Lamp flats are taken daily, usually in following instrumental setups:
WFM (WideFieldMode), NOAO (No AO), N_Blue (Nominal wavelenght
range with Blue filter), SCII1.0 (readout mode)
WFM (WideFieldMode), NOAO (No AO), E_Clear (Extended wavelenght range with Clear filter), SCI1.0 (readout mode)
This vary depending on the period in MUSE operations.
Whenever science observations are executed in a different setup,
the corresponding lamp flat frames are taken as well, e.g, in the AO
(Adaptive Optics) mode.
Example of the raw lamp flat for CHANNEL 5 (EXTNAME=CHAN05).
The full raw lamp flat frame consists of
24 of such extensions - one extension for
each of the 24 channels of MUSE.
The average value (averaged over all detectors) of
the mean flux level of the lamp flat is trended. The
flux level is determined before normalization. It is
derived from the MASTER_FLAT calibrations. Also the rms
of the average flux level is trended.
The IFUs' alignment is checked looking at the average
flux in 4 top raw slices - slice 10, 22, 34, 46, and
average flux in 4 bottom row slices: slice 3, 15, 27,
39. It is monitored as a function of time but also as a
function of ambient temperature (INS.TEMP4.VAL, qc
parameter "temp_ambient").
Only data taken in
the instrumental mode (INS.MODE) WFM-NOAO-N and the read
out mode (DET.READ.CURNAME) SCI1.0 are selected.
The thresholds are set to ensure optimal flux on the detectors and to
warn about malfunction of the lamp. The thresholds are used for the
HC setting - the lamp flat taken in the WFM-NOAO-N and WFM-NOAO-E
modes. All other settings would need individual thresholds but
are taken only sporadically (driven by science observations). Hence a
threshold violation in a HC settings is taken as indication that the
lamp flux level needs to be adjusted.
flat lamps exchanged after showing flux decreasing trend over few months
2015-08-16
calibration lamps were changed
2016-03-14
both halogen lamps were changed
2017-02-23
the Blue halogen lamp was changed and no change was observed in the low flat field flux levels; Suspicion that the lower flux might be due to the liquid fiber degradation
2017-04-10
after recent adjustment of the both halogen lamps and of the integration time the thresholds were modified
2019-04-01
due to recent decrease of the continuum lamp flux the multiplier factor was changed from 3.38 to 3.58
This recipe combines several separate lamp flat images into one master
lamp flatfield file and traces the location of
the slices on the CCD. The master flat contains the combined pixel values of the raw flat exposures, with respect
to the image combination method used, normalized to the mean
flux. The lamp flat mean value for each detector (channel/IFU) is calculated on the master flat before normalization
The alignment parameters topslice_flux and bottomslice_flux are
calculated as average flux in 4 top raw slices - slice 10, 22, 34, 46,
normalized by the average flux in all slices in each channel and average flux in 4 bottom row slices: slice 3, 15, 27, 39, normalized by the average flux in all slices in each channel as well.
Trended are: tilt [deg], measured as angle from
vertical direction, of the left-most and right-most slice, averaged
across all the IFUs (CHANels) and mean value of the width of the
slices [pix], also averaged across all the IFUs (CHANels).
Vignetting of the Calibration Unit mask is monitored by assessing
difference in width of the slices: top left (slice10) and bottom left
(slice 3), as well as top right (slice 46) and bottom right (slice
39).
Only data points extracted from LAMP_FLAT calibrations,
PRO.CATG=TRACE_TABLE product of the muse_flat recipe, taken in the
instrumental mode (INS.MODE) WFM-NOAO-N and the read out mode
(DET.READ.CURNAME) SCI1.0 are selected.
To trace the position of the slices on the CCD, their edges are
located using a threshold method. The edge detection is repeated at
given intervals thereby tracing the central position (the mean of both
edges) and width of each slit vertically across the CCD. The trace table contains polynomials
defining the location of the slices on the CCD.
The vignetting parameters - topslice_width and bottomslice_width are
defined as difference in the width of the top left (slice10) and
bottom left (slice 3), as well as top right (slice 46) and bottom
right (slice 39).