Polarization of Coronal Forbidden Lines

Abstract

Since the magnetic field is responsible for most manifestations of solar activity, one of the most challenging problems in solar physics is the diagnostics of solar magnetic fields, particularly in the outer atmosphere. To this end, it is important to develop rigorous diagnostic tools to interpret polarimetric observations in suitable spectral lines. This paper is devoted to analyzing the diagnostic content of linear polarization imaging observations in coronal forbidden lines. Although this technique is restricted to off-limb observations, it represents a significant tool to diagnose the magnetic field structure in the solar corona, where the magnetic field is intrinsically weak and still poorly known. We adopt the quantum theory of polarized line formation developed in the framework of the density matrix formalism, and synthesize images of the emergent linear polarization signal in coronal forbidden lines using potential-field source-surface magnetic field models. The influence of electronic collisions, active regions, and Thomson scattering on the linear polarization of coronal forbidden lines is also examined. It is found that active regions and Thomson scattering are capable of conspicuously influencing the orientation of the linear polarization. These effects have to be carefully taken into account to increase the accuracy of the field diagnostics. We also found that linear polarization observation in suitable lines can give valuable information on the long-term evolution of the magnetic field in the solar corona.

From polarimetry to helicity: Studies of solar magnetic fields at the Huairou Solar Observing Station

“…• Measurements of magnetic fields in the corona: The Hanle effect is a reduction in the polarization of light when the atoms emitting the light are subject to a magnetic field in a particular direction, and when they have themselves been excited by polarized light. The Hanle effects with polarized light in the corona is notable question for the measure- [92][93][94]. The analysis of the polarized lights due to the Hanle effect for the diagnostic of the coronal magnetic field is still a challenging topic [1].…”

The COMBS Survey – III. The chemodynamical origins of metal-poor bulge stars

“…We incorporate non-LTE (NLTE) line formation for a number of elements using grids of departure coefficients. We use all grids available with SME v574 which includes lithium (Li;Lind et al 2009), oxygen (O; Amarsi et al 2016), Na (Lind et al 2011), magnesium (Mg;Osorio et al 2015), Al (Nordlander & Lind 2017), silicon (Si; Amarsi & Asplund 2017), calcium (Ca; Mashonkina et al 2008), titanium (Ti;Sitnova et al 2020), Fe (Amarsi et al 2016) and Ba (Mashonkina et al 2008).…”

Observations of the solar corona during the total solar eclipse on 21 August 2017

“…On the other hand, measurements of linear polarization of some coronal emission lines have been used to map the direction of coronal magnetic fields in the plane of sky (Tomczyk et al, 2008). It has also been demonstrated that the Hanle effect, a process involving modification of polarization by magnetic fields, could be powerful to diagnose the weak magnetic fields in the upper solar atmosphere (e.g., Trujillo Bueno et al, 2002; Li H et al, 2017). All these techniques require a precise measurement of polarization of coronal emission lines (e.g., Qu ZQ et al, 2009, 2017).…”