The Gemini NICI Planet-Finding Campaign: The Frequency of Giant Planets around Young B and A Stars

TL;DR

This study conducted the largest and deepest high-contrast imaging survey of young B and A stars, finding that giant planets at large separations are rare around such high-mass stars, and introduced a new Bayesian age estimation method.

Contribution

It provides the first comprehensive survey of giant planets around high-mass stars and develops a novel Bayesian technique for more accurate age determination of these stars.

Findings

Fewer than 20% of 2 M_sun stars host giant planets >4 M_Jup between 59-460 AU.

Less than 10% of B and A stars have planets >10 M_Jup between 38-650 AU.

Large-separation giant planets are uncommon around B and A stars.

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_sun) conducted to date and includes the planet hosts beta 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_sun 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.