COMMUNICATIONS / MITTEILUNGEN

B. Szeidl and Hamid A. Mahdy

Period Changes in Dwarf Cepheids, II. YZ Bootis, XX Cygni and DY Herculis

No. 75
Budapest, 1981

Abstract

The period changes in the dwarf cepheids YZ Boo, XX Cyg and DY Her are discussed and O-C diagrams of these stars are constructed. The period of XX Cyg changed abruptly in 1942 (deltaP= +87 x 10^-9 day = +0.0075 sec). Besides the sudden increase of the period, it has also shown small fluctuations. With regard to YZ Boo there may be a slight continuous increase (at a rate Beta = + 10.6 x 10^-13 day cycle^-1 = + 3.2 x 10^-2 sec century^-1) in its period. The period of DY Her has shown a definite continuous decrease at a rate Beta = -37.2 x 10^-13 day cycle^-1 = -7.9 x 10^-2 sec century^-1 during the time interval covered by photoelectric observations (1951-1979).

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