Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011apj...736...15l&link_type=abstract
The Astrophysical Journal, Volume 736, Issue 1, article id. 15 (2011).
Astronomy and Astrophysics
Astronomy
2
Sun: Activity, Sun: Uv Radiation, Techniques: Spectroscopic
Scientific paper
We have investigated seven extreme-ultraviolet (EUV) brightenings in the active region AR 10926 on 2006 December 2 observed by the EUV Imaging Spectrometer on board the Hinode spacecraft. We have determined their Doppler velocities and non-thermal velocities from 15 EUV spectral lines (log T = 4.7 - 6.4) by fitting each line profile to a Gaussian function. The Doppler velocity maps for different temperatures are presented to show the height dependence of the Doppler shifts. It is found that the active region brightenings show two distinct Doppler shift patterns. The type 1 brightening shows a systematic increase of Doppler velocity from -68 km s-1 (strong blueshift) at log T = 4.7 to -2 km s-1 (weak blueshift) at log T = 6.4, while the type 2 brightenings have Doppler velocities in the range from -20 km s-1 to 20 km s-1. The type 1 brightening point is considered to sit in an upward reconnection outflow whose speed decreases with height. In both types of brightenings, the non-thermal velocity is found to be significantly enhanced at log T = 5.8 compared to the background region. We have also determined electron densities from line ratios and derived temperatures from emission measure loci using the CHIANTI atomic database. The electron densities of all brightenings are comparable to typical values in active regions (log Ne = 9.9-10.4). The emission measure loci plots indicate that these brightenings should be multi-thermal whereas the background is isothermal. The differential emission measure as a function of temperature shows multiple peaks in the EUV brightening regions, while it has only a single peak (log T = 6.0) in the background region. Using Michelson Doppler Imager magnetograms, we have found that the type 1 brightening is associated with a canceling magnetic feature with a flux canceling rate of 2.4 × 1018 Mx hr-1. We also found the canceling magnetic feature and chromospheric brightenings in the type 1 brightening from the Hinode SOT and Transition Region and Coronal Explorer data. This observation corroborates our argument that brightening is caused by magnetic reconnection in a low atmosphere.
Cho Kyung-Suk
Choe Gwang-Son
Imada Shin
Kim Sujin
Lee Kyu-Seok
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