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- 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.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/MNRAS/436/3557
- Title:
- HTRU survey: long-period pulsars polarimetry
- Short Name:
- J/MNRAS/436/3557
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a polarimetric analysis of 49 long-period pulsars discovered as part of the High Time Resolution Universe (HTRU) southern survey. The sources exhibit the typical characteristics of 'old' pulsars, with low fractional linear and circular polarization and narrow, multi-component profiles. Although the position angle swings are generally complex, for two of the analysed pulsars (J1622-3751 and J1710-2616) we obtained an indication of the geometry via the rotating vector model. We were able to determine a value of the rotation measure (RM) for 34 of the sources which, when combined with their dispersion measures (DM), yields an integrated magnetic field strength along the line of sight. With the data presented here, the total number of values of RM associated with pulsars discovered during the HTRU southern survey sums to 51. The RMs are not consistent with the hypothesis of a counter-clockwise direction of the Galactic magnetic field within an annulus included between 4 and 6kpc from the Galactic Centre. A partial agreement with a counter-clockwise sense of the Galactic magnetic field within the spiral arms is, however, found in the area of the Carina-Sagittarius arm.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/559
- Title:
- IC 63 and IC 59 magnetic field structure
- Short Name:
- J/MNRAS/465/559
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Bright-rimmed clouds (BRCs) are formed at the periphery of HII regions as the radiation from the central star interacts with dense gas. The ionization and resulting compression of the clouds may lead to cloud disruption causing secondary star formation depending on the stellar and gas parameters. Here we use R-band polarimetry to probe the plane-of-the sky magnetic field for two nearby BRCs, IC 59 and IC 63. Both nebulae are illuminated by {gamma} Cas with the direction of the ionizing radiation being orientated parallel or perpendicular to the local magnetic field, allowing us to probe the importance of magnetic field pressure in the evolution of BRCs. Because of the proximity of the system (~200pc), we have acquired a substantial sample of over 500 polarization measurements for stars that form the background to the nebulae. On large scales, the magnetic field geometries of both clouds are anchored to the ambient magnetic field. For IC 63, the magnetic field is aligned parallel to the head-tail morphology of the main condensation, with a convex morphology relative to the direction of the ionizing radiation. We estimate the plane-of-the-sky magnetic field strength in IC 63 to be ~90{mu}G. In IC 59, the projected magnetic field follows the M-shape morphology of the cloud. Here, field lines present a concave shape with respect to the direction of the ionizing radiation from {gamma} Cas. Comparing our observations to published theoretical models, we find good general agreement, supporting the importance of magnetic fields in BRC evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/628/A132
- Title:
- IK Tau and HIP 20188 visible polarimetric imaging
- Short Name:
- J/A+A/628/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present visible polarimetric imaging observations of the oxygen-rich AGB star IK Tau obtained with SPHERE-ZIMPOL (phase 0.27) as well as interferometric observations with AMBER. The polarimetric imaging capabilities of SPHERE-ZIMPOL have allowed us to spatially resolve clumpy dust clouds at 20-50mas from the central star, which corresponds to 2-5R* when combined with a central star's angular diameter of 20.7+/-1.53 mas measured with AMBER. The diffuse, asymmetric dust emission extends out to ~73R*. We find that the TiO emission extends to 150 mas (15R*). The AMBER data in the CO lines also suggest a molecular outer atmosphere extending to ~1.5R*. The results of our 2-D Monte Carlo radiative transfer modelling of dust clumps suggest that the polarized intensity and degree of linear polarization can be reasonably explained by small-sized (0.1{mu}m) grains of Al_2_O_3, MgSiO_3, or Mg_2_SiO_4 in an optically thin shell ({tau}_550 nm=0.5+/-0.1) with an inner boundary radius of 3.5*. IK Tau's mass-loss rate is 20 to 50 times higher than the previously studied AGB stars W Hya, R Dor, and o Cet. Nevertheless, our observations of IK Tau revealed that clumpy dust formation occurs close to the star as seen in those low mass-rate AGB stars.
- ID:
- ivo://CDS.VizieR/J/A+AS/146/141
- Title:
- Intensive monitoring of OJ 287
- Short Name:
- J/A+AS/146/141
- Date:
- 03 Dec 2021 00:36:11
- Publisher:
- CDS
- Description:
- We present intensive optical, infrared, and radio monitoring observations of the BL Lac object OJ 287, taken between the years 1993-1998. Two large optical outbursts were detected at the predicted times in November 1994 and December 1995. The detection of these outbursts supports the binary black hole model for OJ 287. Optical and radio polarisation observations show large variability in the degree of polarisation and position angle, very similar to those observed during the 1983/84 outburst in OJ 287. The polarisation position angles show very similar behaviour during these observations, indicating that, at least, the magnetic field orientations in radio and optical bands are related in OJ 287. Optical and infrared light curves show continuous variability in time scales ranging from tens of minutes to years. In the radio bands we have observed some of the lowest ever measured flux levels. During the first optical outburst in November 1994 the observed radio flux was very low, but during the second optical outburst radio bands also showed high flux levels. This is a puzzling observation, which can hopefully be used for discriminating between different outburst models. On top of the large outbursts OJ 287 has displayed flaring activity in time scales from days to weeks and shorter time scale flickering.
- ID:
- ivo://CDS.VizieR/J/A+A/384/1050
- Title:
- Interstellar polarization. VI.
- Short Name:
- J/A+A/384/1050
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new interstellar polarization measurements for 116 stars at high galactic latitudes. Our data show that Markkanen's cloud - the main polarization structure seen in the North Galactic Pole area (b>75{deg}) extends further towards lower latitudes. Especially, we have found a new dust formation in the area 35{deg}<l<45{deg}, 57{deg}<b<63{deg}. Interstellar polarization in this part of the sky peaks at 0.7%, which gives a lower limit to the extinction A_V_>0.23mag. Polarization vectors in this cloud are very well aligned along the direction of l=50{deg}. On the IRAS 100 micron map this dust structure shows up as a bright emission area. We discuss the new polarization map extending from circumpolar to lower latitudes and point out features which suggest that Markkanen's cloud may be a part of the dust lane in the inner edge of the local spiral or spur.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A154
- Title:
- IRAS 15398-3359 polarization maps
- Short Name:
- J/A+A/631/A154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnetic fields can significantly affect the star formation process. The theory of the magnetically driven collapse in a uniform field predicts that the contraction initially happens along the field lines. When the gravitational pull grows strong enough, the magnetic field lines pinch inwards, giving rise to a characteristic hourglass shape. We investigate the magnetic field structure of a young Class 0 object, IRAS 15398-3359, embedded in the Lupus I cloud. Previous observations at large scales have suggested that this source evolved in an highly magnetised environment. This object thus appears to be an ideal candidate to study the magnetically driven core collapse in the low-mass regime. We performed polarisation observations of IRAS 15398-3359 at 214um using the SOFIA telescope, thus tracing the linearly polarised thermal emission of cold dust. Our data unveil a significant bend of the magnetic field lines from the gravitational pull. The magnetic field appears ordered and aligned with the large-scale B-field of the cloud and with the outflow direction. We estimate a magnetic field strength of B=78uG, which is expected to be accurate within a factor of two. The measured mass-to-flux parameter is {lambda}=0.95, indicating that the core is in a transcritical regime.
