Bibcode
Dell'Agli, F.; Ventura, P.; Schneider, R.; Di Criscienzo, M.; García-Hernández, D. A.; Rossi, C.; Brocato, E.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 447, Issue 4, p.2992-3015
Fecha de publicación:
3
2015
Número de citas
63
Número de citas referidas
56
Descripción
We calculated theoretical evolutionary sequences of asymptotic giant
branch (AGB) stars, including the formation and evolution of dust grains
in their circumstellar envelopes. By considering stellar populations of
the Large Magellanic Cloud (LMC), we calculate synthetic colour-colour
and colour-magnitude diagrams, which are compared with those obtained by
the Spitzer Space Telescope. The comparison between observations and
theoretical predictions outlines that extremely obscured carbon stars
and oxygen-rich sources experiencing hot bottom burning (HBB) occupy
well-defined, distinct regions in the colour-colour ([3.6] - [4.5],
[5.8] - [8.0]) diagram. The C-rich stars are distributed along a
diagonal strip that we interpret as an evolutionary sequence, becoming
progressively more obscured as the stellar surface layers enrich in
carbon. Their circumstellar envelopes host solid carbon dust grains with
size in the range 0.05 < a < 0.2 μm. The presence of silicon
carbide (SiC) particles is expected only in the more metal-rich stars.
The reddest sources, with [3.6] - [4.5] > 2, are the descendants of
stars with initial mass Min ˜ 2.5-3 M⊙
in the very latest phases of AGB life. The oxygen-rich stars with the
reddest colours ([5.8] - [8.0] > 0.6) are those experiencing HBB, the
descendants of ˜5 M⊙ objects formed 108
yr ago; alumina and silicate dust starts forming at different distances
from the central star. The overall dust production rate in the LMC is
˜4.5 × 10-5 M⊙ yr-1,
the relative percentages due to C and M stars being 85 and 15 per cent,
respectively.
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