Talk abstract

We present the first volume-limited (D $<$ 75 pc) multiplicity survey of over 400 A-type stars over the separation range of 10 to 2000 AU. Understanding the multiplicity of these massive stars allows the investigation of binary formation models, the unexplained X-ray emission of a subset of A-stars, the stability of circumstellar disks and the formation of planetary systems. Utilising adaptive-optics systems at five 3-8m telescopes, we have characterised the binary population of A-type stars to a sensitivity limit reaching the bottom of the Main Sequence. The binary population shows an increase in the multiplicity fraction for early-type primaries relative to lower-mass stars. The peak of the separation distribution is also significantly larger, at 350 AU (c.f. 40 AU for solar-type primaries), which may have implications for planet formation. The companion mass function is also resolved, indicating higher frequency of lower-mass companions. For the youngest subset of the sample, the sensitivity is sufficient to detect brown dwarfs, and we present the first measurement of the frequency of substellar companions to massive stars.