Polarization Calibration of the Chromospheric Lyman-Alpha SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV Range. Part II: In-Flight Calibration

Giono, Gabriel; Ishikawa, R.; Narukage, Noriyuki; Kano, Ryouhei; Katsukawa, Y.; Kubo, Masahito; Ishikawa, Shin-­nosuke; Bando, T.; Hara, Hirohisa; Suematsu, Y.; Winebarger, Amy R.; Kobayashi, K.; Auchère, F.; Bueno, J. Trujillo; Tsuneta, S.; Shimizu, Toshifumi; Sakao, Taro; Cirtain, Jonathan; Champey, Patrick; Ramos, A. Asensio; Štěpán, Jiří; Belluzzi, L.; Sainz, R. Manso; Pontieu, Bart De; Ichimoto, Kiyoshi; Carlsson, Mats; Casini, R.; Goto, M.

doi:10.1007/s11207-017-1062-y

Cited by 9 publications

(5 citation statements)

References 20 publications

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“…Using the wavelength variation of the birefringence (Chandrasekharan & Damany 1969;Laporte et al 1983) the phase retardation at 120.65nm is estimated to be 117°. Combining on-the-ground and in-flight polarization calibrations, the instrumental polarization was measured to be negligibly small compared to our requirement (Giono et al 2016a;Giono et al 2017). Hence we do not apply additional calibration to the demodulated data.…”

Section: Appendix Data Reductionmentioning

confidence: 83%

“…The spatial and spectral resolutions are estimated to be about 3″ and 0.01nm, respectively (Giono et al 2016b). Prior to the limb observation, CLASP conducted observations of the quiet Sun near the disk center for about 10s in order to have data suitable for an in-flight polarization calibration (Giono et al 2017). The Lyα spectra taken at theSun center were averaged along the slit, and the pixel of the line center of the spatially averaged Lyα line is set to 121.567nm.…”

Section: Clasp Observationsmentioning

confidence: 99%

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Indication of the Hanle Effect by Comparing the Scattering Polarization Observed by CLASP in the Lyα and Si iii 120.65 nm Lines

Ishikawa

Bueno

Uitenbroek

et al. 2017

ApJ

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The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding rocket experiment that has provided the first successful measurement of the linear polarization produced by scattering processes in the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In this paper, we report that the Si III line at 120.65nm also shows scattering polarization and we compare the scattering polarization signals observed in the Lyα and Si III lines in order to search for observational signatures of the Hanle effect. We focus on four selected bright structures and investigate how the U/I spatial variations vary between the Lyα wing, the Lyα core, and the Si III line as a function of the total unsigned photospheric magnetic flux estimated from Solar Dynamics Observatory/Helioseismic and Magnetic Imager observations. In an internetwork region, the Lyα core shows an antisymmetric spatial variation across the selected bright structure, but it does not show it in other more magnetized regions. In the Si III line, the spatial variation of U/I deviates from the above-mentioned antisymmetric shape as the total unsigned photospheric magnetic flux increases. A plausible explanation of this difference is the operation of the Hanle effect. We argue that diagnostic techniques based on the scattering polarization observed simultaneously in two spectral lines with very different sensitivities to the Hanle effect, like Lyα and Si III, are of great potential interest for exploring the magnetism of the upper solar chromosphere and transition region.

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Section: Appendix Data Reductionmentioning

confidence: 83%

Section: Clasp Observationsmentioning

confidence: 99%

Indication of the Hanle Effect by Comparing the Scattering Polarization Observed by CLASP in the Lyα and Si iii 120.65 nm Lines

Ishikawa

Bueno

Uitenbroek

et al. 2017

ApJ

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“…Observations at disk center were taken with the same instrumental configuration and observational strategy as for the limb observations, which allowed us to calibrate for spurious instrumental polarization (Manso )-a common strategy for inflight calibration even in modern spectropolarimeters (e.g., Giono et al 2017). Averaging over all the slit positions and wavelengths, we find negligible amounts of circular polarization and Stokes U , but a residual signal Q/I ∼ 0.005 (see Appendix).…”

Section: Limb and Disk-center Observationsmentioning

confidence: 94%

Spectropolarimetry of the Solar Mg II h and k Lines

Sainz

Alemán

Casini

et al. 2019

ApJ

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We report on spectropolarimetric observations across the Mg ii h and k-lines at 2800Å made by the Ultraviolet Spectrometer and Polarimeter onboard the Solar Maximum Mission satellite. Our analysis confirms the strong linear polarization in the wings of both lines observed near the limb, as previously reported, but also demonstrates the presence of a negatively (i.e., radially oriented) polarized signal between the two lines. We find evidence for fluctuations of the polarization pattern over a broad spectral range, resulting in some depolarization with respect to the pure scattering case when observed at very low spatial and temporal resolutions. This is consistent with recent theoretical modeling that predicts this to be the result of redistribution effects, quantum interference between the atomic levels of the upper term, and magneto-optical effects. A first attempt at a quantitative exploitation of these signals for the diagnosis of magnetic fields in the chromosphere is attempted. In active regions, we present observations of circular polarization dominated by the Zeeman effect. We are able to constrain the magnetic field strength in the upper active chromosphere using an analysis based on the magnetograph formula, as justified by theoretical modeling. We inferred a significantly strong magnetic field (∼ 500 G) at the 2.5 σ level on an exceptionally active, flaring region.

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“…Nevertheless, no measurement has been made for the Lyman-α line because the earth's atmosphere is opaque to this line and thus a measurement in space is necessary. Recently, the CLASP (Chromospheric Lyman-Alpha Spectro-Polarimeter) project has carried out a high-precision spectro-polarimetric observation by a sounding rocket for the first time [7] and succeeded in detecting significant polarization signals in the Lyman-α line [8]. Great efforts are now being made to understand the detected polarization signals [9][10][11] and to determine the magnetic field vectors in the chromosphere and transition region from them.…”

Section: Introductionmentioning

confidence: 99%

Analytical Solution of the Hanle Effect in View of CLASP and Future Polarimetric Solar Studies

Goto

Ishikawa

Iida

et al. 2019

Atoms

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We have solved a problem of the Hanle effect for the hydrogen Lyman- α line in an intuitive and straightforward way. The Stokes parameters amid an anisotropic radiation field and a magnetic field are derived as an analytical formula which enables us to conduct immediate analyses of observation data taken by spectro-polarimetry. The derived formula is, in particular, supposed to be used for the analysis of the data taken by CLASP (Chromospheric Lyman-Alpha Spectro-Polarimeter), which has aimed at measuring the linear polarization in the hydrogen Lyman- α line (121.6 nm) and then evaluating the magnetic field in the upper chromosphere and the transition region. The dependence of the Stokes parameters on the strength and direction of the magnetic field and on the observation angle is derived with our analytical model. The results show a satisfactory agreement with those of a more rigorous numerical calculation where the radiative transfer is taken into account and the consistency is assured between the anisotropic randiation field and the polarized atomic state.

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Polarization Calibration of the Chromospheric Lyman-Alpha SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV Range. Part II: In-Flight Calibration

Cited by 9 publications

References 20 publications

Indication of the Hanle Effect by Comparing the Scattering Polarization Observed by CLASP in the Lyα and Si iii 120.65 nm Lines

Indication of the Hanle Effect by Comparing the Scattering Polarization Observed by CLASP in the Lyα and Si iii 120.65 nm Lines

Spectropolarimetry of the Solar Mg II h and k Lines

Analytical Solution of the Hanle Effect in View of CLASP and Future Polarimetric Solar Studies

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