the Production of The Spectroheiiogram of Solar D₂ Line

Spectroheliographic scanning (i.e. Spectroheliogram) is an interesting effective observational means. The photography has been adopted for local regions of the Solar disc on the Na line (NaID₂5890Å) of a 40-cm horizontal spectrogaph of Yunnan Observatory.The basic principle is that the camera in the line focal plane of the spectrograph should make the stable homogeneous synchronous movement in the same direction as the solar image in the telescope focal plane (i. e. the incident slit plane). Therefore, a spectroheliograph, which is used to control the movement of the camera, by the mechanical speed changes of a synchronous motor, is used to substitute for the original photographic device of Na bands. The slit of the spectroheliograph is aligned with the line core of D₂ and move in the line dispersion direction. The micrometer screw, which is located on the mirror mounting in front of the incident slit of the spectrograph and enables the mirror to turn round the vertical center, is driven by a stepping motor so that the solar image can make transverse movement perpendicular to the optical axis. The stepping motor works in double triple-time and the circuit consists of a pulser, a commutator distributar and a power amplifier. The whole control unit enables the solar image and the camera to move syschronously in the same direction.The test indicates that the instrument is in better state (the parameters are stable and the synchronous performance is better). Under the mesoclimate conditions, in the active region data obtained the distinguishable details may be at least 4"~5" and the inhomogeneous structure surrounding the active region can be resolved.