Understanding the HMI pseudocontinuum in white-light solar flares

Abstract

We analyse observations of the X9.3 solar flare (SOL2017-09-06T11:53) observed by SDO/HMI and Hinode/SOT. Our aim is to learn about the nature of the HMI pseudocontinuum Ic used as a proxy for the white-light continuum. From model atmospheres retrieved by an inversion code applied to the Stokes profiles observed by the Hinode satellite we synthesise profiles of the FeI 617.3 nm line and compare them to HMI observations. Based on a pixel-by-pixel comparison we show that the value of Ic represents the continuum level well in quiet-Sun regions only. In magnetised regions it suffers from a simplistic algorithm that is applied to a complex line shape. During this flare both instruments also registered emission profiles in the flare ribbons. Such emission profiles are poorly represented by the six spectral points of HMI, the used algorithm does not account for emission profiles in general, and thus the derived pseudocontinuum intensity does not approximate the continuum value properly.

9 pages, 9 figures, accepted for publication in ApJ

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Cited by in corpus (15)

• High-Density Off-Limb Flare Loops Observed by SDO
• First Detection of Solar Flare Emission in Middle-Ultraviolet Balmer Continuum
• The Statistical Relationship between White-light Emission and Photospheric Magnetic Field Changes in Flares
• A comparative study of two X2.2 and X9.3 solar flares observed with HARPS-N: Reconciling Sun-as-a-star spectroscopy and high-spatial resolution solar observations in the context of the solar-stellar connection
• A White-light Flare Powered by Magnetic Reconnection in the Lower Solar Atmosphere
• Understanding the HMI pseudocontinuum in white-light solar flares
• Flare Induced Photospheric Velocity Diagnostics
• Heating of the solar photosphere during a white-light flare
• Response of SDO/HMI observables to heating of the solar atmosphere by precipitating high-energy electrons
• An overview of HMI off-disk flare observations
• Flare heating of the chromosphere: Observations of flare continuum from GREGOR and IRIS
• Statistics of Photospheric Supergranular Cells Observed by SDO/HMI
• Global energetics of solar powerful events on 6 September 2017
• Rapid Evolution of Bald Patches in a Major Solar Eruption
• Statistical Study of Balmer Continuum Enhancement in Solar Flares