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Coronal Magnetic Field Measurements with the Upgraded Coronal Multi-channel Polarimeter (UCoMP)

Presentation #205.01 in the session Observing and Inferring Solar Chromospheric and Coronal Magnetic Fields II.

Published onOct 20, 2022
Coronal Magnetic Field Measurements with the Upgraded Coronal Multi-channel Polarimeter (UCoMP)

The Upgraded Coronal Multi-channel Polarimeter (UCoMP) is a coronal polarimeter with a narrow-band tunable Lyot filter capable of imaging the intensity, full Stokes polarization, and Doppler shift across a wide range of coronal emission lines in the visible and near-IR regions of the coronal spectrum. The UCoMP is an upgrade of the CoMP instrument with a broader wavelength range, a larger field-of-view and higher spatial resolution than CoMP. The UCoMP demonstrates the technology of a large aperture (50 mm) tunable birefringent filter based on Lithium Niobate crystals. The instrument was deployed to the Mauna Loa Solar Observatory and started taking data May 26, 2021, followed by a period of instrument commissioning.

This talk will briefly describe the UCoMP instrument, then concentrate on the coronal magnetic field measurements available from the UCoMP from two sources. The first is the direction of the Plane-of-Sky (POS) component of the magnetic field obtained from the linear polarization (Stokes Q and U) measurements. The second is the strength of the POS component of the magnetic field obtained from the phase speed of Alfvenic waves propagating in the corona, observed in the time series of Doppler images. Both methods will be demonstrated with example UCoMP measurements. It is possible to obtain the Line-of-Sight (LOS) strength of the coronal magnetic field from the circular polarization (Stokes V) measurements, however the 20-cm aperture of the UCoMP does not collect sufficient photons to routinely achieve the required sensitivity of 10-4 per Gauss for the FeXIII 1074 nm line. These LOS coronal field measurements will be possible with the DKIST and the proposed COSMO Large Coronagraph.

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