379 research outputs found
Evidence for a circumplanetary disk around protoplanet PDS 70 b
We present the first observational evidence for a circumplanetary disk around
the protoplanet PDS~70~b, based on a new spectrum in the band acquired with
VLT/SINFONI. We tested three hypotheses to explain the spectrum: Atmospheric
emission from the planet with either (1) a single value of extinction or (2)
variable extinction, and (3) a combined atmospheric and circumplanetary disk
model. Goodness-of-fit indicators favour the third option, suggesting
circumplanetary material contributing excess thermal emission --- most
prominent at m. Inferred accretion rates (-- yr) are compatible with observational
constraints based on the H and Br lines. For the planet, we
derive an effective temperature of 1500--1600 K, surface gravity , radius , mass , and possible thick clouds.
Models with variable extinction lead to slightly worse fits. However, the
amplitude (mag) and timescale of variation
(~years) required for the extinction would also suggest
circumplanetary material.Comment: 8 pages, 2 figures, 1 table. This is a pre-copyedited,
author-produced PDF of an article accepted for publication in ApJL on 2019
May 1
Image quality and high contrast improvements on VLT/NACO
NACO is the famous and versatile diffraction limited NIR imager and
spectrograph with which ESO celebrated 10 years of Adaptive Optics at the VLT.
Since two years a substantial effort has been put in to understanding and
fixing issues that directly affect the image quality and the high contrast
performances of the instrument. Experiments to compensate the non-common-path
aberrations and recover the highest possible Strehl ratios have been carried
out successfully and a plan is hereafter described to perform such measurements
regularly. The drift associated to pupil tracking since 2007 was fixed in
October 2011. NACO is therefore even better suited for high contrast imaging
and can be used with coronagraphic masks in the image plane. Some contrast
measurements are shown and discussed. The work accomplished on NACO will serve
as reference for the next generation instruments on the VLT, especially those
working at the diffraction limit and making use of angular differential imaging
(i.e. SPHERE, VISIR, possibly ERIS).Comment: 14 pages, 5 figures, SPIE 2012 Astronomical Instrumentation
Proceedin
CO gas inside the protoplanetary disk cavity in HD 142527: disk structure from ALMA
Inner cavities and annular gaps in circumstellar disks are possible signposts
of giant planet formation. The young star HD 142527 hosts a massive
protoplanetary disk with a large cavity that extends up to 140 au from the
central star, as seen in continuum images at infrared and millimeter
wavelengths. Estimates of the survival of gas inside disk cavities are needed
to discriminate between clearing scenarios. We present a spatially and
spectrally resolved carbon monoxide isotopologue observations of the gas-rich
disk HD 142527, in the J=2-1 line of 12CO, 13CO and C18O, obtained with the
Atacama Large Millimeter Array (ALMA). We detect emission coming from inside
the dust-depleted cavity in all three isotopologues. Based on our analysis of
the gas in the dust cavity, the 12CO emission is optically thick, while 13CO
and C18O emission are both optically thin. The total mass of residual gas
inside the cavity is about 1.5-2 Jupiter masses. We model the gas with an
axisymmetric disk model. Our best fit model shows that the cavity radius is
much smaller in CO than it is in millimeter continuum and scattered light
observations, with a gas cavity that does not extend beyond 105 au (at
3-sigma). The gap wall at its outer edge is diffuse and smooth in the gas
distribution, while in dust continuum it is manifestly sharper. The inclination
angle, as estimated from the high velocity channel maps, is 28+/-0.5 degrees,
higher than in previous estimates, assuming a fix central star mass of 2.2
Solar masses.Comment: 13 pages, 10 figures. Accepted for publication in ApJ Main Journa
Integrated and efficient diffusion-relaxometry using ZEBRA
The emergence of multiparametric diffusion models combining diffusion and
relaxometry measurements provide powerful new ways to explore tissue
microstructure with the potential to provide new insights into tissue structure
and function. However, their ability to provide rich analyses and the potential
for clinical translation critically depends on the availability of efficient,
integrated, multi-dimensional acquisitions. We propose a fully integrated
sequence simultaneously sampling the acquisition parameter spaces required for
T1 and T2* relaxometry and diffusion MRI. Slice-level interleaved diffusion
encoding, multiple spin/gradient echoes and slice-shuffling are combined for
higher efficiency, sampling flexibility and enhanced internal consistency.
In-vivo data was successfully acquired on healthy adult brains. Obtained
parametric maps as well as clustering results demonstrate the potential of the
technique regarding its ability to provide eloquent data with an acceleration
of roughly 20 compared to conventionally used approaches. The proposed
integrated acquisition, called ZEBRA, offers significant acceleration and
flexibility compared to existing diffusion-relaxometry studies and thus
facilitates wider use of these techniques both for research-driven and clinical
applications
Circumbinary, not transitional: on the spiral arms, cavity, shadows, fast radial flows, streamers, and horseshoe in the HD 142527 disc
We present 3D hydrodynamical models of the HD142527 protoplanetary disc, a bright and well-studied disc that shows spirals and shadows in scattered light around a 100 au gas cavity, a large horseshoe dust structure in mm continuum emission, together with mysterious fast radial flows and streamers seen in gas kinematics. By considering several possible orbits consistent with the observed arc, we show that all of the main observational features can be explained by one mechanism - the interaction between the disc and the observed binary companion. We find that the spirals, shadows, and horseshoe are only produced in the correct position angles by a companion on an inclined and eccentric orbit approaching periastron - the 'red' family from Lacour et al. Dust-gas simulations show radial and azimuthal concentration of dust around the cavity, consistent with the observed horseshoe. The success of this model in the HD142527 disc suggests other mm-bright transition discs showing cavities, spirals, and dust asymmetries may also be explained by the interaction with central companions
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