Dynamic Properties Along the Neutral Line of a Delta Spot Inferred From High-Resolution Observations

Abstract

Delta (δ) spots are complex magnetic configurations of sunspots characterized by umbrae of opposite polarity sharing a common penumbra. In order to investigate the fine structure of the region separating the two magnetic polarities of a δ spot, we studied the morphology, the magnetic configuration, and the velocity field in such a region using observations of active region (AR) NOAA 11267 obtained with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish Solar Telescope on 2011 August 6. The analysis of CRISP data shows upflows and downflows of ∼±3 km s −1 in proximity of the δ spot polarity inversion line (PIL), and horizontal motions along the PIL of the order of ∼1 km s −1 . The results obtained from the SIR inversion of CRISP data also indicate that the transverse magnetic field in the brighter region separating the two opposite magnetic polarities of the δ spot is tilted about ∼45 • with respect to the PIL. Solar Dynamics Observatory/Helioseismic and Magnetic Imager observations confirm the presence of motions of ∼±3 km s −1 in proximity of the PIL, which were observed to last 15 hr. From the data analyzed, we conclude that the steady, persistent, and subsonic motions observed along the δ spot PIL can be interpreted as being due to Evershed flows occurring in the penumbral filaments that show a curved, wrapped configuration. The fluting of the penumbral filaments and their bending, continuously increased by the approaching motion of the negative umbra toward the positive one, give rise to the complex line-of-sight velocity maps that we observed.

A MULTI-INSTRUMENT ANALYSIS OF a C4.1 FLARE OCCURRING IN a Δ SUNSPOT

“…In Figure 15 (top-left panel) the morphology of AR 267 at the beginning of SST/CRISP observations in the continuum of the Fe I line at 603.15 nm is shown. We remind the reader that the characteristics in the region around the δ-spot PIL in the photosphere have been extensively described by Cristaldi et al (2014). Here, we note that the preceding and the following sunspots appear comparable in size and that light bridges are present in the umbral regions of both sunspots.…”

“…3 ´ . For further details on the SST data sets, we defer the reader to Cristaldi et al (2014), who provide more information about the spectral coverage of the SST/CRISP measurements and the data reduction procedure via the CRISPRED pipeline (de la Cruz Rodríguez et al 2015). Here, we only remind the reader that the application of the multi-object multi-frame blind deconvolution (MOMFBD, van Noort et al 2005) technique to these SST data sets ensured that near diffraction-limited spatial resolution was achieved (0 15 at 557.6 nm).…”

“…The evolution of the AR 267 has already been described by Cristaldi et al (2014) who analyzed a data set with very high spatial resolution (0 15) acquired at the Swedish 1-m Solar Telescope (SST) on 2011 August 6. They studied in detail the morphological, magnetic, and dynamic properties of the region between the opposite polarities of the δ spot in the photosphere, using the observations in the Fe I 557.6 and 630.15 nm lines.…”

“…These motions, lasting about 15 hr, were interpreted as being due to Evershed flows occurring in the wrapped penumbral filaments located in the region between the opposite polarities of the δ spot. However, Cristaldi et al (2014) did not study the C4.1 flare occurring in AR 267, which peaked some minutes before the beginning of the high-resolution observations.…”

“…We analyze the same data set acquired at the SST in the photosphere used by Cristaldi et al (2014) and we add new information by analyzing the Fe I 630.15 nm line as well as the simultaneous Ca II H chromospheric observations of the evolution of the flare during the gradual phase. We also benefit from simultaneous observations in the ultraviolet and magnetic information provided by the the Solar Dynamics Observatory(SDO) satellite, which covers the entire flare evolution.…”