On the possible mechanism of formation of emission rim in hydrogen filaments

Hα filtergrams of the chromosphere show an emission rim in many hydrogen filaments. We suppose that formation of this rim is due to photospheric radiation reflected by the filament in the direction of the chromosphere. The calculations show that: (1) the maximum contrast of the rim relative to the undisturbed chromosphere amounts to 1.4; (2) the larger the optical thickness of the filament and the closer to the solar limb it is situated, the brighter and wider is the rim; (3) the rim was not observed in filaments whose heights exceeds 10000km above the chromosphere. These results are in close agreement with observations.