Reference Files
The wavecorr step uses the WAVECORR reference file, which only
applies to NIRSpec fixed-slit (FS) and MOS exposures.
WAVECORR Reference File
- REFTYPE:
WAVECORR
- Data model:
The WAVECORR reference file contains pixel offset values as a function of
wavelength and source offset within a NIRSpec slit.
It is used when applying the NIRSpec wavelength zero-point correction to
fixed-slit (EXP_TYPE=”NRS_FIXEDSLIT”), bright object TSO
(EXP_TYPE=”NRS_BRIGHTOBJ”), and MSA/MOS spectra (EXP_TYPE=”NRS_MSASPEC”).
This is an optional correction that is turned on by default.
It can be turned off by specifying apply_wavecorr=False when running the step.
Reference Selection Keywords for WAVECORR
CRDS selects appropriate WAVECORR references based on the following keywords. WAVECORR is not applicable for instruments not in the table. Non-standard keywords used for file selection are required.
Instrument |
Keywords |
|---|---|
NIRSpec |
INSTRUME, EXP_TYPE, DATE-OBS, TIME-OBS |
Standard Keywords
The following table lists the keywords that are required to be present in all reference files. The first column gives the FITS keyword names. The second column gives the jwst data model name for each keyword, which is useful when using data models in creating and populating a new reference file. The third column gives the equivalent meta tag in ASDF reference file headers, which is the same as the name within the data model meta tree (second column).
FITS Keyword |
Data Model Name |
ASDF meta tag |
|---|---|---|
AUTHOR |
model.meta.author |
author |
DATAMODL |
model.meta.model_type |
model_type |
DATE |
model.meta.date |
date |
DESCRIP |
model.meta.description |
description |
FILENAME |
model.meta.filename |
N/A |
INSTRUME |
model.meta.instrument.name |
instrument: {name} |
PEDIGREE |
model.meta.pedigree |
pedigree |
REFTYPE |
model.meta.reftype |
reftype |
TELESCOP |
model.meta.telescope |
telescope |
USEAFTER |
model.meta.useafter |
useafter |
NOTE: More information on standard required keywords can be found here: Standard Required Keywords
Type Specific Keywords for WAVECORR
In addition to the standard reference file keywords listed above, the following keywords are required in WAVECORR reference files, because they are used as CRDS selectors (see Reference Selection Keywords for WAVECORR):
Keyword |
Data Model Name |
|---|---|
EXP_TYPE |
model.meta.exposure.type |
Reference File Format
WAVECORR reference files are in ASDF format, with the format and contents
specified by the WaveCorrModel data model schema.