Comparison of different populations of granular features in the solar photosphere
Main category
Natural Sciences (Astrophysics and Astrononmy)
One of the most visible manifestations of convective motions occurring in the uppermost layers of the solar convection zone is the granulation. Strong magnetic fields hinder the convective motions, but the appearance of bright structures such as umbral dots (UDs) and light bridges (LBs) in sunspots also shows that in strong magnetic field regions, the convection is not completely suppressed. To improve the current knowledge of the mechanism behind the appearance of the different bright structures in sunspots, we investigate the properties of the granules identified by a new segmentation algorithm in regions characterized by different magnetic field strength. We analyzed data relevant to a large sunspot with a LB observed in AR NOAA 11263. The data were acquired by the CRisp Imaging SpectroPo- larimeter at the SST on 6 August 2011. We applied a new segmentation algorithm to the data acquired along the Fe I 630.15 nm line. We found that the granules in the LB have a diameter between 0 . 22 ′′ and 0 . 99 ′′ , being smaller than the granules in a nearby plage region (PL) and similar to those of the UDs. The values of the mean continuum inten- sity, between 0.42 Ic and 0.98 Ic for the LB granules, are similar to those of the UDs. PL granules have higher values of continuum intensity, proba- bly reflecting different conditions of the plasma convection. Mean Doppler velocity and mean magnetic field strength have similar values between LB granules and UDs as well. Different values for the physical properties analyzed have been found between the granules of the PL and LB granules of the three analyzed so- lar regions, suggesting that PL and sunspot granules have different physical properties. This clearly depends on the different physical conditions of the regions where these two types of granular structures are embedded and con- firms the recent findings on the similarity between granules in PL and quiet Sun regions. Finally, a noteworthy result is that the granules observed in the faint LB have physical properties similar to those found for UDs.
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