The VAST Survey – III. The multiplicity of A-type stars within 75 pc

Abstract

With a combination of adaptive optics imaging and a multi-epoch common proper motion search, we have conducted a large volume-limited (D 75 pc) multiplicity survey of Atype 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 ± 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 ± 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 +3.8 −4.0 , 32.1 +3.9 −3.5 , 9.0 +2.8 −1.8 , 1.9 +1.8 −0.6 and 0.6 +1.4 −0.2 per cent, respectively.

Precession and accretion in circumbinary discs: the case of HD 104237

“…Duquennoy & Mayor 1991;Raghavan et al 2010;Janson et al 2012;De Rosa et al 2014) and the binary fraction increases towards earlier spectral type. It is also known that binarity increases towards younger ages in pre-main sequence objects (e.g.…”

“…Raghavan et al 2010;Janson et al 2012), but with a strong bias towards equal masses at small binary separations (De Rosa et al 2014). However, Kouwenhoven et al (2005) found that for a sample of young A-stars, the mass ratio is biased towards unequal masses, indicating that accretion at young ages plays an important role in changing the primordial mass ratio into the one observed in older systems.…”

Critical study of the distribution of rotational velocities of Be stars

“…Recent studies based on adaptive optics surveys (De Rosa et al 2014), and VLTI/PIONIER interferometry (Marion et al 2014) note an increase of 13% A-type stars among objects considered single object up to now.…”

Evolution of binary seeds in collapsing protostellar gas clouds

“…They found that binaries have log-normal separation distribution, and the number of binaries with wide separations decreases with increasing q, while the number of binaries with close separations is roughly constant or increase with increasing q. Raghavan et al (2010) and De Rosa et al (2014) found a similar distribution of q for A-type binaries as Duquennoy & Mayor (1991).…”