Abstract
The zero point of galaxy redshifts measured from objective prism plates (dispersion 246 nm/mm at Hγ) as part of the Muenster Redshift Project (MRSP) is obtained through transformation of object positions from the corresponding direct plate. Approximately 1000 G-type stars, classified automatically, are used. On the direct plate, positions are obtained from intensity-weighted first moments. On the objective prism plate, object positions are give through the CaII-break and marginal fits to the unwidened spectra. The transformation equations include quadratic terms in the direction of dispersion. The inclusion of third-order and colour terms is discussed. The mean residuals are approximately 0".33 (5 μm on the plate), corresponding to a redshift error of about 700 km/s at z=0.0. This error results mainly from the uncertainty in locating the CaII-break in the low-dispersion spectra. Radial velocities are obtained from the difference between the expected and the measured positions of the CaII-break in the galaxy spectra.
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