MUSE: Association map
A complete set of MUSE calibrations consists of the following frames:
- dark (optional)
- lamp flat field
- arc lamps
- sky flat field
- standard star
- astrometry (optional)
- geometry table (optional)
They need to be processed in a certain order.
First, the bias frames are combined into a master bias. It is
further used in subsequent reduction steps.
The combined master dark is not expected to be needed for data
processing as the dark current of the MUSE CCDs is small.
The raw lamp flat field frames are combined into a master flat and
trace tables, where the slices are located on the image, their edges
are traced along the wavelength axis (vertical direction) and
bright/dark pixels are identified.
The set of three arc-lamp frames (one lamp each) repeated 5 times
(5x3) is required to create wavelenght solution.
Assumption is that to create the lsf-table the arc-lamps' sequence
has to be repeated 15 times (15x3). The line spread function is
computed for each slice and is later used during the sky
subtraction. Currently it is used in a static form.
Originally, the actual pixel data of the combined sky flat was not
used in further data reduction. Instead, the integrated flux value was
utilized for the later illumination correction as an estimate of the
relative throughput of the IFUs. This changed with adopting pipeline
version 1.0 (2014-12-08). Twilight correction is routinely applied to
the on-sky data.
The response curve for the flux calibration of the science
observations is obtained from the standard star observations using
catalog of reference spectra of the spectrophotometric standard
stars. Also, a static form can be used.
The astrometric calibration is created from the exposure of an
astrometric field. It is needed to set the the world coordinate system
for the science exposure and assign righ ascension and declination to
the spatial elements of the data cube. Since the WCS solution was
verified to be stable, this step in data reduction can be considered
optional. Currently it is used in static form.
The geometry table calibration is created from 80 dedicated
input frames. They are taken occasionally to monitor status of the
instrument, typically once a month. The geometry table is closely
related to the astrometric calibrations, thus, they have to be
processed together. Since it appears to be quite stable with time and
requires heavy processing, it is currently used in static form.
In addition, single input frame illumination flats are used for
processing on-sky data. They are taken close in time to the science
and standard stars' data. Were introduced with pipeline version 1.0
Find the graphical representation of the MUSE calibration cascade here.