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The Periods of NS and EP Cygni


David J. Reiss

Maria Mitchell Observatory, Nantucket, MA 02554


Received: August 7, 1991




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.


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