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Saint-Hippolyte-du-Fort, France

Thalmann C.,Max Planck Institute for Astronomy | Grady C.A.,Eureka Scientific and Goddard Space Flight Center | Goto M.,Max Planck Institute for Astronomy | Wisniewski J.P.,University of Washington | And 51 more authors.
Astrophysical Journal Letters

We present H- and Ks-band imaging data resolving the gap in the transitional disk around LkCa 15, revealing the surrounding nebulosity. We detect sharp elliptical contours delimiting the nebulosity on the inside as well as the outside, consistent with the shape, size, ellipticity, and orientation of starlight reflected from the far-side disk wall, whereas the near-side wall is shielded from view by the disk's optically thick bulk. We note that forward scattering of starlight on the near-side disk surface could provide an alternate interpretation of the nebulosity. In either case, this discovery provides confirmation of the disk geometry that has been proposed to explain the spectral energy distributions of such systems, comprising an optically thick disk with an inner truncation radius of ∼46 AU enclosing a largely evacuated gap. Our data show an offset of the nebulosity contours along the major axis, likely corresponding to a physical pericenter offset of the disk gap. This reinforces the leading theory that dynamical clearing by at least one orbiting body is the cause of the gap. Based on evolutionary models, our high-contrast imagery imposes an upper limit of 21MJup on companions at separations outside of 0. ″1 and of 13MJup outside of 0. ′2. Thus, we find that a planetary system around LkCa 15 is the most likely explanation for the disk architecture. © 2010. The American Astronomical Society. Source

Thalmann C.,University of Amsterdam | Janson M.,University of Toronto | Buenzli E.,ETH Zurich | Brandt T.D.,Princeton University | And 50 more authors.
Astrophysical Journal Letters

We present high-contrast images of HR 4796 A taken with Subaru/HiCIAO in the H band, resolving the debris disk in scattered light. The application of specialized angular differential imaging methods allows us to trace the inner edge of the disk with high precision and reveals a pair of "streamers" extending radially outward from the ansae. Using a simple disk model with a power-law surface brightness profile, we demonstrate that the observed streamers can be understood as part of the smoothly tapered outer boundary of the debris disk, which is most visible at the ansae. Our observations are consistent with the expected result of a narrow planetesimal ring being ground up in a collisional cascade, yielding dust with a wide range of grain sizes. Radiation forces leave large grains in the ring and push smaller grains onto elliptical or even hyperbolic trajectories. We measure and characterize the disk's surface brightness profile, and confirm the previously suspected offset of the disk's center from the star's position along the ring's major axis. Furthermore, we present first evidence for an offset along the minor axis. Such offsets are commonly viewed as signposts for the presence of unseen planets within a disk's cavity. Our images also offer new constraints on the presence of companions down to the planetary mass regime (∼9 M Jup at 0″.5, ∼3M Jup at 1″). © 2011. The American Astronomical Society. All rights reserved. Source

Brandt T.D.,Institute for Advanced Study | McElwain M.W.,NASA | Turner E.L.,Princeton University | Turner E.L.,University of Tokyo | And 54 more authors.
Astrophysical Journal

We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars. The stars cover a wide range of ages and spectral types, and include five detections (κ And b, two60 M J brown dwarf companions in the Pleiades, PZ Tel B, and CD-35 2722B). For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B. We conduct a uniform, Bayesian analysis of all stellar ages using both membership in a kinematic moving group and activity/rotation age indicators. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most of the integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis of the distribution function derived from radial-velocity planets, finding model-dependent values of30-100 AU. Finally, we model the entire substellar sample, from massive brown dwarfs to a theoretically motivated cutoff at5 M J, with a single power-law distribution. We find that p(M, a)M -0.65 ± 0.60 a -0.85 ± 0.39 (1σ errors) provides an adequate fit to our data, with 1.0%-3.1% (68% confidence) of stars hosting 5-70 M J companions between 10 and 100 AU. This suggests that many of the directly imaged exoplanets known, including most (if not all) of the low-mass companions in our sample, formed by fragmentation in a cloud or disk, and represent the low-mass tail of the brown dwarfs. © 2014. The American Astronomical Society. All rights reserved.. Source

Brandt T.D.,Princeton University | McElwain M.W.,NASA | Turner E.L.,Princeton University | Turner E.L.,University of Tokyo | And 46 more authors.
Astrophysical Journal

We describe Algorithms for Calibration, Optimized Registration, and Nulling the Star in Angular Differential Imaging (ACORNS-ADI), a new, parallelized software package to reduce high-contrast imaging data, and its application to data from the SEEDS survey. We implement several new algorithms, including a method to register saturated images, a trimmed mean for combining an image sequence that reduces noise by up to ∼20%, and a robust and computationally fast method to compute the sensitivity of a high-contrast observation everywhere on the field of view without introducing artificial sources. We also include a description of image processing steps to remove electronic artifacts specific to Hawaii2-RG detectors like the one used for SEEDS, and a detailed analysis of the Locally Optimized Combination of Images (LOCI) algorithm commonly used to reduce high-contrast imaging data. ACORNS-ADI is written in python. It is efficient and open-source, and includes several optional features which may improve performance on data from other instruments. ACORNS-ADI requires minimal modification to reduce data from instruments other than HiCIAO. It is freely available for download at www.github.com/t-brandt/acorns-adi under a Berkeley Software Distribution (BSD) license. © 2013. The American Astronomical Society. All rights reserved. Source

Thalmann C.,University of Amsterdam | Janson M.,Princeton University | Buenzli E.,University of Arizona | Brandt T.D.,Princeton University | And 49 more authors.
Astrophysical Journal Letters

We present Subaru/HiCIAO H-band high-contrast images of the debris disk around HIP 79977, whose presence was recently inferred from an infrared excess. Our images resolve the disk for the first time, allowing characterization of its shape, size, and dust grain properties. We use angular differential imaging (ADI) to reveal the disk geometry in unpolarized light out to a radius of 2″, as well as polarized differential imaging to measure the degree of scattering polarization out to 1.″5. In order to strike a favorable balance between suppression of the stellar halo and conservation of disk flux, we explore the application of principal component analysis to both ADI and reference star subtraction. This allows accurate forward modeling of the effects of data reduction on simulated disk images, and thus direct comparison with the imaged disk. The resulting best-fit values and well-fitting intervals for the model parameters are a surface brightness power-law slope of Sout = -3.2[-3.6, -2.9], an inclination of i = 84°[81°, 86°], a high Henyey-Greenstein forward-scattering parameter of g = 0.45[0.35, 0.60], and a non-significant disk-star offset of u = 3.0[-1.5, 7.5] AU = 24[-13, 61] mas along the line of nodes. Furthermore, the tangential linear polarization along the disk rises from 10% at 0.″5 to 45% at 1.″5. These measurements paint a consistent picture of a disk of dust grains produced by collisional cascades and blown out to larger radii by stellar radiation pressure. © 2013. The American Astronomical Society. All rights reserved. Source

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