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Title: An Optical/near-infrared investigation of HD 100546 b with the Gemini Planet Imager and MagAO
Author: Julien Rameau, Katherine B. Follette, Laurent Pueyo, Christian Marois, Bruce Macintosh, Maxwell Millar-Blanchaer, Jason J. Wang, David Vega, Rene Doyon, David Lafreniere, Eric L. Nielsen, Vanessa Bailey, Jeffrey K. Chilcote, Laird M. Close, Thomas M. Esposito, Jared R. Males, Stanimir Metchev, Katie M. Morzinski, Jean-Baptiste Ruffio, Schuyler G. Wolff, S. M. Ammons, Travis S. Barman, Joanna Bulger, Tara Cotten, Robert J. De Rosa, Gaspard Duchene, Michael P. Fitzgerald, Stephen Goodsell, James R. Graham, Alexandra Z. Greenbaum, Pascale Hibon, Li-Wei Hung, Patrick Ingraham, Paul Kalas, Quinn Konopacky, James E. Larkin, Jerome Maire, Franck Marchis, Rebecca Oppenheimer, David Palmer, Jennifer Patience, Lisa Poyneer, Abhijith Rajan, Fredrik T. Rantakyro, Dmitry Savransky, Adam C. Schneider, et al. (7 additional authors not shown)

We present H band spectroscopic and Halpha photometric observations of HD 100546 obtained with GPI and MagAO. We detect H band emission at the location of the protoplanet HD 100546b, but show that choice of data processing parameters strongly affects the morphology of this source. It appears point-like in some aggressive reductions, but rejoins an extended disk structure in the majority of the others. Furthermore, we demonstrate that this emission appears stationary on a timescale of 4.6 yrs, inconsistent at the 2sigma level with a Keplerian clockwise orbit at 59 au in the disk plane. The H band spectrum of the emission is inconsistent with any type of low effective temperature object or accreting protoplanetary disk. It strongly suggests a scattered light origin, as it is consistent with the spectrum of the star and the spectra extracted at other locations in the disk. A non detection at the 5sigma level of HD 100546b in differential Halpha imaging places an upper limit, assuming the protoplanet lies in a gap free of extinction, on the accretion luminosity and accretion rate of 1.7E-4 Lsun and MMdot<6.4E-7Mjup^2/yr for 1Rjup. These limits are comparable to the accretion luminosity and rate of TTauri-stars or LkCa 15b. Taken together, these lines of evidence suggest that the H band source at the location of HD 100546b is not emitted by a planetary photosphere or an accreting circumplanetary disk but is a disk feature enhanced by the PSF subtraction process. This non-detection is consistent with the non-detection in the K band reported in an earlier study but does not exclude the possibility that HD 100546b is deeply embedded.

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RE: HD 100546
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Astronomers peer into the 'amniotic sac' of a planet-hosting star

 Astronomers have successfully peered through the 'amniotic sac' of a star that is still forming to observe the innermost region of a burgeoning solar system for the first time.
In a research paper published today in the journal Monthly Notices of the Royal Astronomical Society, an international team of astronomers describe surprising findings in their observations of the parent star, which is called HD 100546.

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Title: Resolving structure of the disk around HD100546 at 7 mm with ATCA
Author: Christopher Wright, Sarah Maddison, David Wilner, Michael Burton, Dave Lommen, Ewine van Dishoeck, Paola Pinilla, Tyler Bourke, Francois Menard, Catherine Walsh

There is much evidence that planet formation is occurring in the disk around the Herbig Be star HD100546. To learn more about the processes occurring in this disk we conducted high resolution imaging at 43/45 GHz with the Australia Telescope Compact Array (ATCA). Multiple array configurations were used, providing a best spatial resolution of ~ 0.15 arcsec, or 15 AU at HD100546's distance of ~ 100 pc. Significant structure is revealed, but its precise form is dependent on the u-v plane sampling used for the image reconstruction. At a resolution of \leq 30 AU we detected an inner gap in the disk with a radius of ~ 25 AU and a position angle approximately along the known disk major axis. With different weighting, and an achieved resolution of ~ 15 AU, emission appears at the centre and the disk takes on the shape of an incomplete ring, much like a horseshoe, again with a gap radius of ~ 25 AU. The position angle of the disk major axis and its inclination from face-on are determined to be 140°±5° and 40°±5° respectively. The ~ 25 AU gap radius is confirmed by a null in the real part of the binned visibilities at 320±10 k, whilst the non-axisymmetric nature is also confirmed through significant structure in the imaginary component. The emission mechanism at the central peak is most likely to be free-free emission from a stellar or disk wind. Overall our data support the picture of at least one, but probably several, giant planets orbiting HD100546 within 25 AU.

