Flats for the Echelle+CCD spectrograph

Flat fields are notoriously a dramatic issue to cope with in multi-order Echelle spectroscopy. We have developed a new technique to secure them that allows their use in a way similar to the direct imaging approach.

We plan to put in this page the results of our monitoring of the evolution of flats for the Asiago Echelle+CCD on the 1.82 m telescope.

The first flat (preliminary extraction) is for January 24, 1999. A large number of dust grains are visible (of two main families = distances from the CCD), ghosts of overexposed Thorium lamp lines as well as weak (on the right side of the image, 0.2 % intensity, running along the columns) residuals of absorption lines in the telluric A-Band. However, the low- and high-cuts in the image are quite narrow (from 1.020 to 0.960) and therefore the chip cosmetic is still quite satisfactory and all grains can be accurately corrected for. A cleaning of the optics in front of the CCD seems in any case quite appropriate !

Munari, Zwitter, Tomov