X-Rays from Cepheids: Why?
- 1. Harvard-Smithsonian Center for Astrophysics
- 2. Villanova University
- 3. University of Toronto
- 4. MIT
- 5. Iowa State University
- 6. National and Kapodistrian University of Athens
Description
Recent Chandra and XMM X-ray observations have found a burst of X-rays at the surprising phase just after maximum radius. At this phase the photospheric spectrum is indistinguishable from a non-variable supergiant. Significant photospheric disruptions, however, are seen just after minimum radius, as the pulsation wave generated lower in the envelope passes through. The X-ray burst is thought to be caused either from by a shock in the pulsation process or a flare, possibly triggered by the collapse of the atmosphere. We present a first examination of these possibilities by calculating the energy ranges and timescales for each mechanism. A flare-like event is expected to have a strong dependence on local magnetic field strength and present a more rapid energy release due to reconnection. Finally, we estimate how much a hydrodynamic and magnetohydrodynamic compression wave propagating outward in a stratified medium, such as the stellar coronae, could heat the ambient material.
Files
CoolStars20Cepheids.pdf
Files
(2.9 MB)
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