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eJAAVSO

Stellar Photometry Using Old Photographic Plates

 

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A. Davis

K. Barkume

C. Springob

F. Tam

V. Strelnitski

Maria Mitchell Observatory, 3 Vestal Street, Nantucket, MA 02554

 

Received June 21, 2004; revised September 13, 2004

 

Abstract  The precision of various methods of stellar photometry on old photographic plates is investigated using the original plates or their digitized copies from the plate collection of the Maria Mitchell Observatory (MMO). It is shown, in particular, that the simple and fast method of eye photometry is comparable in precision to the traditional “objective” methods using a microphotometer to measure the plates or image analysis software to measure digital copies of small parts of the plates obtained with a CCD camera. All these methods provide photometric accuracy of ±0.1–0.2 magnitude on the MMO plates. It is demonstrated that the high-performance commercially available scanner AgfaScan T5000 used for plate digitization at the MMO produces images that can be measured to a considerably higher precision of ±0.05 magnitude, which is sufficient for most purposes of photographic stellar photometry. The results of this investigation may be of interest to those who use old plates for stellar photometry, as well as to those who look for an adequate, fast, and relatively inexpensive scanner to digitize their plate archive.

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