An Easily Designed and Constructed Optical Polarimeter for Small Telescopes

Abstract

We have designed, constructed, and tested an optical polarimeter for use with the Virginia Military Institute (VMI) 0.5 m, f/13.5 Cassegrain telescope. Our instrument is based on the common dual-beam design that utilizes a rotatable half-wave plate and Wollaston prism to image starlight onto a CCD detector after it has passed through a broadband filter. The usable field of view is ≲10′′ and the operational range of the instrument is 400–700 nm. Measurements of unpolarized stars demonstrate that the instrumental polarization is ≲0.05%. Observations of seven standard stars were in agreement with their accepted values by an order of Δp(%) ≲ 0.23 for the degree of polarization and Δθ(°) ≲ 0.94 for the position angle.

Optical Polarimetry in Undergraduate Education

“…The agreement between the polarization parameters of HD 43384 determined by Topasna et al [17] with their accepted values shows that by using broadband filters on a moderately-sized telescope, students can accurately measure the wavelength dependence of polarization. The determination of these parameters can be quite useful as pointed out in the next section.…”

“…A detailed description of the design and construction of the optical polarimeter used at the VMI observatory is presented by Topasna et al [17] and should be consulted by anyone wishing to learn more about this particular instrument. Briefly presented here, however, is an overview of the design and building process to aid anyone wishing to build a similar type of polarimeter.…”

“…As an example of the Serkowski relationship, Topasna et al [17] determined the wavelength dependence of the star HD 43384 (9 Gem) [their Figure 6 reproduced here as Figure 2] using BVRI broadband filters. From a nonlinear fit to the Serkowski equation the degree of polarization was found to be 3.00 ± 0.01 percent with the wavelength of maximum polarization at (0.526 ± 0.005) µm and a position angle in the V band of 170.2 • ± 0.01 • .…”

Commissioning Results of a New Polarimeter: Denver University Small Telescope Polarimeter (DUSTPol)

“…However, the Savart produces parallel beams, as opposed to the divergent beams split by a Wollaston. While similar dual-beam polarimeters have made use of Wollaston prisms with single detectors (Topasna et al 2013), the parallel beams produced by the Savart offers greater freedom of placement with respect to the detector.…”

“…Additionally, bias inherent in polarization percentages is removed using the Wardle-Kronberg estimator (Wardle & Kronberg 1974). These methods are shared by Topasna et al (2013), and all representations of measurement uncertainty shown in this paper were calculated this way.…”