J/MNRAS/512/3383 Wide binaries eccentricities with Gaia EDR3 (Hwang+, 2022)
The eccentricity distribution of wide binaries and their individual
measurements.
Hwang H.-C., Ting Y.-S., Zakamska N.L.
<Mon. Not. R. Astron. Soc. 512, 3383 (2022)>
=2022MNRAS.512.3383H 2022MNRAS.512.3383H (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Binaries, orbits ; Space velocities ;
Positional data ; Proper motions ; Stars, distances ; Optical
Keywords: binaries: general - binaries: visual - stars: kinematics and dynamics
Abstract:
Eccentricity of wide binaries is difficult to measure due to their
long orbital periods. With Gaia's high-precision astrometric
measurements, eccentricity of a wide binary can be constrained by the
angle between the separation vector and the relative velocity vector
(the v-r angle). In this paper, by using the v-r angles of wide
binaries in Gaia Early Data Release 3, we develop a Bayesian approach
to measure the eccentricity distribution as a function of binary
separations. Furthermore, we infer the eccentricities of individual
wide binaries and make them publicly available. Our results show that
the eccentricity distribution of wide binaries at 102 AU is close to
uniform and becomes superthermal at >103 AU, suggesting two formation
mechanisms dominating at different separation regimes. The close
binary formation, most likely disc fragmentation, results in a uniform
eccentricity distribution at <102 AU. The wide binary formation that
leads to highly eccentric wide binaries at >103 AU may be turbulent
fragmentation and/or the dynamical unfolding of compact triples. With
Gaia, measuring eccentricities is now possible for a large number of
wide binaries, opening a new window to understanding binary formation
and evolution.
Description:
Eccentricity is one of the fundamental orbital parameters in orbital
dynamics. Eccentricity measurement is challenging for resolved binaries
with separations > 100 AU due to their long orbital periods. There is
one particular observable in wide binaries that is tightly related to
the orbital eccentricity: the angle between the separation vector and
the relative velocity vector, dubbed v-r angle.
The space astrometry mission Gaia has revolutionized wide binary
research. With high-quality parallaxes and proper motions available
for billions of stars, a large sample of wide binaries has been made
possible resulting in interesting new findings about binary formation
and evolution. Amazingly, Gaia's proper motion precision is sufficient
to measure the relative velocity of wide binaries and therefore the
v-r angle. In this paper, with about one million wide binaries
available from Gaia EDR3 (El-Badry et al. 2021MNRAS.506.2269E 2021MNRAS.506.2269E), we
develop a Bayesian scheme to derive the eccentricity distribution of
wide binaries and to infer the eccentricity for individual wide
binaries. In contrast to the method of Tokovinin
(2020MNRAS.496..987T 2020MNRAS.496..987T), our method only uses the v-r angles measured
from Gaia without using the magnitude of relative velocity. The
advantage of our method is that it does not reply on mass and parallax
measurements and therefore can include a dramatically larger number of
wide binaries but this statistical improvement occurs at the expense
of larger uncertainties for individual wide binaries eccentricity
measurements (i.e see section Introduction).
We detailed the Bayesian method in the section 2 and secondly we apply
this method in the section 3 for e of gaia wide binaries measurements.
Next, the section 3.4 and 3.5 show Bayesian inference for e
distribution and e values of wide binaries. In these sections, we
explain our most important results (i.e Sep, R, v-r, alpha, e, CI(e)).
We deliver a complete properties sample of 1817594 wide binaries in
the table2.dat.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 276 1817594 Eccentricities estimates of our wide binaries
sample
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See also:
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
J/ApJS/246/4 : Catalog of ultrawide binary stars from Gaia DR2 (Tian+,2020)
J/MNRAS/497/2250 : Gaia DR2 hot Jupiter hosts and contact binaries
(Hwang+, 2020)
J/MNRAS/480/4884 : Gaia wide binaries (El-Badry+, 2018)
J/AJ/153/257 : Comoving stars in Gaia DR1 (Oh+, 2017)
J/MNRAS/456/2070 : Eccentricity distribution of wide binaries (Tokovinin+,2016)
J/ApJS/190/1 : A survey of stellar families (Raghavan+, 2010)
J/A+A/380/238 : Long-period companions of multiple stars (Shatsky, 2001)
https://zenodo.org/record/4435257 : Wide binaries of El-Badry et al.
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaEDR3-1 Gaia EDR3 source_id of the primary
(source_id1)
21- 38 F18.14 deg RAdeg Right ascension of the primary star from
Gaia EDR3 (ICRS) at Ep=2016.0 (ra1)
40- 57 F18.14 deg DEdeg Declination of the primary star from
Gaia EDR3 (ICRS) at Ep=2016.0 (dec1)
59- 77 I19 --- GaiaEDR3-2 Gaia EDR3 source_id of the secondary star
(source_id2)
79- 96 F18.14 deg RA2deg Right ascension of the secondary star from
Gaia EDR3 (ICRS) at Ep=2016.0 (ra2)
98- 115 F18.14 deg DE2deg Declination of the secondary star from
Gaia EDR3 (ICRS) at Ep=2016.0 (dec2)
117- 135 F19.12 AU Sep Projected binary separation as described in
El-Badry et al. 2021MNRAS.506.2269E 2021MNRAS.506.2269E (sep_AU)
(1)
137- 158 E22.15 --- R Probability R of being a chance-alignment
pair as described in El-Badry et al.
2021MNRAS.506.2269E 2021MNRAS.506.2269E (Rchancealign) (1)
160- 177 F18.14 deg v-r ? Measured v-r angle (vr_angle) (2)
179- 198 F20.14 deg e_v-r Mean uncertainty of v-r (vrangleerror)
200- 218 F19.14 --- SigDpm The significance Sig of proper motion
difference Δµ/σΔµ
(dpm_sig) (3)
220- 235 F16.14 --- alpha The power index α used for the prior
eccentricity distribution as described in
equation 25 of the section 3.4 Bayesian
inference for the eccentricity (alpha)
237- 240 F4.2 --- e The most probable eccentricity (e)
242- 258 F17.15 --- b_e The lower eccentricity limit of the 68%
credible interval (e0) (4)
260- 276 F17.15 --- B_e ? The upper eccentricity limit of the 68%
credible interval (e1) (4)
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Note (1): El-Badry et al. (2021MNRAS.506.2269E 2021MNRAS.506.2269E) wide binaries catalogue is
available via this link (https://zenodo.org/record/4435257).
Note (2): There is one particular observable in wide binaries that is tightly
related to the orbital eccentricity: the angle between the separation
vector and the relative velocity vector, dubbed v-r angle. The concept
of using v-r angles to measure the eccentricities was proposed to
demonstrate that different eccentricities result in various
distributions of v-r angles, (i.e more in Introduction section).
Note (3): The Δµ/σΔµ is related to σγ by
σγ ~= 180/π * σΔµ/Δµ
equation 23 of the section 3.1 Notations for observable quantities.
Note (4): b_e & B_e are the 16th percentile and 84th percentile values of the
excentricity e distribution. In other words, 68% credible interval can
be written as [b_e ; B_e].
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 13-Mar-2025