The Secret (X-ray) Lives of Cepheids: Probing the "Warm" Coronae of Cepheids

In this pilot study, XMM observations of the bright Cepheids Polaris, delta Cep, beta Dor and l Car will solve two important recently uncovered puzzles. FUSE spectra of Polaris and beta Dor display prominent emission lines of C III and O VI from hot plasma with T up to at least ~500,000 K. Moreover, the presence of strong emissions in the FUV (IUE/SWP) spectra of all four targets (C III, C IV and, in some cases, He II) makes a strong case that X-ray emitting plasmas may also be present. The contention that Cepheids are X-ray sources is further supported by their possible detections in the Copernicus archives (using the UCLXE instrument). Also, our recent Chandra observation discovered Polaris to be a soft X-ray source, but possibly contaminated by a nearby, early-mid dF companion.