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

TL;DR

This study investigates whether detached shell carbon stars can reveal the thermal pulse history of AGB stars by analyzing their luminosities and shell ages, finding a close match with theoretical models of thermal pulse evolution.

Contribution

The paper demonstrates that detached shell carbon stars' luminosity evolution aligns with thermal pulse models, suggesting they are effective tracers of AGB thermal pulse history.

Findings

Luminosity evolution of detached shell carbon stars matches thermal pulse models.

Detached shell carbon stars likely originate from 2.5-4.0 solar mass progenitors.

These stars can serve as tracers for AGB thermal pulse evolution.

Abstract

We consider whether the subset of carbon-rich asymptotic giant branch (AGB) stars that exhibit detached, expanding circumstellar shells may reveal the past histories of these 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 from $\sim$1000 to $\sim$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 $\sim$2.5-4.0 $M_\odot$ progenitors. We conclude that detached shell carbon stars may serve as effective tracers of the luminosity evolution of AGB thermal pulses.