A New Spectropolarimeter to Study the Polarization of Earth’s Auroral Emission Lines

Abstract:

In the last few years, a lot of efforts were made in order to measure and model the polarization of the auroral red line emission (λ 630nm). This polarization arises due to impact of thermospheric oxygen atoms with precipitating electrons collimated along the geomagnetic field but is diluted by many competing production mechanisms that do not produce polarization, and other loss mechanisms as well. Observations show that the red line emission is polarized at a level of a few percent.

In order to continue investigating this field, we are building a spectropolarimeter able to measure the polarization of the full auroral spectrum between 400 and 700 nm. In particular the blue emission band due to N2+ 1NG (λ 428nm) is a very interesting candidate for polarization as it is produced by impact with precipitating electrons only.

A test campaign with a first version of the spectropolarimeter was carried out in Skibotn, Norway, in December 2014 aiming at validating the experimental concept and estimating the integration times needed to obtain adequate S/N ratios. In the coming months, we will work on improving the design and make some twilight sky observations in Brussels as a calibration test. This presentation will review the principle of the instrument, the observations carried out in Skibotn as well as the recent work and tests made on the instrument.