AAS 195th Meeting, January 2000
Session 75. Intrinsic Variable Stars
Display, Friday, January 14, 2000, 9:20am-6:30pm, Grand Hall

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[75.11] Period Changes in DY Pegasi and CY Aquarii

M.D. Joner, E.G. Hintz, P.B. Warner, L.R. Schwendiman (Brigham Young University)

Since the work of Mahdy & Szeidl (1980) the nature of period changes in the dwarf Cepheid star DY Pegasi have been debated. In the Mahdy & Szeidl paper the period changes were fit by two linear relations centered on a period break, but the possibility of a constant period changed was also mentioned. Pena & Peniche (1986) preferred a constant period change, but the errors did not provide a clear choice for this decision. We report 46 new times of maximum light for DY Peg. From all archival and new times of maximum light we find that DY Peg has experienced a second period break. The best fit solution to all observed times of maximum light is three linear segments. This is similar to the period changes reported by Powell et.al. (1995) for CY Aquarii. We also report new times of maximum light for CY Aqr that support the conclusions of Powell et al. (1995).

Finally, we report on the multi-periodic nature of DY Peg. >From high quality CCD observations we find amplitude variations in the light curve of DY Peg. These results are confirmed by simultaneous observations from two separate telescope/CCD systems.

We acknowledge the support of the Department of Physics & Astronomy, along with the work of many undergraduate observers.

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