Sun center observations of the Evershed effect

Abstract

view Abstract Citations (77) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Sun Center Observations of the Evershed Effect Rimmele, Thomas R. Abstract Results of observations of the Evershed effect for a round sunspot at disk center are presented. Using the 20 mA UBF/FP filter at the VTT of NSO/Sacramento Peak we recorded a 2 hr time sequence of Fe I 5576.099 A velocity maps, Mn I 5394.675 A core intensity maps, and white-light images. By computing the 2 hr time average we were able to filter out the vertical Evershed component of a few hundred m/s from the background of oscillatory and granular velocities, which dominate individual images. The averaged velocity fields show distinct filaments which extend beyond the white-light boundary of the sunspot by as far as 10,000 km. The velocity profile along these filaments is consistent with the picture of an arched magnetic loop carrying the Evershed flow. These loops reach their maximum elevation at less than 300 km above continuum height. The portions of the loops seen in velocity maps have a length of up to 20,000 km. Within the penumbra the velocity filaments are correlated with dark filaments observed in the core intensity map of the temperature-sensitive Mn I line. However, beyond the penumbral boundary the same velocity filaments coincide with enhanced brightness, relative to the photospheric intensity, suggesting that the gas in the downstream legs of the loop is at a higher temperature than the surrounding photospheric material. The temperature excess in the downstream legs is of the order of 200 K. A possible explanation is a standing tube shock that occurs in the downstream legs and near the penumbral boundary as modeled by Montesinos & Thomas (1993). Some velocity filaments end in pore-like features which are 5%-10% darker than the average photosphere and reveal a pronounced redshift. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175716 Bibcode: 1995ApJ...445..511R Keywords: Coronal Loops; Solar Atmosphere; Solar Granulation; Solar Magnetic Field; Sunspots; Velocity Distribution; Data Reduction; Flux Density; Interferometry; Solar Spectra; Solar Physics; SUN: ATMOSPHERE; SUN: SUNSPOTS full text sources ADS |