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Post Info TOPIC: HD142527
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Title: Detailed modeling of dust distribution in the disk of HD 142527
Author: Kang-Lou Soon, Tomoyuki Hanawa, Takayuki Muto, Takashi Tsukagoshi, Munetake Momose

We investigate the dust distribution in the crescent disk around HD 142527 based on the continuum emission at 890 µm obtained by ALMA Cycle 0. The map is divided into 18 azimuthal sectors, and the radial intensity profile in each sector is reproduced with a 2D disk model. Our model takes account of scattering and inclination of the disk as well as the azimuthal dependence in intensity. When the dust is assumed to have the conventional composition and maximum size of 1 mm, the northwestern region (PA=329°-29°) cannot be reproduced. This is because the model intensity gets insensitive to the increase in surface density due to heavy self-scattering, reaching its ceiling much lower than the observed intensity. The ceiling depends on the position angle. When the scattering opacity is reduced by a factor of 10, the intensity distribution is reproduced successfully in all the sectors including those in the northwestern region. The best fit model parameters depend little on the scattering opacity in the southern region where the disk is optically thin. The contrast of dust surface density along PA is derived to be about 40, much smaller than the value for the cases of conventional opacities (70-130). These results strongly suggest that the albedo is lower than considered by some reasons at least in the northwestern region.

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Title: Spiral arms in the disk of HD 142527 from CO emission lines with ALMA
Author: Valentin Christiaens (1), Simon Casassus (1), Sebastian Perez (1), Gerrit van der Plas (1), François Ménard (2) ((1) Universidad de Chile (2) UMI-FCA, CNRS/INSU and Universidad de Chile)

In view of both the size of its gap and the previously reported asymmetries and near-infrared spiral arms, the transition disk of the Herbig Fe star HD 142527 constitutes a remarkable case study. This paper focuses on the morphology of the outer disk through ALMA observations of 12CO J=2-1, 12CO J=3-2 and 13CO J=2-1. Both 12CO J=2-1 and 12CO J=3-2 show spiral features of different sizes. The innermost spiral arm (S1) is a radio counterpart of the first near-infrared spiral observed by Fukagawa et al. (2006), but it is shifted radially outward. However, the most conspicuous CO spiral arm (S2) lies at the outskirts of the disk and had not been detected before. It corresponds to a cold density structure, with both brightness and excitation temperatures of order 13±2 K and conspicuous in the 12CO J=2-1 peak-intensity map, but faint in 12CO J=3-2. There is also a faint counterarm (S3), point-symmetrical of S2 with respect to the star. These three spirals are modelled separately with two different formulae that approximate the loci of density maxima in acoustic waves due to embedded planets. S1 could be fit relatively well with these formulae, compared to S2 and S3. Alternative scenarios such as gravitational instability or external tidal interaction are discussed. The impact of channelization on spectrally and spatially resolved peak intensity maps is also briefly addressed.

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ALMA Sheds Light on Planet-Forming Gas Streams

Astronomers using the Atacama Large Millimetre/submillimetre Array (ALMA) telescope have seen a key stage in the birth of giant planets for the first time. Vast streams of gas are flowing across a gap in the disc of material around a young star. These are the first direct observations of such streams, which are expected to be created by giant planets guzzling gas as they grow. The result is published on 2 January 2013 in the journal Nature.
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Title: High Contrast Imaging of the Close Environment of HD 142527
Authors: J. Rameau, G. Chauvin, A.-M. Lagrange, P. Thebault, J. Milli, J. H. Girard, M. Bonnefoy

Context. It has long been suggested that circumstellar disks surrounding young stars may be the signposts of planets, and still more since the recent discoveries of embedded substellar companions. The planet-disk interaction may create, according to models, large structures, gaps, rings or spirals, in the disk. In that sense, the Herbig star HD 142527 is particularly compelling as, its massive disk displays intriguing asymmetries that suggest the existence of a dynamical peturber of unknown nature.
Aims. Our goal was to obtain deep thermal images of the close circumstellar environment of HD 142527 to re-image the reported close-in structures (cavity, spiral arms) of the disk and to search for stellar and substellar companions that could be connected to their presence.
Results. The circumstellar environment of HD 142527 is revealed at an unprecedented spatial resolution down to the sub arcsecond level for the first time at 3.8 microns. Our images reveal important radial and azimuthal asymmetries which invalidate an elliptical shape for the disk as previously proposed. It rather suggests a bright inhomogeneous spiral arm plus various fainter spiral arms. We also confirm an inner cavity down to 30 AU and two important dips at position angles of 0 and 135 deg. The detection performance in angular differential imaging enables the exploration of the planetary mass regime for projected physical separations as close as 40 AU. The use of our detection map together with Monte Carlo simulations sets stringent constraints on the presence of planetary mass, brown dwarf or stellar companions as a function of the semi-major axis. They severely constrain the presence of massive giant planets with semi-major axis beyond 50AU, i.e. probably within the large disk's cavity that radially extends up to 145 AU or even further outside.

