106 research outputs found
Spiral waves triggered by shadows in transition disks
Circumstellar asymmetries such as central warps have recently been shown to
cast shadows on outer disks. We investigate the hydrodynamical consequences of
such variable illumination on the outer regions of a transition disk, and the
development of spiral arms. Using 2D simulations, we follow the evolution of a
gaseous disk passively heated by the central star, under the periodic forcing
of shadows with an opening angle of 28. With a lower pressure
under the shadows, each crossing results in a variable azimuthal acceleration,
which in time develops into spiral density waves. Their pitch angles evolve
from at the onset, to 11-14,
over 65~AU to 150~AU. Self-gravity enhances the density contrast of the
spiral waves, as also reported previously for spirals launched by planets. Our
control simulations with unshadowed irradiation do not develop structures,
except for a different form of spiral waves seen at later times only in the
gravitationally unstable control case. Scattered light predictions in the
-band show that such illumination spirals should be observable. We suggest
that spiral arms in the case-study transition disk HD~142527 could be explained
as a result of shadowing from the tilted inner disk.Comment: 6 pages, 4 figures, 1 table. Accepted for publication in ApJ
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
Improving direct exoplanet detections using both spatial and spectral data through ML
Advances in observing methods and the advent of instruments such as SINFONI, GPI etc allow to simultaneously produce high contrast images (HCI) and extract high resolution spectra (HRS) of exoplanet targets. This has produced multispectral images of the targets making it possible to simultaneously use the image and spectral dimensions of such data. Such data has been used in detection and characterization of multiple systems such as PDS70 (Haffert et al 2020., Christiaens 2020 etc.), HD142527 (Christiaens 2019) etc. Advanced data science techniques have been proposed to improve the current detection limit taking advantage of the large feature set provided by multispectral imaging. Machine learning (ML) has had a particularly high success rate in the imaging domain (e.g Dahlquist et al 2021, Gomez Gonzales et al 2018). However ML has proven ineffective when using spectra alone (e.g Fisher et al 2020) owing to the a large number of spectral channels that do not contribute discriminatory features from the star. Therefore, dimensionality reduction have been suggested in order to effectively harness HRS data. Consequently, this project investigates if after reducing the dimensionality of HRS, will the spatial diversity provided by the HCI improve the detection limit.
We use SDI cubes from SINFONI. This consist of the HD142527 data cube and an empty data cube with injected companions. We implement dimensionality reduction by replacing the spectral dimension with a relative velocity dimension and the pixel values with cross correlation (CCF) values This produces a spatial CCF map consisting of correlated and uncorrelated pixels. Naturally, pixels which contain spectra closer to the template that it is correlated with have a higher value. However, this map is still contaminated by noise correlations and field rotation.
It has been proven that the application of derotation and STIM algorithms with appropriate thresholding (Pairet et al 2019) to a standard ADI cube produces a reliable detection map. In our case we replace the ADI cube with a CCF cube and apply derotation+STIM. Choice of an appropriate threshold converts this STIM map into a detection map The thresholding in the STIM map has been shown to be somewhat noise dependent. In order to now harness the power of ML to our project we will replace the STIM+thresholding with an appropriate noise independent ML algorithm and summarize the improvement in detectability
Vortex Image Processing (VIP) package for high-contrast direct imaging
VIP is a Python instrument-agnostic toolbox featuring a flexible framework for reproducible and robust data reduction. VIP currently supports three high-contrast imaging observational techniques: angular, reference-star and multi-spectral differential imaging. The code can be downloaded from our git repository on Github: http://github.com/vortex-exoplanet/VI
Dust Traps in the Protoplanetary Disk MWC 758: Two Vortices Produced by Two Giant Planets?
