Paola Testa (1), Jeremy J. Drake (1), Enrico Landi (2) ((1) Smithsonian Astrophysical Observatory, (2) Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor)
The Atmospheric Imaging Assembly (AIA) and the Extreme-ultraviolet Variability Experiment (EVE) onboard the Solar Dynamics Observatory include spectral windows in the X-ray/EUV band. Accuracy and completeness of the atomic data in this wavelength range is essential for interpretation of the spectrum and irradiance of the solar corona, and of SDO observations made with the AIA and EVE instruments. Here we test the X-ray/EUV data in the CHIANTI database to assess their completeness and accuracy in the SDO bands, with particular focus on the 94 Å and 131 Å AIA passbands. Given the paucity of solar observations adequate for this purpose, we use high-resolution X-ray spectra of the low-activity solar-like corona of Procyon obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS). We find that while spectral models overall can reproduce quite well the observed spectra in the soft X-ray range λ ≤ 50 Å, and at the EUV wavelengths λ ≥ 130 Å, they significantly underestimate the observed flux in the 50-130 Å wavelength range. The model underestimates the observed flux by a variable factor ranging from ≈ 1.5, at short wavelengths below ~50 Å, up to ≈ 5-7 in the ~70-125 Å range. In the AIA bands covered by LETGS, i.e. 94 Å and 131 Å, we find that the observed flux can be underestimated by large factors (~3 and ~1.9 respectively, for the case of Procyon presented here). We discuss the consequences for analysis of AIA data and possible empirical corrections to the AIA responses to model more realistically the coronal emission in these passbands.
Complete paper ==> http://arxiv.org/abs/1110.4611