EUV Emission and Scattered Light Diagnostics of Equatorial Coronal Holes as Seen by Hinode/EIS

Abstract

Spectroscopic diagnostics of solar coronal plasmas critically depends on the uncertainty in the measured line intensities. One of the main sources of uncertainty is instrumental scattered light, which is potentially most important in low-brightness areas. In the solar corona, such areas include polar and equatorial coronal holes, which are the source regions of the solar wind; instrument-scattered light must thus pose a significant obstacle to studies of the source regions of the solar wind. In this paper we investigate the importance of instrument-scattered light on observations of equatorial coronal holes made by the Hinode/EIS spectrometer in two different phases of the solar cycle. We find that the instrument-scattered light is significant at all temperatures, and in both regions it amounts to approximately 10% of the average intensity of the neighboring quiet Sun regions. Such contribution dominates the measured intensity for spectral lines formed at temperatures larger than Log T = 6.15 K, and has deep implications for spectroscopic diagnostics of equatorial coronal hole plasmas and studies of the source regions of a large portion of the solar wind which reaches Earth. Our results suggest that the high temperature tail of in the coronal hole plasma distribution with temperature, however small, is an artifact due to the presence of scattered light.

arXiv comment11 pages, 6 figures

References in corpus (11)

• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• Self-consistent Coronal Heating and Solar Wind Acceleration from Anisotropic Magnetohydrodynamic Turbulence
• Alfven Wave Solar Model (AWSoM): Coronal Heating
• CHIANTI - An atomic database for Emission Lines. Version 8
• EUV emission lines and diagnostics observed with Hinode/EIS
• High precision density measurements in the solar corona: I. Analysis methods and results for Fe XII and Fe XIII
• Spectroscopic signature of Alfvén waves damping in a polar coronal hole up to 0.4 solar radii
• Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind \textit{(Invited Review)}
• Hinode/Extreme-Ultraviolet Imaging Spectrometer Observations of the Temperature Structure of the Quiet Corona
• Signatures of impulsive localized heating in the temperature distribution of multi-stranded coronal loops
• The First Stray Light Corrected EUV Images of Solar Coronal Holes

Cited by in corpus (13)

• Exoplanet Statistics and Theoretical Implications
• Statistical Analysis and Catalog of Non-polar Coronal Holes Covering the SDO-era using CATCH
• Low-frequency Alfven Waves Produced by Magnetic Reconnection in the Sun's Magnetic Carpet
• Differential Emission Measure Plasma Diagnostics of a Long-Lived Coronal Hole
• Coronal Plasma Characterization via Coordinated Infrared and Extreme Ultraviolet Observations of a Total Solar Eclipse
• Statistical Approach on Differential EmissionMeasure of Coronal Holes using the CATCH Catalog
• How to Estimate the Far-Side Open Flux using STEREO Coronal Holes
• Sensitivity of solar wind mass flux to coronal temperature
• Scattered light in the Hinode/EIS and SDO/AIA instruments measured from the 2012 Venus transit
• Modeling and removal of optical ghosts in the PROBA-3/ASPIICS externally occulted solar coronagraph
• Fe XII and Fe XIII Line Widths in the Polar Off-limb Solar Corona up to 1.5 Rsun
• Active region upflows in various coronal structures and their coupling to the lower atmosphere
• Formation of Coronal Mass Ejection and Post-eruption Flow of Solar Wind on 2010 August 18 event