Bibcode
Karakas, Amanda I.; García-Hernández, D. A.; Lugaro, Maria
Referencia bibliográfica
The Astrophysical Journal, Volume 751, Issue 1, article id. 8 (2012).
Advertised on:
5
2012
Revista
Número de citas
99
Número de citas referidas
81
Descripción
We present updated calculations of stellar evolutionary sequences and
detailed nucleosynthesis predictions for the brightest asymptotic giant
branch (AGB) stars in the Galaxy with masses between 5 M
&sun; and 9 M &sun;, with an initial
metallicity of Z = 0.02 ([Fe/H] = 0.14). In our previous studies we used
the Vassiliadis & Wood mass-loss rate, which stays low until the
pulsation period reaches 500 days after which point a superwind begins.
Vassiliadis & Wood noted that for stars over 2.5 M
&sun; the superwind should be delayed until P ≈ 750 days
at 5 M &sun;. We calculate evolutionary sequences where we
delay the onset of the superwind to pulsation periods of P ≈ 700-800
days in models of M = 5, 6, and 7 M &sun;. Post-processing
nucleosynthesis calculations show that the 6 and 7 M &sun;
models produce the most Rb, with [Rb/Fe] ≈1 dex, close to the average
of most of the Galactic Rb-rich stars ([Rb/Fe] ≈1.4 ± 0.8
dex). Changing the rate of the 22Ne +α reactions
results in variations of [Rb/Fe] as large as 0.5 dex in models with a
delayed superwind. The largest enrichment in heavy elements is found for
models that adopt the NACRE rate of the 22Ne(α,
n)25Mg reaction. Using this rate allows us to best match the
composition of most of the Rb-rich stars. A synthetic evolution
algorithm is then used to remove the remaining envelope resulting in
final [Rb/Fe] of ≈1.4 dex although with C/O ratios >1. We conclude
that delaying the superwind may account for the large Rb overabundances
observed in the brightest metal-rich AGB stars.
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