An Extra session on Monday

School of Astronomy (SoA) - Weekly Seminar

 The formation of a sunspot penumbra

Reza Rezaei ( Klepenheuer-Institut for Sonnenphysik, Freiburg, Germany)

Abstract:
   
The generation of magnetic flux in the solar interior and its transport to the outer solar atmosphere will be in the focus of solar physics research for the next decades. One key-ingredient is the process of flux emergence into the solar photosphere, and how the magnetic flux reorganizes to form the magnetic phenomena of active regions like
sunspots and pores.
On July 4, 2009, we observed a region of emerging magnetic flux, in which a proto-spot without penumbra forms a penumbra within some 5 hours. This process is documented
by multi-wavelength observations at the German VTT:
(a) imaging, (b) data with high resolution and temporal cadence acquired in Fe I 617.3 nm with the 2D imaging spectropolarimter GFPI, and (c) scans with the slit based spectropolarimeter TIP in Fe I 1089.6 nm.
During the formation of the penumbra, the area and the magnetic flux of the spot increases. The additional magnetic flux is supplied by the adjacent region of emerging magnetic flux: As emerging bipoles separate, the poles of the spot polarity migrate towards the spot, and finally merge with it. As more and more flux is accumulated a penumbra forms.
From fitting the Stokes profiles to an atmosphere with constant magnetic field and
velocity along the line-of-sight, we infer maps of veloctiy, magnetic field inclination, and field strength for our time series. This enables us to witness the onset of the Evershed
flow and the associated enhanced field inclination as individual penumbral filaments
form.

Monday / 24- May-2010 / 3 - Khordad-1389/ 2:00 PM

IPM Larak Building, School of Astronomy
Address: Larak Garden, opposite Araj, Artesh Highway,Tehran, Iran
E-mail: astro(at)ipm.ir