Frame Type¶
Overview¶
Every raw data file ingested by PypeIt is automatically assigned one or more frametype values. This is to separate calibration files, science frames, etc. The assignments are guided by criteria given in the default settings file for each spectrograph (e.g. setttings.kast_blue). One should not modify the default files but if you have a suggestion for improvement consult with the PypeIt authors.
Definitions¶
Here are the frametype values allowed and adopted in PypeIt:
| Frametype | Description |
|---|---|
| arc | Spectrum of one or more calibration arc lamps |
| bias | Bias frame; typically a 0s exposure with the shutter closed |
| dark | Dark frame; typically a >0s exposure to assess dark current (shutter closed) |
| pinhole | 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). |
| pixelflat | Spectrum taken to correct for pixel-to-pixel detector variations Often an exposure using a flat lamp, but for observations in the very blue, this may be on-sky |
| science | Spectrum of one or more science targets |
| standard | Spectrum of spectrophotometric standard star PypeIt includes a list of pre-defined standards |
| trace | Spectrum taken to define the slit edges and correct for illumination variations across the slit. 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. |
| unknown | File could not be automatically identified by PypeIt |
It is possible, and for flats common, that a frame can be assigned more than one frametype. .. _modify_frametype:
Auto-typing¶
PypeIt will, be default, attempt to auto identify the image type based on Header information. For each instrument, there are hard-coded conditions in the settings.instrument file that guide the process. Here are the conditions for a trace frame with the Shane Kast blue camera:
trace check condition1 lampstat01=on|lampstat02=on|lampstat03=on|lampstat04=on|lampstat05=on
trace check condition2 exptime>0 # Required for bias
The syntax uses “|” and “&” for logic and the strings refer to short-hand strings that were taken from the FITS header. It is unlikely that anyone other than a developer will wish to modify any of these conditions.
Regarding science vs. standard star typing (perhaps the most challening aspect), the code takes any source that satisfies the standard conditions to be a standard if it lies with 20arcmin of the PypeIt approved list of Standard Stars.
A file that satisfies all conditions of being a bias frame yet has an exposure time exceeding the minimum value for the detector is typed as a dark.
Modifying a frametype¶
data block¶
If your PypeIt reduction file includes the file-by-file listing of frames to analyze, you can edit the frametype directly in the appropriate column. The values in the .pypeit file will over-ride any assessed by the code. This is the recommend approach for standard users.
spect block¶
One can specify one or more frametype’s for any file in the .pypeit file. Include one or more lines in the Spect block with syntax set frametype filename, e.g.:
set pixelflat b150910_2051.fits.gz
This will over-ride the automatic assignment by PypeIt.