With a combination of adaptive optics imaging and a multi-epoch common proper motion search , we have conducted a large volume-limited ( D \leq 75 pc ) multiplicity survey of A-type stars , sensitive to companions beyond 30 au .
The sample for the Volume- limited A-STar ( VAST ) survey consists of 435 A-type stars : 363 stars were observed with adaptive optics , 228 stars were searched for wide common proper motion companions and 156 stars were measured with both techniques .
The projected separation coverage of the VAST survey extends from 30 to 45,000 au .
A total of 137 stellar companions were resolved , including 64 new detections from the VAST survey , and the companion star fraction , projected separation distribution and mass ratio distribution were measured .
The separation distribution forms a log-normal distribution similar to the solar-type binary distribution , but with a peak shifted to a significantly wider value of 387 ^ { +132 } _ { -98 } au .
Integrating the fit to the distribution over the 30 to 10,000 au observed range , the companion star fraction for A-type stars is estimated as 33.8 \pm 2.6 per cent .
The mass ratio distribution of closer ( < 125 au ) binaries is distinct from that of wider systems , with a flat distribution for close systems and a distribution that tends towards smaller mass ratios for wider binaries .
Combining this result with previous spectroscopic surveys of A-type stars gives an estimate of the total companion star fraction of 68.9 \pm 7.0 per cent .
The most complete assessment of higher order multiples was estimated from the 156-star subset of the VAST sample with both adaptive optics and common proper motion measurements , combined with a thorough literature search for companions , yielding a lower limit on the frequency of single , binary , triple , quadruple and quintuple A-type star systems of 56.4 _ { -4.0 } ^ { +3.8 } , 32.1 _ { -3.5 } ^ { +3.9 } , 9.0 _ { -1.8 } ^ { +2.8 } , 1.9 _ { -0.6 } ^ { +1.8 } and 0.6 _ { -0.2 } ^ { +1.4 } per cent , respectively .