The Secret X-ray Lives of Cepheids: Presenting the First Unambiguous X-ray Detections of Classical Cepheids

Details The Secret X-ray Lives of Cepheids: Presenting the First Unambiguous X-ray Detections of Classical Cepheids The Secret X-ray Lives of Cepheids: Presenting the First Unambiguous X-ray Detections of Classical Cepheids

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21343312e&link_type=abstract

American Astronomical Society, AAS Meeting #213, #433.12; Bulletin of the American Astronomical Society, Vol. 41, p.303

Astronomy and Astrophysics

Astronomy

4

Scientific paper

Chromospheric and transition region emissions have been found in certain Classical Cepheids by previous IUE studies and through our own much more recent FUSE study. However, X-ray emission has long been considered nonexistent in these cool supergiants. Here we report on the surprising discovery of X-ray emissions in three bright, nearby Classical Cepheids recently observed with the XMM-Newton and Chandra satellites - representing the first true detections of this class of variable star at X-ray wavelengths. Polaris (V = +1.98; F7 Ib-II; P = 3.97-d; d 130-pc), β Dor (V = +3.77; F6 Ia; P = 9.84-d; d 318-pc) and δ Cep (V = +4.07; F5 Iab; P = 5.37-d; d 273-pc) are currently the only three Cepheids to have been observed with modern X-ray satellites. However, only Polaris and β Dor have been observed with the FUSE satellite, and β Dor (which has multiple spectra) displays variability in the FUV emission strengths which appears to be correlated to its pulsation period. Unexpectedly, our early analyses of the X-ray data show that these Cepheids, despite their differences in spectral type and pulsation properties, all have log Lx values of 28.8-29 and similarly soft energy distributions. The initial results of our recent X-ray studies are presented along with our FUSE results to bring the high energy activity into better focus. Further FUV/X-ray observations have been proposed with HST/XMM to unambiguously determine the origin and nature of the observed high energy emissions from the targets, possibly arising from warm winds, shocks, or pulsationally induced magnetic activity. We gratefully acknowledge support for this project from NASA grants Chandra-GO6-7011A, 06-FUSE8-099 & XMM-AO7-55241 and NSF grant AST05-07542.

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