Optimal spectral lines for measuring chromospheric magnetic fields

Abstract

This paper identifies spectral lines from X-ray to infrared wavelengths which are optimally suited to measuring vector magnetic fields as high as possible in the solar atmosphere. Instrumental and Earth's atmospheric properties, as well as solar abundances, atmospheric properties and elementary atomic physics are considered without bias towards particular wavelengths or diagnostic techniques. While narrowly-focused investigations of individual lines have been reported in detail, no assessment of the comparative merits of all lines has ever been published. Although in the UV, on balance the Mg+ h and k lines near 2800 Angstroms are optimally suited to polarimetry of plasma near the base of the solar corona. This result was unanticipated, given that longer-wavelength lines offer greater sensitivity to the Zeeman effect. While these lines sample optical depths photosphere to the coronal base, we argue that cores of multiple spectral lines provide a far more discriminating probe of magnetic structure as a function of optical depth than the core and inner wings of a strong line. Thus, together with many chromospheric lines of Fe+ between 2585 and the h line at 2803 Angstrom, this UV region promises new discoveries concerning how the magnetic fields emerge, heat, and accelerate plasma as they battle to dominate the force and energy balance within the poorly-understood chromosphere.

Accepted for publication in the Astrophysical Journal. 12 pages, 2 figures, and 1 table

References in corpus (19)

• Magnetic Diagnostics of the Solar Chromosphere with the Mg II h-k Lines
• Mapping Solar Magnetic Fields from the Photosphere to the Base of the Corona
• The Visible Spectro-Polarimeter of the Daniel K. Inouye Solar Telescope
• The magnetic sensitivity of the Mg ii k line to the joint action of Hanle, Zeeman and magneto-optical effects
• Hinode/EIS measurements of active region magnetic fields
• The magnetic sensitivity of the resonance and subordinate lines of Mg II in the solar chromosphere
• On the Origin of a Sunquake during the 29 March 2014 X1 Flare
• The cause of spatial structure in solar He I 1083 nm multiplet images
• Diagnostics of Coronal Magnetic Fields Through the Hanle Effect in UV and IR Lines
• TIC: A Stokes inversion code for scattering polarization with partial frequency redistribution and arbitrary magnetic fields
• A first spectroscopic measurement of the magnetic field strength for an active region of the solar corona
• Measurements of Photospheric and Chromospheric Magnetic Field Structures Associated with Chromospheric Heating over a Solar Plage Region
• Measuring the magnetic origins of solar flares, CMEs and Space Weather
• Active region chromospheric magnetic fields
• New light on an old problem of the cores of solar resonance lines
• The transfer of polarized radiation in resonance lines with partial frequency redistribution, J-state interference, and arbitrary magnetic fields. A radiative transfer code and useful approximations
• Inference of electric currents in the solar photosphere
• Magnetic connections across the chromosphere-corona transition region
• Spectropolarimetric observations of the solar atmosphere in the H$\alpha$ 6563 Å line