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61. HD 117214 debris disk polarization images
ID:
ivo://CDS.VizieR/J/A+A/635/A19
Title:
HD 117214 debris disk polarization images
Short Name:
J/A+A/635/A19
Date:
21 Oct 2021
Publisher:
CDS
Description:
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. We performed observations of the Sco-Cen F star HD 117214 to search for planetary companions and to characterize the debris disk structure. 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 25mas 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. The debris disk has an axisymmetric ring structure with a radius of 0.42(+/-0.01)" or ~45au and an inclination of 71(+/-2.5){deg} and exhibits a 0.4" (~40au) wide inner cavity. From the polarimetric data, we derive a polarized flux contrast for the disk of (Fpol)_disk_/F*=(3.1+/-1.2)x10^-4^ in the RI band. 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 ~4M_J_ at projected radial separations between 0.2" and 0.4". We can exclude stellar companions at a radial separation larger than 75mas from the star.
62. HD 172555 polarimetric images
ID:
ivo://CDS.VizieR/J/A+A/618/A151
Title:
HD 172555 polarimetric images
Short Name:
J/A+A/618/A151
Date:
21 Oct 2021
Publisher:
CDS
Description:
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 the 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=28.33pc) 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 25mas and an inner working angle of about 0.1". We measured the polarized light of HD 172555, with SPHERE/ZIMPOL, in the very broadband (VBB) or RI filter ({lambda}c=735nm, {Delta}{lambda}290nm) for the projected separations between 0.08" (2.3au) and 0.77" (22au). 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{mu}m. Our image indicates the presence of a strongly inclined (i~=103.5{deg}), roughly axisymmetric dust belt with an outer radius in the range between 0.3" (8.5au) and 0.4" (11.3au). An inner disk edge is not detected in the data. We derive a lower limit for the polarized flux contrast ratio for the disk of (Fpol)disk/F*>(6.2+/-0.6)x10^-5^ in the VBB filter. This ratio is small, only ~9%, when compared to the fractional infrared flux excess (~=7.2x10^-4^). The model simulations show that more polarized light could be produced by the dust located inside ~=2au, which cannot be detected with the instrument configuration used. Our data confirm previous infrared imaging and provide a higher resolution map of the system, which could be further improved with future observations.
63. HD 139614 polarization Stokes Q and U images
ID:
ivo://CDS.VizieR/J/A+A/635/A121
Title:
HD 139614 polarization Stokes Q and U images
Short Name:
J/A+A/635/A121
Date:
21 Oct 2021
Publisher:
CDS
Description:
Shadows in scattered light images of protoplanetary disks are a common feature and support the presence of warps or misalignments between disk regions. These warps are possibly due to an inclined (sub-)stellar companion embedded in the disk. We study the morphology of the protoplanetary disk around the Herbig Ae star HD 139614 based on the first scattered light observations of this disk, which we model with the radiative transfer code MCMax3D. We obtained J- and H-band observations in polarized scattered light with VLT/SPHERE that show strong azimuthal asymmetries. In the outer disk, beyond ~30au, a broad shadow spans a range of ~240{deg} in position angle, in the East. A bright ring at ~16 au also shows an azimuthally asymmetric brightness, with the faintest side roughly coincidental with the brightest region of the outer disk. Additionally, two arcs are detected at ~34au and ~50au. We created a simple 4-zone approximation to a warped disk model of HD 139614 in order to qualitatively reproduce these features. The location and misalignment of the disk components were constrained from the shape and location of the shadows they cast. We find that the shadow on the outer disk covers a range of position angle too wide to be explained by a single inner misaligned component. Our model requires a minimum of two separate misaligned zones -- or a continuously warped region -- to cast this broad shadow on the outer disk. A small misalignment of ~4{deg} between adjacent components can reproduce most of the observed shadow features. Multiple misaligned disk zones, potentially mimicking a warp, can explain the observed broad shadows in the HD 139614 disk. A planetary mass companion in the disk, located on an inclined orbit, could be responsible for such a feature and for the dust depleted gap responsible for a dip in the SED.
