Freiburg 2008 – wissenschaftliches Programm

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EP: Fachverband Extraterrestrische Physik

EP 7: The Sun and Heliosphere I

EP 7.4: Vortrag

Dienstag, 4. März 2008, 15:15–15:30, KGI-Aula

Doppler shifts on the full solar disk in the chromosphere: The chromospheric network and coronal holes — •Christian Bethge¹, Hardi Peter¹, and Christian Beck² — ¹Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, D-79104 Freiburg, Germany — ²Instituto de Astrofisica de Canarias (CSIC), Via Lactea, E-38320 La Laguna, Tenerife, Spain

The Chromospheric Telescope (ChroTel) on Tenerife observes the full solar disk on a 2048 x 2048 detector in the three most prominent chromospheric lines, Ca II K (393 nm), H alpha (656 nm) and He I (1083 nm). Due to a tunable Lyot filter in the Helium channel it is possible create full-disk Doppler maps. As those spotlight chromospheric dynamics within a velocity range of 2-80 km/s and down to a length scale of about 3'', they will serve as a useful tool not only to understand the onset and dissolution of eruptive events, but also the influence of the chromosphere on contiguous solar layers and phenomenons therein, e.g. the origin of the fast solar wind in coronal holes.

Since ChroTel is a filtergraph instrument and not a spectrograph, one has to think of rather unconventional methods to obtain reliable Doppler maps with an accuracy in velocity of some 2 km/s. For this purpose, we use a genetic algorithm to solve an optimization problem employing high-resolution solar spectra obtained with a spectrograph at the 70 cm VTT at the same site.

The method itself and first results will be presented. The emphasis here is on the relation of the Doppler shifts with the chromospheric cell-network structure and with the outflow in (polar) coronal holes.