Heidelberg 2006 – scientific programme

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EP: Extraterrestrische Physik

EP 17: Sonne: Atmosph
äre

EP 17.6: Fachvortrag

Thursday, March 16, 2006, 10:30–10:45, B

First VUV Sun-as-a-star spectrum compared to other cool stars — •Hardi Peter — Kiepenheuer-Institut für Sonnenphysik. 79104 Freiburg

This paper reports the first full-Sun vacuum ultraviolet (VUV) emission line profile originating from the transition region from the chromosphere to the corona. It is based on a raster scan of the whole solar disk using SUMER/SOHO. The full-Sun spectrum has a spectral resolution which allows an investigation of details in the line profile as well as a thorough comparison to stellar spectra as obtained, e.g. with FUSE or STIS/HST.

The full-Sun spectrum shows enhanced emission in the wings, and is well described by a double Gaussian fit with a narrow and a broad component. It is shown that the broad component is due to structures on the solar surface. Thus it is proposed that the broad components of other solar-like stars are also a consequence of the mixture of surface structures, and not necessarily a signature of small-scale heating processes like explosive events, as it is commonly argued.

A comparison to spectra of luminous cool stars shows that the line asymmetries of these stars might also be a surface structure effect and not or only partly due to opacity effects in their cool dense winds.

These comparisons show the potential of high quality full-Sun VUV spectra and their value for the study of solar-stellar connections. As an example, this study proposes that α Cen A has a considerably higher amount of magnetic flux concentrated in the chromospheric magnetic network than the Sun.