Bibcode
Ventura, P.; Karakas, A. I.; Dell'Agli, F.; García-Hernández, D. A.; Boyer, M. L.; Di Criscienzo, M.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 457, Issue 2, p.1456-1467
Advertised on:
4
2016
Número de citas
28
Número de citas referidas
26
Descripción
The stars in the Magellanic Clouds with the largest degree of
obscuration are used to probe the highly uncertain physics of stars in
the asymptotic giant branch (AGB) phase of evolution. Carbon stars in
particular provide key information on the amount of third dredge-up and
mass-loss. We use two independent stellar evolution codes to test how a
different treatment of the physics affects the evolution on the AGB. The
output from the two codes is used to determine the rates of dust
formation in the circumstellar envelope, where the method used to
determine the dust is the same for each case. The stars with the largest
degree of obscuration in the Large Magellanic Cloud (LMC) and Small
Magellanic Cloud (SMC) are identified as the progeny of objects of
initial mass 2.5-3 M⊙ and ˜1.5 M⊙,
respectively. This difference in mass is motivated by the difference in
the star formation histories of the two galaxies, and offers a simple
explanation of the redder infrared colours of C-stars in the LMC
compared to their counterparts in the SMC. The comparison with the
Spitzer colours of C-rich AGB stars in the SMC shows that a minimum
surface carbon mass fraction X(C) ˜ 5 × 10-3 must
have been reached by stars of initial mass around 1.5 M⊙.
Our results confirm the necessity of adopting low-temperature opacities
in stellar evolutionary models of AGB stars. These opacities allow the
stars to obtain mass-loss rates high enough (≳10-4
M⊙ yr-1) to produce the amount of dust needed
to reproduce the Spitzer colours.