Rb-RICH ASYMPTOTIC GIANT BRANCH STARS IN THE MAGELLANIC CLOUDS

Journal Article · Sun Nov 01 04:00:00 EST 2009 · Astrophysical Journal (Online)

DOI:https://doi.org/10.1088/0004-637X/705/1/L31· OSTI ID:21378415

GarcIa-Hernandez, D A; Manchado, A ^[1]; Lambert, D L ^[2]; Plez, B ^[3]; GarcIa-Lario, P ^[4]; D'Antona, F ^[5]; Lugaro, M ^[6]; Karakas, A I ^[7]

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1. Instituto de Astrofisica de Canarias, C/Via Lactea s/n, 38200 La Laguna (Spain)
2. W. J. McDonald Observatory, University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States)
3. GRAAL, Universite Montpellier 2, CNRS, Montpellier (France)
4. Herschel Science Centre, European Space Astronomy Centre, Research and Scientific Support Department of ESA, Villafranca del Castillo, P.O. Box 50727, E-28080 Madrid (Spain)
5. INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Roma (Italy)
6. Centre for Stellar and Planetary Astrophysics, Monash University, Clayton 3800, Victoria (Australia)
7. Research School of Astronomy and Astrophysics, Mt. Stromlo Observatory, Weston Creek ACT 2611 (Australia)

We present high-resolution (R approx 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 A in four Rb-rich LMC stars at luminosities equal to or greater than the standard adopted luminosity limit for AGB stars (M{sub bol} approx -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{sub 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 approx6-7 M{sub sun}. Our abundance analyses show that these Rb-rich stars are extremely enriched in Rb by up to 10{sup 3}-10{sup 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 {sup 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.

• OSTI ID: 21378415
• Journal Information: Astrophysical Journal (Online), Journal Name: Astrophysical Journal (Online) Journal Issue: 1 Vol. 705; ISSN 1538-4357
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
ASYMPTOTIC SOLUTIONS
ATMOSPHERES
EVEN-EVEN NUCLEI
EVOLUTION
GALAXIES
ISOTOPES
LIGHT NUCLEI
LUMINOSITY
MAGELLANIC CLOUDS
MASS
MATHEMATICAL SOLUTIONS
NEON 22
NEON ISOTOPES
NUCLEAR REACTIONS
NUCLEI
NUCLEOSYNTHESIS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
S PROCESS
STABLE ISOTOPES
STAR EVOLUTION
STARS
SYNTHESIS