56 research outputs found
Shadows and spirals in the protoplanetary disk HD 100453
Understanding the diversity of planets requires to study the morphology and
the physical conditions in the protoplanetary disks in which they form. We
observed and spatially resolved the disk around the ~10 Myr old protoplanetary
disk HD 100453 in polarized scattered light with SPHERE/VLT at optical and
near-infrared wavelengths, reaching an angular resolution of ~0.02", and an
inner working angle of ~0.09". We detect polarized scattered light up to ~0.42"
(~48 au) and detect a cavity, a rim with azimuthal brightness variations at an
inclination of 38 degrees, two shadows and two symmetric spiral arms. The
spiral arms originate near the location of the shadows, close to the semi major
axis. We detect a faint spiral-like feature in the SW that can be interpreted
as the scattering surface of the bottom side of the disk, if the disk is
tidally truncated by the M-dwarf companion currently seen at a projected
distance of ~119 au. We construct a radiative transfer model that accounts for
the main characteristics of the features with an inner and outer disk
misaligned by ~72 degrees. The azimuthal brightness variations along the rim
are well reproduced with the scattering phase function of the model. While
spirals can be triggered by the tidal interaction with the companion, the close
proximity of the spirals to the shadows suggests that the shadows could also
play a role. The change in stellar illumination along the rim, induces an
azimuthal variation of the scale height that can contribute to the brightness
variations. Dark regions in polarized images of transition disks are now
detected in a handful of disks and often interpreted as shadows due to a
misaligned inner disk. The origin of such a misalignment in HD 100453, and of
the spirals, is unclear, and might be due to a yet-undetected massive companion
inside the cavity, and on an inclined orbit.Comment: A&A, accepte
Post conjunction detection of Pictoris b with VLT/SPHERE
With an orbital distance comparable to that of Saturn in the solar system,
\bpic b is the closest (semi-major axis \,9\,au) exoplanet that has
been imaged to orbit a star. Thus it offers unique opportunities for detailed
studies of its orbital, physical, and atmospheric properties, and of
disk-planet interactions. With the exception of the discovery observations in
2003 with NaCo at the Very Large Telescope (VLT), all following astrometric
measurements relative to \bpic have been obtained in the southwestern part of
the orbit, which severely limits the determination of the planet's orbital
parameters. We aimed at further constraining \bpic b orbital properties using
more data, and, in particular, data taken in the northeastern part of the
orbit.
We used SPHERE at the VLT to precisely monitor the orbital motion of beta
\bpic b since first light of the instrument in 2014. We were able to monitor
the planet until November 2016, when its angular separation became too small
(125 mas, i.e., 1.6\,au) and prevented further detection. We redetected \bpic b
on the northeast side of the disk at a separation of 139\,mas and a PA of
30 in September 2018. The planetary orbit is now well constrained.
With a semi-major axis (sma) of au (1 ), it
definitely excludes previously reported possible long orbital periods, and
excludes \bpic b as the origin of photometric variations that took place in
1981. We also refine the eccentricity and inclination of the planet. From an
instrumental point of view, these data demonstrate that it is possible to
detect, if they exist, young massive Jupiters that orbit at less than 2 au from
a star that is 20 pc away.Comment: accepted by A&
Observations of fast-moving features in the debris disk of AU Mic on a three-year timescale:Confirmation and new discoveries
Imaging radial velocity planets with SPHERE
We present observations with the planet finder SPHERE of a selected sample of
the most promising radial velocity (RV) companions for high-contrast imaging.
Using a Monte Carlo simulation to explore all the possible inclinations of the
orbit of wide RV companions, we identified the systems with companions that
could potentially be detected with SPHERE. We found the most favorable RV
systems to observe are : HD\,142, GJ\,676, HD\,39091, HIP\,70849, and HD\,30177
and carried out observations of these systems during SPHERE Guaranteed Time
Observing (GTO).
To reduce the intensity of the starlight and reveal faint companions, we used
Principle Component Analysis (PCA) algorithms alongside angular and spectral
differential imaging. We injected synthetic planets with known flux to evaluate
the self-subtraction caused by our data reduction and to determine the
5 contrast in the J band separation for our reduced images. We
estimated the upper limit on detectable companion mass around the selected
stars from the contrast plot obtained from our data reduction.
