SDO AIA and Hinode EIS observations of “warm” loops

• Published in: Astronomy and astrophysics (Berlin) Vol. 535; p. A46
• Main Authors: Del Zanna, G., O’Dwyer, B., Mason, H. E.
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.11.2011
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Sun: corona; techniques: spectroscopic; Second order; Transition temperature; Plasma diagnostics; SDO satellite; Sun: corona; techniques: spectroscopic; Modelling; Emission measure; Emission line; Transition zone; Sun; Simultaneous observation
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201117470

We present simultaneous observations of active region “warm” (1 MK) loops using the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and Hinode EUV Imaging Spectrometer (EIS). Sample EIS spectra for a loop footpoint and a lop leg region are presented, and are used to describe the spectral lines which contribute to the six AIA EUV channels, both directly and predicted with DEM modeling. We find good overall agreement between observed and predicted count rates for the 131 Å, 193 Å, and 335 Å bands, but highlight a number of problems, partly to be ascribed to inter-calibration issues, partly due to the fact that a large number of lines remain unidentified for the 94 Å, 171 Å, and 211 Å bands. We also found that the 335 Å band is severely affected by cross-talk with the 131 Å band and by second order contributions. We extend our previous work where we highlighted the multi-thermal nature of the SDO AIA bands to show that emission from lines formed at typical transition region temperatures (log T[K] = 5.0–5.8) can be significant for all the EUV channels, and even dominant in some cases. We also assess the possibility of deriving accurate emission measures from the AIA observations. We have found that the inversion of the AIA data to obtain a description of the thermal characteristics of warm loops is unreliable. We highlight the need for further work on the relevant atomic data before the AIA data can be reliably used for plasma diagnostic purposes.