Leibniz Institute for Astrophysics | Large Binocular Telescope | 2019 Mar 19
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. ...
A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes and interferometers. This technique, referred to as Doppler imaging (DI) or Doppler tomography, requires a high-resolution spectrograph, usually a large telescope, lots of observing time, and nifty analysis software. Each atomic spectral line can be seen as a compressed one-dimensional “image” of the stellar surface, which, if the star rotates, becomes broadened by the Doppler-effect. If a star has spots on its surface, just like our Sun has sunspots, the Doppler-broadened spectral line profiles will be selectively deformed. A time series of such spectral line profiles taken over a full stellar rotation can then be converted to a temperature (or brightness) image of the otherwise unresolved stellar surface, just like in medical brain tomography.
But PEPSI can go a major step further. Because its two polarimeters also feed polarized light to the spectrograph, PEPSI captures the otherwise hidden profile deformation due to the Zeeman-effect. The Zeeman-effect is the splitting and polarization of spectral lines due to an external magnetic field. Combined with the rotational Doppler-effect it allows the reconstruction of the star’s surface magnetic field geometry. The cartography in polarized light is thus called Zeeman-Doppler-Imaging or in short just ZDI. ...
Warm and cool starspots with opposite polarities. A high-resolution
Zeeman-Doppler-Imaging study of II Pegasi with PEPSI ~ K.G. Strassmeier, T.A. Carroll, I.V. Ilyin
- Astronomy & Astrophysics (accepted 18 Feb 2019) DOI: 10.1051/0004-6361/201834906
- arXiv.org > astro-ph > arXiv:1902.11201 > 28 Feb 2019