Technetium and the third dredge up in AGB stars. I. Field stars

• Published in: arXiv.org
• Main Authors: Lebzelter, T, Hron, J
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 01.10.2003
• Subjects: Astronomical models; Asymptotic giant branch stars; Line spectra; Luminosity; Mass distribution; Stellar evolution; Stellar luminosity; Technetium
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.0310018

We searched for Tc in a sample of long period variables selected by stellar luminosity derived from Hipparcos parallaxes. Tc, as an unstable s-process element, is a good indicator for the evolutionary status of stars on the asymptotic giant branch (AGB). In this paper we study the occurrence of Tc as a function of luminosity to provide constraints on the minimum luminosity for the third dredge up as estimated from recent stellar evolution models. A large number of AGB stars above the estimated theoretical limit for the third dredge up are found not to show Tc. We confirm previous findings that only a small fraction of the semiregular variables show Tc lines in their spectra. Contrary to earlier results by Little et al. (1987) we find also a significant number of Miras without Tc. The presence and absence of Tc is discussed in relation to the mass distribution of AGB stars. We find that a large fraction of the stars of our sample must have current masses of less than 1.5 M_{\sun}. Combining our findings with stellar evolution scenarios we conclude that the fraction of time a star is observed as a SRV or a Mira is dependent on its mass.