Astronomy and Astrophysics, volume 564, L4-4 (2014/4-1)
Circumstellar effects on the Rb abundances in O-rich AGB stars.
ZAMORA O., GARCIA-HERNANDEZ D.A., PLEZ B. and MANCHADO A.
Abstract (from CDS):
For the first time we explore the circumstellar effects on the Rb (and Zr) abundance determination in O-rich asymptotic giant branch (AGB) stars by considering the presence of a gaseous circumstellar envelope with a radial wind. A modified version of the spectral synthesis code Turbospectrum was used to deal with extended atmosphere models and velocity fields. The Rb and Zr abundances were determined from the resonant 7800Å Rb I line and the 6474Å ZrO bandhead, respectively, in five representative O-rich AGB stars with different expansion velocities and metallicities. By using our new dynamical models, the Rb I line profile (photospheric and circumstellar components) is very well reproduced. Interestingly, the derived Rb abundances are much lower (by 1-2dex) in those O-rich AGB stars showing the higher circumstellar expansion velocities. The Zr abundances, however, remain close to the solar values. The Rb abundances and [Rb/Zr] ratios derived here significantly resolve the problem of the present mismatch between the observations of intermediate-mass (4-8M☉) Rb-rich AGB stars and the AGB nucleosynthesis theoretical predictions.