Photofission production of technetium and synthetic asymptotic giant branch evolution

John C. Lattanzio, Robert A. Malaney

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We carry out synthetic asymptotic giant branch (AGB) evolution calculations in order to investigate further the recent suggestion that detectable quantities of technetium could be produced in the atmospheres of AGB stars following the photofission of any actinide isotopes intially present. We find that any technetium so produced can only become detectable when the envelope mass is reduced below about 0.2 MO, which corresponds to the final stage of the star's evolution on the AGB. We estimate that stars with masses (at the first thermal pulse) in the range 1-2 MO are most likely to give rise to a detectable technetium abundance when values of Mbol between -4.5 and -6 are reached. We note that this coincides with the Mira phase of evolution, where most of the stellar technetium detections are made. Although some quantitative differences between this photofission production theory and observation may exist, we argue that more serious difficulties are associated with an s-process production mechanism for technetium. We present possible observational tests which can discriminate between the photofission and s-process production of technetium based on the abundances of 99Tc and 93Zr. We conclude that the mere detection of technetium in AGB stars cannot be regarded as irrefutable proof of a recent s-process episode. This will be especially true as future detectors allow for ever-increasing sensitivity in the detection of stellar technetium.

Original languageEnglish
Pages (from-to)989-997
Number of pages9
JournalThe Astrophysical Journal
Publication statusPublished - 15 Dec 1989
Externally publishedYes


  • Nucleosynthesis
  • Stars: Abundances
  • Stars: Evolution
  • Stars: Interiors
  • Stars: Long-period variables

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