What are solar faculae?

Abstract

Results are presented of observations of the facula area near the solar disc center. Observations were performed at the German Vacuum Tower Telescope of the Observatorio del Teide (Tenerife) with the simultaneous use of two instruments, i.e., TESOS in the Ba IIλ 455.4 nm line to measure intensity variations in the photosphere and, at the same time, TIP in the Fe I (λλ 1564.3–1565.8 nm) line to measure Stokes parameters. Using the Fourier filtering technique, we separated the convective and wave components of the intensity field. Stokes parameters Fe I λ 1564.8 nm and λ 1565.2 nm were inverted by the SIR inversion code to estimate the magnetic field strength. We found that the contrast of intergranular lines of the facula in the continuum is almost independent of the magnetic field strengh (in the range from 30 to 160 mT). This result casts doubt on the assertion that solar faculae are a cluster of magnetic flux tubes. Most likely, due to the decrease of transparency of the matter in a strong (approximately 1 kilogauss) magnetic field, we can see the hot walls of granules.