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211. Rotation measures in radio source pairs
ID:
ivo://CDS.VizieR/J/ApJ/878/92
Title:
Rotation measures in radio source pairs
Short Name:
J/ApJ/878/92
Date:
03 Mar 2022 08:14:01
Publisher:
CDS
Description:
Faraday rotation measures (RMs) of extragalactic radio sources provide information on line-of-sight magnetic fields, including contributions from our Galaxy, source environments, and the intergalactic medium (IGM). Looking at differences in RMs, {Delta}RM, between adjacent sources on the sky can help isolate these different components. In this work, we classify adjacent polarized sources in the NRAO VLA Sky Survey (NVSS) as random or physical pairs. We recompute and correct the uncertainties in the NVSS RM catalog, since these were significantly overestimated. Our sample contains 317 physical and 5111 random pairs, all with Galactic latitudes |b|>=20{deg}, polarization fractions >=2%, and angular separations between 1.5' and 20'. We find an rms {Delta}RM of 14.9+/-0.4 and 4.6+/-1.1rad/m^2^ for the random and physical pairs, respectively. This means that polarized extragalactic sources that are close on the sky but at different redshifts have larger differences in RM than two components of one source. This difference of ~10rad/m^2^ is significant at 5{sigma} and persists in different data subsamples. While there have been other statistical studies of {Delta}RM between adjacent polarized sources, this is the first unambiguous demonstration that some of this RM difference must be extragalactic, thereby providing a firm upper limit on the RM contribution of the IGM. If the {Delta}RMs originate local to the sources, then the local magnetic field difference between random sources is a factor of 2 larger than that between components of one source. Alternatively, attributing the difference in {Delta}RMs to the intervening IGM yields an upper limit on the IGM magnetic field strength of 40nG.
212. Rotation measures of extragalactic radio sources
ID:
ivo://CDS.VizieR/J/ApJ/755/21
Title:
Rotation measures of extragalactic radio sources
Short Name:
J/ApJ/755/21
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the Milky Way disk and halo magnetic field, determined from observations of Faraday rotation measure (RM) toward 641 polarized extragalactic radio sources in the Galactic longitude range 100{deg}-117{deg}, within 30{deg} of the Galactic plane. For |b|<15{deg}, we observe a symmetric RM distribution about the Galactic plane. This is consistent with a disk field in the Perseus arm of even parity across the Galactic mid-plane. In the range 15{deg}<|b|<30{deg}, we find median RMs of -15+/-4rad/m2 and -62+/-5rad/m2 in the northern and southern Galactic hemispheres, respectively. If the RM distribution is a signature of the large-scale field parallel to the Galactic plane, then this suggests that the halo magnetic field toward the outer Galaxy does not reverse direction across the mid-plane. The variation of RM as a function of Galactic latitude in this longitude range is such that RMs become more negative at larger |b|. This is consistent with an azimuthal magnetic field of strength 2{mu}G (7{mu}G) at a height 0.8-2kpc above (below) the Galactic plane between the local and the Perseus spiral arm. We propose that the Milky Way could possess spiral-like halo magnetic fields similar to those observed in M51.
213. Rotation measures of extragalactic sources in SGPS
ID:
ivo://CDS.VizieR/J/ApJ/663/258
Title:
Rotation measures of extragalactic sources in SGPS
Short Name:
J/ApJ/663/258
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new Faraday rotation measures (RMs) for 148 extragalactic radio sources behind the southern Galactic plane (253{deg}<=l<=356{deg}, |b|<=1.5{deg}), and use these data in combination with published data to probe the large-scale structure of the Milky Way's magnetic field. We show that the magnitudes of these RMs oscillate with longitude in a manner that correlates with the locations of the Galactic spiral arms. The observed pattern in RMs requires the presence of at least one large-scale magnetic reversal in the fourth Galactic quadrant, located between the Sagittarius-Carina and Scutum-Crux spiral arms. To quantitatively compare our measurements to other recent studies, we consider all available extragalactic and pulsar RMs in the region we have surveyed, and jointly fit these data to simple models in which the large-scale field follows the spiral arms.
