Proper Motions of Sunspots’ Umbral Dots at High Temporal and Spatial Resolution

Abstract

To deepen the analysis of the photometric properties of the umbra of a sunspot, we study proper motions of small features such as umbral dots (UDs) inside a single sunspot observed by SOT of Hinode close to the disk center. We consider horizontal flows with high precision and details to study transient motion behavior of UDs in short time intervals. Blue continuum images were first deconvolved with the PSF, such that the stray light is precisely removed and the original resolution is improved. Several images were co-added to improve the S/N ratio keeping a reasonable temporal resolution and checking that the results are reproducible. The Fourier local correlation tracking (FLCT) technique is applied to the new corrected time sequence of images and horizontal velocity maps were obtained both for the whole umbra (16 ×12 ) and for a high resolution small region of the umbra (3.5 ×3.5 ) to study the smallest details of the velocity fields. We used two different Gaussian tracking windows (0.8 and 0.2 arcsec) which reveals two types of horizontal motions for umbral features. First, a global inner penumbra and peripheral umbra inward motion directed to the central parts is revealed as an overall proper motion of bright peripheral fine structures. Second, motions matching small cells inside the darkest parts of the umbra with apparent sink and source areas suggesting possible upflows and downflows appearing in different bright and dark locations without a definite answer regarding their brightness identification with a convective or a buoyant cell.

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

“…The sunspot magnetic fields are believed to be near vertical in the umbra and more inclined in the penumbra (Thomas et al 2002). Inside the dark sunspots, many small-scale structures with inhomogeneous brightness have been studied, such as umbral dots (Beckers & Schröter 1968;Sobotka et al 1997;Riethmüller et al 2008;Goodarzi et al 2018), light bridges (Muller 1979;Lites et al 1991;Sobotka et al 1994;Leka 1997;Berger & Berdyugina 2003;Katsukawa et al 2007a;Rouppe van der Voort et al 2010;Lagg et al 2014;Felipe et al 2017;Wang et al 2018;Durán et al 2020), penumbral filaments (Muller 1973;Schlichenmaier et al 1998;Scharmer et al 2002;Ichimoto et al 2007; Movies associated to Figs. 1, 2, and 4 are available at https:// www.aanda.org 2007; Su et al 2010;Tiwari et al 2013), and umbral filaments (Kleint & Sainz Dalda 2013;Guglielmino et al 2017Guglielmino et al , 2019.…”

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

“…The sunspot magnetic fields are believed to be near vertical in the umbra and more inclined in the penumbra (Thomas et al 2002). Inside the dark sunspots, many small-scale structures with inhomogeneous brightness have been studied, such as umbral dots (Beckers & Schröter 1968;Sobotka et al 1997;Riethmüller et al 2008;Goodarzi et al 2018), light bridges (Muller 1979;Lites et al 1991;Sobotka et al 1994;Leka 1997;Berger & Berdyugina 2003;Katsukawa et al 2007b;Rouppe van der Voort et al 2010;Lagg et al 2014;Felipe et al 2017;Wang et al 2018;Durán et al 2020), penumbral filaments (Muller 1973;Schlichenmaier et al 1998;Scharmer et al 2002;Ichimoto et al 2007;Langhans et al 2007;Su et al 2010;Tiwari et al 2013), and umbral filaments (Kleint & Sainz Dalda 2013;Guglielmino et al 2017Guglielmino et al , 2019. Umbral dots are bright dot-like features embedded in the umbral background, and their number rapidly increases with decreasing diameter (Sobotka et al 1997).…”