The astronomical quantity of interest is an array of flux as a function of wavelength. Hence, a relationship must be established between each grating scanner position (measured by a Linear Voltage Differential Transducer (LVDT) and colloquially given the units `LVDT') as contained in the ERD and its corresponding wavelength. The relation is calculated in two steps: first the scanner position is converted to a scanner angle using a calibration file. Then the following equation can be applied to calculate the wavelength of light falling on the detectors:
and D are constants, taken from calibration file 16 . The spectral order N is determined by calculating all the orders that give wavelengths consistent with the transmission limits of the band/order/aperture/filter combination. For valid observations only one order should give a wavelength that satisfies this criterion.
The wavelength range - band/order/aperture/filter combination relationship is shown in Table 7.3.
For the Fabry-Pérot , first the grating wavelength is calculated. Calibration file 12 then transforms the nominal FP-position (an engineering parameter of no interest to the observer) into a FP-gap . This mechanical gap width must be corrected to get the optical gap width. The wavelength which passes through the FP is the one of which a whole multiple fits exactly in two times the optical gap width.
|1A||S4||1||1||2.38 - 2.61|
|1B||S3||1||1||2.60 - 3.03|
|SW||1D||S3||2||1||3.02 - 3.53|
|section||1E||S2||2||1||3.52 - 4.08|
|2A||S2||2||2||4.05 - 5.31|
|2B||S1||2||2||5.30 - 7.01|
|2C||S1||3||2||7.00 - 12.1|
|3A||L2||1||3||12.0 - 16.6|
|LW||3C||L2||2||3||16.5 - 19.6|
|section||3D||L1||2||3||19.5 - 27.6|
|3E||L1||3||3||27.5 - 29.0|
|4||L1||3||4||28.9 - 45.2|
|FP||5A||L3||1||5||11.4 - 12.2|
|5B||L2||1||5||12.2 - 16.0|
|5C||L2||2||5||16.0 - 19.0|
|5D||L1||2||5||19.0 - 26.0|
|6||L1||4||6||26.0 - 44.5|