The Kinematical Behaviour of the Plasma Tail of Comet Tago-Sato- Kosaka 1969 IX

Summary. 20 pictures of Comet Tago-Sato-Kosaka, taken on 4 days between January 5 and 12, 1970 with the Hamburg Schmidt-telescope of Boyden Observatory, and 4 exposures made with the Curtis Schmidt telescope at Cerro Tololo (Chile) were used for an analysis of the kinematical behaviour of the tail material. The aberration angles between the tail and the comet- sun-line were brought into connection with the solar wind parameters taken from Satellite observations and geophysical data. The following main results could be deduced: 1) The motion of ion structures which could be identified on consecutive plates was in all cases directed parallel or nearly parallel to the tail axis. 2) The velocities of the structures were lower in the inner parts of the tail close to the axis (between 40 and 100 km/s) than in the outer parts (up to 300 km/s). The mean values were different on the four days, slightly decreasing from January 5 to January 12. Accelerations could not be deduced in the central parts of the tail, because of the large scatter of the values, whereas in the outer parts the velocities showed a more systematical increase. 3) Of the overall structure visible on the Boyden films of Jan. 10.8, only a few pronounced condensations could be identified after 7 hours on a Cerro Tololo plate while turbulence and diffusion had destroyed most of the characteristic features. A comparison with the Cerro Tololo exposures taken 18 hours earlier did not allow any identification, indicating that the life time of the ion structures was in the range of several hours to 1/2 day This is in accordance with observations in other comets. 4) In a detailed analysis it is shown that the measured aberration angles between the tail axis and the radius vector are compatible with a tangential component of the solar wind velocity up to 20 km/s, while the assumption of a purely radial solar wind flow leads on some days to solar wind velocities incompatible with the geophysical and satellite data. Key words: comets - ionized tail velocities - solar wind