An Instrument to Measure Coronal Emission Line Polarization

Abstract

We have constructed an instrument to measure the polarization of light emitted by the solar corona in order to constrain the strength and orientation of coronal magnetic fields. We call this instrument the Coronal Multichannel Polarimeter (CoMP). The CoMP is integrated into the Coronal One Shot coronagraph at Sacramento Peak Observatory and employs a combination birefringent filter and polarimeter to form images in two wavelengths simultaneously over a 2.8R field of view. The CoMP measures the complete polarization state at the 1074.7 and 1079.8 Fe XIII coronal emission lines, and the 1083.0 nm He I chromospheric line. In this paper we present design drivers for the instrument, provide a detailed description of the instrument, describe the calibration methodology, and present some sample data along with estimates of the uncertainty of the measured magnetic field.

Controlling Influence of Magnetic Field on Solar Wind Outflow: An Investigation Using Current Sheet Source Surface Model

“…Measuring coronal magnetic field is extremely difficult and routine measurements remained nearly impossible due to the extremely low intensity of coronal magnetic field and certain technical difficulties until the Coronal Multi-Channel Polarimeter (CoMP; Tomczyk et al 2008;Bak-Steslicka et al 2013;Judge et al 2013;Kramar et al 2016). Though CoMP is capable of measuring coronal magnetic field as a line of sight integration, producing routine synoptic maps of coronal magnetic fields, similar to the photospheric maps, is still a challenge.…”

“…During the period of study, extended over solar cycle23 and beginning of solar cycle24, we found that the coefficients of the fitted quadratic equation representing the FTE-SWS inverse relation exhibited significant temporal variation, implying the changing pattern of the influence of FTE on SWS over time. A particularly noteworthy feature is an anomaly in the behavior of the fitted coefficients during the extended minimum, 2008-2010 (CRs 2073 -2092, which is considered due to the particularly complex nature of the solar magnetic field during this period. However, this variation was significant only for the CSSS model, though not a systematic dependence on the phase of the solar cycle.…”

Solar magnetism eXplorer (SolmeX)

“…The large distance to the external occulter, located on the occulting spacecraft, enables high spatial resolution to be achieved in both the IR and the VL channel. The IR spectro-polarimeter design is based on the HAO/NCAR Coronal Multichannel Polarimeter [CoMP;36], which is now a part of HAO's Mauna Loa Solar Observatory in Hawaii. The 2.5 R × 2.5 R FOV (Fig.…”

Magnetic Nulls and Super-radial Expansion in the Solar Corona

“…More recently, routine measurements of magnetism in its lower atmosphere, or chromosphere, have become possible (Ariste 2002;Harvey 2006). At higher coronal altitudes, emission-line measurements of circular polarization -sensitive to line-of-sight (LOS) oriented magnetic-field strength -have been rare (Harvey 1969;Lin & Casini 2000;Lin et al 2004;Tomczyk et al 2008). Obtaining routine circular-polarization measurements at the level of one Gauss in 15 minutes generally requires a larger-aperture telescope than the 20-cm CoMP (Tomczyk et al 2016).…”