X-rays from Cepheid Upper Atmospheres
Abstract
The Cepheid pulsation cycle is driven by a wave generated in the envelope. As the wave passes through the photosphere and chromosphere at minimum radius there are many signatures of the disturbance, such as ultraviolet lines in emission and an increase in microturbulence. At this phase, however, X-rays have a low level of flux which lasts through most of the cycle. However a burst of X-ray flux occurs just after maximum radius, with a rapid rise, short duration and rapid fall similar to a stellar flare. So far observations have provided 4 examples of this, including two cycles of for Delta Cep itself. This appears to be driven by the pulsation process since it is linked to a specific phase. This is estimated to be about 0.13 stellar radii above the photosphere and may be related to the circumstellar envelopes found via interferometry, at higher levels particularly in the infrared. These new upper atmosphere diagnostics may ultimately answer questions about possible pulsation driven mass-loss.
- Publication:
-
American Astronomical Society Meeting Abstracts #231
- Pub Date:
- January 2018
- Bibcode:
- 2018AAS...23114609E