c0c05w311y wrote:Some questions about variable stars and related topics:
1. What is the mechanism of variability for classical cepheid stars? Name the specific process/mechanism and explain what it is.
2. What determines whether a section of a star is primarily convective or radiative? Which sections of high/low mass stars are convective/radiative?
3. How is it possible for LBV stars to exceed their Eddington luminosity?
4. What principle is the Eddington Luminosity based on? How do you calculate the Eddington luminosity?
5. What are the two instability strips on the HR diagram, and what kinds of stars are found in each?
This thread has been dead for far too long.
1. I don't know how to write greek letters here, but its called the kappa mechanism, Kappa denotes opacity here. basically, because of compression (decrease of volume) in the stellar atmosphere, increase in temperature and pressure occurs, which ionizes He I to He II, which is more opaque. This means that the He II absorbs radiation, making it hotter. In turn, this will expand the star, make it cooler, since it will radiate more energy away. Since it's cooler, the He II takes an electron and becomes He I, which is transparent, and lets light through. Then, since it isn't as hot, it will shrink again, and process repeats.
2. Mass. High mass stars have convective cores, and radiative envelope (don't know if that's the right word). This is the opposite in lower mass stars.
3.I'm not sure how correct this is, but I believe that the Eddington luminosity talk about the brightest a
stable object without losing mass. LBVs are unstable, and when they do exceed the Eddington Luminosity, LBV stars are shedding a significant amount of mass, and are unstable.
4.The Eddington Luminosity is the theoretical maximum luminosity of a hydrostatically stable object. (It is the luminosity that an object would have to be to generate enough outward force to match/exceed gravitational force) It is calculated by setting the outward force to the gravitational force and solving for luminosity.
5.I thought there was only one instability strip, and so I don't know the answer to this one. I'm still posting though, to revive this thread.