Removing H lines from the telluric standard spectrum

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This topic contains 1 reply, has 2 voices, and was last updated by  jgagne 3 years, 7 months ago.

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    Dear All,

    The standard procedure to remove telluric absorption from a NIR spectrum is use an spectrum of a star observed with similar airmass to model of this features. Typically an A0V star is used for this purpose. However several H lines are present in the NIR spectrum. In order to get an accurate telluric subtraction these H lines need to be modeled and removed from the spectrum of the telluric standard.

    This can be done either modeling the profile of the H lines using a Lorentzian (or Gaussian) profile or using the spectrum of Vega, smoothed for the instrumental resolution of the instrument, as a template for the H lines.

    Which one do you prefer/use? Please share if you know a better/different way to do it…

    • This topic was modified 3 years, 6 months ago by achene achene.


    Most of the time I use the IDL routine that is available as part of the spextool reduction package, which you can download here:

    I’m not sure exactly what functional form is used to model the H lines, but I believe that it is a Lorentz profile convolved with a Gaussian and a rotation Kernel (if you enter a value for v sin i) – you typically use the deepest H line to build a model for the kernel, and then you can adjust the relative strength of each line as a subsequent step to make sure that they fit your observed telluric well.

    The only downside to using is that you need to have IDL and to feed it spectra that are formatted in a special way – the header must contain several key entries. If you would like to try it, you will need to open the routine (also part of the spextool package) and see how they output the data.

    If you are using Flamingos II data specifically, I will soon be posting a complete IDL pipeline to reduce F II data on this forum, and it will makes use of, so you will see exactly how the data needs to be formatted.

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