[astrophysics] Will the Sun have a RGB/Horizontal Branch phase?

[EDG]

Following on from a question I asked ages ago here ( http://www.bautforum.com/space-astro...ion-grids.html ) I'm a bit perplexed by the latest Stellar Evolution Grids (the ones by A. Claret, 2004).

Stars from 0.8 to 2.0 solar masses don't appear to have an RGB branch in those grids. The 2.0 one sorta has a Horizontal Branch (you can see it if you plot Age vs L), but there isn't the big spike in luminosity before that, which one would expect to see if it had a proper RGB phase.

The other grids I was using before (by Schaerer, 1993) didn't have these phases for the lower mass stars either. However, grids by Charbonnel (VI, 1996) did have a horizontal branch and RGB phase for stars between 0.8 and 1.7 solar masses.

So presumably these stars do have HB and RGB phases, but if they do then why don't the major evolution grids show them?! Does it happen so quickly for a 2.0 solar mass star that it's been and gone between timesteps? Are there any more complete grids for these stars beyond the ones found at http://cdsarc.u-strasbg.fr/viz-bin/q...stellar+models ?

[EDG]

To illustrate, here's the Age vs Luminosity plot for the 2.0 solar mass star, and the one below it is the same plot for the 2.5 solar mass star. The first little peak on the 2.5 solar mass graph is the RGB phase, note that it's missing on the 2.0 solar mass graph (there's a tiny kink there though, is that where it's supposed to be?).

[EDG]

And here's the 2.5 solar mass star:

[EDG]

And to answer my own question, Claret didn't extend the grids to the HB/AGB phases for the lower mass stars (not sure why). Oh well, I'll just use the old ones then.

[Ken G]

It sounds like you know as much about the issue as any of us. Stellar evolution codes are very "black boxy", so detailed differences between them could be traced to any of a number of assumptions made. A more reliable answer would probably come from observational data, when available, though there are difficulties in obtaining enough data and knowing the abundances, ages, distances, and so forth. One has to trust the modelers to describe the differences in their results, relative to previous models and the existing observations, and if they don't, then their results are not worth a whole lot.