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Post Info TOPIC: Low-Mass Stars
Blobrana


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Title: Elemental abundances of low-mass stars in nearby young associations: AB Doradus, Carina Near, and Ursa Major
Authors: K. Biazzo (1), V. D'Orazi (2,4), S. Desidera (3), E. Covino (1), J. M. Alcalá (1), M. Zusi (1) ((1) INAF - Capodimonte Astronomical Observatory, Italy, (2) Department of Physics and Astronomy, Macquarie University, Australia, (3) INAF - Padova Astronomical Observatory, Italy, (4) Monash Centre for Astrophysics, Australia)

We present stellar parameters and abundances of 11 elements (Li, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, and Zn) of 13 F6-K2 main-sequence stars in the young groups AB Doradus, Carina Near, and Ursa Major. The exoplanet-host star \iota Horologii is also analysed.
The three young associations have lithium abundance consistent with their age. All other elements show solar abundances. The three groups are characterised by a small scatter in all abundances, with mean [Fe/H] values of 0.10 (\sigma=0.03), 0.08 (\sigma=0.05), and 0.01 (\sigma=0.03) dex for AB Doradus, Carina Near, and Ursa Major, respectively. The distribution of elemental abundances appears congruent with the chemical pattern of the Galactic thin disc in the solar vicinity, as found for other young groups. This means that the metallicity distribution of nearby young stars, targets of direct-imaging planet-search surveys, is different from that of old, field solar-type stars, i.e. the typical targets of radial velocity surveys.
The young planet-host star \iota Horologii shows a lithium abundance lower than that found for the young association members. It is found to have a slightly super-solar iron abundance ([Fe/H]=0.16±0.09), while all [X/Fe] ratios are similar to the solar values. Its elemental abundances are close to those of the Hyades cluster derived from the literature, which seems to reinforce the idea of a possible common origin with the primordial cluster.

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Blobrana


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Posts: 131433
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Title: A New Twist In the Evolution of Low-Mass Stars
Authors: Pavel A. Denissenkov (University of Victoria)

We show that the evolutionary track of a low-mass red giant should make an extended zigzag on the Hertzsprung-Russel diagram just after the bump luminosity, if fast internal rotation and enhanced extra mixing in the radiative zone bring the temperature gradient close to the adiabatic one. This can explain both the location and peculiar surface chemical composition of Li-rich K giants studied by Kumar, Reddy, & Lambert (2011). We also discuss a striking resemblance between the photometric and composition peculiarities of these stars and giant components of RS CVn binaries. We demonstrate that the observationally constrained values of the temperature gradient in the Li-rich K giants agree with the required rate of extra mixing only if the turbulence which is believed to be responsible for this extra mixing is highly anisotropic, with its associated transport coefficients in the horizontal direction strongly dominating over those in the vertical direction.

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