A search for polarization in Ellerman bombs

Abstract

Ellerman bombs, also called ‘moustaches’, are transient brightenings at tiny (< 1 arc sec) points in the lower chromosphere whose spectra are characterized by elongated emission wings on the hydrogen Balmer lines. Babin and Koval recently found linear polarization as high as 20% in bombs, but no physical process that could produce such a high degree of polarization was suggested. A new observational study of polarization in Ellerman bombs is reported here. Images of 32 bombs were obtained with a digital video system viewing the Sun through a 6 Å filter at the Sacramento Peak Vacuum Tower Telescope. A novel polarizing beamsplitter divided each image into two interleaved polarized components which passed simultaneously through a single set of optics and were separated only during data analysis. The sensitivity threshold of the measurements was ∼ 1%. In 4 cases out of 32, linear polarization above 2% was detected. The higher incidence of > 2% polarization reported by Babin and Koval is not confirmed.