330 research outputs found
Optimized Principal Component Analysis on Coronagraphic Images of the Fomalhaut System
We present the results of a study to optimize the principal component
analysis (PCA) algorithm for planet detection, a new algorithm complementing
ADI and LOCI for increasing the contrast achievable next to a bright star. The
stellar PSF is constructed by removing linear combinations of principal
components, allowing the flux from an extrasolar planet to shine through. The
number of principal components used determines how well the stellar PSF is
globally modelled. Using more principal components may decrease the number of
speckles in the final image, but also increases the background noise. We apply
PCA to Fomalhaut VLT NaCo images acquired at 4.05 micron with an apodized phase
plate. We do not detect any companions, with a model dependent upper mass limit
of 13-18 M_Jup from 4-10 AU. PCA achieves greater sensitivity than the LOCI
algorithm for the Fomalhaut coronagraphic data by up to 1 magnitude. We make
several adaptations to the PCA code and determine which of these prove the most
effective at maximizing the signal-to-noise from a planet very close to its
parent star. We demonstrate that optimizing the number of principal components
used in PCA proves most effective for pulling out a planet signal.Comment: Accepted for publication in ApJ, 7 pages, 9 figure
Multiple spiral patterns in the transitional disk of HD 100546
Protoplanetary disks around young stars harbor many structures related to
planetary formation. Of particular interest, spiral patterns were discovered
among several of these disks and are expected to be the sign of gravitational
instabilities leading to giant planets formation or gravitational perturbations
caused by already existing planets. In this context, the star HD100546 presents
some specific characteristics with a complex gas and dusty disk including
spirals as well as a possible planet in formation. The objective of this study
is to analyze high contrast and high angular resolution images of this
emblematic system to shed light on critical steps of the planet formation. We
retrieved archival images obtained at Gemini in the near IR (Ks band) with the
instrument NICI and processed the data using advanced high contrast imaging
technique taking advantage of the angular differential imaging. These new
images reveal the spiral pattern previously identified with HST with an
unprecedented resolution, while the large-scale structure of the disk is mostly
erased by the data processing. The single pattern at the southeast in HST
images is now resolved into a multi-armed spiral pattern. Using two models of a
gravitational perturber orbiting in a gaseous disk we attempted to bring
constraints on the characteristics of this perturber assuming each spiral being
independent and we derived qualitative conclusions. The non-detection of the
northeast spiral pattern observed in HST allows to put a lower limit on the
intensity ratio between the two sides of the disk, which if interpreted as
forward scattering yields a larger anisotropic scattering than derived in the
visible. Also, we found that the spirals are likely spatially resolved with a
thickness of about 5-10AU. Finally, we did not detect the candidate forming
planet recently discovered in the Lp band, with a mass upper limit of 16-18 MJ.Comment: Accepted for publication in Astronomy and Astrophysics, 10 pages, 8
figure
Searching for gas giant planets on Solar System scales - A NACO/APP L'-band survey of A- and F-type Main Sequence stars
We report the results of a direct imaging survey of A- and F-type main
sequence stars searching for giant planets. A/F stars are often the targets of
surveys, as they are thought to have more massive giant planets relative to
solar-type stars. However, most imaging is only sensitive to orbital
separations 30 AU, where it has been demonstrated that giant planets are
rare. In this survey, we take advantage of the high-contrast capabilities of
the Apodizing Phase Plate coronagraph on NACO at the Very Large Telescope.
Combined with optimized principal component analysis post-processing, we are
sensitive to planetary-mass companions (2 to 12 ) at Solar System
scales (30 AU). We obtained data on 13 stars in L'-band and detected one
new companion as part of this survey: an M dwarf companion around HD
984. We re-detect low-mass companions around HD 12894 and HD 20385, both
reported shortly after the completion of this survey. We use Monte Carlo
simulations to determine new constraints on the low-mass (80 )
companion frequency, as a function of mass and separation. Assuming solar-type
planet mass and separation distributions, normalized to the planet frequency
appropriate for A-stars, and the observed companion mass-ratio distribution for
stellar companions extrapolated to planetary masses, we derive a truncation
radius for the planetary mass companion surface density of 135 AU at 95%
confidence.Comment: Accepted for publication in MNRAS, 8 pages, 4 figure
Observability of Forming Planets and their Circumplanetary Disks I. -- Parameter Study for ALMA
We present mock observations of forming planets with ALMA. The possible
detections of circumplanetary disks (CPDs) were investigated around planets of
Saturn, 1, 3, 5, and 10 Jupiter-masses that are placed at 5.2 AU from their
star. The radiative, three dimensional hydrodynamic simulations were then
post-processed with RADMC3D and the ALMA Observation Simulator. We found that
even though the CPDs are too small to be resolved, they are hot due to the
accreting planet in the optically thick limit, therefore the best chance to
detect them with continuum observations in this case is at the shortest ALMA
wavelengths, such as Band 9 (440 microns). Similar fluxes were found in the
case of Saturn and Jupiter-mass planets, as for the 10
