While the [OII] 3727Å emission lines are excellent diagnostics for the confirmation of additional heating of the WIM, they are outside the spectral range of WHAM. A new instrument capable of detecting these emission lines has been developed - the Spatial Heterodyne Spectrometer (SHS).

The SHS is a modified Michelson Interferometer. The mirrors of the Michelson Interferometer have been replaced by diffraction gratings and prisms have been inserted in front of the diffraction gratings for field widening purposes. With such a configuration, the SHS is able to obtain sensitivities close to WHAM’s with a resolving power comparable to other interferometers of similar size. A filter is used to “tune” the SHS for observations at the desired wavelengths. In this case the SHS has been “tuned” to 3727Å.

The two diffraction gratings of the SHS produce a "raw interferogram" (shown below) of superimposed Fizeau fringes with a wavelength dependent crossing-angle between the two wavefronts imaged on the detector(CCD chip).

Intro • SHS • Research • UW-Madison REU • Student Research