Characteristic Dependence of Umbral Dots on their Magnetic Structure

Abstract

Umbral dots (UDs) were observed in a stable sunspot in NOAA 10944 by the Hinode Solar Optical Telescope on 2007 March 1. The observation program consisted of blue continuum images and spectropolarimetric profiles of Fe I 630 nm line. An automatic detection algorithm for UDs was applied to the 2-hour continuous blue continuum images, and using the obtained data, the lifetime, size, and proper motion of UDs were calculated. The magnetic structure of the sunspot was derived through the inversion of the spectropolarimetric profiles. We calculated the correlations between UD's parameters (size, lifetime, occurrence rate, proper motion) and magnetic fields (field strength, inclination, azimuth), and obtained the following results: (1) Both the lifetime and size of UDs are almost constant regardless of the magnetic field strength at their emergence site. (2) The speed of UDs increases as the field inclination angle at their emergence site gets larger. (3) The direction of movement of UDs is nearly parallel to the direction of the horizontal component of magnetic field in the region with strongly inclined field, while UDs in the region with weakly inclined field show virtually no proper motion. Our results describe the basic properties of magnetoconvection in sunspots. We will discuss our results in comparison to recent MHD simulations by Schussler & Vogler (2006) and Rempel et al. (2009).

22 pages, 10 figures, accepted for publication in ApJ

References in corpus (4)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• Magneto-convection in a sunspot umbra
• MHD simulations of penumbra fine structure
• Convection and the origin of Evershed flows in sunspot penumbrae

Cited by in corpus (20)

• Magnetic Structure of Sunspots
• Ellerman Bombs at high resolution: I. Morphological evidence for photospheric reconnection
• Properties of simulated sunspot umbral dots
• Temporal Evolution of Velocity and Magnetic Field in and around Umbral Dots
• High Resolution Observations of Chromospheric Jets in Sunspot Umbra
• Dynamics in Sunspot Umbra as Seen in New Solar Telescope and Interface Region Imaging Spectrograph Data
• Properties of Umbral Dots from Stray Light Corrected Hinode Filtergrams
• Properties of Umbral Dots as Measured from the New Solar Telescope Data and MHD Simulations
• Absolute velocity measurements in sunspot umbrae
• New views on the emission and structure of the solar transition region
• Observations of Umbral Dots and their Physical Models
• Investigation of Umbral Dots with the New Vacuum Solar Telescope
• Physical Characteristics of Umbral Dots Derived from a High Resolution Observation
• Investigating the relation between sunspots and umbral dots
• Sunspot Bright Points
• Investigation of the subsurface structure of a sunspot based on the spatial distribution of oscillation centers inferred from umbral flashes
• Proper Motions of Sunspots' Umbral Dots at High Temporal and Spatial Resolution
• Ti I lines at 2.2 $\mu$m as probes of the cool parts of sunspots
• Umbral Dynamics in the Near Infrared Continuum
• Similarities of magnetoconvection in the umbra and in the penumbra of sunspots