David Alexander Schleuning

The Far-Infrared Polarization Spectrum: First Results and Analysis

We present data on the polarization of the thermal emission from Galactic Clouds at 60 μm, 100 μm, and 350 μm. There are examples of rising polarization spectra in dense cloud cores [P(350 μm/P(100 μm)≈2], and falling spectra in cloud envelopes [P(350)/P(100 μm)≈0.6]. We also present data showing that the relationship, P(τ), between polarization and optical depth in cloud cores is different from that in cloud envelopes. We review the principles governing the far-infrared polarization spectrum and discuss applications to the data on P(λ) and P(τ). We conclude that the cloud envelopes we have observed must contain two populations of grains that differ in their polarization efficiencies and in their emission spectra. We propose a model for cloud envelopes in which the contrasting populations reside in domains of different mean temperatures where the warmer domains contain the aligned grains.

FAR-INFRARED POLARIMETRY OF GALACTIC CLOUDS FROM THE KUIPER AIRBORNE OBSERVATORY

In this paper we present a complete summary of the data obtained with the far-infrared polarimeter, Stokes, in flights of the Kuiper Airborne Observatory. We have observed 12 Galactic clouds and have made over 1100 individual measurements at 100 ?m and 60 ?m. The median P for all of the 60 ?m and 100 ?m measurements is 3.6% and 2.6% respectively. We also present flux maps obtained simultaneously with the polarimetry.

HERTZ, A SUBMILLIMETER POLARIMETER

We describe a 32 pixel polarimeter, Hertz, for use at the Caltech Submillimeter Observatory. We present polarization maps of the Orion molecular cloud (OMC-1) at 350 μm (46 detections) and 450 μm (19 detections) with 3σ or better statistical significance. The 350 μm polarization ranges from 1.4 to 6.8% with a median value of 3.3%. The position angles are fairly uniform across the souce at an angle of ~30 degrees (east of north). We describe the design and performance characteristics of the polarimeter and discuss systematic effects due to telescope and instrumental polarization, atmospheric fluctuations, and reference beam flux.

Polarized far-infrared emission from the core and envelope of the sagittarius b2 molecular cloud

We have detected linear polarization in the 115 μm continuum radiation from the giant molecular cloud Sagittarius B2. We found polarization at nine positions in the dense cloud core and at 15 positions in the less-dense envelope. The polarization in the core is due to absorption by magnetically aligned grains and that in the envelope is due to emission from magnetically aligned grains. The inferred magnetic field direction is roughly north-south everywhere, but with spatially smooth variations of up to 30°. By considering our data together with Zeeman splitting observations we are able to set a conservative lower limit of 150 μG on the strength of the large-scale field in the envelope. If large-scale fields this strong are common in Galactic center clouds, they could be detectable via large-beam Zeeman measurements. For positions in the envelope that are furthest from the core, the field is nearly parallel to the plane of the Galaxy. This is consistent with the idea of a globally azimuthal magnetic field in the Galactic center neutral gas layer, which is expected if gravitational forces dominate magnetic forces.

Polarizing Grids, Their Assemblies, and Beams of Radiation

This paper gives an analysis of the behavior of polarizing grids and reflecting polarizers by solving Maxwells equations, for arbitrary angles of incidence and grid rotation, for cases where the excitation is provided by an incident plane wave or a beam of radiation. The scattering and impedance matrix representations are derived and used to solve more complicated configurations of grid assemblies. The results are also compared with data obtained in the calibration of reflecting polarizers at the Owens Valley Radio Observatory. From this analysis, we propose a method for choosing the optimum grid parameters (wire radius and spacing). We also provide a study of the effects of two types of errors (in wire separation and radius size) that can be introduced in the fabrication of a grid.

Hertz: An imaging polarimeter

The University of Chicago polarimeter, Hertz, is designed for observations at the Caltech Submillimeter Observatory in the 350 micrometer atmospheric window. Initial observations with this instrument, the first array polarimeter for submillimeter observations, have produced over 700 measurements at 3(sigma) or better. This paper summarizes the characteristics of the instrument, presents examples of its performance including polarization maps of molecular clouds and regions near the Galactic center, and outlines the opportunities for improvements with emphasis on requirements for mapping widely extended sources.