Stratification of sunspot umbral dots from inversion of stokes profiles recorded by Hinode

T. L. Riethmüller, S. K. Solanki, A. Lagg

Research output: Contribution to journalArticleScientificpeer-review

1 Citation (Scopus)

Abstract

This work aims to constrain the physical nature of umbral dots (UDs) using high-resolution spectropolarimetry. Full Stokes spectra recorded by the spectropolarimeter on Hinode of 51 UDs in a sunspot close to the disk center are analyzed. The height dependence of the temperature, magnetic field vector, and line-of-sight velocity across each UD is obtained from an inversion of the Stokes vectors of the two Fe i lines at 630 nm. No difference is found at higher altitudes [-3 ≤ log (τ500) ≤ -2] between the UDs and the diffuse umbral background. Below 500 that level the difference rapidly increases, so that at the continuum formation level [log (τ500) = 0] we find on 500 average a temperature enhancement of 570 K, a magnetic field weakening of 510 G, and upflows of 800 m s-1 for peripheral UDs, whereas central UDs display an excess temperature of on average 550 K, a field weakening of 480 G, and no significant upflows. The results for, in particular, the peripheral UDs, including cuts of magnetic vector and velocity through them, look remarkably similar to the output of recent radiation MHD simulations. They strongly suggest that UDs are produced by convective upwellings.

Original languageEnglish
Pages (from-to)L15-L160
JournalAstrophysical Journal
Volume678
Issue number2
Publication statusPublished - 10 May 2008
MoE publication typeA1 Journal article-refereed

Keywords

  • Sun: photosphere
  • Sunspots
  • Techniques: spectroscopic

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