Diagnostic of spectral lines in magnetized solar atmosphere: Formation of the Hβ line in sunspots

Abstract

Formation of the H$\beta$ $\lambda$4861.34 \AA{} line is an important topic related to the diagnosis of the basic configuration of magnetic fields in the solar and stellar chromospheres. Specifically, broadening of the H$\beta$ $\lambda$4861.34 \AA{} line occurs due to the magnetic and micro-electric fields in the solar atmosphere. The formation of H$\beta$ in the model umbral atmosphere is presented based on the assumption of non-local thermodynamic equilibrium. It is found that the model umbral chromosphere is transparent to the Stokes parameters of the H$\beta$ line, which implies that the observed signals of magnetic fields at sunspot umbrae via the H$\beta$ line originate from the deep solar atmosphere, where $\lg \tau_c\approx-1$ (about 300 km in the photospheric layer for our calculations). This is in contrast to the observed Stokes signals from non-sunspot areas, which are thought to primarily form in the solar chromosphere.