Wavelength Calibration¶

The wavelength of the spectra needs to be calibrated. The most common way of doing such this calibration for an echelle spectrograph is to compare the positions of science spectra with that of a hollow cathode lamp with known wavelengths, e.g., the Thorium-Argon (ThAr) lamp or Uranium-Neon (UNe) lamp. The wavelengths (λ) for any pixel (x) in a given order (m) can be built by fitting a 2-D polynomial from the positons of spectral features, of which the wavelengths have been precisely determined.

In GAMSE, there are several modes of wavelength calibration. They are designed to fulfill the various requirements. These are summaried as below.

For a spectrograph with unkown echelle formats, GAMSE will display a graphical user interface (GUI), which helps the users to identify the spectral lines by hand.
In the case that there are more than one frames with the same hollow cathode lamp under the same configuration (e.g., resolution, CCD binning), users can identify the wavelengths by hand for only one of them, and all the others will be identified automatically taking the references of the manually-identified spectra, suppose that the positions of the spectra on the detector have only small amounts of drift.
If the camera or the detector rotated by 180° or the order positions move by a large amount of pixels on the detector over a long-term, GAMSE is still be able to find the correct echelle order number (m) and identify the wavelengths automatically.

APIs¶

calibration functions:

`wlcalib`
`recalib`
`fit_wavelength`
`get_wavelength`
`guess_wavelength`
`find_order`
`find_drift`
`find_local_peak`
`find_shift_ccf`
`find_shift_ccf2`
`load_ident`
`save_ident`
`is_identified`
`load_linelist`
`search_linelist`
`reference_wl`
`reference_wl_new`
`get_aperture_coeffs_in_header`
`select_calib_from_database`