VLT-MAN-ESO-14650-4942
P96
24.06.2015
108 of 161
ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
6.3 Flat-field and Wavelength calibrations
WARNING: ALL EXPOSURE TIMES WILL BE REVISED TO PROVIDE BETTER
CALIBRATION FRAMES.
Flatfield spectra allow to correct for the pixel-to-pixel variations in detector sensitivity as a
function of impinging wavelength of the light and to correct for the structures introduced by
imperfections of the slits. They also provide a good correction of the blaze function of the
For each arm, a dedicated halogen lamp with appropriate balancing filters is available to give
well-exposed, flat continuum spectra at all wavelengths within a reasonably short exposure
time (see Table 17). A deuterium lamp is used for the spectral region shortwards of 350 nm.
Flatfielding the whole spectral range therefore requires four exposures (2 in UVB, 1 in VIS
and ON/OFF in NIR) that have to be taken sequentially. Flatfield templates are:
XSHOOTER_slt_cal_UVBLowLampFlat (UVB deuterium-D
2
- lamp flat)
XSHOOTER_slt_cal_UVBHighLampFlat (UVB halogen lamp flat)
XSHOOTER_slt_cal_VISLampFlat
XSHOOTER_slt_cal_NIRLampFlat
And their equivalent for IFU flatfield named XSHOOTER_ifu_cal_...LampFlat.
Note that low frequency fringes with peak-to-valley amplitudes up to ~5% are present in the
red part of the VIS spectra.
Table 17: exposure time for arc frames and flat field frames. Values are given for the fast readout,
low gain mode (in UVB and VIS) for a 1.0" or 0.9" slit and the IFU. For the flatfield, values can be
adapted to other slit widths and readout modes applying a simple scaling. These values depend
on the lamp but should be closed to those indicated in this table.
To Next Page
Loading...