SPECKLE SPECTROGRAPHY OF EXTENDED OBJECTS

We present a method to obtain diffraction limited spectrograms of exte nded sources from a series of ground-based slit-spectrograms. The meth od is a combination of speckle deconvolution (Keller and von der Luhe 1992) and a rapid spectrograph scanning scheme (Johannesson et al. 199 2). The slit of a spectrograph is scanned over the solar surface while simultaneous slit-jaw images and spectrograms are recorded. The expos ure time is short with respect to seeing-induced variations. A Knox-Th ompson speckle reconstruction scheme is applied to the slit jaw images . From the individual slit-jaw images and their speckle reconstruction the instantaneous point spread function can be determined for any loc ation. The spectrograms are reconstructed by inverting a matrix that d escribes the action of the point-spread function on the spectrograms. The final product is a three-dimensional cube formed by the two spatia l coordinates and the wavelength. In the spatial domain the data is ne arly diffraction limited while the spectral resolution is not affected by the reconstruction. The method is applied to observations of the q uiet solar granulation.