High-resolution H alpha observations of proper motion in NOAA 8668: Evidence for filament mass injection by chromospheric reconnection

There have been two different kinds of explanations for the source of cool material in prominences or filaments: coronal condensations from above and cool plasma injections from below. In this paper, we present observational results which support filament mass injection by chromospheric reconnection . The observations of an active filament in the active region NOAA 8668 wer e performed on 17 August 1999 at a wavelength of H alpha -0.6 Angstrom usin g the 65 cm vacuum reflector, a Zeiss H alpha birefringent filter, and a 12 -bit SMD digital camera of Big Bear Solar Observatory. The best image was s elected every 12 s for an hour based on a frame selection algorithm. All th e images were then co-aligned and corrected for local distortion due to the seeing. The time-lapse movie of the data shows that the filament was under going ceaseless motion. The H alpha flow field has been determined as a fun ction of time using local correlation tracking. Time-averaged flow patterns usually trace local magnetic field lines, as inferred from H alpha fibrils and line-of-sight magnetograms. An interesting finding is a transient flow field in a system of small H alpha loops, some of which merge into the fil ament. The flow is associated with a cancelling magnetic feature which is l ocated at one end of the loop system. Initially a diverging flow with speed s below 10 km s(-1) is visible at the flux cancellation site. The flow is s oon directed along the loops and accelerated up to 40 km s(-1) in a few min utes. Some part of the plasma flow then merges into and moves along the fil ament. This kind of transient flow takes place several times during the obs ervations. Our results clearly demonstrate that reconnection in the photosp here and chromosphere is a likely way to supply cool material to a filament , as well as re-organizing the magnetic field configuration, and, hence, is important in the formation of filaments.