J/A+A/708/A249 Binary component masses from Gaia (Bailer-Jones+, 2026)
Component masses in stellar and substellar binaries from Gaia astrometry and
photometry.
Bailer-Jones C.A.L., Kreidberg L.
<Astron. Astrophys. 708, A249 (2026)>
=2026A&A...708A.249B 2026A&A...708A.249B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, masses ; Exoplanets ; Binaries, orbits ; Optical
Keywords: methods: statistical - catalogs - astrometry -
planets and satellites: fundamental parameters -
binaries: general - stars: fundamental parameters
Abstract:
The masses of stars and planets can be measured dynamically in binary
systems. For an unresolved binary, time series astrometry yields some
orbital parameters, but it cannot provide the component masses,
because we observe only the motion of the system's photocentre.
However, as a star's luminosity is related to its mass, the observable
photometry of both components together provides information on the
system mass. Here we develop a method to determine the individual
component masses of an unresolved binary using the astrometric orbit
together with three-band photometry from Gaia. We use a mass-flux
relation fitted from stellar isochrone models for each Gaia band to
infer the unknown flux ratio. This enables our method to distinguish
between near equal-mass, near equal-brightness stellar binaries and
star-planet binaries, which otherwise have identical astrometric
signatures. Using a likelihood approach, we sample the posterior
probability distribution over the stellar parameters, marginalizing
over system age and metallicity to get the individual masses. We apply
this to 20000 systems with a main sequence primary within 300pc of the
Sun using data from the Gaia data release 3 non-single star catalogue.
Primary masses can be determined with a precision (one-sigma posterior
width) of 10-20% in 90% of cases. Secondary masses, which extend down
to planetary-mass objects, are less precise, although half are more
than 25% precise. Interestingly, adding either infrared photometry or
spectroscopic orbits from Gaia does not change the mass estimates much
(less than 4% and 1% respectively). Interstellar extinction likewise
has little impact for this sample. This work shows that reasonably
precise masses can be obtained for stars and substellar objects using
just the Gaia astrometry and photometry without need for extensive
follow-up.
Description:
Masses (with asymmetric lower and upper uncertainties) for both
components of astrometric stellar and substellar binaries selected
from Gaia DR3 for the Orbital300 sample described in the paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 250 20334 Binary component masses
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Gaia DR3 source identifier (source_id)
21- 39 F19.17 Msun M1 Mass primary, median (m1)
41- 61 F21.19 Msun e_M1 Mass primary, lower uncertainty (m1_lo)
63- 81 F19.17 Msun E_M1 Mass primary, upper uncertainty (m1_up)
83-103 F21.19 Msun M2 Mass secondary, median (m2)
105-125 F21.19 Msun e_M2 Mass secondary, lower uncertainty (m2_lo)
127-146 F20.18 Msun E_M2 Mass secondary, upper uncertainty (m2_up)
148-168 F21.18 AU ap Photometric semi-major axis (ap)
170-191 F22.20 AU e_ap Uncertainty in ap (ap_uncertainty)
193-212 F20.15 d Period Orbital period (period)
214-227 F14.9 d e_Period Uncertainty in period
(period_uncertainty)
229-250 E22.14 --- log(FluxRatio) log10 G-band flux ratio (logfluxratio)
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Acknowledgements:
Coryn Bailer-Jones, calj(at)mpia.de
(End) Coryn Bailer-Jones [MPIA], Patricia Vannier [CDS] 04-Mar-2026