Discovery of an equal-mass “twin” binary population reaching 1000+ AU separations. (arXiv:1906.10128v1 [astro-ph.SR])

Discovery of an equal-mass “twin” binary population reaching 1000+ AU separations. (arXiv:1906.10128v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+El_Badry_K/0/1/0/all/0/1">Kareem El-Badry</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rix_H/0/1/0/all/0/1">Hans-Walter Rix</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tian_H/0/1/0/all/0/1">Haijun Tian</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Duchene_G/0/1/0/all/0/1">Gaspard Duch&#xea;ne</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Moe_M/0/1/0/all/0/1">Maxwell Moe</a>

We use a homogeneous catalog of 42,000 main-sequence wide binaries identified
by Gaia to measure the mass ratio distribution, p(q), of binaries with primary
masses $0.1 < M_1/M_{odot} < 2.5$, mass ratios $0.1 < q < 1$, and separations $50

We use a homogeneous catalog of 42,000 main-sequence wide binaries identified
by Gaia to measure the mass ratio distribution, p(q), of binaries with primary
masses $0.1 < M_1/M_{odot} < 2.5$, mass ratios $0.1 < q < 1$, and separations
$50 <s/{rm AU} < 50,000$. A well-understood selection function allows us to
constrain p(q) in 35 independent bins of primary mass and separation, with
hundreds to thousands of binaries in each bin. Our investigation reveals a
sharp excess of equal-mass “twin” binaries that is statistically significant
out to separations of 1,000 to 10,000 AU, depending on primary mass. The excess
is narrow: a steep increase in p(q) at $0.95 lesssim q < 1$, with no
significant excess at $qlesssim 0.95$. A range of tests confirm that the
signal is real, not a data artifact or selection effect. Combining the Gaia
wide binary constraints with those from close binaries, we show that the twin
excess decreases with increasing separation, but its width ($qgtrsim 0.95$) is
constant over $0.01 < a/{rm AU} < 10,000$. The wide twin population would be
difficult to explain if the components of all wide binaries formed via core
fragmentation, which is not expected to produce strongly correlated component
masses. We conjecture that twin wide binaries formed at closer separations (a <
100 AU), likely via accretion from circumbinary disks, and were subsequently
widened by dynamical interactions in their birth environments. The
separation-dependence of the twin excess then constrains the efficiency of
dynamical widening and disruption of binaries in young clusters. We also
constrain p(q) across $0.1 lesssim q < 1$. Besides changes in the twin
fraction, p(q) is independent of separation at fixed primary mass over 100 <
s/AU < 50,000. It is flatter than expected for random pairings from the IMF but
more bottom-heavy for wide binaries than for binaries with a < 100 AU.

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