Defining the Termination of the Asymptotic Giant Branch

Abstract

I suggest a theoretical quantitative definition for the termination of the asymptotic giant branch (AGB) phase and the beginning of the post-AGB phase. I suggest that the transition will be taken to occur when the ratio of the dynamical time scale to the the envelope thermal time scale, Q, reaches its maximum value. Time average values are used for the different quantities, as the criterion does not refer to the short time-scale variations occurring on the AGB and post-AGB, e.g., thermal pulses (helium shell flashes) and magnetic activity. Along the entire AGB the value of Q increases, even when the star starts to contract. Only when a rapid contraction starts does the value of Q start to decrease. This criterion captures the essence of the transition from the AGB to the post AGB phase, because Q is connected to the stellar effective temperature, reaching its maximum value at T~4000-6000 K, it is related to the mass loss properties, and it reaches its maximum value when rapid contraction starts and envelope mass is very low.

Submitted to ApJ Letters

References in corpus (2)

• A spectroscopic atlas of post-AGB stars and planetary nebulae selected from the IRAS Point Source Catalogue
• An evolutionary catalogue of Galactic post-AGB and related objects

Cited by in corpus (6)

• On the role of recombination in common-envelope ejections
• Close stellar binary systems by grazing envelope evolution
• A Phenomenological Model for the Extended Zone Above AGB Stars
• A Red Giants' Toy Story
• Detailed spectroscopy of post-AGB supergiant GSC 04050$-$02366 in IRAS Z02229+6208 IR source system
• New in the optical spectrum and kinematic state of the atmosphere of the variable V1027\,Cyg (= IRAS 20004+2955)