Fe XII and Fe XIII Line Widths in the Polar Off-limb Solar Corona up to 1.5 Rsun

Abstract

The nonthermal broadening of spectral lines formed in the solar corona is often used to seek the evidence of Alfvén waves propagating in the corona. To have a better understanding of the variation of line widths at different altitudes, we measured the line widths of the strong Fe \textsc{xii} 192.4, 193.5, and 195.1 \mboxÅ and Fe \textsc{xiii} 202.0 \mboxÅ in an off-limb southern coronal hole up to 1.5 $R_{\odot }$ observed by the Extreme Ultraviolet Spectrometer (EIS) on board the \textit{Hinode} satellite. We compared our measurements to the predictions from the Alfvén Wave Solar Model (AWSoM) and the SPECTRUM module. We found that the Fe \textsc{xii} and Fe \textsc{xiii} line widths first increase monotonically below 1.1 $R_{\odot }$, and then keep fluctuating between 1.1 and 1.5 $R_{\odot }$. The synthetic line widths of Fe \textsc{xii} and Fe \textsc{xiii} below 1.3 $R_{\odot }$ are notably lower than the observed ones. We found that the emission from a streamer in the line of sight significantly contaminates the coronal hole line profiles even up to 1.5 $R_{\odot }$ both in observations and simulations. We suggest that either the discrepancy between the observations and simulations is caused by insufficient nonthermal broadening at the streamer in the AWSoM simulation or the observations are less affected by the streamer. Our results emphasize the importance of identifying the origin of the coronal EUV emission in off-limb observations.

arXiv comment17 pages, 13 figures, accepted by ApJ

References in corpus (25)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The NumPy array: a structure for efficient numerical computation
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• 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 - Paper XV: Version 9, improvements for the X-ray satellite lines
• Data analysis recipes: Fitting a model to data
• On the nature of kink MHD waves in magnetic flux tubes
• High precision density measurements in the solar corona: I. Analysis methods and results for Fe XII and Fe XIII
• MHD Waves and Coronal Heating: Unifying Empirical and MHD Turbulence Models
• The Properties of the Solar Corona and Its Connection to the Solar Wind
• Signatures of Alfven waves in the polar coronal holes as seen by EIS/Hinode
• A revised radiometric calibration for the Hinode/EIS instrument
• Evidence of Wave Damping at Low Heights in a Polar Coronal Hole
• The Absolute Calibration of the EUV Imaging Spectrometer on Hinode
• Spectroscopic signature of Alfvén waves damping in a polar coronal hole up to 0.4 solar radii
• Observational Quantification of the Energy Dissipated by Alfvén Waves in a Polar Coronal Hole: Evidence that Waves Drive the Fast Solar Wind
• Ion Temperatures in the Low Solar Corona: Polar Coronal Holes at Solar Minimum
• Solar off-limb line widths: Alfven waves, ion-cyclotron waves, and preferential heating
• Hinode EIS line widths in the quiet corona up to 1.5 Rsun
• Laboratory Calibrations of Fe XII-XIV Line-Intensity Ratios for Electron Density Diagnostics
• Revisiting the relation between nonthermal line widths and transverse MHD wave amplitudes
• EUV Emission and Scattered Light Diagnostics of Equatorial Coronal Holes as Seen by Hinode/EIS

Cited by in corpus (1)

• Propagating Kink Waves in an Open Coronal Magnetic Flux Tube with Gravitational Stratification: Magnetohydrodynamic Simulation and Forward Modelling