Although our observations enabled contrasts larger than 15 mag at a few
tenths of arcsec from the host stars, we detected no planets. However, we were
able to set upper mass limits around the stars using AMES-COND evolutionary
models. We can exclude the presence of companions more massive than 25-28 \MJup
around these stars, confirming the substellar nature of these RV companions.Comment: 14 pages, 11 figures, accepted by MNRA
VizieR Online Data Catalog: 51 Eri b SPHERE/IFS spectra & atmosphere models (Samland+, 2017)
One fits file for each spectrum of 51 Eridani b (SPHERE IFS-YJ, IFS-YH, Samland et al., 2017, this work; GPI-H band, Macintosh et al., 2015, Cat. J/other/Sci/350.64). The first extension of the file contains the spectrum used in the paper (fits-table). The second extension contains the correlation matrix for the uncertainty of the spectral points (fits-image). The petitCODE (a self-consistent 1d radiative-convective equilibrium code, see Molliere et al., 2015ApJ...813...47M, 2017A&A...600A..10M) atmospheric model grids (cloudy and clear) as used and described in Samland et al. 2017, this work, are provided as fits-files. The first extension contains the wavelength sampling of the model cube at a resolution of 1000 (same for all models). The second extension contains the table of all model parameter combinations (each row one model, columns represent parameters). The third extension contains the flattened model cube as 2D-fits image (index of row of table in 2nd ext. corresponds to index of model in 3rd extension). The header of the 3rd extension gives the dimensions of the model cube prior to flattening to make it easy to restore the non-flattened shape if necessary. Units and descriptions can always be found in the respective headers. (2 data files)
Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE
51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0-type
star, recently discovered by direct imaging. Being only 0.5" away from its host
star it is well suited for spectroscopic analysis using integral field
spectrographs. We aim to refine the atmospheric properties of this and to
further constrain the architecture of the system by searching for additional
companions. Using the SPHERE instrument at the VLT we extend the spectral
coverage of the planet to the complete Y- to H-band range and provide
photometry in the K12-bands (2.11, 2.25 micron). The object is compared to
other cool and peculiar dwarfs. Furthermore, the posterior probability
distributions of cloudy and clear atmospheric models are explored using MCMC.
We verified our methods by determining atmospheric parameters for the two
benchmark brown dwarfs Gl 570D and HD 3651B. For probing the innermost region
for additional companions, archival VLT-NACO (L') SAM data is used. We present
the first spectrophotometric measurements in the Y- and K-bands for the planet
and revise its J-band flux to values 40% fainter than previous measurements.
Cloudy models with uniform cloud coverage provide a good match to the data. We
derive the temperature, radius, surface gravity, metallicity and cloud
sedimentation parameter f_sed. We find that the atmosphere is highly
super-solar (Fe/H~1.0) with an extended, thick cloud cover of small particles.
The model radius and surface gravity suggest planetary masses of about 9 M_jup.
The evolutionary model only provides a lower mass limit of >2 M_jup (for pure
hot-start). The cold-start model cannot explain the planet's luminosity. The
SPHERE and NACO/SAM detection limits probe the 51 Eri system at Solar System
scales and exclude brown-dwarf companions more massive than 20 M_jup beyond
separations of ~2.5 au and giant planets more massive than 2 M_jup beyond 9 au.Comment: 29 pages, 31 figures, accepted for publication in A&
Des sources du savoir aux médicaments du futur : actes du 4e congrès européen d'ethnopharmacologie = From the sources of knowledge to the medicines of the future = proceedings of the 4th European Congress on Ethnopharmocology
The search for disks or planetary objects around directly imaged companions: a candidate around DH Tauri B
Context. In recent decades, thousands of substellar companions have been discovered with both indirect and direct methods of detection. While the majority of the sample is populated by objects discovered using radial velocity and transit techniques, an increasing number have been directly imaged. These planets and brown dwarfs are extraordinary sources of information that help in rounding out our understanding of planetary systems.
Aims. In this paper, we focus our attention on substellar companions detected with the latter technique, with the primary goal of investigating their close surroundings and looking for additional companions and satellites, as well as disks and rings. Any such discovery would shed light on many unresolved questions, particularly with regard to their possible formation mechanisms.
Methods. To reveal bound features of directly imaged companions, whether for point-like or extended sources, we need to suppress the contribution from the source itself. Therefore, we developed a method based on the negative fake companion technique that first estimates the position in the field of view (FoV) and the flux of the imaged companion with high precision, then subtracts a rescaled model point spread function (PSF) from the imaged companion, using either an image of the central star or another PSF in the FoV. Next it performs techniques, such as angular differential imaging, to further remove quasi-static patterns of the star (i.e., speckle contaminants) that affect the residuals of close-in companions.
Results. After testing our tools on simulated companions and disks and on systems that were chosen ad hoc, we applied the method to the sample of substellar objects observed with SPHERE during the SHINE GTO survey. Among the 27 planets and brown dwarfs we analyzed, most objects did not show remarkable features, which was as expected, with the possible exception of a point source close to DH Tau B. This candidate companion was detected in four different SPHERE observations, with an estimated mass of ~1MJup, and a mass ratio with respect to the brown dwarf of 1∕10. This binary system, if confirmed, would be the first of its kind, opening up interesting questions for the formation mechanism, evolution, and frequency of such pairs. In order to address the latter, the residuals and contrasts reached for 25 companions in the sample of substellar objects observed with SPHERE were derived. If the DH Tau Bb companion is real, the binary fraction obtained is ~7%, which is in good agreement with the results obtained for field brown dwarfs.
Conclusions. While there may currently be many limitations affecting the exploration of bound features to directly imaged exoplanets and brown dwarfs, next-generation instruments from the ground and space (i.e., JWST, ELT, and LUVOIR) will be able to image fainter objects and, thus, drive the application of this technique in upcoming searches for exo-moons and circumplanetary disks
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