2 MSDP imaging spectroscopy: High resolution in space and time

Since 1970, several MSDPs were built and operated in several telescopes:

- the Meudon Solar Tower (Mein 1977)

- the Turret Dome of Pic-du-Midi (Mein 1981) - the German VTT telescope of Tenerife (Mein 1991)

- the Wroclaw large coronagraph (Rompolt B. 1993) The THEMIS MSDP is the most powerful one. We shall detail in the next section its specific capabilities. Let us recall that, as did the previous ones, this MSDP extracts a 2D-field of the solar image (typically $10\hbox{$^{\prime\prime}$ }\times 170\hbox{$^{\prime\prime}$ }$) and dispatches the photons over a number of 2D channels (typically 16 for one line profile) recorded by CCD cameras. The pixel size is around 0.2 arcsec.

In order to achieve the best spatial resolution in imaging spectroscopy, the MSDP avoids the convolution by a slit-width (unlike the slit-spectroscopy) and differential blurring between successive wavelengths by seeing effects (unlike narrow-band filters). A general description of the MSDP principle can be found in Mein (1995).

By using successive steps across the solar disk, large areas can be scanned within short times. The speed of the MSDPs is appreciated in coordinated campaigns involving ground-based and space telescopes.