Three-dimensional temperature mapping of solar photospheric fine structure using Ca ii H filtergrams

¹ Institute for Solar Physics, Royal Swedish Academy of Sciences, Albanova University Center, 106 91 Stockholm, Sweden
² Stockholm Observatory, Dept. of Astronomy, Stockholm University, Albanova University Center, 106 91 Stockholm, Sweden
e-mail: vasco@astro.su.se

Received: 6 September 2012
Accepted: 10 October 2012

Abstract

Context. The wings of the Ca ii H and K lines provide excellent photospheric temperature diagnostics. At the Swedish 1-m Solar Telescope (SST), the blue wing of Ca ii H is scanned with a narrowband interference filter mounted on a rotation stage. This provides up to 0$\stackrel{\mathrm{″}}{.}$10 spatial resolution filtergrams at high cadence that are concurrent with other diagnostics at longer wavelengths.

Aims. The aim is to develop observational techniques that provide photospheric temperature stratification at the highest spatial resolution possible and use them to compare simulations and observations at different heights.

Methods. We use filtergrams in the Ca ii H blue wing that were obtained with a tiltable interference filter at the SST. Synthetic observations are produced from three-dimensional (3D) hydro and magneto-hydrodynamic numerical simulations and degraded to match the observations. The temperature structure obtained from applying the method to the synthetic data is compared with the known structure in the simulated atmospheres and with observations of an active region. Cross-correlation techniques using restored non-simultaneous continuum images are used to reduce high-altitude, small-scale seeing signal introduced from the non-simultaneity of the frames when differentiating data.

Results. Temperature extraction using high-resolution filtergrams in the Ca ii H blue wing works reasonably well when tested with simulated 3D atmospheres. The cross-correlation technique successfully compensates for the problem of small-scale seeing differences and provides a measure of the spurious signal from this source in differentiated data. Synthesized data from the simulated atmospheres (including pores) match well the observations morphologically at different observed heights and in vertical temperature gradients.