http://arxiv.org/abs/1901.05972

The origin of ultra-wide massive binaries wider than >$10^3$ astronomical units (AUs) and their properties are not well characterized nor understood. Here we use the second Gaia data release to search for wide astrometric companions (orbital separations $10^3-$few$\times 10^5$ a.u.) to main-sequence Galactic O5-B5 stars which share similar parallax and proper motion with the primaries. We find an ultra-wide multiplicity fraction of $8\pm1$ per cent, to our completeness limit (up to $\approx 17$ mag; down to G-stars at distances of 0.5-2 kpc). Assuming a Kroupa mass function for the secondaries, the overall ultra-wide multiplicity fraction down to M-dwarfs is consistent with $48\pm6$ per cent. We use these data as a verification sample to test the existence of ultra-wide binaries among neutron stars and black holes. In particular, if a compact object is formed in an ultra-wide binary and receives a very-little/no natal kick, such a binary should not be disrupted but rather survive as a common proper motion pair. We, therefore, use Gaia data to search for ultra-wide astrometric companions to pulsars (normal or millisecond ones) and X-ray binaries. We find no reliable pairs with angular separation less than 25 arcsec. This is to be compared with the $5\pm1\%$ found for our OB-binaries verification sample located at similar distances. Therefore, we confirm the general picture that most compact objects receive strong natal kicks. We note that outside the most reliable angular separation interval we found two potential ultra-wide binaries, including a candidate companion to the slowest pulsar in our sample with projected separation of $2.7\times 10^5$ a.u. and a companion to a high-mass X-ray binary with projected separation of $3.78\times 10^5$ a.u. In both cases, however, the detection is marginal given the false positive probability of a few percents.

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A. Igoshev and H. Perets
Mon, 21 Jan 19
20/50

Comments: 16 pages, 12 figures, submitted to the MNRAS