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

Abstract

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.

arXiv comment10 pages, 4 figures, accepted for publication in A&A

References in corpus (9)

• Nucleosynthesis and mixing on the Asymptotic Giant Branch. III. Predicted and observed s-process abundances
• s-Process Nucleosynthesis in AGB Stars: A Test for Stellar Evolution
• s-Process Nucleosynthesis in Carbon Stars
• Reprocessing the Hipparcos data for evolved stars III Revised Hipparcos period-luminosity relationship for galactic long-period variable stars
• Towards the absolute planes: a new calibration of the Bolometric Corrections and Temperature scales for Population II Giants
• Synthetic Spectra and Color-Temperature Relations of M Giants
• Hipparcos red stars in the HpV_{T2} and VI_C systems
• Long Period Variable Stars: galactic populations and infrared luminosity calibrations
• AGB Stars: Summary and Warning

Cited by in corpus (15)

• Carbon and oxygen isotopic ratios for nearby miras
• Technetium and the third dredge up in AGB stars II. Bulge stars
• AGB stars of the intermediate-age LMC cluster NGC 1846 II. Dredge up along the AGB
• Fundamental parameters of 16 late-type stars derived from their angular diameter measured with VLTI/AMBER
• CRIRES-POP: A library of high resolution spectra in the near-infrared
• Inner dusty envelope of the AGB stars W~Hydrae, SW\,Virginis, and R~Crateris using SPHERE/ZIMPOL
• Interplay between pulsation, mass loss, and third dredge-up: More about Miras with and without technetium
• Correlation between technetium and lithium in a sample of oxygen-rich AGB variables
• Period -- mass-loss rate relation of Miras with and without technetium
• Galactic vs. Extragalactic Origin of the Peculiar Transient SCP 06F6
• The impact of third dredge-up on the mass loss of Mira variables
• Spectral analysis of the barium central star of the planetary nebula Hen 2-39
• TYC 8606-2025-1: a mild barium star surrounded by the ejecta of a very late thermal pulse
• Millimetre observations of the S-type AGB star $\chi$ Cygni: variability of the emission of the inner envelope
• Technetium-rich M Stars: Prime diagnostics of recent third dredge-up events on the Asymptotic Giant Branch