Resolved ALMA and VLA observations indicate the existence of two dust traps in the protoplanetary disc MWC 758. By means of two-dimensional gas+dust hydrodynamical simulations post-processed with three-dimensional dust radiative transfer calculations, we show that the spirals in scattered light, the eccentric, asymmetric ring and the crescent-shaped structure in the (sub)millimetre can all be caused by two giant planets: a 1.5-Jupiter mass planet at 35 au (inside the spirals) and a 5-Jupiter mass planet at 140 au (outside the spirals). The outer planet forms a dust-trapping vortex at the inner edge of its gap (at ∼85 au), and the continuum emission of this dust trap reproduces the ALMA and VLA observations well. The outer planet triggers several spiral arms that are similar to those observed in polarized scattered light. The inner planet also forms a vortex at the outer edge of its gap (at ∼50 au), but it decays faster than the vortex induced by the outer planet, as a result of the disc’s turbulent viscosity. The vortex decay can explain the eccentric inner ring seen with ALMA as well as the low signal and larger azimuthal spread of this dust trap in VLA observations. Finding the thermal and kinematic signatures of both giant planets could verify the proposed scenario
Confirmation and Keplerian motion of the gap-carving protoplanet HD 169142 b
We present the re-detection of a compact source in the face-on protoplanetary
disc surrounding HD 169142, using VLT/SPHERE data in YJH bands. The source is
found at a separation of 0.''319 (37 au) from the star. Three lines of
evidence argue in favour of the signal tracing a protoplanet: (i) it is found
in the annular gap separating the two bright rings of the disc, as predicted by
theory; (ii) it is moving at the expected Keplerian velocity for an object at
37 au in the 2015, 2017 and 2019 datasets; (iii) we also detect a
spiral-shaped signal whose morphology is consistent with the expected outer
spiral wake triggered by a planet in the gap, based on dedicated hydrodynamical
simulations of the system. The YJH colours we extracted for the object are
consistent with tracing scattered starlight, suggesting that the protoplanet is
enshrouded in a significant amount of dust, as expected for a circumplanetary
disc or envelope surrounding a gap-clearing Jovian-mass protoplanet.Comment: Accepted for publication in MNRAS Letters. 5 pages, 5 figure
A Direct Imaging Survey of Spitzer detected debris disks: Occurrence of giant planets in dusty systems
We describe a joint high contrast imaging survey for planets at Keck and VLT
of the last large sample of debris disks identified by the Spitzer Space
Telescope. No new substellar companions were discovered in our survey of 30
Spitzer-selected targets. We combine our observations with data from four
published surveys to place constraints on the frequency of planets around 130
debris disk single stars, the largest sample to date. For a control sample, we
assembled contrast curves from several published surveys targeting 277 stars
which do not show infrared excesses. We assumed a double power law distribution
in mass and semi-major axis of the form f(m,a) = , where
we adopted power law values and logarithmically flat values for the mass and
semi-major axis of planets. We find that the frequency of giant planets with
masses 5-20 and separations 10-1000 AU around stars with debris
disks is 6.27% (68% confidence interval 3.68 - 9.76%), compared to 0.73% (68%
confidence interval 0.20 - 1.80%) for the control sample of stars without
disks. These distributions differ at the 88% confidence level, tentatively
suggesting distinctness of these samples.Comment: Accepted to A
Signatures of an eccentric disc cavity: Dust and gas in IRS 48
We test the hypothesis that the disc cavity in the `transition disc' Oph IRS
48 is carved by an unseen binary companion. We use 3D dust-gas
smoothed-particle hydrodynamics simulations to demonstrate that marginally
coupled dust grains concentrate in the gas over-density that forms in in the
cavity around a low binary mass ratio binary. This produces high contrast ratio
dust asymmetries at the cavity edge similar to those observed in the disc
around IRS 48 and other transition discs. This structure was previously assumed
to be a vortex. However, we show that the observed velocity map of IRS 48
displays a peculiar asymmetry that is not predicted by the vortex hypothesis.
We show the unusual kinematics are naturally explained by the non-Keplerian
flow of gas in an eccentric circumbinary cavity. We further show that
perturbations observed in the isovelocity curves of IRS 48 may be explained as
the product of the dynamical interaction between the companion and the disc.
The presence of a 0.4 M companion at a 10 au separation
can qualitatively explain these observations. High spatial resolution line and
continuum imaging should be able to confirm this hypothesis.Comment: 9 pages, 7 figures, accepted for publication in MNRA
Non-Keplerian spirals, a gas-pressure dust trap and an eccentric gas cavity in the circumbinary disc around HD 142527
We present ALMA observations of the CO, CO, CO J=2-1
transitions and the 1.3\,mm continuum emission for the circumbinary disc around
HD 142527, at an angular resolution of \,0\farcs3. We observe multiple
spiral structures in intensity, velocity and velocity dispersion for the
CO and CO gas tracers. A newly detected CO spiral
originates from the dust horseshoe, and is rotating at super-Keplerian velocity
or vertically ascending, whilst the inter-spiral gas is rotating at
sub-Keplerian velocities. This new spiral possibly connects to a previously
identified spiral, thus spanning > 360. A spatial offset of ~30 au is
observed between the CO and CO spirals, to which we hypothesize
that the gas layers are propagating at different speeds (``surfing'') due to a
non-zero vertical temperature gradient. Leveraging the varying optical depths
between the CO isotopologues, we reconstruct temperature and column density
maps of the outer disc. Gas surface density peaks at r\,\,180\,au,
coincident with the peak of continuum emission. Here the dust grains have a
Stokes number of \,1, confirming radial and azimuthal trapping in the
horseshoe. We measure a cavity radius at half-maximum surface density of
\,100\,au, and a cavity eccentricity between 0.3 and 0.45
Is the gap in the DS Tau disc hiding a planet?
Recent mm-wavelength surveys performed with the Atacama Large Millimeter
Array (ALMA) have revealed protoplanetary discs characterized by rings and
gaps. A possible explanation for the origin of such rings is the tidal
interaction with an unseen planetary companion. The protoplanetary disc around
DS Tau shows a wide gap in the ALMA observation at 1.3 mm. We construct a
hydrodynamical model for the dust continuum observed by ALMA assuming the
observed gap is carved by a planet between one and five Jupiter masses. We fit
the shape of the radial intensity profile along the disc major axis varying the
planet mass, the dust disc mass, and the evolution time of the system. The best
fitting model is obtained for a planet with and a
disc with . Starting from this
result, we also compute the expected signature of the planet in the gas
kinematics, as traced by CO emission. We find that such a signature (in the
form of a "kink" in the channel maps) could be observed by ALMA with a velocity
resolution between and a beam size between 30 and 50
mas.Comment: 16 pages, 15 figures, accepted for publication on MNRA
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