Context. The consortium of the Spectro-Polarimetric High-contrast Exoplanet REsearch installed at the Very Large Telescope (SPHERE/VLT) has been operating its guaranteed observation time (260 nights ...over five years) since February 2015. The main part of this time (200 nights) is dedicated to the detection and characterization of young and giant exoplanets on wide orbits. Aims. The large amount of data must be uniformly processed so that accurate and homogeneous measurements of photometry and astrometry can be obtained for any source in the field. Methods. To complement the European Southern Observatory pipeline, the SPHERE consortium developed a dedicated piece of software to process the data. First, the software corrects for instrumental artifacts. Then, it uses the speckle calibration tool (SpeCal) to minimize the stellar light halo that prevents us from detecting faint sources like exoplanets or circumstellar disks. SpeCal is meant to extract the astrometry and photometry of detected point-like sources (exoplanets, brown dwarfs, or background sources). SpeCal was intensively tested to ensure the consistency of all reduced images (cADI, Loci, TLoci, PCA, and others) for any SPHERE observing strategy (ADI, SDI, ASDI as well as the accuracy of the astrometry and photometry of detected point-like sources. Results. SpeCal is robust, user friendly, and efficient at detecting and characterizing point-like sources in high contrast images. It is used to process all SPHERE data systematically, and its outputs have been used for most of the SPHERE consortium papers to date. SpeCal is also a useful framework to compare different algorithms using various sets of data (different observing modes and conditions). Finally, our tests show that the extracted astrometry and photometry are accurate and not biased.
The pyramid wavefront sensor (PWFS) is the currently preferred design for high-sensitivity adaptive optics (AO) systems for extremely large telescopes (ELTs). Yet, nonlinearities of the signal ...retrieved from the PWFS pose a significant problem for achieving the full correction potential using this sensor, a problem that will only worsen with the increasing dimension of telescopes. This paper investigates the so-called optical gain (OG) phenomenon, a sensitivity reduction and an overall modification of the sensor response induced by the residual wavefront itself, with considerable effects in standard observation conditions for ELT-sized AO systems. Through extensive numerical analysis, this work proposes a formalism to measure and minimize the first-order nonlinearity error caused by optical gain variation, which uses a modal compensation technique of the calibrated reconstructor; this enables a notable increase in performance in faint guide stars or important seeing scenarios, for example from 16 to 30% H-band Strehl ratio for a sixteenth magnitude star in r0 = 13 cm turbulence. Beyond the performance demonstrated by this compensation, a complete algorithm for realistic operation conditions is designed, which from dithering a few deformable mirror modes retrieves the optimal gains and updates the command matrix accordingly. The performance of this self-updating technique – which successfully allows automatic OG compensation regardless of the turbulent conditions, and its minimal interference with the scientific instrument are demonstrated through extensive end-to-end numerical simulations, all at the scale of an ELT instrument single-conjugate AO system.
Context.
During the evolution of protoplanetary disks into planetary systems we expect to detect signatures that trace mechanisms such as planet–disk interaction. Protoplanetary disks display a large ...variety of structures in recently published high-spatial resolution images. However, the three-dimensional morphology of these disks is often difficult to infer from the two-dimensional projected images we observe.
Aims.
We aim to detect signatures of planet–disk interaction by studying the scattering surface of the protoplanetary disk around HD 34282.
Methods.
We spatially resolved the disk using the high-contrast imager VLT/SPHERE in polarimetric imaging mode. We retrieved a profile for the height of the scattering surface to create a height-corrected deprojection, which simulates a face-on orientation.
Results.
The detected disk displays a complex scattering surface. An inner clearing or cavity extending up to
r
< 0.′′28 (88 au) is surrounded by a bright inclined (
i
= 56°) ring with a position angle of 119°. The center of this ring is offset from the star along the minor axis with 0.′′07, which can be explained with a disk height of 26 au above the midplane. Outside this ring, beyond its southeastern ansa we detect an azimuthal asymmetry or blob at
r
~ 0.′′4. At larger separation, we detect an outer disk structure that can be fitted with an ellipse, which is compatible with a circular ring seen at
r
= 0.′′62 (=190 au) and a height of 77 au. After applying a height-corrected deprojection we see a circular ring centered on the star at 88 au; what had seemed to be a separate blob and outer ring could now both be part of a single-armed spiral.
