The wings of Ca II H and K as solar fluxtube diagnostics

¹ Main Astronomical Observatory, National Academy of Sciences of the Ukraine, 27 Akademika Zabolotnoho St., 03680 Kiev, Ukraine e-mail: shem@mao.kiev.ua
² Sterrekundig Instituut, Utrecht University, Postbus 80 000, 3508 TA Utrecht, The Netherlands
³ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
⁴ Center of Mathematics for Applications, University of Oslo, PO Box 1053 Blindern, 0316 Oslo, Norway

Received: 22 December 2004
Accepted: 15 March 2005

Abstract

We combine high-resolution Ca II H and K spectrograms from the Swedish Vacuum Solar Telescope with standard fluxtube modeling to derive photospheric temperature and velocity stratifications within individual magnetic elements in plage near a sunspot. We find that 1D on-axis modeling gives better consistency than spatial averaging over flaring-fluxtube geometry. Our best-fit temperature stratifications suggest that magnetic elements are close to radiative equilibrium throughout their photospheres. Their brightness excess throughout the H and K wings compared with the quiet photosphere is primarily due to low density, not to mechanical heating. We conclude that the extended H and K wings provide excellent fine-structure diagnostics for both high-resolution observations and simulations of the solar photosphere.