Recipe muse_wavecal: Detect arc emission lines and determine the wavelength solution for each slice.

Data Structures

struct  muse_wavecal_params_s
 Structure to hold the parameters of the muse_wavecal recipe. More...

Typedefs

typedef struct
muse_wavecal_params_s 
muse_wavecal_params_t
 Structure to hold the parameters of the muse_wavecal recipe.

Detailed Description

Author:
Peter Weilbacher

This recipe detects arc emission lines and fits a wavelength solution to each slice of the instrument. The wavelength calibration table contains polynomials defining the wavelength solution of the slices on the CCD.

Processing trims the raw data and records the overscan statistics, subtracts the bias (taking account of the overscan, if --overscan is not "none") and converts them from adu to count. Optionally, the dark can be subtracted and the data can be divided by the flat-field, but this is not recommended. The data is then combined using input parameters, first into separate images for each lamp. If --lampwise is not given or if --resample is given, these lamp-separate exposures are summed to create a single combined master arc.

To compute the wavelength solution, arc lines are detected at the center of each slice (using threshold detection on a S/N image) and subsequently assigned wavelengths, using pattern matching to identify lines from the input line catalog. Each line is then traced to the edges of the slice, using Gaussian centering in each CCD column. The Gaussians not only yield center, but also centering error, and line properties (e.g. FWHM). Deviant fits are detected using polynomial fits to each arc line (using the xorder parameter) and rejected. If --lampwise is switched on, these analysis and measuring steps are carried out separately on images exposed by the different arc lamps, reducing the amount of blending, that can otherwise influence line identification and Gaussian centering. The final two-dimensional fit uses all positions (of all lamps), their wavelengths, and the given polynomial orders to compute the final wavelength solution for each slice, iteratively rejecting outliers. This final fit can be either unweighted (fitweighting="uniform", for fastest processing) or weighted (other values of fitweighting, for higher accuracy).


Typedef Documentation

Structure to hold the parameters of the muse_wavecal recipe.

This structure contains the parameters for the recipe that may be set on the command line, in the configuration, or through the environment.


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