Some properties of sunspot umbral dots.

Details Some properties of sunspot umbral dots. Some properties of sunspot umbral dots.

May 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...321..643t&link_type=abstract

Astronomy and Astrophysics, v.321, p.643-651

Astronomy and Astrophysics

Astrophysics

13

Solar Activity, Sunspots, Umbral Dots

Scientific paper

High resolution Stokes-I spectra of the Zeeman-sensitive lines at λ846.85nm and λ 630.25nm were used to determine the magnetic field strength and the brightness temperature of a simple, relatively symmetric sunspot umbra and its umbral dots (UDs). We find a decrease in brightness temperature for central (~30%) and peripheral UDs (20-25%) compared to the surrounding quiet sun. This corresponds to a difference in temperature of about 1600K and 1200-1400K respectively. The magnetic field strength within the umbra is derived from the Zeeman splitting of the Stokes-I profile. Field strengths within the umbra vary between 1500 and 3000G. Further analysis of the λ846.85nm spectra indicates that the magnetic field strength within the umbral features is not significantly reduced neither for centrally (<=3%) nor for peripherically located UDs (1-2%). The λ630.25nm line yields an enhanced weakening of field strength of 7% for an isolated located UD. The measured properties of UDs do not vary significantly during a 40min observation sequence.

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