en:praktikum:sonnenrotation

S1 - Solar Rotation

Calculate the rotational period of the sun from the Doppler shift of solar spectral lines at the eastern and western rim of the sun, respectively.

The observation will be performed with the solar telescope in the “Einsteinturm”.

Data reduction for data taken before 2016:

The analysis can be done with a Python script (see ~/scripts/s1s2/comparespecs.py) that needs to be copied to your own directory, too. This script allows to cut those lines from the image matrix that shall be displayed as a spectrum. Open the script with a text editor, e.g.

kate comparespecs.py

In the upper part of the script, find “Script Parameters”. Edit the names of the input files and the range of lines that shall be extracted. To find the latter, also open the image with ds9 and select the coordinates of useful strips for the spectra. Choose those lines that are equally exposed and that contain as few (obvious) pixel errors as possible. Especially pay attention to the range where the spectral lines are situated. Once all required input parameters are set, save the script file and execute it by

python comparespecs.py

to obtain a PDF file spectrum.pdf, which can be opened with okular

okular spectrum.pdf &

This figure should now show the spectrum of the lines previously selected from the image. From this figure the Doppler shift of the spectral lines can be determined. To do this, the best strategy is to shift the spectra (with the help of the Python script) against each other, so that (1) the solar iron lines are superimposed and (2) the telluric oxygen lines are superimposed. The dispersion (nm/pixel) can be determined from the given wavelengths (see the following Table).

$\lambda_0\,[\mathrm{nm}]$
Fe 630.151
Fe 630.250
O2 629.846
O2 629.923
O2 630.200
O2 630.276

Using the Doppler shift one can determine the rotational velocity of the sun and from that its rotational period. Note, that the observation has not necessarily been performed at the sun's equator.

A usual report has to be prepared for both experiments, S1 and S2, together. A combined outline for the report's content is given in the description for S2.

Overview: Laboratory courses

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  • en/praktikum/sonnenrotation.txt
  • Last modified: 2023/07/21 21:24
  • by rhainich