Dainis Dravins (Lund Observatory)

Radial Velocities and Wavelength Shifts - Stellar spectra and exoplanet detection
When Oct 10, 2019 from 02:30 PM to 03:30 PM
What
  • Colloquium
Where SH Lecture Hall
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High-precision spectroscopy offers challenges such as finding Earth-like exoplanets or monitoring the secular change of cosmological redshifts.  While required instrumental precisions are close to being achieved, limitations appear in understanding the complexities of spectral line formation in either stars or in the intergalactic medium.
Radial motions are measured by ‘Doppler shifts’, displacements of spectral line ‘wavelengths’.  Issues arise in the meaning of ‘wavelength’ since all spectral lines are somewhat asymmetric (being formed in dynamic gas flows) and, in practice, only their central portions can be measured.  Signatures differ between different types of lines, change between stars, vary across stellar disks, and are modulated by magnetic activity.  Spatially resolved spectroscopy across stellar disks is now becoming possible (using transiting exoplanets as spatial probes), permitting to test stellar hydrodynamics also in stars other than the Sun.  An adequate understanding of line formation and of spectrometer performance should enable to disentangle effects from stellar atmospheres from those induced by small Earth-like exoplanets.