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181. Polarization of 125 stars in NGC 1817 open cluster
ID:
ivo://CDS.VizieR/J/AJ/160/256
Title:
Polarization of 125 stars in NGC 1817 open cluster
Short Name:
J/AJ/160/256
Date:
21 Oct 2021
Publisher:
CDS
Description:
Multiband linear polarimetric observations of 125 stars in the region of the cluster NGC1817 have been carried out intending to study properties of interstellar dust and grains in that direction. The polarization is found to be wavelength-dependent, being maximum in the V-band with an average value of 0.95%. The foreground interstellar dust grains appear to be the main source of linear polarization of starlight toward the direction of NGC1817. The average value of the position angle in the V-band of 119.2{deg} is found to be less than the direction of the Galactic parallel in the region, indicating that the dust grains in the direction are probably not yet relaxed. Spatial distribution of dust appears to be more diverse in the coronal region than the core region of the cluster. The maximum value of the degree of polarization is estimated to be 0.93% for members of the cluster using the Serkowski relation. The average value of wavelength corresponding to the maximum polarization of 0.54{+/-}0.02{mu}m indicates that the size distribution of dust grains in the line of sight is similar to that of the general interstellar medium. Several variable stars in the cluster were also observed polarimetrically and pulsating variables appear to have a slightly lower value of polarization from other nonvariable member stars of the cluster. There are indications of the existence of dust layers in front of those clusters which are located close to galactic plane while for clusters located away from galactic plane no major dust layers are observed.
182. Polarization of stars in Taurus
ID:
ivo://CDS.VizieR/J/ApJ/741/21
Title:
Polarization of stars in Taurus
Short Name:
J/ApJ/741/21
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present maps of the plane-of-sky magnetic field within two regions of the Taurus molecular cloud: one in the dense core L1495/B213 filament and the other in a diffuse region to the west. The field is measured from the polarization of background starlight seen through the cloud. In total, we measured 287 high-quality near-infrared polarization vectors in these regions. In L1495/B213, the percent polarization increases with column density up to A_V_~9mag, the limits of our data. The radiative torques model for grain alignment can explain this behavior, but models that invoke turbulence are inconsistent with the data. We also combine our data with published optical and near-infrared polarization measurements in Taurus. Using this large sample, we estimate the strength of the plane-of-sky component of the magnetic field in nine subregions. This estimation is done with two different techniques that use the observed dispersion in polarization angles. Our values range from 5 to 82uG and tend to be higher in denser regions. In all subregions, the critical index of the mass-to-magnetic flux ratio is sub-unity, implying that Taurus is magnetically supported on large scales (~2pc). Within the region observed, the B213 filament takes a sharp turn to the north and the direction of the magnetic field also takes a sharp turn, switching from being perpendicular to the filament to becoming parallel. This behavior can be understood if we are observing the rim of a bubble. We argue that it has resulted from a supernova remnant associated with a recently discovered nearby gamma-ray pulsar.
183. Polarization & photom. of stars toward LDN1225
ID:
ivo://CDS.VizieR/J/ApJ/875/64
Title:
Polarization & photom. of stars toward LDN1225
Short Name:
J/ApJ/875/64
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results based on the optical R-band observations of the polarization of 280 stars distributed toward the dark globule LDN1225. Parallaxes from Gaia data release 2 along with the polarization data of ~200 stars have been used to (a) constrain the distance of LDN 1225 as 830+/-83pc, (b) determine the contribution of interstellar polarization, and (c) characterize the dust properties and delineate the magnetic field (B-field) morphology of LDN 1225. We find that B-fields are more organized and exhibit a small dispersion of 12{deg}. Using the ^12^CO molecular line data from the Purple Mountain Observatory, along with the column density and dispersion in B-fields, we estimate the B-field strength to be ~56+/-10{mu}G, the ratio of magnetic to turbulent pressure to be ~3+/-2, and the ratio of mass to magnetic flux (in units of the critical value) to be <1. These results indicate the dominant role of B-fields in comparison to turbulence and gravity in rendering the cloud support. B-fields are aligned parallel to the low-density parts (traced by a ^12^CO map) of the cloud; in contrast, they are neither parallel nor perpendicular to the high-density core structures (traced by ^13^CO and C^18^O maps). LDN1225 hosts two 70{mu}m sources, which seem to be low-mass Class 0 sources. The ratio of total to selective extinction derived using optical and near-infrared photometric data is found to be anomalous (RV=3.4), suggesting the growth of dust grains in LDN 1225. The polarization efficiency of dust grains follows a power law with an index of -0.7, implying that optical polarimetry traces B-fields in the outer parts of the cloud.
