Every raw data file ingested by PypeIt must be given a frame type. This identifies how the frame should be treated and included in the data reduction.
Frame typing can be done automatically by running pypeit_setup, which is
a simple wrapper for
PypeItSetup. The type of frame
for each data file is automatically identified as one or more of the types
listed in the table below; any files that could not be identified are given a
frame type set to
The robustness of the automated typing of calibration
frames varies with some Spectrographs being much more robust
than others. Automated typing of
standard frames is
generally not robust for any instrument. Always inspect your
PypeIt Reduction File to ensure the frame typing is correct!
The possible frame types defined by PypeIt and a brief description can be listed as follows:
from pypeit.core.framematch import FrameTypeBitMask
More detailed descriptions are given in the table below.
Used to align spatial positions in multiple slits. This frame is particularly useful for slit-based IFU, such as Keck KCWI.
Spectrum of one or more calibration arc lamps
Bias frame; typically a 0s exposure with the shutter closed
Dark frame; typically a >0s exposure to assess dark current (shutter closed)
Spectrum taken to correct illumination profile of the slit(s). This is often the same as the trace flat (below).
Spectrum taken to remove persistence from lamp on flat exposures and/or thermal emission from the telescope and dome. Usually this is an exposure using a flat with lamps OFF
Spectrum taken through a pinhole slit (i.e. a very short slit length), and is used to define the centre if a slit (currently, this frame is only used for echelle data reduction). Often this is an exposure using a flat lamp, but one can in principle use a standard star frame too (or a science frame if the spectrum is uniform).
Spectrum taken to correct for pixel-to-pixel detector variations Often an exposure using a dome (recommended) or internal flat lamp, but for observations in the very blue, this may be on-sky
Spectrum of one or more science targets
Spectrum of spectrophotometric standard star PypeIt includes a list of pre-defined standards
Spectrum taken to define the slit edges. Often this is an exposure using a flat lamp, but for observations in the very blue, this may be on-sky. The slit length of a trace frame should be the same as the science slit.
Exposure used to trace the tilt in the wavelength solution. Often the same file(s) as the arc.
On-sky observation of the sky used for background subtraction
File could not be automatically identified by PypeIt
It is possible (and even common for arc and flats images) that a frame can be assigned more than one frame type.
Automated typing of files is performed by pypeit_setup.
PypeItSetup builds a table of
metadata for all files found using the search key provided to its
from_file_root() method. The
metadata itself is gathered and maintained by
PypeItMetaData based on a set of header
keywords that are defined for each supported spectrograph. For
example, the metadata keywords for Keck DEIMOS reductions are:
Metadata Key Header Card
which can be obtained by executing
pypeit_obslog keck_deimos -k
uses the metadata to try to identify each frame type. With a couple
exceptions, however, this method is largely a wrapper for the
check_frame_type method of each spectrograph; e.g., see
for DEIMOS. The relevant exposure time for each frame can be refined
using parameters in the pypeit file. For example, to edit the
exposure time for
pixelflat images to be between 15 and 30
seconds, you can include the following lines in your PypeIt Reduction File:
exprng = 15, 30
Note that you can set either (or both) of the limits to
that it is undefined. I.e.:
from pypeit.spectrographs.keck_deimos import KeckDEIMOSSpectrograph
shows the default exposure-time range for pixel flats is
30], meaning there is no lower limit on the exposure time for the
pixel-flats. At the moment, only the exposure time can be altered
programmatically for the frame type determination; all other
conditions are hard-coded.