The possible origin of facular brightness in the solar atmosphere

Abstract

This paper studies the dependence of the Ca ii H line core brightness on the strength and inclination of the photospheric magnetic field, and on the parameters of convective and wave motions in a facular region at the center of the solar disc. We use three simultaneous data sets that were obtained at the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife): (1) spectra of Ba ii 4554 Å line, registered with the instrument TESOS to measure the variations of intensity and velocity through the photosphere up to the temperature minimum; (2) spectropolarimetric data in Fe i 1.56 µm lines (registered with the instrument TIP II) to measure photospheric magnetic fields; (3) filtergrams in Ca ii H that give information about brightness fluctuations in the chromosphere. The results show that the Ca ii H brightness in the facula strongly depends on the power of waves with periods in the 5-min range, which propagate upwards, and also on the phase shift between velocity oscillations at the bottom photosphere and around the temperature minimum height that is measured from Ba ii line. The Ca ii H brightness is maximum at locations where the phase shift between temperature and velocity oscillations lies within 0 • -100 • . There is an indirect influence of convective motions on the Ca ii H brightness. The higher the amplitude of convective velocities is and the greater the height is where they change their direction of motion, the brighter the facula. In summary, our results lead to conclusions that facular regions appear bright not only because of the Wilson depression in magnetic structures, but also owing to real heating.

Calibration of Differential Light Curves for Physical Analysis of Starspots

“…These are magnetic features that are generally found not only in the vicinity of starspots but in magnetically active regions that don't produce spots (e.g. Kostik & Khomenko (2016) and references therein). An excellent summary of the effects of magnetic regions on precision photometry in the solar case has been presented by Shapiro et al (2017).…”

Long-period quasi-periodic oscillations of a small-scale magnetic structure on the Sun

“…Freij et al (2016) detected oscillations with periods from 3 to 20 min in the intensity of two isolated magnetic pores and interpreted them in terms of a slow magnetoacoustic sausage wave. Similarly, facular brightness was found to be dependent on the convective and wave motions in a facular region in Kostik & Khomenko (2016). Periodicities in the 5-min range were detected.…”

Structure of solar faculae

“…Nevertheless, observers still refer to this model: Quintero et al (2016). Kostik & Khomenko (2016), analyzing the causes of the observed brightness of facular tubes, likewise come to the conclusion that " facular regions appear bright not only because of the Wilson depression in magnetic structures, but also owing to real heating". Earlier, the same opinion has been expressed in (Chapman & Klabunde,1982).…”