2016/06/15 by Paola Testa, Bart De Pontieu, Viggo Hansteen · 47 citations
Physics and Astronomy · #Doppler broadening #Doppler effect #Emission spectrum #Extreme ultraviolet #Imaging spectrometer #Ionosphere and magnetosphere dynamics #Radiative transfer #Solar and Space Plasma Dynamics #Spatial distribution #Spectral line #Spectral resolution #Spectrometer #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.3847/0004-637x/827/2/99
published in The Astrophysical Journal 827(2), 99 (IOP Publishing) · Accepted for publication on The Astrophysical Journal. 17 pages, 15 figures
arxiv created 2016/06/15 · openalex created_date 2016/06/24 · openalex publication_date 2016/08/11 · arxiv updated 2016/08/17 · openalex updated_date 2026/08/06
ABSTRACT We use UV spectral observations of active regions with the Interface Region Imaging Spectrograph ( IRIS ) to investigate the properties of the coronal Fe xii 1349.4 Å emission at unprecedented high spatial resolution (∼0.33″). We find that by using appropriate observational strategies (i.e., long exposures, lossless compression), Fe xii emission can be studied with IRIS at high spatial and spectral resolution, at least for high-density plasma (e.g., post-flare loops and active region moss). We find that upper transition region (TR; moss) Fe xii emission shows very small average Doppler redshifts ( ∼ 3 km s −1 ) as well as modest non-thermal velocities (with an average of ∼24 km s −1 and the peak of the distribution at ∼15 km s −1 ). The observed distribution of Doppler shifts appears to be compatible with advanced three-dimensional radiative MHD simulations in which impulsive heating is concentrated at the TR footpoints of a hot corona. While the non-thermal broadening of Fe xii 1349.4 Å peaks at similar values as lower resolution simultaneous Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) measurements of Fe xii 195 Å, IRIS observations show a previously undetected tail of increased non-thermal broadening that might be suggestive of the presence of subarcsecond heating events. We find that IRIS and EIS non-thermal line broadening measurements are affected by instrumental effects that can only be removed through careful analysis. Our results also reveal an unexplained discrepancy between observed 195.1/1349.4 Å Fe xii intensity ratios and those predicted by the CHIANTI atomic database.