Solar Transients and Space Weather (STSW)

The Prominence Magnetometer (ProMag) Deployed to NSO

The ProMag is a spectro-polarimeter that was deployed in August 2009 at the Evans Solar Facility of the NSO/Sacramento Peak. and was designed to perform spectro-polarimetric analysis of the chromosphere (in particular prominences and filaments) simultaneously in the HeI lines at 587.6nm ("D3"), 1083.0nm and Hα (656.3nm). However, it can also be used to observe the corona in the forbidden emission lines of Fe XIII at 1µm. ProMag is designed to achieve a spatial resolution of better than 3" and a spectral resolution of 50 m, at 587.6 nm.

The instrument consists of a polarimeter (modulator + analyzer) placed at the prime focus (F1) of the 40-cm Evans coronagraph, and a grating-based spectrograph placed on the East bench of the Evans facility on Sacramento Peak, MN. The polarimeter itself consists of an ferro-electric liquid crystal (FLC) based polychromatic modulator (implementing two FLCs and a fixed waveplate). This configuation allows for efficient modulation (better than 40%) over a spectral range encompassing the solar lines listed above. A Wollaston prism beam-splitter is adopted as the "analyzer" component. The spectrograph consists of an image rotator, slit assembly, dispersion grating, and two camera packages, one for the visible and one for the near-IR spectra. The function of the image rotator is to keep the separation direction of the two beams from the polarimeter always aligned with the slit. The polarimeter can also be rotated to align the slit to any given direction on the solar disk. The mapping of a solar structure is performed by stepping the slit across the image plane.

The spectrograph has one visible and one IR channel. The order selection of the grating was optimized for the simultaneous observation of the two HeI lines. However Hα and HeI 10830 can also be observed simultaneously, with only minor vignetting. The detectors are a 652x496 px Pluto camera for the visible range, and a 320x256 px FLIR alpha-NIR camera. The ProMag instrument has undergone a full round of engineering tests, and it is now ready for community observation. Preliminary, calibrated data, are shown below.