Data Reduction 3

The telluric lines

Although they are aestetically unpleasing, these features do provide a convenient set of reference lines. Ebbets,1980.

We amateur spectroscopists live on the floor of a deep ocean of air consisting mostly of nitrogen, oxygen, water vapor. This water vapor hampers the region around Hα with impressive absorption lines.

real stellar and synthetic telluric lines
A small normalized cutout from the real stellar spectrum in blue. Overplotted is a synthetic telluric spectrum in magenta.

We use the telluric lines to improve the wavelength calibration of our spectrum. The shift is typically less than 0.02 Å.

With the help of our synthetic telluric spectrum we can try to weaken the contamination of the stellar spectrum. First adjust the line width and the amplitude of the tellurics and then divide the stellar spectrum by the modified telluric. In theory the telluric lines should vanish from the stellar spectrum. But sometimes we have to apply a little shift and even a very moderate stretch to the tellurics. Nevertheless some artifacts will remain.

original and dried spectrum
The original spectrum in blue was captured in October 2022. It suffers from strong lines of water vapor. Humidity was 93%. Find in red the result of the attempt to remove these telluric lines.

I use the synthetic spectra computed by Peter Schlatter provided with his SpectroTools.

Last modified: 2022 Dec 23

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