We present initial results from Hertz/VPM, the first submillimeter polarimeter employing the dual Variable-delay Polarization Modulator (dual-VPM). This device differs from previously used polarization modulators in that it operates in translation rather than mechanical rotation. We discuss the basic theory behind this device, and its potential advantages over the commonly used half wave plate (HWP). The dual-VPM was tested both at the Submillimeter Telescope Observatory (SMTO) and in the lab. In each case we present a detailed description of the setup. We discovered that properties of the VPM wire grids (diameter and spacing) caused behavior that differs from theoretical predictions for ideal wire grid performance. Modifying the polarimeter settings to compensate for this behavior, we found that the dual-VPM system is robust, operating with high efficiency and low instrumental polarization. This device is well suited for air and space-borne applications, and is also advantageous for multi-wavelength polarimetry applications. One such application concerns submillimeter spectropolarimetry of T Tauri Star (TTS) disks, to probe the grains in this environment. We present 350 micron polarimetry of the circumstellar disk of DG Tau. Comparison with a previous measurement made at 850 microns suggests that there is considerable structure in the submillimeter polarization spectrum. We also discuss theoretical models for polarized emission from TTS disks, both simple toy models developed at Northwestern and a more sophisticated model published more recently by J. Cho and A. Lazarian. The data do not agree with this more recent model, but it is plausible that this could be due to the larger mass of the DG Tau disk in comparison to the model disk

Last modified

• 09/16/2018

Creator

• Megan M Krejny

DOI

• https://doi.org/10.21985/N23X7D

Subject

• Physics and Astronomy

Keyword

• protoplanetary disks
• submillimeter polarimetry
• polarization modulation

Date created

• 2008-10-13

Resource type

• Dissertation

Rights statement

• In Copyright