Detached Shell Carbon Stars: Tracing Thermal Pulses on the Asymptotic Giant Branch

  • Datum: –16.00
  • Plats: Online, Zoom
  • Föreläsare: Joel Kastner, Rochester Institute of Technology, USA
  • Arrangör: Avdelningen för astronomi och rymdfysik, institutionen för fysik och astronomi
  • Kontaktperson: Sofia Ramstedt
  • Seminarium

I present new results concerning the subset of carbon-rich asymptotic giant branch (AGB) stars that exhibit detached, expanding circumstellar shells (Kastner & Wilson 2021, ApJ, in press; arxiv:2108.08940). In particular, we consider whether the presence of detached shells may reveal the past histories of these carbon stars as having undergone helium shell flashes (thermal pulses) on the AGB. We exploit newly available Gaia parallaxes and photometry, along with archival infrared photometry, to obtain refined estimates of the luminosities of all (12) known detached shell carbon stars. We examine the relationship between these luminosities and the estimated dynamical ages (ejection times) of the detached shells associated with the 12 stars, which range up to ~30000 yr. When arranged according to detached shell dynamical age, the (implied) luminosity evolution of the known detached shell carbon stars closely follows the predicted ``light curves'' of individual thermal pulses obtained from models of AGB stars. The comparison between data and models suggests that detached shell carbon stars are descended from ~2.5-4.0 M_sun progenitors. We conclude that detached shell carbon stars may serve as effective tracers of the luminosity evolution of AGB thermal pulses, and comment on various implications of these results for intermediate-mass stellar evolution.



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