This page contains information about recently discovered problems and new instrument artefacts, especially those that are not yet described in the FLAMES or UVES User Manuals.

The trap mentioned in the UVES User Manual at column x=1609 of the red upper (MIT-LL) CCD has changed its features since 2003-09-19. It consists of two columns, one column has pixel values around 1000, the other around 380. These values are now almost independent of the exposure level so that the columns are very prominent in, for example, bias frames. Previously, the columns could be seen only in well exposed frames like flat fields. Depending on the signal of the science target, the effect of these traps may be a broad emission or absorption feature in the extracted spectrum. An example (UVES-Echelle, 580nm central wavelength) is shown below.