...801..105X)
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Byte-by-byte Description of file: tablec1.dat tabled1.dat tablee1.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR2 Gaia DR2 object identifier
21- 25 I5 pc d Distance
27- 30 I4 pc E_d Upper error on d
32- 35 I4 pc e_d Lower error on d
37- 39 I3 km/s vGC Total velocity in the galactic rest frame
41- 43 I3 km/s E_vGC Upper error on vGC
45- 47 I3 km/s e_vGC Lower error on vGC
49- 52 F4.2 --- Pub Probability of being unbound from the
Galaxy (G1)
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Global Notes:
Note (G1): We estimate the probability Pub of being unbound from the Galaxy
as the fraction of Monte Carlo realizations that result in a total
velocity vGC greater than the escape speed from the MW at that
given position
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 23-Jan-2023