Spectroscopic Reduction

Top: Linearity correction, when number photons detected starts to saturate near full well.

Middle: Illustration of affects of curvature along dispersion direction, and distortion along slit direction, for two orders of an echelle spectrometer, and the corrected frame. Continuum sources extend across the full spectral range, night sky lines across the full slit length, and nebula emission lines just along the portion of the slit within the nebula.

Bottom: Example of typical slit profile, caused by eneven jaw width of long slit spectrometer.

Considering long slit spectrometers, including echelles (with multiple orders). The steps involve:

• Linearization, as above.
• Bias and dark subtraction, as above.
• Flatfielding.
• Slit distortion; eg S-shaped spatial orientation.
• distortion; eg curved dispersion.
• Slit profile (uneven width of jaws).
• Sky subtract (either end of slit or two stage process involving first subtracting separate sky frame and then residual sky at ends of slit).
• Extract spectrum (multiple orders for echelle).
• calibrate, including scrunching onto uniform wavelength scale.
• Flux calibrate.
• Join orders.