Coronagraphic Observations of Si x λ14301 and Fe xiii λ10747 Linearly Polarized Spectra Using the SOLARC Telescope

• Published in: The Astrophysical journal Vol. 877; no. 2; pp. 144 - 153
• Main Authors: Dima, Gabriel I., Kuhn, Jeffrey R., Schad, Thomas A.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.06.2019; IOP Publishing
• Subjects: Apertures; Astrophysics; Brightness; Calibration; Corona; Coronagraphs; Coronal magnetic fields; Diagnostic systems; Emission lines; Iron; Linear polarization; Magnetic fields; Resolution; Sample variance; Solar corona; Solar magnetic field; Spectra; Spectral resolution; Sun: corona; Sun: infrared; Uncertainty; Wavelengths
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab1cb7

The forbidden Si x emission line at 14301 has been identified as a potentially valuable polarized diagnostic for solar coronal magnetic fields; however, the only polarized Si x measurements achieved to date have been during eclipses and at comparatively low spatial and spectral resolution. Here we report spectropolarimetric observations of both the Si x 14301 and more well-established Fe xiii 10747 coronal lines acquired with the 0.45 m aperture SOLARC coronagraph atop Haleakal . Using its fiber-based integral field spectropolarimeter, we derive observations sampled at radial intervals of 0.05 (i.e., ∼50″) with a spectral resolving power of 36,000. Results for both lines, which represent averages over different active and nonactive regions of the corona, indicate a relatively flat radial variation for the line widths and line centers and a factor of 2-3 decrease in polarized brightness between 1.05 and 1.45 . Averaging over all the measurements the mean and standard deviations of line properties for Si x 14301 and Fe xiii 10747 are, respectively, FWHM of 3.0 0.4 and 1.6 0.1 , line-integrated polarized brightness of 0.07 0.03 and 0.3 0.3 erg s−2 cm−2 sr−1, where the uncertainty quoted reflects a large sample variance, and line center wavelengths 14300.7 0.2 and 10746.3 0.1 . The polarized brightness for both lines may be underestimated by up to a factor of 5 due to limitations in the photometric calibration. When accounting for this uncertainty we find consistency between our observations and previous measurements of the two lines as well as theoretical calculations and affirm the potential of the Si x line as a polarized diagnostic of the solar corona.