A Review of Maser Polarization and Magnetic Fields

Through polarization observations masers are unique probes of the magnetic field in a variety of different astronomical objects, with the different maser species tracing different physical conditions. In recent years maser polarization observations have provided insights in the magnetic field strength and morphology in, among others, the envelopes around evolved stars, Planetary Nebulae (PNe), massive star forming regions and supernova remnants. More recently, maser observations have even been used to determine the magnetic field in megamaser galaxies. This review will present an overview of maser polarization observations and magnetic field determinations of the last several years and discuss the implications of the magnetic field measurements for several important fields of study, such as aspherical PNe creation and massive star formation.Comment: 10 pages, Review paper from IAU symposium 242 "Astrophysical Masers and their Environments

Polarization Observations with the Cosmic Background Imager

We describe polarization observations of the CMBR with the Cosmic Background Imager, a 13 element interferometer which operates in the 26-36 GHz band from Llano de Chajnantour in northern Chile. The array consists of 90-cm Cassegrain antennas mounted on a steerable platform which can be rotated about the optical axis to facilitate polarization observations. The CBI employs single mode circularly polarized receivers which sample multipoles from ℓ~400 to ℓ~4250. The instrumental polarization of the CBI was calibrated with 3C279, a bright polarized point source which was monitored with the VLA

Polarization observations of nine southern millisecond pulsars

Mean pulse profiles and polarization properties are presented for nine southern pulsars. The observations were made using the Parkes radio telescope at frequencies near 1330 MHz; three of the nine pulsars were also observed at 660 MHz. A very high degree of circular polarization was observed in PSR J1603-7202. Complex position angle variations which are not well described by the rotating-vector model were observed in PSRs J2124-3358 and J2145-0750, both of which have very wide profiles. Rotation measures were obtained for all nine pulsars, with two implying relatively strong interstellar magnetic fields.Comment: 24 pages, 11 figs, accepted by Ap

Optical polarization observations with the MASTER robotic net

We present results of optical polarization observations performed with the MASTER robotic net for three types of objects: gamma-ray bursts, supernovae, and blazars. For the Swift gamma-ray bursts GRB100906A, GRB110422A, GRB121011A, polarization observations were obtained during very early stages of optical emission. For GRB100906A it was the first prompt optical polarization observation in the world. Photometry in polarizers is presented for Type Ia Supernova 2012bh during 20 days, starting on March 27, 2012. We find that the linear polarization of SN 2012bh at the early stage of the envelope expansion was less than 3%. Polarization measurements for the blazars OC 457, 3C 454.3, QSO B1215+303, 87GB 165943.2+395846 at single nights are presented. We infer the degree of the linear polarization and polarization angle. The blazars OC 457 and 3C 454.3 were observed during their periods of activity. The results show that MASTER is able to measure substantially polarized light; at the same time it is not suitable for determining weak polarization (less than 5%) of dim objects (fainter than 16$^m$). Polarimetric observations of the optical emission from gamma-ray bursts and supernovae are necessary to investigate the nature of these transient objects.Comment: 31 pages, 12 figures, 4 tables; Exposure times in Table 2 have been correcte

Submillimeter and Far-Infrared Polarimetric Observations of Magnetic Fields in Star-Forming Regions

Observations of star-forming regions by the current and upcoming generation of submillimeter polarimeters will shed new light on the evolution of magnetic fields over the cloud-to-core size scales involved in the early stages of the star formation process. Recent wide-area and high-sensitivity polarization observations have drawn attention to the challenges of modeling magnetic field structure of star forming regions, due to variations in dust polarization properties in the interstellar medium. However, these observations also for the first time provide sufficient information to begin to break the degeneracy between polarization efficiency variations and depolarization due to magnetic field sub-beam structure, and thus to accurately infer magnetic field properties in the star-forming interstellar medium. In this article we discuss submillimeter and far-infrared polarization observations of star-forming regions made with single-dish instruments. We summarize past, present and forthcoming single-dish instrumentation, and discuss techniques which have been developed or proposed to interpret polarization observations, both in order to infer the morphology and strength of the magnetic field, and in order to determine the environments in which dust polarization observations reliably trace the magnetic field. We review recent polarimetric observations of molecular clouds, filaments, and starless and protostellar cores, and discuss how the application of the full range of modern analysis techniques to recent observations will advance our understanding of the role played by the magnetic field in the early stages of star formation.Comment: 29 pages, 12 figures, 1 table, published in Frontiers in Astronomy and Space Sciences. Open-access, available here: https://www.frontiersin.org/articles/10.3389/fspas.2019.00015/ful

Deriving Telescope Mueller Matrices Using Daytime Sky Polarization Observations

Telescopes often modify the input polarization of a source so that the measured circular or linear output state of the optical signal can be signficantly different from the input. This mixing, or polarization "cross-talk", is defined by the optical system Mueller matrix. We describe here an efficient method for recovering the input polarization state of the light and the full 4 x 4 Mueller matrix of the telescope with an accuracy of a few percent without external masks or telescope hardware modification. Observations of the bright, highly polarized daytime sky using the Haleakala 3.7m AEOS telescope and a coude spectropolarimeter demonstrate the technique.Comment: Accepted for publication in PAS

Optical polarization observations in the Scorpius region: NGC 6124

We have obtained optical multicolour (UBVRI) linear polarimetric data for 46 of the brightest stars in the area of the open cluster NGC 6124 in order to investigate the properties of the interstellar medium (ISM) that lies along the line of sight toward the cluster. Our data yield a mean polarization efficiency of $P_V/E_{B-V}=3.1\pm$0.62, i.e., a value lower than the polarization produced by the ISM with normal efficiency for an average color excess of $E_{B-V}=0.80$ as that found for NGC 6124. Besides, the polarization shows an orientation of $\theta \sim 8^\circ$.1 which is not parallel to the Galactic Disk,an effect that we think may be caused by the Lupus Cloud. Our analysis also indicates that the observed visual extinction in NGC 6124 is caused by the presence of three different absorption sheets located between the Sun and NGC 6124. The values of the internal dispersion of the polarization ($\Delta P_V\sim 1.3$) and of the colour excess ($\Delta E_{B-V}\sim 0.29$ mag) for the members of NGC 6124 seem to be compatible with the presence of an intra-cluster dust component. Only six stars exhibit some evidence of intrinsic polarization.Our work also shows that polarimetry provides an excellent tool to distinguish between member and non-member stars of a cluster

Radar studies of the moon Quarterly progress report no. 2, 1 Feb. - 30 Apr. 1966

Radar study of lunar surface - scattering of radio waves, polarization observations, shadowing effect on wave backscattering, and computer program for Haystack radar mappin