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Title: The dynamically disrupted gap in HD 142527
Authors: S. Casassus (1), S. Perez M. (1), A. Jordán (2), F. Ménard (3,4), J. Cuadra (2), M. R. Schreiber (5), A. S. Hales (6), B. Ercolano (7) ((1) Universidad de Chile, (2) Universidad Católica de Chile, (3) UMI-FCA 3386, CNRS / INSU at Universidad de Chile, (4) IPAG, Grenoble, France, (5) Universidad Valparaiso, (6) Joint ALMA Observatory, (7) Ludwig-Maximillians University, Munich)

The vestiges of planet formation have been observed in debris disks harboring young and massive gaseous giants. The process of giant planet formation is terminated by the dissipation of gas in the protoplanetary disk. The gas-rich disk around HD142527 features a small inner disk, a large gap from \sim10 to \sim140AU, and a massive outer disk extending out to \sim300AU. The gap could have been carved-out by a giant planet. We have imaged the outer regions of this gap using the adaptive-optics camera NICI on Gemini South. Our images reveal that the disk is dynamically perturbed. The outer boundary of the roughly elliptical gap appears to be composed of several segments of spiral arms. The stellar position is offset by 0.17±0.02" from the centroid of the cavity, consistent with earlier imaging at coarser resolutions. These transient morphological features are expected in the context of disk evolution in the presence of a perturbing body located inside the cavity. We perform hydro-dynamical simulations of the dynamical clearing of a gap in a disk. A 10Mjup body in a circular orbit at r = 90AU, perturbs the whole disks, even after thousands of orbits. By then the model disk has an eccentric and irregular cavity, flanked by tightly wound spiral arms, but it is still evolving far from steady state. A particular transient configuration that is a qualitative match to HD142527 is seen at 1.7Myr.

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HD142527_square 14
Position(2000): RA =15 56 41.8 Dec = -42 19 23
Size 14'1 x 14'1

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A close look at the protoplanetary disk around a young star by two teams of astronomers using the Subaru telescope on Mauna Kea has led to the unexpected discovery of two banana-shaped arcs facing each other. The disk, which surrounds the star HD142527, also shows a gap that could be the tumultuous birthplace of a planet, and an extended arc that could have formed during a recent encounter with a stellar neighbour. This discovery adds yet more variety to the bewildering diversity of protoplanetary disk shapes —ranging from donuts to spirals— that astronomers are finding as they study the birthing grounds of planets around other stars.

The astronomers used two different instruments on Subaru to observe the disk around HD 142527. A team from Nagoya University, the National Astronomical Observatory of Japan/Graduate University for Advanced Studies (NAOJ/Sokendai) and Kobe University observed the protoplanetary disk using the Coronagraphic Imager with Adaptive Optics (CIAO) in the near-infrared at 1.65 and 2.2 microns with a resolution of 0.13 arcseconds. This allowed the team to see details of the disk on a scale comparable to the orbit of Uranus and Neptune in our own solar system. Adaptive optics technology minimized the effect of Earth's atmosphere to improve the image quality. Coronagraphy, which hid the central star to make fainter material around it easier to detect, also contributed to the successful observations.

HD142527
Image of HD142527's protoplanetary disk in 24.5 microns from COMICS. The right had panel overlays contours of CIAO's near-infrared results on top of the COMICS image.

Another set of observations made by researchers from the University of Tokyo, Japan Aerospace Exploration Agency (JAXA), NAOJ/Sokendai,and Ibaraki University focused on the protoplanetary disk in mid-infrared wavelengths of 18.8 and 24.5 microns using Subaru's Cooled Mid-Infrared Camera and Spectrograph (COMICS). The images, with spatial resolutions of 0.5 arcseconds and 0.6 arcseconds, show radiation emitted by the disk out to beyond 100 astronomical units, or three times the distance between Neptune and the Sun. This is the first time that a protoplanetary disk has been detected in the mid-infrared to such a distance.
Before obtaining these detailed images, astronomers expected to find smooth disks around young stars. Yet, recent observations of disks around the stars GG Tauri and AB Aurigae have changed the picture. GG Tauri has a donut-shaped disk, and the disk around AB Aurigae is distinctly spiral-shaped. HD142527's "banana split" construction now seems to be a variation on the theme of diverse protoplanetary disks.

The most likely explanation for the "banana-split" shape of HD 142527 is the presence of another object orbiting the star, a much dimmer companion star or possibly a planet. The extended arc is most likely due to the gravitational tug of a passing star sometime in the last thousand years. Because astronomers expect most stars to be born in groups along with other stars, many features of HD142427's newly charted disk may be common to other stars born with companions.

The new images are the first images of HD142527's protoplanetary disk ever obtained, and among the very few examples of successful direct imaging of a protoplanetary disk from an Earth-based telescope. HD142527 lies only about 650 light-years from Earth, yet despite this star's proximity, turbulence in our own planet's atmosphere makes clear images of its faint protoplanetary disk extremely difficult to
get. The successful observations that led to these results relied on the size, stability and location of the Subaru telescope and its instruments, along with the use of its adaptive optics and coronagraphic technology.

Source naoj

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