64. HD61005 SPHERE H and Ks images
ID:
ivo://CDS.VizieR/J/A+A/591/A108
Title:
HD61005 SPHERE H and Ks images
Short Name:
J/A+A/591/A108
Date:
21 Oct 2021
Publisher:
CDS
Description:
Debris disks offer valuable insights into the latest stages of circumstellar disk evolution, and can possibly help us to trace the outcomes of planetary formation processes. In the age range 10 to 100Myr, most of the gas is expected to have been removed from the system, giant planets (if any) must have already been formed, and the formation of terrestrial planets may be on-going. Pluto-sized planetesimals, and their debris released in a collisional cascade, are under their mutual gravitational influence, which may result into non-axisymmetric structures in the debris disk. Here we present new VLT/SPHERE and ALMA observations of the debris disk around the 40Myr-old solar-type star HD61005. We resolve the disk at unprecedented resolution both in the near-infrared (in scattered and polarized light) and at millimeter wavelengths. We perform a detailed modeling of these observations, including the spectral energy distribution. Thanks to the new observations, we propose a solution for both the radial and azimuthal distribution of the dust grains in the debris disk. We find that the disk has a moderate eccentricity and that the dust density is two times larger at the pericenter compared to the apocenter. With no giant planets detected in our observations, we investigate alternative explanations besides planet-disk interactions to interpret the inferred disk morphology. We postulate that the morphology of the disk could be the consequence of a massive collision between 1000km-sized bodies at 61 au. If this interpretation holds, it would put stringent constraints on the formation of massive planetesimals at large distances from the star.
65. HD142527 SPHERE polarimetric images
ID:
ivo://CDS.VizieR/J/A+A/648/A110
Title:
HD142527 SPHERE polarimetric images
Short Name:
J/A+A/648/A110
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present high-precision photometry and polarimetry based on visual and near-infrared imaging data for the protoplanetary disk surrounding the Herbig Ae/Be star HD 142527, with a strong focus on determining the light scattering parameters of the dust located at the surface of the large outer disk. We re-reduced existing polarimetric differential imaging data of HD 142527 in the VBB (735nm) and H-band (1625nm) from the ZIMPOL and IRDIS subinstruments of SPHERE at the VLT. With polarimetry and photometry based on reference star differential imaging (RDI), we were able to measure the linearly polarized intensity and the total intensity of the light scattered by the circumstellar disk with high precision. We used simple Monte Carlo simulations of multiple light scattering by the disk surface to derive constraints for three scattering parameters of the dust: the maximum polarization of the scattered light Pmax, the asymmetry parameter g, and the single-scattering albedo {omega}. We measure a reflected total intensity of 51.4+/-1.5mJy and 206+/-12mJy and a polarized intensity of 11.3+/-0.3mJy and 55.1+/-3.3mJy in the VBB and H-band, respectively. We also find in the visual range a degree of polarization that varies between 28% on the far side of the disk and 17% on the near side. In the H-band, the degree of polarization is consistently higher by about a factor of 1.2. The disk also shows a red color for the scattered light intensity and the polarized intensity, which are about twice as high in the near-infrared when compared to the visual. We determine with model calculations the scattering properties of the dust particles and find evidence for strong forward scattering (g {prop.to} 0.5-0.75), relatively low single-scattering albedo ({omega} {prop.to} 0.2-0.5), and high maximum polarization (Pmax {prop.to} 0.5-0.75) at the surface on the far side of the disk for both observed wavelengths. The optical parameters indicate the presence of large aggregate dust particles, which are necessary to explain the high maximum polarization, the strong forward-scattering nature of the dust, and the observed red disk color.
66. High cadence polarization monitoring of OJ287
ID:
ivo://CDS.VizieR/J/A+A/619/A88
Title:
High cadence polarization monitoring of OJ287
Short Name:
J/A+A/619/A88
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a multifrequency, dense radio monitoring program of the blazar OJ287 using the 100-m Effelsberg radio telescope. The program aims to test different binary supermassive black hole (SMBH) scenarios and studying the physical conditions in the central region of this bright blazar. Between December 2015 and January 2017 (MJD 57370-57785), the radio electric vector position angle (EVPA) showed a large clockwise (CW) rotation by about 340{deg} with a mean rate of -1.04{deg}/day. Based on concurrent polarized Very Long Baseline Array (VLBA) data, the rotation seems to originate within the jet core at 43GHz. Optical polarization data show a similar monotonic CW EVPA rotation of about -1.1{deg}/day, superposed by shorter and faster rotations of about 7.8{deg}/day, mainly in the CW sense. When combined, the single dish, VLBI and optical polarization data are consistent with a polarized emission component propagating on a helical trajectory within a bent jet. We constrained the helix arc length (0.26pc) and radius (about 0.04pc) and the projected jet bending arc length (about 1.9-7.6pc). The helical trajectory covers only a part of the jet width, possibly its spine. In addition, we found a stable polarized component with EVPA (-10{deg}) perpendicular to the large scale jet, suggesting dominance of the poloidal magnetic field component.
67. High-frequency polarization of Kuehr sources
ID:
ivo://CDS.VizieR/J/A+A/415/549
Title:
High-frequency polarization of Kuehr sources
Short Name:
J/A+A/415/549
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have observed 250 of the 258 southern sources in the complete 5GHz 1Jy sample by Kuehr et al. (1981, Cat. <VIII/5>) using the Australia Telescope Compact Array (ATCA) at 18.5GHz. This paper focuses on the polarization properties of this sample, while other properties will be addressed in a future paper.
