Cepheids and X-ray emission. The study “X-rays in Cepheids: XMM-Newton Observations of η Aql” of N. R. Evans (SAO-CfA) recently appeared on AJ
Cepheids are stars of great importance, since they allow to determine the distance of galaxies within a few hundreds of million of light years from us. This is due to the pulsations that characterize these giant stars, which are going through an instable phase of their evolution. Because of these pulsations, the luminosity of these stars varies with a period
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