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    Rb-Rich Asymptotic Giant Branch Stars in the Magellanic Clouds

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    Date
    2009-11
    Author
    Garcia-Hernandez, D. A.
    Manchado, A.
    Lambert, David L.
    Plez, B.
    Garcia-Lario, P.
    D'Antona, F.
    Lugaro, M.
    Karakas, A. I.
    van Raai, M. A.
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    Abstract
    We present high-resolution (R similar to 60,000) optical spectra of a carefully selected sample of heavily obscured and presumably massive O-rich asymptotic giant branch (AGB) stars in the Magellanic Clouds. We report the discovery of strong Rb I lines at 7800 angstrom in four Rb-rich LMC stars at luminosities equal to or greater than the standard adopted luminosity limit for AGB stars (M(bol) similar to -7.1), confirming that "hot bottom burning" may produce a flux excess in the more massive AGB stars. In the SMC sample, just one of the five stars with M(bol) < -7.1 was detected in Rb; the other stars may be massive red supergiants. The Rb-rich LMC AGB stars might have stellar masses of at least similar to 6-7 M(circle dot). Our abundance analyses show that these Rb-rich stars are extremely enriched in Rb by up to 10(3)-10(5) times solar but seem to have only mild Zr enhancements. The high Rb/Zr ratios, if real, represent a severe problem for the s-process, even if the (22)Ne source is operational as expected for massive AGB stars; it is not possible to synthesize copious amounts of Rb without also overproducing Zr. The solution to the problem may lie with an incomplete present understanding of the atmospheres of luminous AGB stars.
    Department
    McDonald Observatory
    Subject
    nuclear reactions, nucleosynthesis, abundances
    stars: abundances
    stars: agb and post-agb
    stars: atmospheres
    stars: evolution
    stars:
    late-type
    long-period variables
    agb stars
    red giants
    lithium
    abundances
    enrichment
    evolution
    mass
    lmc
    astronomy & astrophysics
    URI
    http://hdl.handle.net/2152/42983
    Citation
    García-Hernández, D. A., Arturo Manchado, David L. Lambert, Bertrand Plez, Pedro Garcia-Lario, Francesca D'Antona, Maria Lugaro, A. I. Karakas, and M. A. Van Raai. "Rb-rich asymptotic giant branch stars in the Magellanic Clouds." The Astrophysical Journal Letters, Vol. 705, No. 1 (Nov., 2009): L31.
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