J/A+A/704/A294 Gaia DR3 high radial velocity stars (Katz+, 2025)
Gaia DR3 high radial velocity stars: Genuine fast-moving objects or outliers?
Katz D., Gomez A., Caffau E., Bonifacio P., Hottier C., Vanel O.,
Soubiran C., Panuzzo P., Chosson D., Sartoretti P., Lallement R.,
Di Matteo P., Haywood M., Robichon N., Baker S., Barbier A., Bashi D.,
Benson K., Blomme R., Brouillet N., Casamiquella L., Chemin L., Cropper M.,
Damerdji Y., Dolding C., Faigler S., Fremat Y., Gosset E., Guerrier A.,
Haigron R., Huckle H.E., Leclerc N., Lobel A., Marchal O., Mazeh T.,
Mints A., Royer F., Seabroke G.M., Smith M., Snaith O., Thevenin F.,
Weingrill K.
<Astron. Astrophys. 704, A294 (2025)>
=2025A&A...704A.294K 2025A&A...704A.294K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, high-velocity ; Radial velocities ;
Effective temperatures ; Abundances, [Fe/H]
Keywords: techniques: radial velocities - catalogs -
stars: kinematics and dynamics
Abstract:
The third Gaia data release includes 33.8 million radial velocity
measurements, extending to a magnitude of GRVS=14. To reach this
magnitude limit, spectra were processed down to a signal-to-noise
ratio (S/N) of 2. In this very low S/N regime, noise-induced peaks in
the cross-correlation function can result in spurious radial velocity
determinations. Quality filters were applied to the dataset to
mitigate such artefacts as much as possible prior to publication.
Nevertheless, the high radial velocity (HRV) stars -- defined here as
those with radial velocities below -500 or above +500km/s -- are so
sparsely populated that even a few hundred spurious measurements can
lead to significant contamination.
The objectives of the present study are as follows: (i) to confirm or
refute the radial velocity values of the order of one hundred Gaia DR3
HRV stars, (ii) to evaluate the rate of spurious radial velocities in
the Gaia DR3 catalogue as a function of S/N and radial velocity, and
(iii) to examine the properties of the genuine HRV stars.
A total of 134 Gaia DR3 HRV stars were observed using the SOPHIE and
UVES spectrographs. Their radial velocities were determined via
cross-correlation or template-matching methods. These measurements
were subsequently combined with radial velocities from the APOGEE,
GALAH, GES, LAMOST, and RAVE catalogues in order to assess the rate of
erroneous Gaia DR3 radial velocities as a function of S/N and radial
velocity range. Finally, the orbits of a clean sample of HRV stars
were integrated using an axisymmetric Galactic gravitational
potential.
Ground-based measurements confirm the Gaia DR3 radial velocities of
104 out of our 134 targets, and they refute those of the remaining 30.
The combination of these data with the spectroscopic surveys mentioned
above enabled an assessment of the rate of spurious measurements as a
function of S/N and across three intervals of absolute value of the
radial velocity: [0, 200), [200, 400), and [400, 1000)km/s. The
outlier rate reaches up to 83% in the S/N range [2, 3) and velocity
interval [400, 1000)km/s, and it decreases rapidly with increasing
S/N and/or with decreasing absolute value of the radial velocity. The
confirmed radial velocities were then combined with Gaia DR3 HRV stars
having S/N>10, in order to construct a clean sample of HRV stars.
The majority of these stars follow retrograde orbits. Their location
in the energy-vertical component of the angular momentum diagram
coincides with the region where several structures associated with
past merging events have been identified: Sequoia, Arjuna and I'itoi,
Antaeus, ED-2, and ED-3. It is likely that most of these HRV stars
were accreted.
Description:
Table A1 lists the 134 observed targets along with their
characteristics (including the radial velocities measured with the
SOPHIE and UVES spectrographs). Some stars were observed on multiple
occasions. Each observation is represented by a separate entry,
amounting to a total of 169. For the SB2 star Gaia_432, the reported
radial velocity (for each of its four entries) corresponds to the mean
value of its two components.
Table B1 contains the atmospheric parameters, metallicities and alpha-
elements over iron abundance ratios for 50 stars observed with SOPHIE.
There are two entries for the star Gaia_42, corresponding to two
different spectra.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 106 169 Coordinates and radial velocities
tableb1.dat 65 51 Atmospheric parameters, metallicities and
alpha-elements over iron abundance ratios
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/A+A/651/A20 : Gaia RVS benchmark stars. I. (Caffau+, 2021)
J/A+A/683/A72 : Gaia RVS benchmark stars. II. (Caffau+, 2024)
J/AN/346/70025 : Gaia RVS benchmark stars. III. (Caffau+, 2025)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Gaia DR3 source_id
22- 30 A9 --- Target Identifier used throughout the paper
33- 40 F8.4 deg RAdeg Gaia DR3 right ascension (ICRS) at Ep=2016.0)
43- 50 F8.4 deg DEdeg Gaia DR3 declination (ICRS) at Ep=2016.0)
53- 57 F5.2 mag Gmag Gaia DR3 G magnitude
60- 65 A6 --- Spectr Spectrograph employed: SOPHIE or UVES
68- 79 F12.6 d MJD Modified Julian Date: start of exposure
82- 83 A2 --- Meth Method used: CC (cross-correlation) or
TM (template-matching)
86- 93 F8.3 km/s RV ? Radial velocity
96-100 F5.3 km/s e_RV ? Radial velocity uncertainty
103-106 A4 --- Status Status: Conf (confirmed) or Spur (spurious)
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Target Identifier used throughout the paper
12- 15 I4 K Teff Effective temperature
18- 21 F4.2 [cm/s2] logg logarithm of the surface gravity
24- 28 F5.2 --- [Fe/H] Metallicity
31- 34 F4.2 --- e_[Fe/H] Metallicity uncertainty
37- 40 F4.2 --- [alpha/Fe] ? alpha-elements over iron abundance ratio
43- 44 I2 --- SN Spectrum S/N at 500nm
47- 65 I19 --- GaiaDR3 Gaia DR3 source_id
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Acknowledgements:
David Katz, david.katz(at)obspm.fr
(End) Patricia Vannier [CDS] 18-Nov-2025