Observations of the forward scattering Hanle effect in the Ca i 4227 Å line

Abstract

Chromospheric magnetic fields are notoriously diffcult to measure. The chromospheric lines are broad, while the fields are producing a minuscule Zeeman-effect polarization. A promising diagnostic alternative is provided by the forward-scattering Hanle effect, which can be recorded in chromospheric lines such as the He i 10830 Å and the Ca i 4227 Å lines. We present a set of spectropolarimetric observations of the full Stokes vector obtained near the center of the solar disk in the Ca i 4227 Å line with the ZIMPOL polarimeter at the IRSOL observatory.We detect a number of interesting forward-scattering Hanle effect signatures, which we model successfully using polarized radiative transfer. Here we focus on the observational aspects, while a separate companion paper deals with the theoretical modeling.

4 pages, 5 figures, to be published as a Letter in Astronomy & Astrophysics

References in corpus (1)

• Scattering Polarization of the Ca II IR Triplet for Probing the Quiet Solar Chromosphere

Cited by in corpus (10)

• Solar magnetic fields as revealed by Stokes polarimetry
• Chromospheric diagnosis with Ca II lines: forward modeling in forward scattering (I)
• Center to limb observations and modeling of the Ca I 4227 A line
• Modeling the scattering polarization of the solar Ca i 4227 Å line with angle-dependent partial frequency redistribution
• Solar disk center shows scattering polarization in the Sr I 4607 Å line
• Spatio-temporal evolution of Hanle and Zeeman synthetic polarization in a chromospheric spectral line
• Optimal spectral lines for measuring chromospheric magnetic fields
• Hanle rotation signatures in Sr I 4607 Å
• The key role of solar dynamics in the chromospheric Hanle polarization
• Collisional effects on the formation of the second solar spectrum of the Sr {\sc ii} $\lambda$4078 line