Kinematics and Magnetic Properties of a Light Bridge in a Decaying Sunspot

Abstract

We present the results obtained by analysing high spatial and spectral resolution data of the solar photosphere acquired by the CRisp Imaging SpectroPolarimeter at the Swedish Solar Telescope on 6 August 2011 of a large sunspot with a light bridge (LB) observed in NOAA AR 11263. These data are complemented by simultaneous Hinode Spectropolarimeter (SP) observation in the Fe I 630.15 nm and 630.25 nm lines. The continuum intensity map shows a discontinuity in the radial distribution of the penumbral filaments in correspondence with the LB, which shows a dark lane (\({\approx}\,0.3''\) wide and \({\approx}\,8.0''\) long) along its main axis. The available data were inverted with the Stokes Inversion based on Response functions (SIR) code and physical parameters maps were obtained. The line-of-sight (LOS) velocity of the plasma along the LB derived from the Doppler effect shows motions towards and away from the observer up to \(0.6~\mbox{km}\,\mbox{s}^{-1}\) that are lower in value than the LOS velocities observed in the neighbouring penumbral filaments. The noteworthy result is that we find motions towards the observer of up to \(0.6~\mbox{km}\,\mbox{s}^{-1}\) in the dark lane where the LB is located between two umbral cores, while the LOS velocity motion towards the observer is strongly reduced where the LB is located between an umbral core at one side and penumbral filaments on the other side. Statistically, the LOS velocities correspond to upflows or downflows, and comparing these results with Hinode/SP data, we conclude that the surrounding magnetic field configuration (whether more or less inclined) could have a role in maintaining the conditions for the process of plasma pile-up along the dark lane. The results obtained from our study support and confirm outcomes of recent magneto-hydrodynamic simulations showing upflows along the main axis of an LB.

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Acknowledgements

We are grateful to the University of Catania for providing the funds necessary to carry out the Observational Campaign in La Palma. The 1-m Swedish Solar Telescope is operated on the island of La Palma by the Institute for Solar Physics (ISP) of Stockholm University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Hinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in co-operation with ESA and NSC (Norway). The HMI/SDO data used in this paper are courtesy of NASA/SDO and the HMI science team. Use of NASA’s Astrophysical Data System is gratefully acknowledged. We are grateful to Dr. Rolf Schlichenmaier for the useful discussions and helpful suggestions. This research has received funding from the EC 7th Framework Programme FP7/2007-2013 under the grant agreement eHEROES (project n. 284461). We are grateful to the SOLARNET project for providing the grant for the Young Researches Mobility (project n. 312495). This work was also supported by the Instituto Nazionale di Astrofisica (PRIN INAF 2014), and by the University of Catania (PRIN MIUR 2012).

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Falco, M., Borrero, J.M., Guglielmino, S.L. et al. Kinematics and Magnetic Properties of a Light Bridge in a Decaying Sunspot. Sol Phys 291, 1939–1955 (2016). https://doi.org/10.1007/s11207-016-0944-8

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Keywords

  • Sun: photosphere
  • Sun: magnetic fields
  • Sun: sunspots
  • Sun: high resolution observations