Reference File¶
The barshadow step does uses the barshadow reference file.
CRDS Selection Criteria¶
The Barshadow reference file is selected only for exposures with EXP_TYPE=NRS_MSASPEC. All other EXP_TYPEs should return N/A.
Reference File Format¶
The barshadow reference file is a FITS file that contains four extensions:
| EXTNAME | NAXIS | Dimensions | Data type |
|---|---|---|---|
| DATA1X1 | 2 | 101x1001 | float |
| VAR1X1 | 2 | 101x1001 | float |
| DATA1X3 | 2 | 101x1001 | float |
| VAR1X3 | 2 | 101x1001 | float |
The slow direction has 1001 rows and gives the dependence of the bar shadow correction on the Y location of a pixel from the center of the shutter. The fast direction has 101 rows and gives the dependence of the bar shadow correction of wavelength. The WCS keywords CRPIX1/2, CRVAL1/2 and CDELT1/2 tell how to convert the pixel location in the reference file into a Y location and wavelength. The initial version of the reference file has Y varying from -1.0 for row 1 to +1.0 at row 1001, and the wavelength varying from 0.6x10^-6m to 5.3x10^-6m.
The extension headers look like this:
| XTENSION | = | ‘IMAGE ‘ | / | Image extension |
| BITPIX | = | -64 | / | array data type |
| NAXIS | = | 2 | / | number of array dimensions |
| NAXIS1 | = | 101 | ||
| NAXIS2 | = | 1001 | ||
| PCOUNT | = | 0 | / | number of parameters |
| GCOUNT | = | 1 | / | number of groups |
| EXTNAME | = | ‘DATA1x1 ‘ | / | extension name |
| BSCALE | = | 1.0 | ||
| BZERO | = | 0.0 | ||
| BUNIT | = | ‘UNITLESS’ | ||
| CTYPE1 | = | ‘METER ‘ | ||
| CTYPE2 | = | ‘UNITLESS’ | ||
| CDELT1 | = | 4.7E-08 | ||
| CDELT2 | = | 0.002 | ||
| CRPIX1 | = | 1.0 | ||
| CRPIX2 | = | 1.0 | ||
| CRVAL1 | = | 6E-07 | ||
| CRVAL2 | = | -1.0 | ||
| APERTURE | = | ‘MOS1x1 ‘ | ||
| HEIGHT | = | 0.00020161 |