The International Deep Planet Survey

Abstract

Breakthrough direct detections of planetary companions orbiting A-type stars confirm the existence of massive planets at relatively large separations, but dedicated surveys are required to estimate the frequency of similar planetary systems. To measure the first estimation of the giant exoplanetary systems frequency at large orbital separation around A-stars, we have conducted a deep-imaging survey of young (8−400 Myr), nearby (19−84 pc) A-and F-stars to search for substellar companions in the ∼10−300 AU range. The sample of 42 stars combines all A-stars observed in previous AO planet search surveys reported in the literature with new AO observations from VLT/NaCo and Gemini/NIRI. It represents an initial subset of the International Deep Planet Survey (IDPS) sample of stars covering M-to B-stars. The data were obtained with diffraction-limited observations in H-and K s -band combined with angular differential imaging to suppress the speckle noise of the central stars, resulting in typical 5σ detection limits in magnitude difference of 12 mag at 1 , 14 mag at 2 and 16 mag at 5 which is sufficient to detect massive planets. A detailed statistical analysis of the survey results is performed using Monte Carlo simulations. Considering the planet detections, we estimate the fraction of A-stars having at least one massive planet (3−14 M Jup ) in the range 5−320 AU to be inside 5.9−18.8% at 68% confidence, assuming a flat distribution for the mass of the planets. By comparison, the brown dwarf (15−75 M Jup ) frequency for the sample is 2.0−8.9% at 68% confidence in the range 5−320 AU. Assuming power law distributions for the mass and semimajor axis of the planet population, the AO data are consistent with a declining number of massive planets with increasing orbital radius which is distinct from the rising slope inferred from radial velocity (RV) surveys around evolved A-stars and suggests that the peak of the massive planet population around A-stars may occur at separations between the ranges probed by existing RV and AO observations. Finally, we report the discovery of three new close M-star companions to HIP 104365 and HIP 42334.

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

“…The median of this offset for these 28 stars is 135 Myr, an increase in age of 55%, which significantly increases the minimum detectable mass around these stars. The typical contrast achieved at 2" in Vigan et al (2012) is 14.2 mags, which for 26 of these 28 stars corresponds to planetary masses using their ages and the Baraffe et al (2003) evolutionary models for companion luminosity. When we instead adopt the median of our Bayesian age distributions for these stars, only 18 stars reach planetary masses at 2", and the median increase in detectable mass at 2" for these 18 stars is 22%.…”

“…Moór et al (2006) and Rhee et al (2007) expanded this method to other high mass stars with debris disks, noting that many of these stars also lay near the bottom of the color-magnitude diagram. Vigan et al (2012) use a similar approach by defining the dereddened single-star sequence of high mass stars in the Pleiades on the same [M V , B − V ] color-magnitude diagram and then assigning the age of the Pleiades (125 Myr, Stauffer et al 1998) to stars with similar color-magnitude positions as the Pleiades A stars. However, this common approach to flagging young A stars is likely too optimistic in many cases, due to two effects: (1) the degeneracy between the effects of age and metallicity, and (2) the increase of main-sequence lifetime with decreasing stellar mass.…”

“…As expected, the Bayesian approach results in a significant tail at large ages (>200 Myr). By contrast, almost half of the Vigan et al (2012) ages (17/39) are incorrectly assumed to be 125 Myr, the age of the Pleiades. For stars not in young moving groups, we compute the offset from the Vigan et al (2012) ages to the median age from our Bayesian analysis.…”

“…By contrast, almost half of the Vigan et al (2012) ages (17/39) are incorrectly assumed to be 125 Myr, the age of the Pleiades. For stars not in young moving groups, we compute the offset from the Vigan et al (2012) ages to the median age from our Bayesian analysis. The median of this offset for these 28 stars is 135 Myr, an increase in age of 55%, which significantly increases the minimum detectable mass around these stars.…”

“…The four HR 8799 planets were found as part of the International Deep Planet Survey (IDPS), and an analysis of the frequency of giant planets around A stars was presented recently by Vigan et al (2012). Based on their sample of 38 A stars and 4 early-F stars, they find that between 6 and 19% of A stars have a giant planet between 5 and 320 AU at 68% confidence.…”