On the geometry of sunspot penumbral filaments

Free access article

Issue		A&A Volume 421, Number 2, July II 2004


Page(s)		735 - 739
Section		The Sun
DOI		http://dx.doi.org/10.1051/0004-6361:20047181

A&A 421, 735-739 (2004)
DOI: 10.1051/0004-6361:20047181

On the geometry of sunspot penumbral filaments

W. Schmidt and G. Fritz

Kiepenheuer-Institut für Sonnenphysik, Schöneckstraße 6, 79104 Freiburg, Germany

(Received 2 February 2004 / Accepted 15 March 2004 )

Abstract
We investigate the center-to-limb variation of the brightness of the penumbrae of sunspots. The analysis includes narrow-band and broad-band continuum images of about 80 sunspots observed with the Vacuum Tower Telescope on Tenerife and with the Transition Region And Coronal Explorer (TRACE). We find that the azimuthal intensity variation depends on the viewing angle, i.e. on the position of the spot on the solar disk. With increasing viewing angle, the average intensity remains almost constant on the center side and on the limb side of the spot, but increases in the lateral parts. This is explained by the existence of elevated bright filaments that, when observed from the side and at increasing viewing angle, more and more hide the dark and deeper lying background. In addition to this azimuthal intensity modulation, we observe an enhanced brightness on the limb-side penumbra for large viewing angles.

Key words: Sun: sunspots

Offprint request: W. Schmidt, wolfgang@kis.uni-freiburg.de

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.