J/MNRAS/472/675 Wide binaries in Tycho-Gaia: search method (Andrews+, 2017)
Wide binaries in Tycho-Gaia:
Search method and the distribution of orbital separations.
Andrews J.J., Chaname J., Agueros M.A.
<Mon. Not. R. Astron. Soc. 472, 675-699 (2017)>
=2017MNRAS.472..675A 2017MNRAS.472..675A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Positional data ;
Parallaxes, trigonometric
Keywords: astrometry - parallaxes - proper motions - binaries: visual
Abstract:
We mine the Tycho-Gaia astrometric solution (TGAS) catalogue for wide
stellar binaries by matching positions, proper motions and astrometric
parallaxes. We separate genuine binaries from unassociated stellar
pairs through a Bayesian formulation that includes correlated
uncertainties in the proper motions and parallaxes. Rather than
relying on assumptions about the structure of the Galaxy, we calculate
Bayesian priors and likelihoods based on the nature of Keplerian
orbits and the TGAS catalogue itself. We calibrate our method using
radial velocity measurements and obtain 7108 high-confidence candidate
wide binaries with projected separations s≲1pc. The normalization of
this distribution suggests that at least 0.7 per cent of TGAS stars
have an associated, distant TGAS companion in a wide binary. We
demonstrate that Gaia's astrometry is precise enough that it can
detect projected orbital velocities in wide binaries with orbital
periods as large as 106yr. For pairs with s≲4x104au,
characterization of random alignments indicates our contamination to
be 5-10 per cent. For s≲5x103au, our distribution is consistent
with Opik's law. At larger separations, the distribution is steeper
and consistent with a power-law P(s)∝s-1.6; there is no
evidence in our data of any bimodality in this distribution for
s≲1pc. Using radial velocities, we demonstrate that at large
separations, i.e. of order s∼1pc and beyond, any potential sample of
genuine wide binaries in TGAS cannot be easily distinguished from
ionized former wide binaries, moving groups or contamination from
randomly aligned stars.
Description:
Our catalogue of wide binaries identified in the Tycho-Gaia
Astrometric Solution catalogue. The Gaia source IDs, Tycho IDs,
astrometry, posterior probabilities for both the log-flat prior and
power-law prior models, and angular separation are presented.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 197 7108 Catalogue of wide binaries in Tycho-Gaia
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- Gaia-ID1 Gaia ID for primary
21- 32 A12 --- TYC-ID1 Tycho ID for primary
33- 45 F13.9 deg RAdeg1 Right ascension (ICRS) at epoch 2015.0
for primary
47- 59 F13.9 deg DEdeg1 Declination (ICRS) at epoch 2015.0
for primary
61- 69 F9.3 mas/yr pmRA1 Proper motion (RA part) for primary
71- 78 F8.3 mas/yr pmDE1 Proper motion (DE part) for primary
80- 86 F7.3 mas plx1 Parallax for primary
88-106 I19 --- Gaia-ID2 Gaia ID for secondary
108-118 A11 --- TYC-ID2 Tycho ID for secondary
120-132 F13.9 deg RAdeg2 Right ascension (ICRS) at epoch 2015.0
for secondary
134-146 F13.9 deg DEdeg2 Declination (ICRS) at epoch 2015.0
for secondary
148-156 F9.3 mas/yr pmRA2 Proper motion (RA part) for secondary
158-165 F8.3 mas/yr pmDE2 Proper motion (DE part) for secondary
167-173 F7.3 mas plx2 Parallax for secondary
175-181 F7.5 --- P(logflat) [0/1] Posterior probability of a genuine
binary using the log-flat prior (1)
183-189 F7.5 --- P(powerlaw) [0/1] Posterior probability of a genuine
binary using the power-law prior (1)
191-197 F7.2 arcsec Sep Angular separation of pair
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Note (1): Two separate posterior probabilities for each pair being a genuine
binary are provided, depending on whether they are generated using a
log-flat prior or a power-law prior. In many cases these probabilities
disagree. See Section 7.4 for a discussion about how to use this catalogue.
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Acknowledgements:
Jeff J. Andrews, andrews(at)physics.uoc.gr
(End) Jeff J. Andrews [U. of Crete], Patricia Vannier [CDS] 20-Nov-2017