Theoretical AGB and post-AGB Models for Synthetic Population Studies

Near the end of their evolution, moderate-mass stars
(approximatively between 1 and 8 solar masses) go through the
asymptotic giant branch (AGB) phase. The AGB and the transition to
the ensuing post-AGB are very time (both computational and human)
consuming to simulate. Hence, large grids of models originating
from detailed calculations are rare; only few stars are generally
computed. Some stellar libraries have nonetheless been constituted
in the past. These are very sought-after by population synthesis
modelers, as they try to reproduce observed properties of larger
stellar systems by assembling together many individual models.
However such AGB and post-AGB grids can rapidly become outdated
because of constant input-physics ameliorations. So-called
synthetic AGB models are a solution as they are computationally
less time demanding: nonetheless their major drawback is that they
remain approximations. In this context, new detailed models for
stars of 1 to 6 solar masses, and compositions with a total heavy
element content that corresponds to values between a fortieth and a
double of the solar one (for two different relative scalings), have
been computed. They evolve through all stellar phases from the main
sequence to the white dwarf stage; here focus is on the AGB and
post-AGB parts. The parameter space coverage is comparable only
with the latest synthetic grids, as none of the previous detailed
stellar libraries extend over such wide mass/metallicity intervals.
Furthermore, the most recent physics, relevant for the AGB and
post-AGB, are included. These updates, at the level of
sophistication brought by this work, are present neither in
synthetic nor in any detailed computations. Because they are of
paramount importance, their inclusion is the major asset of this
work. Specifically, three updates have been implemented: a) new
chemistry-dependent low-temperature opacities b) up-to-date
chemistry-dependent mass-loss prescriptions c) convective
overshooting. With overshooting, envelope mixing will be more
efficient and dredge-up additional material from deeper layers. The
stellar surface will thus be converted from an oxygen- to a
carbon-rich one, and changes will directly affect the opacities and
in turn the mass-loss rates. While ignored in previous models,
these transformations are now taken into account. We show, how such
amendments were a necessity by comparing the results with older
grids, and how models are in agreement, without any prior
calibration, with observations. The new stellar library contains
100 AGB and 60 post-AGB sequences. The AGB tracks cover the entire
parameter space. Post-AGB models are also available for the full
metallicity range but, because of convergence issues, only for star
between 1 and 2 solar masses. To our knowledge this work provides
the scientific community with the most up-to-date, self-consistent
and extended grid, originating from detailed AGB and post-AGB
models. It is expected to be a valuable input-tool for population
synthesis work and aims to supersede the more than 10-year old
outdated tracks that are currently still being used