Issue |
A&A
Volume 430, Number 3, February II 2005
|
|
---|---|---|
Page(s) | 1035 - 1047 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20041347 | |
Published online | 26 January 2005 |
Time dependent mixing in He-burning cores: The case of NGC 1866
Osservatorio Astronomico di Roma, via Frascati, 33 00040 MontePorzio Catone, Italy e-mail: [ventura;m.castellani]@mporzio.astro.it
Received:
25
May
2004
Accepted:
26
September
2004
We examine the helium burning phase of the convective core of
intermediate
mass stars, and investigate the role of the coupling of nuclear burning
and mixing on the extension and duration of the blue loop phase.
We compare the theoretical scenario with the distribution of stars
in the colour–magnitude (CM) diagram of the Large Magellanic
Cloud (LMC) cluster NGC 1866, whose densely populated clump of He-burning
stars is equally populated on the blue and red side.
We compare the distributions expected by adopting either
a diffusive scheme within the instability
regions, in which nuclear burning and mixing are self-consistently coupled, or the traditional
instantaneous mixing approximation.
We analyze with particular care the sensitivity of the results to:
a) the e-folding distance with which
the velocity of convective eddies decays outside the formal border of
the convective regions fixed by the Schwarzschild criterion;
b) the convective model adopted to evaluate the temperature
gradient; c) the rate of reaction O.
Models not including convective overshoot are also commented.
Key words: stars: evolution / stars: interiors / stars: Hertzprung Russell (HR) and C-M diagrams
© ESO, 2005
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