Astrometric Identification of Nearby Binary Stars I: Predicted Astrometric Signals. (arXiv:2111.10380v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Penoyre_Z/0/1/0/all/0/1">Zephyr Penoyre</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Belokurov_V/0/1/0/all/0/1">Vasily Belokurov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Evans_N/0/1/0/all/0/1">N. Wyn Evans</a>
We examine the capacity to identify binary systems from astrometric
deviations alone. We generate a broad catalog of simulated binary systems
within 100 pc, and examine synthetic observations matching the textit{Gaia}
survey’s scanning law and astrometric data processing routine. We show how the
Unit Weight Error (UWE) and Proper Motion Anomaly (PMA) vary as a function of
period, and the properties of the binary. Both UWE and PMA peak for systems
with a binary period close to the time baseline of the survey. Thus UWE can be
expected to increase or remain roughly constant as we observe the same system
over a longer baseline, and we suggest $UWE_{eDR3}>1.25$ and $Delta
UWE/UWE_{eDR3}>-0.25$ as criteria to select astrometric binaries whilst
excluding other sources of astrometric noise. We show that for stellar binaries
we would expect to detect significant astrometric deviations for 80-90% of our
simulated systems with periods ranging from months to decades. We confirm that
for systems with periods less than the survey’s baseline the observed $UWE$
scales $propto varpi$ (parallax), $a$ (semi-major axis) and $Delta
=frac{|q-l|}{(1+q)(1+l)}$ where $q$ and $l$ are the mass and light ratio
respectively, with a modest dependence on viewing angle. We show that for
longer periods the signal is suppressed by a factor of roughly $propto P^{-2}$
(period). PMA is largest in orbits with slightly longer periods but obeys the
same approximate scaling relationships. We are able to predict the distribution
of multiple observable astrometric indicators and show that binary systems in
the above period range will be distinct and differentiable from single stars.
We examine the capacity to identify binary systems from astrometric
deviations alone. We generate a broad catalog of simulated binary systems
within 100 pc, and examine synthetic observations matching the textit{Gaia}
survey’s scanning law and astrometric data processing routine. We show how the
Unit Weight Error (UWE) and Proper Motion Anomaly (PMA) vary as a function of
period, and the properties of the binary. Both UWE and PMA peak for systems
with a binary period close to the time baseline of the survey. Thus UWE can be
expected to increase or remain roughly constant as we observe the same system
over a longer baseline, and we suggest $UWE_{eDR3}>1.25$ and $Delta
UWE/UWE_{eDR3}>-0.25$ as criteria to select astrometric binaries whilst
excluding other sources of astrometric noise. We show that for stellar binaries
we would expect to detect significant astrometric deviations for 80-90% of our
simulated systems with periods ranging from months to decades. We confirm that
for systems with periods less than the survey’s baseline the observed $UWE$
scales $propto varpi$ (parallax), $a$ (semi-major axis) and $Delta
=frac{|q-l|}{(1+q)(1+l)}$ where $q$ and $l$ are the mass and light ratio
respectively, with a modest dependence on viewing angle. We show that for
longer periods the signal is suppressed by a factor of roughly $propto P^{-2}$
(period). PMA is largest in orbits with slightly longer periods but obeys the
same approximate scaling relationships. We are able to predict the distribution
of multiple observable astrometric indicators and show that binary systems in
the above period range will be distinct and differentiable from single stars.
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