Robert De Rosa  (University of Exeter)

Title: A volume-limited multiplicity survey of A-type stars

We present the initial results of the first volume-limited (D<75 pc)
AO multiplicity survey of A-stars. This project is an international
collaboration, utilizing the Gemini, CFHT, Palomar, Lick and WHT
Observatories, and is part of an ongoing programme to define target
samples for the upcoming Gemini Planet Imager (GPI) instrument. The
recently imaged planets orbiting dusty, young A-type stars highlights
the promise of future AO planet searches around massive stars and
reinforces the need to understand the environment in which they
form. The primary results from this study -- the characterisation of
the binary frequency and distribution of separations and mass ratios
-- provide insight into the formation processes of these multiple
systems and the impact on planet formation. Analysis of the extant
data (~85% of the sample, 290 stars) reveals a trend of increasing
multiplicity with higher primary mass suggested by previous surveys of
lower mass stars. An investigation of the binary mass ratio
distribution of this volume-limited sample also provides a statistical
tests of binary formation theories. In addition to providing the first
comprehensive statistical constraints on the A-star stellar binary
population in the ~20-2000 AU separation range, we have been able to
search for brown dwarfs around a substantial portion of our sample;
there are 18 candidate sub-stellar candidates that are awaiting
follow-up observations to test for common proper motion.