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Title: Planet or Brown Dwarf? Inferring the Companion Mass in HD 100546 from the Wall Shape using Mid-Infrared Interferometry
Authors: Gijs D. Mulders, Sijme-Jan Paardekooper, Olja Panic, Carsten Dominik, Roy van Boekel, Thorsten Ratzka

Giant planets form in protoplanetary disks while these disks are still gas-rich, and can reveal their presence through the annular gaps they carve out. HD 100546 is a gas-rich disk with a wide gap between a radius of ~1 and 13 AU, possibly cleared out by a planetary companion or planetary system. We want to identify the nature of the unseen companion near the far end of the disk gap. We use mid-infrared interferometry at multiple baselines to constrain the curvature of the disk wall at the far end of the gap. We use 2D hydrodynamical simulations of embedded planets and brown dwarfs to estimate viscosity of the disk and the mass of a companion close to the disk wall. We find that the disk wall at the far end of the gap is not vertical, but rounded-off by a gradient in the surface density. Such a gradient can be reproduced in hydrodynamical simulations with a single, heavy companion (>=30...80 Jupiter masses) while the disk has viscosity of at least \alpha{} >~ 5 10^-3. Taking into account the changes in the temperature structure after gap opening reduces the lower limit on the planet mass and disk viscosity to 20 Jupiter masses and \alpha{} = 2 10^-3. The object in the disk gap of HD 100546 that shapes the disk wall is most likely a 60(+20)(-40) Jupiter mass brown dwarf, while the disk viscosity is estimated to be at least \alpha{} = 2 10^-3. The disk viscosity is an important factor in estimating planetary masses from disk morphologies: more viscous disks need heavier planets to open an equally deep gap.

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Title: A young protoplanet candidate embedded in the circumstellar disk of HD100546
Authors: Sascha P. Quanz (1), Adam Amara (1), Michael R. Meyer (1), Matthew A. Kenworthy (2), Markus Kasper (3), Julien H. Girard (4) ((1) ETH Zurich, (2) Sterrewacht Leiden, (3) ESO Garching, (4) ESO Santiago de Chile)

We present high-contrast observations of the circumstellar environment of the Herbig Ae/Be star HD100546. The final 3.8 micron image reveals an emission source at a projected separation of 0.48" ±0.04" (corresponding to ~47 ±4 AU at a position angle of 8.9 ±0.9 degree. The emission appears slightly extended with a point source component with an apparent magnitude of 13.2 ±0.4 mag. The position of the source coincides with a local deficit in polarization fraction in near-infrared polarimetric imaging data, which probes the surface of the well-studied circumstellar disk of HD100546. This suggests a possible physical link between the emission source and the disk. Assuming a disk inclination of ~47 degree the de-projected separation of the object is ~68 AU. Assessing the likelihood of various scenarios we favour an interpretation of the available high-contrast data with a planet in the process of forming. Follow-up observations in the coming years can easily distinguish between the different possible scenarios empirically. If confirmed, HD100546 "b" would be a unique laboratory to study the formation process of a new planetary system, with one giant planet currently forming in the disk and a second planet possibly orbiting in the disk gap at smaller separations.

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Candidate protoplanet spotted inside its stellar womb

Astronomers using ESO's Very Large Telescope have obtained what is likely the first direct observation of a forming planet still embedded in a thick disc of gas and dust. If confirmed, this discovery will greatly improve our understanding of how planets form and allow astronomers to test the current theories against an observable target.
An international team led by Sascha Quanz (ETH Zurich, Switzerland) has studied the disc of gas and dust that surrounds the young star HD 100546, a relatively nearby neighbour located 335 light-years from Earth. They were surprised to find what seems to be a planet in the process of being formed, still embedded in the disc of material around the young star. The candidate planet would be a gas giant similar to Jupiter.
 
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Title: Resolving HD 100546 disc in the mid-infrared: Small and asymmetric inner disc inside a bright symmetric edge of the outer disc
Authors: O. Panic, Th. Ratzka, G. D. Mulders, C. Dominik, R. van Boekel, Th. Henning, W. Jaffe, M. Min

A region of roughly half of the Solar system scale around the star HD 100546 is largely cleared of gas and dust, in contrast to the outer disc extending to about 400 AU. However, some material is observed in the immediate vicinity of the star, called the inner disc. Studying the structure of the inner and the outer disc is a first step to establish the origin of the gap between them and possibly link it to presence of planets. We answer how the dust is distributed within and outside the gap, and constrain the disc geometry. We observe the disc with VLTI interferometer N-band instrument MIDI. At these wavelengths disc completely dominates over the stellar emission. With baseline lengths of 40m our long baseline observations (8.2m telescopes) are most sensitive to the inner few AU from the star, and we combine them with observations at shorter, 15m baselines (1.8m telescopes), to probe emission beyond the gap at up to 20AU from the star. We derive an upper limit of 0.7AU for the mid-infrared size of the inner disc, from our longest baseline data. The chromatic phases show that the N-band brightness of the inner disc is not point-symmetric. Our short baseline data place a bright symmetric ring of emission at 11AU. This is consistent with prior observations of the transition region between the gap and the outer disc, known as the disc wall. The ring inclination and position angles are constrained by our data to i=53±8deg and PA=145±5deg. These values are close to known estimates of the rim and disc geometry and suggest co-planarity. Micron-sized dust is distributed asymmetrically in the region from the dust sublimation radius to less than 0.7AU from HD100546 in observations from 2004 Jun to 2005 Dec. This small dusty disc is separated from the symmetric edge of the outer disc by a large, ~10AU wide gap cleared of micron-sized dust but possibly populated by planetesimals and/or planets.