184. Polarization towards open cluster NGC 6823
ID:
ivo://CDS.VizieR/J/MNRAS/403/1577
Title:
Polarization towards open cluster NGC 6823
Short Name:
J/MNRAS/403/1577
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present multiwavelength linear polarimetric observations of 104 stars towards the region of young open cluster NGC 6823. The polarization towards NGC 6823 is dominated by foreground dust grains and we found evidence for the presence of several layers of dust towards the line of sight. The first layer of dust is approximately located within 200pc towards the cluster, which is much closer to the Sun than the cluster itself (~2.1kpc). The radial distribution of the position angles for the member stars is found to show a systematic change, while the polarization is found to reduce towards the outer parts of the cluster and the average position angle of the coronal region of the cluster is very close to the inclination of the Galactic parallel (~32{deg}). The size distribution of the grains within NGC 6823 is similar to those in the general interstellar medium. The patchy distribution of foreground dust grains is suggested to be mainly responsible for both differential reddening and polarization towards NGC 6823. The majority of the observed stars do not show evidence of intrinsic polarization in their light.
185. Polarized DRAO sources
ID:
ivo://CDS.VizieR/J/ApJ/733/69
Title:
Polarized DRAO sources
Short Name:
J/ApJ/733/69
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Dominion Radio Astrophysical Observatory Deep Field polarization study has been matched with the Spitzer Wide-Area Infrared Extragalactic Survey of the European Large Area Infrared Space Observatory Survey North 1 field. We have used Very Large Array observations with a total intensity rms of 87uJy/beam to match SWIRE counterparts to the radio sources. Infrared color analysis of our radio sample shows that the majority of polarized sources are elliptical galaxies with an embedded active galactic nucleus. Using available redshift catalogs, we found 429 radio sources of which 69 are polarized with redshifts in the range of 0.04<z<3.2. We find no correlation between redshift and percentage polarization for our sample. However, for polarized radio sources, we find a weak correlation between increasing percentage polarization and decreasing luminosity.
186. Polarized images of MWC758
ID:
ivo://CDS.VizieR/J/A+A/578/L6
Title:
Polarized images of MWC758
Short Name:
J/A+A/578/L6
Date:
21 Oct 2021
Publisher:
CDS
Description:
The study of dynamical processes in protoplanetary disks is essential to understand planet formation. In this context, transition disks are prime targets because they are at an advanced stage of disk clearing and may harbor direct signatures of disk evolution. We aim to derive new constraints on the structure of the transition disk MWC758, to detect non-axisymmetric features and understand their origin. We obtained infrared polarized intensity observations of the protoplanetary disk MWC758 with SPHERE/VLT at 1.04 microns to resolve scattered light at a smaller inner working angle (0.093") and a higher angular resolution (0.027") than previously achieved. We observe polarized scattered light within 0.53" (148AU) down to the inner working angle (26AU) and detect distinct non-axisymmetric features but no fully depleted cavity. The two small-scale spiral features that were previously detected with HiCIAO are resolved more clearly, and new features are identified, including two that are located at previously inaccessible radii close to the star. We present a model based on the spiral density wave theory with two planetary companions in circular orbits. The best model requires a high disk aspect ratio (H/r~0.20 at the planet locations) to account for the large pitch angles which implies a very warm disk. Our observations reveal the complex morphology of the disk MWC758. To understand the origin of the detected features, the combination of high-resolution observations in the submillimeter with ALMA and detailed modeling is needed.
