Convective Nature of Sunspot Penumbral Filaments: Discovery of Downflows in the Deep Photosphere

摘要

We study the velocity structure of penumbral filaments in the deepphotosphere to obtain direct evidence for the convective nature of sunspotpenumbrae. A sunspot was observed at high spatial resolution with the 1-mSwedish Solar Telescope in the deep photospheric C I 5380 {\AA} absorptionline. The Multi-Object Multi-Frame Blind Deconvolution (MOMFBD) method is usedfor image restoration and straylight is filtered out. We report here thediscovery of clear redshifts in the C I 5380 {\AA} line at multiple locationsin sunspot penumbral filaments. For example, bright head of filaments showlarger concentrated blueshift and are surrounded by darker, redshifted regions,suggestive of overturning convection. Elongated downflow lanes are also locatedbeside bright penumbral fibrils. Our results provide the strongest evidence yetfor the presence of overturning convection in penumbral filaments and highlightthe need to observe the deepest layers of the penumbra in order to uncover theenergy transport processes taking place there.