Conclusions.
We present the first scattered-light image of the disk around HD 34282 and resolve a disk with an inner cavity up to
r
≈ 90 au and a highly structured scattering surface of an inclined disk at a large height
H
scat
∕
r
= 0.′′29 above the midplane at the inner edge of the outer disk. Based on the current data it is not possible to conclude decisively whether
H
scat
∕
r
remains constant or whether the surface is flared with at most
H
scat
∝
r
1.35
, although we favor the constant ratio based on our deprojections. The height-corrected deprojection allows for a more detailed interpretation of the observed structures, from which we discern the first detection of a single-armed spiral in a protoplanetary disk.
The pyramid wavefront sensor (PWFS) is the currently preferred design for adaptive optics (AO) systems for extremely large telescopes, as focal plane wavefront sensing bears potential for a large ...intrinsic sensitivity gain when compared to Shack–Hartmann (SH) sensors. Yet, obtaining a high quality pyramidal prism and a model-consistent assembly remains a critical design factor. We demonstrate that the traditional gradient sensing controller is extremely sensitive to prism shape defects and assembly misalignments. We show that even optimal registration of quadrants on the detector may be insufficient to prevent misalignment induced performance loss through a theoretical analysis of the impact of detection plane quadrants sampling errors and individual translations, which may be induced by a variety of mechanical defects. These misalignments displace wavefront information to terms not included in the conventional gradient-like slopes maps and high spatial frequencies become invisible to the sole X− and Y− axis differences. We introduce expanded space control (ESC) for quad-cell signal by generalizing output measurements of the PWFS and demonstrate its insensitivity to misalignment-induced information loss, therefore dramatically relaxing machining and alignment constraints for PWFS engineering. This work presents the theoretical developments leading to ESC design, along with validating performance and robustness results, both in end-to-end numerical simulations and on a PWFS demonstrator bench at LESIA.
Context. The SAO 206462 (HD 135344B) disk is one of the few known transitional disks showing asymmetric features in scattered light and thermal emission. Near-infrared scattered-light images revealed ...two bright outer spiral arms and an inner cavity depleted in dust. Giant protoplanets have been proposed to account for the disk morphology. Aims. We aim to search for giant planets responsible for the disk features and, in the case of non-detection, to constrain recent planet predictions using the data detection limits. Methods. We obtained new high-contrast and high-resolution total intensity images of the target spanning the Y to the K bands (0.95–2.3 μm) using the VLT/SPHERE near-infrared camera and integral field spectrometer. Results. The spiral arms and the outer cavity edge are revealed at high resolutions and sensitivities without the need for aggressive image post-processing techniques, which introduce photometric biases. We do not detect any close-in companions. For the derivation of the detection limits on putative giant planets embedded in the disk, we show that the knowledge of the disk aspect ratio and viscosity is critical for the estimation of the attenuation of a planet signal by the protoplanetary dust because of the gaps that these putative planets may open. Given assumptions on these parameters, the mass limits can vary from ~2–5 to ~4–7 Jupiter masses at separations beyond the disk spiral arms. The SPHERE detection limits are more stringent than those derived from archival NaCo/L′ data and provide new constraints on a few recent predictions of massive planets (4–15 MJ) based on the spiral density wave theory. The SPHERE and ALMA data do not favor the hypotheses on massive giant planets in the outer disk (beyond 0.6′′). There could still be low-mass planets in the outer disk and/or planets inside the cavity.