187. Polarized NVSS sources SEDs
ID:
ivo://CDS.VizieR/J/ApJS/212/15
Title:
Polarized NVSS sources SEDs
Short Name:
J/ApJS/212/15
Date:
21 Oct 2021
Publisher:
CDS
Description:
An understanding of cosmic magnetism requires converting the polarization properties of extragalactic radio sources into the rest-frame in which the corresponding polarized emission or Faraday rotation is produced. Motivated by this requirement, we present a catalog of multiwavelength linear polarization and total intensity radio data for polarized sources from the NRAO VLA Sky Survey. We cross-match these sources with a number of complementary measurements --combining data from major radio polarization and total intensity surveys such as AT20G, B3-VLA, GB6, NORTH6CM, Texas, and WENSS, together with other polarization data published over the last 50 years. For 951 sources, we present spectral energy distributions (SEDs) in both fractional polarization and total intensity, each containing between 3 and 56 independent measurements from 400MHz to 100GHz. We physically model these SEDs, and where available provide the redshift of the optical counterpart. For a superset of 25649 sources we provide the total intensity spectral index, {alpha}. Objects with steep versus flat {alpha} generally have different polarization SEDs: steep-spectrum sources exhibit depolarization, while flat-spectrum sources maintain constant polarized fractions over large ranges in wavelength. This suggests the run of polarized fraction with wavelength is predominantly affected by the local source environment, rather than by unrelated foreground magnetoionic material. In addition, a significant fraction (21%) of sources exhibit "repolarization," which further suggests that polarized SEDs are affected by different emitting regions within the source, rather than by a particular depolarization law. This has implications for the physical interpretation of future broadband polarimetric surveys.
188. Polarized point sources in LOTSS-HETDEX
ID:
ivo://CDS.VizieR/J/A+A/613/A58
Title:
Polarized point sources in LOTSS-HETDEX
Short Name:
J/A+A/613/A58
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have produced a catalog of 92 polarized radio sources at 150MHz at 4.3-arcmin resolution and 1mJy rms sensitivity, which is the largest catalog of polarized sources at such low frequencies. The data used was from the LOFAR Two-Meter Sky Survey (LOTSS) initial release (Shimwell et al., 2017, Cat. J/A+A/598/A104), (10h45m-15h30m right ascension, 45-57{deg} declination, 570 square degrees).
189. Polarized SiO masers of VX Sgr
ID:
ivo://CDS.VizieR/J/ApJ/728/149
Title:
Polarized SiO masers of VX Sgr
Short Name:
J/ApJ/728/149
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Submillimeter Array observations of high-frequency SiO masers around the supergiant VX Sgr and the semi-regular variable star W Hya. The J=5-4, v=1^28^SiO and v=0^29^SiO masers of VX Sgr are shown to be highly linearly polarized with a polarization from ~5% to 60%. Assuming the continuum emission peaks at the stellar position, the masers are found within ~60mas of the star, corresponding to ~100AU at a distance of 1.57kpc. The linear polarization vectors are consistent with a large-scale magnetic field, with position and inclination angles similar to that of the dipole magnetic field inferred in the H_2_O and OH maser regions at much larger distances from the star. We thus show for the first time that the magnetic field structure in a circumstellar envelope can remain stable from a few stellar radii out to ~1400AU. This provides further evidence supporting the existence of large-scale and dynamically important magnetic fields around evolved stars. Due to a lack of parallactic angle coverage, the linear polarization of masers around W Hya could not be determined. For both stars, we observed the ^28^SiO and ^29^SiO isotopologues and find that they have a markedly different distributions and that they appear to avoid each other. Additionally, emission from the SO 5_5_-4_4_ line was imaged for both sources. Around W Hya, we find a clear offset between the red- and blueshifted SO emission. This indicates that W Hya is likely host to a slow bipolar outflow or a rotating disk-like structure.
190. (Possible spiral in the disk around HD34282
ID:
ivo://CDS.VizieR/J/A+A/649/A25
Title:
(Possible spiral in the disk around HD34282
Short Name:
J/A+A/649/A25
Date:
22 Feb 2022
Publisher:
CDS
Description:
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. We aim to detect signatures of planet-disk interaction by studying the scattering surface of the protoplanetary disk around HD34282 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. The detected disk displays a complex scattering surface. An inner clearing or cavity extending up to r<0.28" (88au) is surrounded by a bright inclined (i=56{deg}) ring with a position angle of 119{deg}. 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 26au 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" (=190au) and a height of 77au. 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. We present the first scattered-light image of the disk around HD 34282 and resolve a disk with an inner cavity up to r~90au 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_ {prop.to} 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.