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Title: Warm gas at 50 AU in the disk around Herbig Be star HD 100546
Authors: M. Goto (1), G. van der Plas (2), M. van den Ancker (3), C. P. Dullemond (1,4), A. Carmona (5), Th. Henning (1), G. Meeus (6), H. Linz (1), B. Stecklum (7) ((1) MPIA, (2) University van Amsterdam, (3) ESO, (4) Universität Heidelberg, (5) University of Geneva, (6) Universidad Autónoma de Madrid, (7) Thüringer Landessternwarte Tautenburg)

The disk atmosphere is one of the fundamental elements of theoretical models of a protoplanetary disk. However, the direct observation of the warm gas (>> 100 K) at large radius of a disk (>> 10 AU) is challenging, because the line emission from warm gas in a disk is usually dominated by the emission from an inner disk. Our goal is to detect the warm gas in the disk atmosphere well beyond 10 AU from a central star in a nearby disk system of the Herbig Be star HD 100546. We measured the excitation temperature of the vibrational transition of CO at incremental radii of the disk from the central star up to 50 AU, using an adaptive optics system combined with the high-resolution infrared spectrograph CRIRES at the VLT. The observation successfully resolved the line emission with 0".1 angular resolution, which is 10 AU at the distance of HD 100546. Population diagrams were constructed at each location of the disk, and compared with the models calculated taking into account the optical depth effect in LTE condition. The excitation temperature of CO is 400-500 K or higher at 50 AU away from the star, where the blackbody temperature in equilibrium with the stellar radiation drops as low as 90 K. This is unambiguous evidence of a warm disk atmosphere far away from the central star.

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HD100546
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Title: Detection of CH+ emission from the disc around HD100546
Authors: W.-F. Thi, F. Ménard, G. Meeus, C. Martin-Zaïdi, P. Woitke, E. Tatulli, M. Benisty, I. Kamp, I. Pascucci, C. Pinte, C. A. Grady, S. Brittain, G.J. White, C. D. Howard, G. Sandell, C. Eiroa

Despite its importance in the thermal-balance of the gas and in the determination of primeval planetary atmospheres, the chemistry in protoplanetary discs remains poorly constrained with only a handful of detected species. We observed the emission from disc around the Herbig Be star HD 100546 with the PACS instrument in the spectroscopic mode on board the Herschel Space Telescope as part of the Gas in Protoplanetary Systems (GASPS) programme and used archival data from the DIGIT programme to search for the rotational emission of CH+. We detected in both datasets an emission line centred at 72.16 micron that most likely corresponds to the J=5-4 rotational emission of CH+. The J=3-2 and 6-5 transitions are also detected albeit with lower confidence. Other CH+ rotational lines in the PACS observations are blended with water lines. A rotational diagram analysis shows that the CH+ gas is warm at 323 (+2320/-151) K with a mass of 3e-14-5e-12 M_Sun. We modelled the CH+ chemistry with the chemo-physical code ProDiMo using a disc density structure and grain parameters that match continuum observations and near- and mid-infrared interferometric data. The model suggests that CH+ is most abundant at the location of the disc rim at 10-13 AU from the star where the gas is warm, consistent with previous observations of hot CO gas emission.

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HD 100546
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Title: Constraining the structure of the planet-forming region in the disk of the Herbig Be star HD 100546
Authors: E. Tatulli, M. Benisty, F. Ménard, P. Varnière, C. Martin-Zaidi, W.-F. Thi, C. Pinte, F. Massi, G. Weigelt, K.-H. Hofmann, R. G. Petrov

Studying the physical conditions in circumstellar disks is a crucial step toward understanding planet formation. Of particular interest is the case of HD 100546, a Herbig Be star that presents a gap within the first 13 AU of its protoplanetary disk, that may originate in the dynamical interactions of a forming planet. We gathered a large amount of new interferometric data using the AMBER/VLTI instrument in the H- and K-bands to spatially resolve the warm inner disk and constrain its structure. Then, combining these measurements with photometric observations, we analyse the circumstellar environment of HD 100546 in the light of a passive disk model based on 3D Monte-Carlo radiative transfer. Finally, we use hydrodynamical simulations of gap formation by planets to predict the radial surface density profile of the disk and test the hypothesis of ongoing planet formation. The SED and the NIR interferometric data are adequately reproduced by our model. We show that the H- and K-band emissions are coming mostly from the inner edge of the internal dust disk, located near 0.24 AU from the star, i.e., at the dust sublimation radius in our model. We directly measure an inclination of 33° ±11° and a position angle of 140° ±16° for the inner disk. This is similar to the values found for the outer disk (i \simeq 42°, PA \simeq 145°), suggesting that both disks may be coplanar. We finally show that 1 to 8 Jupiter mass planets located at ~ 8 AU from the star would have enough time to create the gap and the required surface density jump of three orders of magnitude between the inner and outer disk. However, no information on the amount of matter left in the gap is available, which precludes us from setting precise limits on the planet mass, for now.

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