Observing the solar spectrum at different limb angles

 

Spectra of the Sun are available at very high spectral resolving power and signal-to-noise ratio. The spectra are useful to investigate the physics of the Sun, and as templates for stellar spectroscopy. Due to projection effects, the solar spectrum appears different if observed at different limb angles, i.e., at different positions on the apparent solar disk. So far, no high-precision atlas exists that systematically shows the differences of spectral lines as a function of limb angle. Potential applications for such an atlas include comparison with 3D magneto-hydrodynamic models of the Sun and high-precision radial velocity measurements in stars, as for example used for the search for extrasolar planets.

The Institute for Astrophysics at Göttingen University operates a high-resolution Fourier Transform Spectrograph that can be fed from the institute's 50cm siderostat. The instrumentation shall be used to obtain spectral atlases of the solar surface taken at different limb angles. Particularly close to the solar limb, image stabilization is a challenge and requires hardware upgrades of the existing facilities. The work requires interest in solar/stellar spectroscopy and technical skills for operation and upgrade of the hardware.

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