White dwarfs and the age of the universe

[ceimeifukan]

Hi,

I'm doing a bit of research into white dwarfs and cosmochronology as part of my uni course, it seems like a fantasticaly interesting field but I've got a couple of questions which i haven't yet been able to find answers to.

Firstly, several papers i have read refer to a luminosity of log(L/Lsolar) = -4.5 when referring to ages on a luminosity/Age graph. I assume this is reffering to a specific point at which stars with a lower luminosity have not been found and so corresponds to the oldest stars?

Secondly I am unclear about the conditions which lead to convection zones being formed in the envelope and what governs their progression through the atmosphere to the degenerate core. I understand the effect they have on the overall cooling rates but not why they should only be present below specific temperatures.

If anybody could shine any light on these i would be in your debt

Many thanks Phil

 

[Aaron Bex]

Hi Phil,

It sounds like you're doing some really interesting research! Regarding the first question, I believe the log(L/Lsolar) = -4.5 is used to represent the oldest stars because stars with a lower luminosity have not been found. As for the second question, convection zones in white dwarf atmospheres are formed when the temperature of the atmosphere drops below a certain critical temperature. The convection zone then progresses through the atmosphere until it reaches the degenerate core. Hope this helps!