Observations on spatial variations of the Sr~{\sc i} 4607~Å~scattering polarization signals at different limb distances with ZIMPOL

Abstract

The Sr~{\sc i} 4607~Å spectral line shows one of the strongest scattering polarization signals in the visible solar spectrum. The amplitude of this polarization signal is expected to vary at granular spatial scales, due to the combined action of the Hanle effect and the local anisotropy of the radiation field. Observing these variations would be of great interest because it would provide precious information on the small-scale activity of the solar photosphere. At present, few detections of such spatial variations have been reported. This is due to the difficulty of these measurements, which require combining high spatial ($\sim$ 0.1"), spectral ($\le$ 20 mÅ), and temporal resolution (< 1 min) with increased polarimetric sensitivity ($\sim$ 10${}^{-}$${}^4$). Aims. We aim to detect spatial variations at granular scales of the scattering polarization peak of the Sr~{\sc i} 4607~Å line at different limb distances, and to study the correlation with the continuum intensity. Methods.Using the Zurich IMaging POLarimeter (ZIMPOL) system mounted at the GREGOR telescope and spectrograph in Tenerife, Spain, we carried out spectro-polarimetric measurements to obtain the four Stokes parameters in the Sr~{\sc i} line at different limb distances, from $\mu =0.2$ to $\mu =0.8$, on the solar disk. Results.Spatial variations of the scattering polarization signal in the Sr~{\sc i} 4607~Å line, with a spatial resolution of about 0.66", are clearly observed at every $\mu$. The spatial scale of these variations is comparable to the granular size. A statistical analysis reveals that the linear scattering polarization amplitude in this Sr~{\sc i} spectral line is positively correlated with the intensity in the continuum, corresponding to the granules, at every $\mu$.

arXiv comment8 pages, 6 figures, accepted for publication in A&A

References in corpus (6)

• A Substantial Amount of Hidden Magnetic Energy in the Quiet Sun
• A novel investigation of the small-scale magnetic activity of the quiet Sun via the Hanle effect in the Sr I 4607 Å line
• High-resolution, high-sensitivity, ground-based solar spectropolarimetry with a new fast imaging polarimeter
• The Scattering Polarization of the Sr I 4607 ÅLine at the Diffraction Limit Resolution of a 1-m Telescope
• Spatial variations of the Sr i 4607 Å scattering polarization peak
• Detection of spatially structured scattering polarization of Sr I $4607.3$ Å\ with the Fast Solar Polarimeter

Cited by in corpus (8)

• The European Solar Telescope
• GREGOR: Optics Redesign and Updates from 2018-2020
• Solar disk center shows scattering polarization in the Sr I 4607 Å line
• Mapping the hidden magnetic field of the quiet Sun
• Observational indications of magneto-optical effects in the scattering polarization wings of the Ca I 4227 Å line
• The impact of limited time resolution on the forward-scattering polarization in the solar Sr I 4607 Å line
• Assessment of the CRD approximation for the observer's frame RIII redistribution matrix
• Observational insights into Sr I 4607 Å scattering polarization with DKIST/ViSP