The observed limb effect in Fraunhofer lines, I

Pierce, A. Keith

doi:10.1007/bf00149887

Cited by 7 publications

(1 citation statement)

References 22 publications

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“…More information about the instrumentally scattered polarization is contained in our previous paper (Keller & Sheeley 1999). Also, Pierce (1991) gives a plot of scattered light in the McMath-Pierce facility during 1988-1990, showing large reductions in scattered light after realuminizations of the heliostat.…”

Section: Photospheric Light Scattered From the Heliostatmentioning

confidence: 99%

Linear Polarization Measurements of Chromospheric Emission Lines

Sheeley¹,

.²,

Keller³

2003

ApJ

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We have used the Zurich Imaging Stokes Polarimeter (ZIMPOL I) with the McMath-Pierce 1.5 m main telescope on Kitt Peak to obtain linear polarization measurements of the off-limb chromosphere with a sensitivity better than 1 Â 10 À5 . We found that the off-disk observations require a combination of good seeing (to show the emission lines) and a clean heliostat (to avoid contamination by scattered light from the Sun's disk). When these conditions were met, we obtained the following principal results:1. Sometimes self-reversed emission lines of neutral and singly ionized metals showed linear polarization caused by the transverse Zeeman effect or by instrumental cross talk from the longitudinal Zeeman effect in chromospheric magnetic fields. Otherwise, these lines tended to depolarize the scattered continuum radiation by amounts that ranged up to 0.2%.2. Lines previously known to show scattering polarization just inside the limb (such as the Na i 5889 D2 and the He i 5876 D3 lines) showed even more polarization above the Sun's limb, with values approaching 0.7%.3. The O i triplet at 7772, 7774, and 7775 showed a range of polarizations. The 7775 line, whose maximum intrinsic polarizability, P max , is less than 1%, revealed mainly Zeeman contributions from chromospheric magnetic fields. However, the more sensitive 7772 (P max ¼ 19%) and 7774 (P max ¼ 29%) lines had relatively strong scattering polarizations of approximately 0.3% in addition to their Zeeman polarizations. At times of good seeing, the polarization spectra resolve into fine structures that seem to be chromospheric spicules.

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Section: Photospheric Light Scattered From the Heliostatmentioning

confidence: 99%