Gaia Photocenter Binaries
Gaia is a European Space Agency telescope launched in 2013 to the Sun-Earth L2 Lagrange point 1.5
million kilometers from Earth. See https://en.wikipedia.org/wiki/Gaia_(spacecraft) for details. Data on
over 1 billion objects (mostly stars within our galaxy) have been gathered. Data Release 3 (DR3), which
covers ~ three years of Gaia observations, identified a number of “non-single” stars. See
https://www.cosmos.esa.int/web/gaia/dr3-non-single-stars. Many of these non-single stars are
identified as (or suspected of being) binary stars. They are divided into three major categories: (1)
astrometric binaries, (2) photometric (eclipsing) binaries, and (3) spectroscopic binaries. The astrometric
binaries are further broken down into three categories: (1) binaries with Gaia orbital solutions, (2)
constant acceleration suspected binaries, and (3) variable acceleration suspected binaries.
One of the constant acceleration suspected binaries identified by Gaia has 14 Earth-based speckle
interferometry measurements made between 2011 and 2022. These published measurements were
entered in the Washington Double Star (WDS) Catalog under WDS 05403+1521 YSC 186 Aa,Ab. These
observational values are shown in the Table below. The columns are the Date (year and fractional year),
PA (position angle), Sep (separation), Ap (aperture of the telescope), # (number of nights observed), Ref
(reference code to the literature), Tq (the technique used to make the observations, all speckle
interferometry in this case), x and y (the x, y Cartesian coordinates transformed from polar PA, Sep
coordinate values).
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The online graphing calculator, Desmos, was used to plot these observations (positions of the fainter
secondary star relative to the brighter primary star) as shown in the screen shot from Desmos shown
below. The points appear to be along a curve that may be typical of the elliptical curve of a binary. The
five ellipse parameter sliders on the Desmos program were then adjusted to fit an ellipse to the
observations. A good fit was obtained for an apparent (as viewed from Earth) orbit with the parameters
as shown in the left of the figure. These parameters: a is the semi-major axis, b is the semi-minor axis, q
is the rotation angle of the ellipse, and h and k are the offsets of the ellipse from the origin along the
semi-major and semi-minor axes respectively.
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This Desmos solution can be uploaded to any (free) Desmos account
https://www.desmos.com/calculator/koyztxluqh
