The Gemini NICI Planet-Finding Campaign: The Frequency of Giant Planets around Young B and A Stars
Nielsen, Eric L.; Lin, Douglas N. C.; Shkolnik, Evgenya L.; Reid, I. Neill; Wahhaj, Zahed; Alencar, Silvia H. P.; Gregorio-Hetem, Jane; Biller, Beth A.; Liu, Michael C.; Close, Laird M.; Males, Jared R.; Boss, Alan; Ida, Shigeru; Kuchner, Marc; Skemer, Andrew J.; Hayward, Thomas L.; Chun, Mark; Ftaclas, Christ; Artymowicz, Pawel; Clarke, Fraser; de Gouveia Dal Pino, Elisabete; Hartung, Markus; Tecza, Matthias; Thatte, Niranjan; Toomey, Douglas W.
United States, Chile, Germany, Brazil, Canada, United Kingdom, Japan
Abstract
We have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf and planetary companions as part of the Gemini NICI Planet-Finding Campaign. Our survey represents the largest, deepest survey for planets around high-mass stars (≈1.5-2.5 M ⊙) conducted to date and includes the planet hosts β Pic and Fomalhaut. We obtained follow-up astrometry of all candidate companions within 400 AU projected separation for stars in uncrowded fields and identified new low-mass companions to HD 1160 and HIP 79797. We have found that the previously known young brown dwarf companion to HIP 79797 is itself a tight (3 AU) binary, composed of brown dwarfs with masses 58^{+21}_{-20} M Jup and 55^{+20}_{-19} M Jup, making this system one of the rare substellar binaries in orbit around a star. Considering the contrast limits of our NICI data and the fact that we did not detect any planets, we use high-fidelity Monte Carlo simulations to show that fewer than 20% of 2 M ⊙ stars can have giant planets greater than 4 M Jup between 59 and 460 AU at 95% confidence, and fewer than 10% of these stars can have a planet more massive than 10 M Jup between 38 and 650 AU. Overall, we find that large-separation giant planets are not common around B and A stars: fewer than 10% of B and A stars can have an analog to the HR 8799 b (7 M Jup, 68 AU) planet at 95% confidence. We also describe a new Bayesian technique for determining the ages of field B and A stars from photometry and theoretical isochrones. Our method produces more plausible ages for high-mass stars than previous age-dating techniques, which tend to underestimate stellar ages and their uncertainties.