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Instrumental parameters

Certain fixed parameters which specify details of the instrumental setup are held internally by LEXT so that they can be accessed automatically by any routine.

These are:

• CAMFIELD: the field of the camera in (mm)
• COLFIELD: the field of the collimator in (arcmin)
• DETECTOR: the detector ID (for information only)
• DISPERSION: the dispersion at the detector (Å/mm)
• FRED: the focal reduction factor between the focal (mask) plane and the detector
• FTRANS and BTRANS: the files (.DST or .SDF) used for forward and backward distortion correction - set to NONE if not specified
• LAMBLAZE: the blaze (strictly the undeviated) wavelength (Å)
• LAMMAX: wavelength corresponding to the red extreme of the spectrum (Å).
• LAMMIN: wavelength corresponding to the blue extreme of the spectrum (Å)
• LAMZERO: the position of the zero-order images, expressed as a wavelength of the first order spectrum (Å)
• MISVAL: the magic value used to designate an invalid pixel
• OBJECT: the name of the current field. This is used to generate the names given to the files containing the extracted spectra.
• OBJECTEXTENT: the typical extent of an object on the sky (arcsec).
• ROTATION: the rotation between the mask and detector coordinate systems (degrees measured clockwise on the detector)
• TILT: the value of the inclination of the spectra within the boxes (degrees measured clockwise). This variable is used when plotting BOXES and in the weighting scheme used by SQUASH, but is currently ignored in the extraction routines, which have other ways of dealing with small tilts. NB: TILT does not mean a tilt of the whole spectra relative to the detector, but only a tilt of the locus of the object.
• XCENTRE and YCENTRE: the (,) coordinate on the detector which corresponds to the origin of the mask coordinate system (pixel)
• XPIX and YPIX: the size of the detector pixels (m)
• XSLIT and YSLIT: the default length of the slit in and (m)
• X_FORMAT and Y_FORMAT: the size of the detector (pixels)

These can also be assigned values with the SET command, although some can also be redefined as a result of certain LEXT operations such as LFIT.