EDP Sciences
Free access
Volume 365, Number 2, January II 2001
Page(s) 186 - 197
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20000016

A&A 365, 186-197 (2001)
DOI: 10.1051/0004-6361:20000016

Properties of EUV and X-ray emission in solar active regions

S. A. Matthews1 , J. A. Klimchuk2 and L. K. Harra1 .

1  Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Surrey RH5 6NT, UK
2  Space Science Division, Code 7675, Naval Research Laboratory, Washington, DC 20375-5352, USA

(Received 9 November 1999 / Accepted 5 October 2000 )

Using observations from the Coronal Diagnostic Spectrometer (CDS) on SoHO and the Soft X-ray Telescope (SXT) on Yohkoh we investigate how the spatial properties of active region emission observed in the EUV and X-ray range varies with temperature. We examine the contrast per unit area of the EUV emission from a number of active regions, and employ correlation techniques and Fourier methods with which we obtain the two dimensional power spectrum of the intensity distribution for a number of images in emission lines formed at different temperatures. Integrating this over polar angle we find isotropic power-law behaviour at all temperatures in a number of topologically different active regions, with a tendency for flatter spectra at lower temperatures. The existence of power-law spectra indicates that there is no preferred length scale within the regions, at least not a resolvable one, while flatter spectra at lower temperatures indicate that the structures are relatively smaller in this temperature range, possibly providing support for the idea of a multi-component transition region (TR). Implications for various heating models are discussed.

Key words: Sun: UV radiation -Sun: Corona -Sun: transition region

Offprint request: S. A. Matthews

© ESO 2001