Wave-Length Studies of Early Type Stars

Abstract

Measuring wave lengths on stellar spectrograms is essentially a question of determining accurately the position on the spectrogram of the stellar lines with respect to the position of lines in the comparison spectrum and interpolating for wave length. The plate to be measured is set on the table of a measuring machine and either viewed with a microscope or viewed by projection. A magnification of 20 to 50 is usually required. Position along the plate may be measured by counting the rotations of a long screw, 1 mm or 0.5 mm pitch, and using a divided head so that one can read to 0.001 unit, or by measuring against a fixed scale, as in an Abbe comparator.