<title>Compact Doppler magnetograph</title>

Abstract

We designed a low-cost flight instrument that images the full solar disk through two narrowband filters at the red and blue "wings" of the solar potassium absorption line. The images are produced on a 1024x1024 charge-coupled device with a resolution of 2 arcsec per pixel. Four filtergrams taken in a very short time at both wings in the left and right states of circular polarization are used to yield a Dopplergrani and a magnetogram simultaneously. The noise-equivalent velocity associated with each pixel is less than 3 rn/s. The measured signal is linearly proportional to the velocity in the range 4000 rn/s. The range ofmagnetic fields is from 3 to 3000 Gauss. The optical system ofthe instrument is simple and easily aligned. With a pixel size of 12 m, the effective focal length is 126 cm. A Raleigh resolution limit of 4 arcsec is achieved with a 5-cm entrance aperture, providing an f/25 focalratio. The foreoptic is a two-component telephoto lens serving to limit the overall optical length to 89 cm or less. The mass of the instrument is 14 kg. The power required is less than 30 Watts. The Compact Doppler Magnetograph can be used in space missions with severe mass and power requirements. It can also be effectively used for ground-based observations: Large telescope, dome or other observatory facilities are not required.

Optical Design of a Miniaturised Solar Magnetograph for Space Applications

“…Ground-based telescopes having successfully implemented the MOF technology include, for example, MOTH at the Mees Solar Observatory in Hawaii, MOTH II, located at the South Pole in Antarctica [13], and the Tor Vergata Synoptic Solar Telescope (TSST) in La Palma, Spain [14,15]. Previous studies have demonstrated that the use of a magneto-optical filter could lead to a space-based magnetograph design of reduced size and mass (e.g., [16][17][18]). The study of [18] conceived a space-based magnetograph of mass 14 kg with dimensions 850 × 150 × 150 mm.…”

“…Previous studies have demonstrated that the use of a magneto-optical filter could lead to a space-based magnetograph design of reduced size and mass (e.g., [16][17][18]). The study of [18] conceived a space-based magnetograph of mass 14 kg with dimensions 850 × 150 × 150 mm. In this paper, we build on the previous work to make steps towards a conceptual design of a compact (800 mm × 200 mm × 200 mm) lightweight (<15 kg) magnetograph.…”