Friday, June 7, 2013

1306.1233 (Eric L. Nielsen et al.)

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

Eric L. Nielsen, Michael C. Liu, Zahed Wahhaj, Beth A. Biller, Thomas L. Hayward, Laird M. Close, Jared R. Males, Andrew J. Skemer, Mark Chun, Christ Ftaclas, Silvia H. P. Alencar, Pawel Artymowicz, Alan Boss, Fraser Clarke, Elisabete de Gouveia Dal Pino, Jane Gregorio-Hetem, Markus Hartung, Shigeru Ida, Marc Kuchner, Douglas N. C. Lin, I. Neill Reid, Evgenya L. Shkolnik, Matthias Tecza, Niranjan Thatte, Douglas W. Toomey
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.
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