Showing papers by "Roger H. Hildebrand published in 2002"

On the Measurement of the Magnitude and Orientation of the Magnetic Field in Molecular Clouds

Abstract: We demonstrate that the combination of Zeeman, polarimetry, and ion-to-neutral molecular line width ratio measurements permits the determination of the magnitude and orientation of the magnetic field in the weakly ionized parts of molecular clouds. Zeeman measurements provide the strength of the magnetic field along the line of sight, polarimetry measurements give the field orientation in the plane of the sky, and the ion-to-neutral molecular line width ratio determines the angle between the magnetic field and the line of sight. We apply the technique to the M17 star-forming region using a HERTZ 350 μm polarimetry map and HCO+-to-HCN molecular line width ratios to provide the first three-dimensional view of the magnetic field in M17.

A Cryogenic Half-Wave Plate Module to Measure Polarization at Multiple FIR Passbands

Abstract: One of the key components in a far-infrared polarimeter that is being designed at the University of Chicago is a locally-powered half-wave plate module. This compact, lightweight, and reliable module will operate at cryogenic temperatures, rotating a half-wave plate about its axis within the optical path. By doing so, polarization measurements can be made. Further, by utilizing multiple half-wave plate modules within the polarimeter, multiple wavelengths or passbands can be studied. In this paper, we describe the design and performance of a relatively inexpensive prototype module that was assembled and tested successfully, outline the difficulties that had to be overcome, and recommend improvements to future modules. This effort now lays some of the groundwork for a next-generation polarimeter for far-infrared astronomy.