Testing Evolutionary Models with Observations of Galactic Bulge AGB Stars

Details Testing Evolutionary Models with Observations of Galactic Bulge AGB Stars Testing Evolutionary Models with Observations of Galactic Bulge AGB Stars

Apr 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aipc.1001..313u&link_type=abstract

IXTH TORINO WORKSHOP ON EVOLUTION AND NUCLEOSYNTHESIS IN AGB STARS AND THE IIND PERUGIA WORKSHOP ON NUCLEAR ASTROPHYSICS. AIP C

Astronomy and Astrophysics

Astrophysics

Stellar Structure, Interiors, Evolution, Nucleosynthesis, Ages, Giant And Subgiant Stars, Abundances, Chemical Composition, Galactic Center, Bar, Circumnuclear Matter, And Bulge

Scientific paper

We performed spectroscopic observations of a sample of oxygen-rich long-period AGB variables in the outer Galactic Bulge and use these data to test evolutionary models of the AGB phase in various respects.
The detection of the radioactively unstable element technetium (Tc) can be used to test model predictions for the onset of the third dredge-up (3DUP) mixing episode. No Tc-rich stars below the predicted lower luminosity limit for 3DUP are found, confirming this limit. From the luminosity of the least luminous Tc-rich star the minimum core mass required for 3DUP is estimated from our observations.
Surprisingly, lithium (Li) was detected in some of our sample stars. The occurrence of this fragile element is interpreted as the result of an ``extra mixing'' process going on between the convective envelope and the H-burning shell. We propose the name ``Extended Envelope Mixing'' for this phenomenon. An estimate for the mass circulation rate for the most Li-rich sample star is given, and considerations about extra mixing and 3DUP are made.
Finally, we were also able to measure the abundance of fluorine (F) in one of the sample stars, and conclude that F is produced only in small quantities in low-mass AGB stars, as predicted by theoretical models.

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