UVES master FLATs: fringes

Example: master flats 860d2_1x1

The strongest kind of structure on the CCD isfringing in the red setting 860d2. The displays show the redL master flat (full frame and an extracted part thereof). Strong fringing is visible on large scales down to the scale of a few pixels. There are also telluric absorption lines plus some structure due to the slit function.

The first figure shows three selected rows of the master flat. The top row shows a fringing amplitude of about +/- 25%, the middle one still about 10% (peak-to-peak).

The second figure shows the ratio of corresponding rows from the two master flats (same setting, same slit width) taken on 2001-03-04 and 2001-04-09. Though different in intensity, and different in spectral format (the echelle orders have moved upwards), the fringing perfectly cancels out. Residuals are due to variations in the slit function. The last display shows the ratio frame, with the same region as the second display.

derivX setting 860d2_1x1, 0.5" slit master redL from 2001-03-04 same, closeup     rows 30, 1040, 1970 (click for larger view) row 1970 in 2001-03-04 and 2001-04-09 (red), with the ratio plotted blue ratio frame