THE GEMINI/NICI PLANET-FINDING CAMPAIGN: THE FREQUENCY OF PLANETS AROUND YOUNG MOVING GROUP STARS*

摘要

We report results of a direct imaging survey for giant planets around 80 members of the β Pic, TW Hya, Tucana-Horologium, AB Dor, and Hercules-Lyra moving groups, observed as part of the Gemini/NICI Planet-Finding Campaign. For this sample, we obtained median contrasts of ΔH = 13.9 mag at 1'' in combined CH4 narrowband ADI+SDI mode and median contrasts of ΔH = 15.1 mag at 2'' in H-band ADI mode. We found numerous (70) candidate companions in our survey images. Some of these candidates were rejected as common-proper motion companions using archival data; we reobserved with Near-Infrared Coronagraphic Imager (NICI) all other candidates that lay within 400?AU of the star and were not in dense stellar fields. The vast majority of candidate companions were confirmed as background objects from archival observations and/or dedicated NICI Campaign followup. Four co-moving companions of brown dwarf or stellar mass were discovered in this moving group sample: PZ Tel B (36 ± 6 M Jup, 16.4 ± 1.0?AU), CD–35 2722B (31 ± 8 M Jup, 67 ± 4?AU), HD?12894B (0.46?± 0.08 M ☉, 15.7 ± 1.0?AU), and BD+07 1919C (0.20 ± 0.03 M ☉, 12.5 ± 1.4?AU). From a Bayesian analysis of the achieved H band ADI and ASDI contrasts, using power-law models of planet distributions and hot-start evolutionary models, we restrict the frequency of 1-20 M Jup companions at semi-major axes from 10-150?AU to 18% at a 95.4% confidence level using DUSTY models and to 6% at a 95.4% using COND models. Our results strongly constrain the frequency of planets within semi-major axes of 50?AU as well. We restrict the frequency of 1-20 M Jup companions at semi-major axes from 10-50?AU to 21% at a 95.4% confidence level using DUSTY models and to 7% at a 95.4% using COND models. This survey is the deepest search to date for giant planets around young moving group stars.