L.R. Bellot Rubio. L.R., Langhans, K., Schlichenmaier, R.

Multi-line spectroscopy of dark-cored penumbral filaments

Abstract.

Dark-cored filaments could be the basic building blocks of sunspot penumbrae. Yet, their nature and physical conditions are unknown. In an attempt to improve this situation, we present the first high-resolution spectra of dark-cored penumbral filaments. Several such filaments were observed near the umbra/penumbra boundary of a sunspot located at heliocentric angles of 5 and 20 degrees. Our data reveal (a) significantly larger Doppler shifts in the dark cores as compared to their lateral brightenings; (b) Doppler shifts that increase with depth in the photosphere, up to 1.5 km/s; and (c) Doppler shifts that increase with increasing heliocentric distance. The Doppler velocities measured in the dark cores are almost certainly produced by upflows. In addition, dark-cored penumbral filaments exhibit weaker fields than their surroundings (by 100-300 G). These results provide new constraints for models of dark-cored penumbral filaments.