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Physical Properties of Umbral Dots Observed in Sunspots: A Hinode Observation

Abstract

Umbral dots (UDs) are small-scale bright features observed in the umbral part of sunspots and pores. It is well established that they are manifestations of magnetoconvection phenomena inside umbrae. We study the physical properties of UDs in different sunspots and their dependence on decay rate and filling factor. We have selected high-resolution, G-band continuum filtergrams of seven sunspots from Hinode to study their physical properties. We have also used Michelson Doppler Imager (MDI) continuum images to estimate the decay rate of selected sunspots. An identification and tracking algorithm was developed to identify the UDs in time sequences. The statistical analysis of UDs exhibits an averaged maximum intensity and effective diameter of 0.26 \(I_{\mathrm{QS}}\) and 270 km. Furthermore, the lifetime, horizontal speed, trajectory length, and displacement length (birth–death distance) of UDs are 8.19 minutes, 0.5 km s−1, 284 km, and 155 km, respectively. We also find a positive correlation between intensity–diameter, intensity–lifetime, and diameter–lifetime of UDs. However, UD properties do not show any significant relation with the decay rate or filling factor.

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Acknowledgements

Hinode is a Japanese mission developed and launched by ISAS/JAXA, collaborating with NAOJ as a domestic partner, NASA and STFC (UK) as international partners. The scientific operation of the Hinode mission is conducted by the Hinode science team organized at ISAS/JAXA. This team mainly consists of scientists from institutes in the partner countries. Support for the post-launch operation is provided by JAXA and NAOJ (Japan), STFC (UK), NASA, ESA, and NSC (Norway). R. Yadav thanks R.E. Louis for useful discussions of the manuscript. We thank the anonymous referee for providing insightful comments that have improved the presentation of the manuscript.

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Correspondence to Rahul Yadav.

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Yadav, R., Mathew, S.K. Physical Properties of Umbral Dots Observed in Sunspots: A Hinode Observation. Sol Phys 293, 54 (2018). https://doi.org/10.1007/s11207-018-1272-y

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Keywords

  • Sunspots
  • Magnetic fields