Upgraded Coronal Multi-channel Polarimeter (UCoMP)

UCoMP on the MLSO spar

Figure 1. UCoMP on the MLSO spar.

The Upgraded Coronal Multi-channel Polarimeter (UCoMP) is a 20-cm aperture Lyot coronagraph with a Stokes polarimeter and a narrow-band electro-optically tuned birefringent filter. It can image the intensity, full Stokes polarization, Doppler shift and line width across coronal emission lines in the visible and near-IR. The UCoMP is an upgrade of the Coronal Multi-channel Polarimeter (CoMP) instrument (Tomczyk, Card, Darnell et al., 2008); see Table 1 for performance comparison. The expanded capabilities of UCoMP provide polarization measurements over a wide range of coronal temperatures and out to greater coronal heights to explore the magneto-thermal structure of the corona in coronal holes, ‘quiet’ corona and active regions. The evolution of CMEs from build-up to eruption can be explored and MHD wave observations can be viewed to much greater heights, and over a wide range of coronal conditions. The tunable filter allows UComp to combine the strengths of simultaneous 2-D imaging and high-resolution spectroscopy into a single instrument. UCoMP is located at the Mauna Loa Solar Observatory (MLSO) operated by HAO/NCAR. UCoMP was installed in the spring of 2021, began acquiring data May 26, 2021, and is currently completing commissioning.

UCoMP in final stages of assembly at HAO/NCAR in Boulder

Figure 2. UCoMP in final stages of assembly at HAO/NCAR in Boulder.

The UCoMP demonstrates the technology of a large aperture (50 mm) tunable birefringent filter based on Lithium Niobate crystals and is a pathfinder instrument for the Coronal Solar Magnetism Observatory (COSMO) (Tomczyk et al., 2016) large coronagragh (LC). The LC will observe full Stokes polarimetry (intensity, linear and circular polarization) over a comparable wavelength range but with an aperture of 1.5 meters. COSMO consists of the LC, a chromospheric magnetometer (ChroMag) and the white light K-coronagraph (K-Cor). For more information on COSMO science and capabilities please see: Tomczyk et al. 2016.

PROPERTYCoMPUCoMP
Field-of_View [Rsun]1.05 to 1.31.03 to 1.95 (see figure 3)
Spectral Range [nm]1074 to 1083530 to 1083
Spatial Resolution [arcsec]9 (4.5 arcsec/pixel)6 (3 arcsec/pixel)

Table 1. CoMP vs. UCoMP

UCoMP Description

UCoMP intensity image at 1074.7 nm used to illustrate the FOV

Figure 3. UCoMP intensity image at 1074.7 nm used to illustrate the FOV.

Plot of UCoMP spectral resolution vs. wavelength

Figure 4. Plot of UCoMP spectral resolution vs. wavelength.

Internally occulted refractive coronagraph
Aperture: 20 cm uncoated singlet objective lens
Field-of-view (FOV): 1.03 to 1.56/1.95 Rsun (see Figure 3)
Spatial resolution: 6 arcsec (3 arcsec / pixel)
Spectral Lines observed: Shown in Table 2 and Figure 5.
Spectral Resolution: Set by the birefringence of the Lithium Niobate crystals in the birefringent filter (see Figure 4)

SPECTRAL LINEWAVELENGTH [nm]logTeff
FeXIV [corona]530.36.15 to 6.49
FeX [corona]637.45.80 to 6.24
ArXI [corona]691.86.04 to 6.52
FeXV [corona]706.26.20 to 6.63
FeXi [corona]789.45.92 to 6.30
FeXIII [corona]1074.76.08 to 6.41
FeXIII [corona]1079.86.08 to 6.41
HI [chromosphere]656.34.01 to 4.29
HeI [chromosphere]10834.01 to 4.57

Table 2. Spectral Lines Observed by UCoMP

A sample of five of the nine spectral lines acquired with UCoMP showing coronal structures at various temperatures. These images were recorded on Feb 5, 2022. The coronal images are taken at ~1 minute exposure and the HI (Halpha) image is taken at 80 msec exposure.

Figure 5. A sample of five of the nine spectral lines acquired with UCoMP showing coronal structures at various temperatures. These images were recorded on Feb 5, 2022. The coronal images are taken at ~1 minute exposure and the HI (Halpha) image is taken at 80 msec exposure.

Examples of some UCoMP Level 1 and Level 2 data products are shown in Figure 6 for a single spectral line (FeXIII 1074 nm). These products are created for each spectral line observed. Figure 6 shows Stokes I (Intensity), Stokes Q/I and U/I that correspond to the percent linear polarization horizontally and at 45 degrees, respectively, and the ratio of L/I where L is the linear polarization = sqrt (Q2 + U2). The rotation of the corona is visible as the blue to red variation in the line-of-sight (LOS) Doppler velocity. The line width includes the instrumental profile. The Azimuth of the magnetic field is measured CCW from horizontal and is subject to a 180-degree ambiguity. The Radial Azimuth of the magnetic field is the azimuth measured CCW from the local radial direction. Zero-degree Radial Azimuth corresponds to magnetic field pointing in the radial direction.

Some UCoMP Level-1 and -2 data products

Figure 6. Some UCoMP Level-1 and -2 data products. See text for details. .

Additional information about the UCoMP instrument and science objectives are available; please see: Tomczyk et al. 2021 and Landi et al. 2016.