Lecture 25. C. Cepheid Variables
Lecture 25. C. Cepheid Variables
Variables pulsate,
contracting and expanding
- contraction causes internal pressure increase
- pressure increase pushes back on infalling gas,
causes rebound
- rebounding gas overshoots equilibrium and gravity slows
- contraction begins, overshoots equilibrium
- goto step 1!
This behavior is "oscillation about equilibrium" --
just like a pendulum!
Brightening Mechanism
- as with Sun, light escapes from core over
> 106 years --
so core (fusion) does not change with oscillations
(days long)
- during contraction,
temperature is higher --
photons escape outer layers more easily in higher temps!
Cool
Cepheid web page!*
Q: Why aren't Cepheids plotted
on H-R diagrams?