Telluric lines

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Telluric lines#

This tutorial is part of the spectral reduction steps, and details how to generate the static files that contain the list of molecule properties and spectral lines required for the telluric correction.

Full list#

The synthetic telluric models need as input a list of all spectroscopic lines that fall in a given wavelength range, for each molecule that you want to include in the model. These lines are independent from the specific characteristics of the detector but they do depend on the wavelength range covered by the instrument. Specific static files have thus been computed for several molecules and spectrographs, and are used by default by ANTARESS. A new file can be generated for a given molecule MolNAME and spectrograph specNAME by following these steps:

  1. Use the HITRAN database to get the total internal partition sum of MolNAME and its spectroscopic linelist across the wavelength range covered by specNAME. Download them as .txt files in a directory of your choosing, ideally /src/antaress/ANTARESS_corrections/Telluric_processing/Input_files_statics/Molecules/molNAME/specNAME/. If you want to use another source than HITRAN you need to adapt the static_hitran_file() function in /src/antaress/ANTARESS_corrections/Telluric_processing/Create_static_files_ALL.py.

  2. Import the static_hitran_file() function from Create_static_files_ALL and run it as:

    static_hitran_file( linelist_file , QT_file , MolNAME , specNAME , save_dir,  S_cut = S_cut)

    where:

    • linelist_file and QT_file are the paths to the downloaded files.

    • S_cut is a lower threshold on the lines intensity, set by default to \(10^{-26}\)

    • save_dir/ is the path to the directory where the output Static_hitran_qt_MolName.fits file will be saved.

    You can now store this static file in /src/antaress/ANTARESS_corrections/Telluric_processing/Static_model/specNAME/, ensuring that a similar file does not already exist or should be replaced.

Fit list#

Telluric correction is performed by computing CCFs of synthetic and observed spectra across a subset of the full molecule’s linelist. Default fit linelists, built by selecting the first tens or so strongest lines, are included in the ANTARESS distribution. Custom fit linelists can be built by running the lines_to_fit() function, imported from Create_static_files_ALL, as:

lines_to_fit( specNAME , Static_hitran_qt_MolName.fits , MolNAME , wav_bounds , n_lines = 10 , wav_excluded_l = [] , save_dir = None , delta_rv_blend = 40. , contrast_range = None )

Where:

  • delta_rv_blend (in 40 km/s) is the half-width of telluric line for blend rejection. Lines are rejected if their centers are closer than twice delta_rv_blend.

  • wav_bounds = [ [ \(\lambda_1\) , \(\lambda_2\) ] , [ \(\lambda_3\) , \(\lambda_4\) ] , …] (in \(\\A\), at rest) is the list of wavelengths intervals over which lines are selected.

  • wav_excluded_l = [ \(\lambda_1\) , \(\lambda_2\) , …] (in \(\\A\) at rest, empty by default) are the approximate wavelengths of lines to exclude from selection.

  • n_lines is the number of lines to be selected (10 by default), starting from the strongest ones (based on the intrinsic intensity of their transition).

  • contrast_range = [ \(c_{min}\) , \(c_{max}\) ] (c in [0,1]). If this field is defined, a maximum of n_lines lines are selected within the chosen contrast range, starting with the ones with deeper contrast.

  • save_dir/ is the path to the directory where the output Static_hitran_strongest_lines_molNAME.fits file will be saved.

You can now store this static file in /src/antaress/ANTARESS_corrections/Telluric_processing/Static_model/specNAME/, ensuring that a similar file does not already exist or should be replaced. The default static files have been optimized for the complete spectral range of a given spectrograph. The above settings can be adjusted to optimize the telluric correction according to your needs, such as an increased RV precision or accurate transmission spectra in a given spectral range. To facilitate this optimization the static file can be generated internally as part of a given ANTARESS processing, so that it is direcly used instead of the default one. This is done by controlling the above settings with the gen_dic[“tell_fit_custom”] field in ANTARESS configuration file. You can assess the impact of changing the fit linelist by using the plots associated with the telluric correction module. Activate plot_dic[‘flux_sp’] = ‘pdf’ and use the ‘plot_tell_HITRANS_list’ option to overplot the selected fit linelist to the telluric-absorbed (set ‘plot_pre’ to ‘raw’), telluric-corrected (set ‘plot_post’ to ‘tell’), and telluric model (set ‘plot_tell’ to ‘True’) spectra.

Note

Look here if you want to propose your custom static files for permanent integration in the stable version of ANTARESS.

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