gas-giant, due to temperature weighted optical depth effects: when no deep gap
is carved, the planet region is blanketed by the optically thick circumstellar
disk leading to a less efficient cooling there. A test was made for a 52 AU
orbital separation, showed that optically thin CPDs are also detectable in band
7 but they need longer integration times (5hrs). Comparing the gap profiles
of the same simulation at various ALMA bands and the hydro simulation confirmed
that they change significantly, first because the gap is wider at longer
wavelengths due to decreasing optical depth; second, the beam convolution makes
the gap shallower and at least 25% narrower. Therefore, caution has to be made
when estimating planet masses based on ALMA continuum observations of gaps.Comment: Accepted for publication at MNRAS. Typos are corrected since previous
version. 11 pages, 5 tables, 4 figure
Deeply embedded objects and shocked molecular hydrogen: The environment of the FU Orionis stars RNO 1B/1C
We present Spitzer IRAC and IRS observations of the dark cloud L1287. The mid-infrared (MIR) IRAC images show deeply embedded infrared sources in the vicinity of the FU Orionis objects RNO 1B and RNO 1C suggesting their association with a small young stellar cluster. For the first time we resolve the MIR point source associated with IRAS 00338+6312 which is a deeply embedded intermediate-mass protostar driving a known molecular outflow. The IRAC colors of all objects are consistent with young stars ranging from deeply embedded Class 0/I sources to Class II objects, part of which appear to be locally reddened. The two IRS spectra show strong absorption bands by ices and dust particles, confirming that the circumstellar environment around RNO 1B/1C has a high optical depth. Additional hydrogen emission lines from pure rotational transitions are superimposed on the spectra. Given the outflow direction, we attribute these emission lines to shocked gas in the molecular outflow powered by IRAS 00338+6312. The derived shock temperatures are in agreement with high velocity C-type shocks
Europium as a lodestar: diagnosis of radiogenic heat production in terrestrial exoplanets
Long-lived radioactive nuclides, such as K, Th, U and
U, contribute to persistent heat production in the mantle of
terrestrial-type planets. As refractory elements, the concentrations of Th and
U in a terrestrial exoplanet are implicitly reflected in the photospheric
abundances in the stellar host. However, a robust determination of these
stellar abundances is difficult in practice owing to the general paucity and
weakness of the relevant spectral features. We draw attention to the
refractory, process element europium, which may be used as a convenient and
practical proxy for the population analysis of radiogenic heating in
exoplanetary systems. As a case study, we present a determination of Eu
abundances in the photospheres of Cen A and B. We find that europium
is depleted with respect to iron by 0.1 dex and to silicon by
0.15 dex compared to solar in both binary components. To first order, the
measured Eu abundances can be converted to the abundances of Th,
U and U with observational constraints while the abundance of
K is approximated independently with a Galactic chemical evolution
model. We find that the radiogenic heat budget in an -Cen-Earth is
TW upon its formation and TW at the
present day, respectively % and % lower than that in the
Hadean and modern Earth. As a consequence, mantle convection in an
-Cen-Earth is expected to be overall weaker than that of the Earth
(assuming other conditions are the same) and thus such a planet would be less
geologically active, suppressing its long-term potential to recycle its crust
and volatiles. With Eu abundances being available for a large sample of
Sun-like stars, the proposed approach can extend our ability to make
predictions about the nature of other rocky worlds.Comment: Accepted for publication in Astronomy & Astrophysics. 11 pages, 4
figures, and 4 table
Detection of scattered light from the hot dust in HD 172555
Debris disks or belts are important signposts for the presence of colliding
planetesimals and, therefore, for ongoing planet formation and evolution
processes in young planetary systems. Imaging of debris material at small
separations from the star is very challenging but provides valuable insights
into the spatial distribution of so-called hot dust produced by solid bodies
located in or near the habitable zone. We report the first detection of
scattered light from the hot dust around the nearby (d = 28.33 pc) A star HD
172555. We want to constrain the geometric structure of the detected debris
disk using polarimetric differential Imaging (PDI) with a spatial resolution of
25 mas and an inner working angle of about 0.1. We measured the polarized
light of HD 172555, with SPHERE-ZIMPOL, in the very broad band (VBB;
nm) filter for the projected separations between 0.08 (2.3
au) and 0.77 (22 au). We constrained the disk parameters by fitting models
for scattering of an optically thin dust disk taking the limited spatial
resolution and coronagraphic attenuation of our data into account. The
geometric structure of the disk in polarized light shows roughly the same
orientation and outer extent as obtained from thermal emission at 18 m.
Our image indicates the presence of a strongly inclined (),
roughly axisymmetric dust belt with an outer radius in the range between
0.3 (8.5 au) and 0.4 (11.3 au). We derive a lower limit for the
polarized flux contrast ratio for the disk of in the VBB filter. This ratio is small, only
9 %, when compared to the fractional infrared flux excess (). The model simulations show that more polarized light could be
produced by the dust located inside 2 au, which cannot be detected with the
instrument configuration used.Comment: 16 pages, 10 figure
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