Harvard Plate Stacks MC Series Notes

Harvard-Smithsonian Center for Astrophysics
Harvard Observatory Plate Stacks
MC Series Notes

This instrument, the most powerful refractors in the northern station up to 1936, is especially valuable for faint objects where the large scale is of benefit. When the plates are used for photometric purposes it is well to take precautions, since the color coefficient is large and the distance correction is both large and variable from one plate to another. The images are usually beautiful, so that accidental errors will be minimized when working with MC plates; but systematic errors depending on color and position in the field should be carefully guarded against. Photometry of extended objects (such as nebulae) is safer than the photometry of focal images.

The instrument was refigured after about 3500 plates have been taken; the distance correction was thereby diminished, but the color coefficient was practically unchanged. In general, it is well to avoid plates taken before the re-figuring for accurate photometric work. All plates subsequent to MC 4171 were taken with the curved plate holder, which demonstrates [sic? diminishes?] the distance correction due to curvature of the field, but there is still a certain variation from plate to plate. These plates are to be preferred to previous ones, because of their smaller distance corrections, but it is inadvisable for precise photometry to work far from the center of an MC plate. [Doesn't that sound familiar?]

Excellent plates may be found, both blue and yellow, both single and in series with the Pole and the Harvard Standard Regions [these are regularly photographed regions with many variable stars]. In addition, a few red plates, both single, and in series with the Pole, may be found for certain regions. Note that there exists extensive material for the determination of photo visual sequences, especially for long period variables.