Infrared Two-Color Diagrams for AGB stars, post-AGB stars, and Planetary Nebulae

TL;DR

This study uses infrared two-color diagrams and radiative transfer models to analyze the evolution of AGB stars, post-AGB stars, and planetary nebulae, revealing their dust envelope structures and evolutionary pathways.

Contribution

It introduces a comprehensive analysis combining observational data and theoretical models to trace the evolution from AGB stars to planetary nebulae on IR 2CDs.

Findings

Theoretical dust shell tracks align with observed star populations.

End points of post-AGB models converge to PNe regions on 2CDs.

IR 2CDs reveal dust envelope evolution and star structure.

Abstract

We present various infrared two-color diagrams (2CDs) for AGB stars, post-AGB stars, and Planetary Nebulae (PNe) and investigate possible evolutionary tracks. We use catalogs from the available literature for the sample of 4903 AGB stars (3373 O-rich; 1168 C-rich; 362 S-type), 660 post-AGB stars (326 post-AGB; 334 pre-PNe), and 1510 PNe in our Galaxy. For each object in the catalog, we cross-identify the IRAS, AKARI, MSX, and 2MASS counterparts. The IR 2CDs can provide useful information about the structure and evolution of the dust envelopes as well as the central stars. To find possible evolutionary tracks from AGB stars to PNe on the 2CDs, we investigate spectral evolution of post-AGB stars by making simple but reasonable assumptions on the evolution of the central star and dust shell. We perform radiative transfer model calculations for the detached dust shells around evolving central stars in the post-AGB phase. We find that the theoretical dust shell model tracks using dust opacity functions of amorphous silicate and amorphous carbon roughly coincide with the densely populated observed points of AGB stars, post-AGB stars, and PNe on various IR 2CDs. Even though some discrepancies are inevitable, the end points of the theoretical post-AGB model tracks are generally converged to the region of the observed points of PNe on most 2CDs.