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Studies of Yellow Semiregular(SRd) Variables

Percy, John R.; Kolin, David L.

We have used the Hipparcos database of epoch photometry to study the variability of several yellow semiregular(SRd) variables. For some of the stars (V847 Cas, RW Cep, BM Sco, CE Vir), the results were inconclusive. For SX Lac and TY Vir, the periods found were consistent with the General Catalogue of Variable Stars (190 and 50 days respectively).…

Period Changes in Population II Cepheids: TX Del and W Vir

Percy, John R.; Hoss, Jonathan X.

We have used the Hipparcos database of epoch photometry to study the variability of two Population II Cepheids: TX Del and W Vir. We have constructed (O-c) diagrams for these stars, using the new data and data from the literature. The period of TX Del is decreasing, at a rate which is consistent with evolutionary predictions. THe periodchange of W…