214. Rotation Measure synthesis of WSRT obs.
ID:
ivo://CDS.VizieR/J/A+A/549/A56
Title:
Rotation Measure synthesis of WSRT obs.
Short Name:
J/A+A/549/A56
Date:
21 Oct 2021
Publisher:
CDS
Description:
Rotation Measure synthesis (RM synthesis) of the Westerbork Synthesis Radio Telescope (WSRT) observations at 2m wavelength of the FAN region at l=137deg, b=+7deg shows the morphology of structures in the ionized interstellar medium.
215. SAO 206462 polarised Ks image
ID:
ivo://CDS.VizieR/J/A+A/560/A105
Title:
SAO 206462 polarised Ks image
Short Name:
J/A+A/560/A105
Date:
21 Oct 2021
Publisher:
CDS
Description:
Transitional disks represent a short stage of the evolution of circumstellar material. Studies of dust grains in these objects can provide pivotal information on the mechanisms of planet formation. Dissimilarities in the spatial distribution of small ({mu}m-size) and large (mm-size) dust grains have recently been pointed out. Constraints on the small dust grains can be obtained by imaging the distribution of scattered light at near-infrared wavelengths. We aim at resolving structures in the surface layer of transitional disks (with particular emphasis on the inner 10-50AU), thus increasing the scarce sample of high-resolution images of these objects. We obtained VLT/NACO near-IR high-resolution polarimetric differential imaging observations of SAO 206462 (HD135344B). This technique allows one to image the polarized scattered light from the disk without any occulting mask and to reach an inner working angle of ~0.1". A face-on disk is detected in H and K_s_ bands between 0.1" and 0.9". No significant differences are seen between the H and K_s_ images. In addition to the spiral arms, these new data allow us to resolve for the first time an inner disk cavity for small dust grains. The cavity size (=~28AU) is much smaller than what is inferred for large dust grains from (sub-)mm observations (39 to 50AU). This discrepancy cannot be ascribed to any resolution effect. The interaction between the disk and potential orbiting companion(s) can explain both the spiral arm structure and the discrepant cavity sizes for small and large dust grains. One planet may be carving out the gas (and, thus, the small grains) at 28AU, and generating a pressure bump at larger radii (39AU), which holds back the large grains. We analytically estimate that, in this scenario, a single giant planet (with a mass between 5 and 15M_J_) at 17 to 20AU from the star is consistent with the observed cavity sizes.
216. SCUPOL Legacy polarimetry of SCUBA
ID:
ivo://CDS.VizieR/J/ApJS/182/143
Title:
SCUPOL Legacy polarimetry of SCUBA
Short Name:
J/ApJS/182/143
Date:
21 Oct 2021
Publisher:
CDS
Description:
SCUPOL, the polarimeter for SCUBA on the James Clerk Maxwell Telescope, was the most prolific thermal imaging polarimeter built to date. Between 1997 and 2005, observations of 104 regions were made at 850um in the mapping mode. The instrument has produced ~50 refereed journal publications, and that number is still growing. We have systematically re-reduced all imaging polarimetry made in the standard "jiggle-map" mode from the SCUBA archive (2800+ individual observations) to produce a catalog of SCUPOL images and tables. We present the results of our analysis with figures and data tables produced for all 83 regions where significant polarization was detected. In addition, the reduced data cubes and data tables can be accessed online. In many cases, the data included in this paper have been previously published elsewhere. However, this publication includes unpublished data sets, in whole or in part, toward 39 regions, including cores in Rho Ophiuchus, Orion's OMC-2 region, several young stellar objects, and the galaxy M87.