Context. Transition disks are considered sites of ongoing planet formation, and their dust and gas distributions could be signposts of embedded planets. The transition disk around the T Tauri star RY ...Lup has an inner dust cavity and displays a strong silicate emission feature. Aims. Using high-resolution imaging we study the disk geometry, including non-axisymmetric features, and its surface dust grain, to gain a better understanding of the disk evolutionary process. Moreover, we search for companion candidates, possibly connected to the disk. Methods. We obtained high-contrast and high angular resolution data in the near-infrared with the VLT/SPHERE extreme adaptive optics instrument whose goal is to study the planet formation by detecting and characterizing these planets and their formation environments through direct imaging. We performed polarimetric imaging of the RY Lup disk with IRDIS (at 1.6 μm), and obtained intensity images with the IRDIS dual-band imaging camera simultaneously with the IFS spectro-imager (0.9–1.3 μm). Results. We resolved for the first time the scattered light from the nearly edge-on circumstellar disk around RY Lup, at projected separations in the 100 au range. The shape of the disk and its sharp features are clearly detectable at wavelengths ranging from 0.9 to 1.6 μm. We show that the observed morphology can be interpreted as spiral arms in the disk. This interpretation is supported by in-depth numerical simulations. We also demonstrate that these features can be produced by one planet interacting with the disk. We also detect several point sources which are classified as probable background objects.
Context.
Young stars with debris disks are the most promising targets for an exoplanet search because debris indicate a successful formation of planetary bodies. Debris disks can be shaped by planets ...into ring structures that give valuable indications on the presence and location of planets in the disk.
Aims.
We performed observations of the Sco-Cen F star HD 117214 to search for planetary companions and to characterize the debris disk structure.
Methods.
HD 117214 was observed with the SPHERE subsystems IRDIS, IFS, and ZIMPOL at optical and near-IR wavelengths using angular and polarimetric differential imaging techniques. This provided the first images of scattered light from the debris disk with the highest spatial resolution of 25 mas and an inner working angle <0.1″. With the observations with IRDIS and IFS we derived detection limits for substellar companions. The geometrical parameters of the detected disk were constrained by fitting 3D models for the scattering of an optically thin dust disk. Investigating the possible origin of the disk gap, we introduced putative planets therein and modeled the planet–disk and planet–planet dynamical interactions. The obtained planetary architectures were compared with the detection limit curves.
Results.
The debris disk has an axisymmetric ring structure with a radius of 0.42(±0.01)″ or ~45 au and an inclination of 71(±2.5)° and exhibits a 0.4″ (~40 au) wide inner cavity. From the polarimetric data, we derive a polarized flux contrast for the disk of (
F
pol
)
disk
/
F
∗
= (3.1 ± 1.2) × 10
−4
in the
RI
band.
Conclusions.
The fractional scattered polarized flux of the disk is eight times lower than the fractional IR flux excess. This ratio is similar to the one obtained for the debris disk HIP 79977, indicating that dust radiation properties are similar for these two disks. Inside the disk cavity we achieve high-sensitivity limits on planetary companions with a mass down to ~4
M
J
at projected radial separations between 0.2″ and 0.4″. We can exclude stellar companions at a radial separation larger than 75 mas from the star.
Calibration of flight model CCDs for CoRoT mission Lapeyrere, V.; Bernardi, P.; Buey, J.-T. ...
Monthly Notices of the Royal Astronomical Society,
February 2006, Letnik:
365, Številka:
4
Journal Article
Recenzirano
Odprti dostop
CoRoT (Convection, Rotation and Transit) is a mission of high-accuracy photometry with two scientific programmes: asteroseismology and planet finding, using CCDs as detectors. Ten 2048×4096 CCDs ...manufactured by E2V (42-80) were calibrated on Meudon test bench in order to choose the best ones for flight. A very high instrument stability is needed. Taking into account the environmental perturbations (temperature, attitude control system jitter, radiations, etc.) we studied sensitivity of CCD gain and quantum efficiency to temperature and sensitivity of the output signal to bias voltages. Special attention was paid to pixel capacity and noise sources coming from dark current and pixel response non-uniformity. The calibration results together with the expected voltages and temperature fluctuations are compared with the specifications.
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