Detalles de publicación
PP 019018
Exploring circumstellar effects on the lithium and calcium abundances in massive Galactic O-rich AGB stars
(1) Instituto de Astrofísica de Canarias (IAC), (2) Universidad de La Laguna (ULL), (3) Laboratoire Univers et Particules de Montpellier, (4) Consejo Superior de Investigaciones Científicas (CSIC), (5) Monash Centre for Astrophysics, (6) Konkoly Observatory
We previously explored the circumstellar effects on the Rb and Zr abundances in a sample (21) of massive Galactic O-rich
asymptotic giant branch stars. Here we are interested in clarifying the role of the extended atmosphere in the case of Li and Ca. Li is
an important indicator of hot bottom burning while the total Ca abundances in these stars could be affected by neutron captures.
We report new Li and Ca abundances in a larger sample (30) of massive Galactic O-rich asymptotic giant branch stars by
using more realistic extended model atmospheres. The Li abundances were previously studied with hydrostatic models, while the Ca
abundances have been determined here for the first time.
We use a modified version of the spectral synthesis code Turbospectrum and consider the presence of a gaseous circumstellar
envelope and radial wind in the modelling of the spectra of these massive asymptotic giant branch stars. The Li and Ca abundances
are obtained from the 6708 Å Li I and 6463 Å Ca I resonance lines, respectively. In addition, we study the sensitivity of the pseudo-
dynamical models to variations of the stellar and wind parameters.
The Li abundances derived with the pseudo-dynamical models are very similar to those obtained from hydrostatic models
(the average difference is 0.18 dex, σ 2 = 0.02), with no difference for Ca. This indicates that the Li and Ca content in these stars
is only slightly affected by the presence of a circumstellar envelope. We also found that the Li I and Ca I line profiles are not very
sensitive to variations of the model wind parameters.
The new Li abundances confirm the Li-rich (and super Li-rich, in some cases) nature of the sample stars, supporting
the activation of hot bottom burning in massive Galactic asymptotic giant branch stars. This is in good agreement with the theoretical
predictions for solar metallicity asymptotic giant branch models from ATON, Monash, and NuGrid/MESA but is at odds with the
FRUITY database, which predicts no hot bottom burning leading to the production of Li. Most (20) sample stars display nearly
solar (within the estimated errors and considering possible non-local thermodynamic equilibrium effects) Ca abundances that are
consistent with the available s-process nucleosynthesis models for solar metallicity massive asymptotic giant branch stars, which
predict overproduction of 46Ca relatively to the other Ca isotope and the creation of the radiactive isotope 41Ca (half life of 0.1 Myr)
but no change in the total Ca abundance. A minority (5) of the sample stars seem to show a significant Ca depletion (by up to 1.0 dex).
Possible explanations are offered to explain their apparent and unexpected Ca depletion.
asymptotic giant branch stars. Here we are interested in clarifying the role of the extended atmosphere in the case of Li and Ca. Li is
an important indicator of hot bottom burning while the total Ca abundances in these stars could be affected by neutron captures.
We report new Li and Ca abundances in a larger sample (30) of massive Galactic O-rich asymptotic giant branch stars by
using more realistic extended model atmospheres. The Li abundances were previously studied with hydrostatic models, while the Ca
abundances have been determined here for the first time.
We use a modified version of the spectral synthesis code Turbospectrum and consider the presence of a gaseous circumstellar
envelope and radial wind in the modelling of the spectra of these massive asymptotic giant branch stars. The Li and Ca abundances
are obtained from the 6708 Å Li I and 6463 Å Ca I resonance lines, respectively. In addition, we study the sensitivity of the pseudo-
dynamical models to variations of the stellar and wind parameters.
The Li abundances derived with the pseudo-dynamical models are very similar to those obtained from hydrostatic models
(the average difference is 0.18 dex, σ 2 = 0.02), with no difference for Ca. This indicates that the Li and Ca content in these stars
is only slightly affected by the presence of a circumstellar envelope. We also found that the Li I and Ca I line profiles are not very
sensitive to variations of the model wind parameters.
The new Li abundances confirm the Li-rich (and super Li-rich, in some cases) nature of the sample stars, supporting
the activation of hot bottom burning in massive Galactic asymptotic giant branch stars. This is in good agreement with the theoretical
predictions for solar metallicity asymptotic giant branch models from ATON, Monash, and NuGrid/MESA but is at odds with the
FRUITY database, which predicts no hot bottom burning leading to the production of Li. Most (20) sample stars display nearly
solar (within the estimated errors and considering possible non-local thermodynamic equilibrium effects) Ca abundances that are
consistent with the available s-process nucleosynthesis models for solar metallicity massive asymptotic giant branch stars, which
predict overproduction of 46Ca relatively to the other Ca isotope and the creation of the radiactive isotope 41Ca (half life of 0.1 Myr)
but no change in the total Ca abundance. A minority (5) of the sample stars seem to show a significant Ca depletion (by up to 1.0 dex).
Possible explanations are offered to explain their apparent and unexpected Ca depletion.