68. High-precision polarimetry of nearby stars
ID:
ivo://CDS.VizieR/J/A+A/635/A46
Title:
High-precision polarimetry of nearby stars
Short Name:
J/A+A/635/A46
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the linear polarization produced by interstellar dust aligned by the magnetic field in the solar neighborhood (d<50pc). We also look for intrinsic effects from circumstellar processes, specifically in terms of polarization variability and wavelength dependence. We aim to detect and map dust clouds which give rise to statistically significant amounts of polarization of the starlight passing through the cloud, and to determine the interstellar magnetic field direction from the position angle of the observed polarization. High-precision broad-band (BVR) polarization observations are made of 361 stars in spectral classes F to G, with detection sensitivity at the level of or better than 10E-5 (0.001%). The sample consists of 125 stars in the magnitude range 6-9 observed at the 2.2m UH88 telescope on Mauna Kea, 205 stars in the magnitude range 3-6 observed at the Japanese (Tohoku) T60 telescope on Haleakala, and 31 stars in the magnitude range 4-7 observed at the 1.27m H127 telescope of the Greenhill Observatory, Tasmania. Identical copies of the Dipol-2 polarimeter are used on these three sites. Statistically significant (>3sigma) polarization is found in 115 stars, and >2sigma detection in 178 stars, out of the total sample of 361 stars. Polarization maps based on these data show filament-like patterns of polarization position angles which are related to both the heliosphere geometry, the kinematics of nearby clouds, and the Interstellar Boundary EXplorer (IBEX) ribbon magnetic field. From long-term multiple observations, a number (18) of stars show evidence of intrinsic variability at the 10E-5 level. This can be attributed to circumstellar effects (e.g., debris disks and chromospheric activity). The star HD 101805 shows a peculiar wavelength dependence, indicating size distribution of scattering particles different from that of a typical interstellar medium. Our high-S/N measurements of nearby stars with very low polarization also provide a useful dataset for calibration purposes.
69. HR4796A dust ring Stokes images
ID:
ivo://CDS.VizieR/J/A+A/626/A54
Title:
HR4796A dust ring Stokes images
Short Name:
J/A+A/626/A54
Date:
21 Oct 2021
Publisher:
CDS
Description:
The scattering properties of the dust originating from debris discs are still poorly known. The analysis of scattered light is however a powerful remote-sensing tool to understand the physical properties of dust particles orbiting other stars. Scattered light is indeed widely used to characterise the properties of cometary dust in the solar system. We aim to measure the morphology and scattering properties of the dust from the debris ring around HR4796A in polarised optical light. We obtained high-contrast polarimetric images of HR4796A in the wavelength range 600-900nm with the SPHERE/ZIMPOL instrument on the Very Large Telescope. We measured for the first time the polarised phase function of the dust in a debris system over a wide range of scattering angles in the optical. We confirm that it is incompatible with dust particles being compact spheres under the assumption of the Mie theory, and propose alternative scenarios compatible with the observations, such as particles with irregular surface roughness or aggregate particles.
70. HR4796 debris disk Qphi and Uphi images
ID:
ivo://CDS.VizieR/J/A+A/630/A142
Title:
HR4796 debris disk Qphi and Uphi images
Short Name:
J/A+A/630/A142
Date:
21 Oct 2021
Publisher:
CDS
Description:
Debris disks are the natural by-products of the planet formation process. Scatte red or polarized light observations are mostly sensitive to small dust grains that are released from the grinding down of bigger planetesimals. High angular resolution observations at optical wavelengths can provide key constraints on the radial and azimuthal distribution of the small dust grains. These constraints can help us better understand where most of the dust grains are released upon collisions. We present SPHERE/ZIMPOL observations of the debris disk around HR 4796A, and model the radial profiles along several azimuthal angles of the disk with a code that accounts for the effect of stellar radiation pressure. This enables us to derive an appropriate description for the radial and azimuthal distribution of the small dust grains. Even though we only model the radial profiles along (or close to) the semi-major axis of the disk, our best-fit model is not only in good agreement with our observations but also with previously published datasets (from near-IR to sub-mm wavelengths). We find that the reference radius is located at 76.4+/-0.4au, and the disk has an eccentricity of 0.076_-0.010_^+0.016^, with the pericenter located on the front side of the disk (north of the star). We find that small dust grains must be preferentially released near the pericenter to explain the observed brightness asymmetry. Even though parent bodies spend more time near the apocenter, the brightness asymmetry implies that collisions happen more frequently near the pericenter of the disk. Our model can successfully reproduce the shape of the outer edge of the disk, without having to invoke an outer planet shepherding the debris disk. With a simple treatment of the effect of the radiation pressure, we conclude that the parent planetesimals are located in a narrow ring of about 3.6au in width.