3D Temperature Mapping of Solar Photospheric Fine Structure Using Ca II H Filtergrams

TL;DR

This study develops high-resolution observational techniques using Ca II H filtergrams to map the solar photospheric temperature structure, validating methods with 3D simulations and applying them to real active region data.

Contribution

It introduces a novel method combining high-resolution Ca II H filtergrams and cross-correlation techniques to accurately derive temperature stratification in the solar photosphere.

Findings

Temperature extraction is effective with simulated atmospheres.

Cross-correlation reduces seeing-induced errors.

Synthetic data matches observed temperature structures.

Abstract

Context. The wings of the Ca II H and K lines provide excellent photospheric temperature diagnostics. At the Swedish 1-meter Solar Telescope the blue wing of Ca II H is scanned with a narrowband interference filter mounted on a rotation stage. This provides up to 0"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 the photospheric temperature stratification at the highest spatial resolution possible and use those to compare simulations and observations at different heights. Methods. We use filtergrams in the Ca II H blue wing obtained with a tiltable interference filter at the SST. Synthetic observations are produced from 3D HD and 3D MHD 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 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.