Coronal One-Shot CCD Tests

Several tests were run with the Coronal One-Shot coronagraph at NSO/SP during late October 1996. The Lyot filter pass band was measured on the ESF Littrow spectrograph, and the orientations of the entrance and exit polaroids were determined for on-band, off-band, and red and blue wing tunings. When coupled with the proper prefilters, the Lyot filter transmits 0.1 nm pass bands centered on the green [Fe XIV] 530.3 nm and red [Fe X] 637.4 nm coronal lines, and at H 656.3 nm. The old prefilters were also tested and found to have spatial irregularities and to have drifted in wavelength.

Nevertheless, the filter system was re-installed on the coronagraph, and a Thomson 1024 x 1024 CCD was borrowed from the VTT and placed in the One-Shot focal plane. During one day of good skies, several test images were taken in the green line and H. The figure shows a sample H disk image and an occulted coronal green-line image. Each image is produced by subtracting sequential on-band and off-band CCD frames. The coronal activity was very low, and the calibrated intensity of the green line structure is about 10 millionths of the disk brightness. With a few more control systems interfaced to the instrument computer, and with a dedicated CCD detector in the film plane, the One-Shot will be capable of high spatial resolution, photometric, automated coronal imaging.

Matt Penn, Fritz Stauffer, Larry Wilkins, Steve Hegwer, Joe Elrod, Todd Brown, Ed Leon