217. SDSS optically selected BL Lac candidates
ID:
ivo://CDS.VizieR/J/A+A/569/A95
Title:
SDSS optically selected BL Lac candidates
Short Name:
J/A+A/569/A95
Date:
21 Oct 2021
Publisher:
CDS
Description:
Deep optical surveys open the avenue for finding large numbers of BL Lac objects that are hard to identify because they lack the unique properties classifying them as such. While radio or X-ray surveys typically reveal dozens of sources, recent compilations based on optical criteria alone have increased the number of BL Lac candidates considerably. However, these compilations are subject to biases and may contain a substantial number of contaminating sources. In this paper we extend our analysis of 182 optically selected BL Lac object candidates from the SDSS with respect to an earlier study. The main goal is to determine the number of bona fide BL Lac objects in this sample. We examine their variability characteristics, determine their broad-band radio-UV spectral energy distributions (SEDs), and search for the presence of a host galaxy. In addition we present new optical spectra for 27 targets with improved signal-to-noise ratio with respect to the SDSS spectra. At least 59% of our targets have shown variability between SDSS DR2 and our observations by more than 0.1-0.27mag depending on the telescope used. A host galaxy was detected in 36% of our targets. The host galaxy type and luminosities are consistent with earlier studies of BL Lac host galaxies. Simple fits to broad-band SEDs for 104 targets of our sample derived synchrotron peak frequencies between 13.5<=log_10_({nu}_peak_)<=16 with a peak at log_10_~14.5. Our new optical spectra do not reveal any new redshift for any of our objects. Thus the sample contains a large number of bona fide BL Lac objects and seems to contain a substantial fraction of intermediate-frequency peaked BL Lacs.
218. Small-diameter sources in Sino-German 6cm survey
ID:
ivo://CDS.VizieR/J/A+A/561/A55
Title:
Small-diameter sources in Sino-German 6cm survey
Short Name:
J/A+A/561/A55
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have carried out the Sino-German 6cm polarisation survey of the Galactic plane at 6cm in total and polarised intensity using the Urumqi 25-m telescope of Xinjiang (formerly Urumqi) Astronomical Observatory, Chinese Academy of Sciences. The angular resolution is 9.5-arcmin. The surveyed area covers 10{deg} to 230{deg} in Galactic longitude and absolute Galactic latitudes of up to 5{deg}. The measured rms-noise is about 6.1 mJy/beam area for total intensities and 3.05mJy/beam area for polarised intensities. The survey maps are accessible from http://zmtt.bao.ac.cn/6cm/ .
219. Southern Hemisphere ISM FORS2 spectropolarimetry
ID:
ivo://CDS.VizieR/J/A+A/608/A146
Title:
Southern Hemisphere ISM FORS2 spectropolarimetry
Short Name:
J/A+A/608/A146
Date:
21 Oct 2021
Publisher:
CDS
Description:
Polarimetric studies of light transmitted through interstellar clouds may give constraints on the properties of the interstellar dust grains. Traditionally, broadband linear polarisation (BBLP) measurements have been considered an important diagnostic tool for the study of the interstellar dust, while comparatively less attention has been paid to spectropolarimetric measurements. However, spectropolarimetry may offer stronger constraints than BBLP, for example by revealing narrowband features, and by allowing us to distinguish the contribution of dust from the contribution of interstellar gas. Therefore, we have decided to carry out a Large Interstellar Polarisation Survey (LIPS) using spectropolarimetric facilities in both hemispheres. Here we present the results obtained in the Southern Hemisphere with the FORS2 instrument of the ESO Very Large Telescope.
220. Southern peculiar early-type stars polarimetry
ID:
ivo://CDS.VizieR/J/A+AS/131/401
Title:
Southern peculiar early-type stars polarimetry
Short Name:
J/A+AS/131/401
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present and discuss optical polarimetry of a large group (60 objects) of peculiar early-type stars (Herbig Ae/Be stars and candidate members, B[e] stars, extreme emission line objects etc.). Most were taken from ``A new catalogue of members and candidate members of Herbig Ae/Be stellar group'' The et al. (1994, Cat. <J/A+AS/104/315>). For 40 out of the 60 objects polarization was measured for the first time. On the basis of the data we draw conclusions about the circumstellar shell configuration and orientation for several objects. Polarimetric variability on different time-scales (minutes...hours...days) was investigated, as well as comparison with earlier measurements to investigate variability over longer time-scales. No circular polarization was detected to a 5{sigma} level in most of the investigated stars. Polarimetric data obtained here as well as data available from the literature were analyzed from the point of investigating the evolutionary status of the objects. The relationship between the polarimetric and photometric data was also investigated.