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Title: The formation of IRIS diagnostics. III. Near-ultraviolet spectra and images

The Mg II h and k lines are the prime chromospheric diagnostics of NASA's Interface Region Imaging Spectrograph (IRIS). In the previous papers of this series, we used a realistic three-dimensional radiative magnetohydrodynamics model to calculate the h and k lines in detail and investigated how their spectral features relate to the underlying atmosphere. In this work, we employ the same approach to investigate how the h and k diagnostics fare when taking into account the finite resolution of IRIS and different noise levels. In addition, we investigate the diagnostic potential of several other photospheric lines and near-continuum regions present in the near-ultraviolet (NUV) window of IRIS and study the formation of the NUV slit-jaw images. We find that the instrumental resolution of IRIS has a small effect on the quality of the h and k diagnostics; the relations between the spectral features and atmospheric properties are mostly unchanged. The peak separation is the most affected diagnostic, but mainly due to limitations of the simulation. The effects of noise start to be noticeable at a signal-to-noise ratio (S/N) of 20, but we show that with noise filtering one can obtain reliable diagnostics at least down to a S/N of 5.more » The many photospheric lines present in the NUV window provide velocity information for at least eight distinct photospheric heights. Using line-free regions in the h and k far wings, we derive good estimates of photospheric temperature for at least three heights. Both of these diagnostics, in particular the latter, can be obtained even at S/Ns as low as 5.« less
Authors:
; ; ;  [1] ;  [2]
  1. Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, NO-0315 Oslo (Norway)
  2. NSO/Sacramento Peak, P.O. Box 62 Sunspot, NM 88349-0062 (United States)
Publication Date:
OSTI Identifier:
22341935
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 778; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CHROMOSPHERE; FILTERS; INTERFACES; MAGNESIUM; MAGNETOHYDRODYNAMICS; NASA; NEAR ULTRAVIOLET RADIATION; NOISE; RADIANT HEAT TRANSFER; RESOLUTION; SIGNAL-TO-NOISE RATIO; SIMULATION; SPECTRA; SPECTROSCOPY; SUN; THREE-DIMENSIONAL CALCULATIONS; ULTRAVIOLET RADIATION; ULTRAVIOLET SPECTRA