Letter to the Editor

Multi-line spectroscopy of dark-cored penumbral filaments

¹ Instituto de Astrofísica de Andalucía (CSIC), Apdo 3004, 18080 Granada, Spain e-mail: lbellot@iaa.es
² Institute for Solar Physics, Royal Swedish Academy of Sciences, Alba Nova University Center, 10691 Stockholm, Sweden
³ Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany

Received: 1 July 2005
Accepted: 3 September 2005

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°. 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^-1; 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.