The Periods of NS and EP Cygni

Volume 20 number 1 (1991)

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David J. Reiss

Maria Mitchell Observatory, Nantucket, MA 02554

Abstract

An examination of photographic plates at the Maria Mitchell Observatory reveals that times and maxima of NS Cygni, an RR-Lyrae variable, cannot be represented by a single linear set of elements; the period of this star has changed at least three times between 1930 and 1990. It has returned at least once to a previous period, years after it had changed. Elements valid for 1983-1990 are: JD_max = 2447220.6414 + 0.5503287 E. The period of EP Cygni, a Cepheid variable, has remained constant. Revised elements, valid for 1967-1990, are: JD_max = 2444003.096 + 4.288963 E.