KITP: white dwarfs

All day discussion on white dwarfs today: cooling, kinematics, destruction etc
Starts off with Lars tutoring us in the morning...

Basics:

white dwarf origins - they are degenerate burnt out cores of low-to-medium mass main seqeunce stars
key issues still not fully resolved:
what is the relationship between the main sequence initial mass and the white dwarf final mass?
to what extent does it depend on main sequence composition?
binary companion? formation of He core white dwarfs due to envelope stripping - see white dwarfs with He cores and masses less than 0.48 solar mass, so no He core burning
is it really a liner relationship?
if so, why are all local white dwarfs just over half a solar mass, except of course for Sirius B? is it just observational bias?

For solar composition, main sequence stars with initial mass less than 2.2 solar masses have passive degenerate helium cores that ignite at 0.48 solar masses - mild compositional dependence.

Mass loss on the RGB.
The structure of the horizontal branch/extended horizontal branch.
The Second Parameter
AAAAAARRRRRGGGGGGGHHHHHH!!!!!!!!!!
Phew. That felt better.

white dwarf structure - well that is simple, degenerate polytrope, going to fully relativistic in high mass limit; with some annoying atmospheric layers, H/He and settling
oh, and maybe crystalline as it cools - the heat capacity is anomalous due to coulomb correlations - NB electrons are degenerate and have negligible heat capacity
and magnetic fields...
He core vs C/O core vs O/Ne/Mg core

Helium white dwarfs have higher heat capacity but start off at lower temperatures
their hydrogen content is poorly constrained - might be ongoing slow fusion in He white dwarfs, which would make them look younger than the look
probably the case that if M_He,core > 0.2 M_solar then any residual hydrogen burns through CNO cycle in a few unstable pulses, down to at least 10^-4 solar masses of H. No stable burning solutions - have to burn up H or regrow RGB envelope. Always left tiny bit of H at the end?
For lower mass He white dwarfs, there is stable pp cycle fusion and the white dwarf cooling slows down around 10,000K Teff and it lingers for Gyrs at anomalously high temperatures and luminosities.
We should see those in the CMDs as pile up in the effective temperture curve, if a lot of these are made in globulars.

white dwarfs galore

ionization state, DA vs DB vs DZ
Cooling, role of opacity at low temperatures
red white dwarfs that are blue in the red

heat sources - accretion: slow burning