Dissecting the Spitzer color-magnitude diagrams of extreme LMC AGB stars

Abstract

We trace the full evolution of low- and intermediate-mass stars ($1M_{\odot }\le M\le 8M_{\odot }$) during the Asymptotic Giant Branch (AGB) phase in the {\it Spitzer} two-color and color-magnitude diagrams. We follow the formation and growth of dust particles in the circumstellar envelope with an isotropically expanding wind, in which gas molecules impinge upon pre--existing seed nuclei, favour their growth. These models are the first able to identify the main regions in the {\it Spitzer} data occupied by AGB stars in the Large Magellanic Cloud (LMC). The main diagonal sequence traced by LMC extreme stars in the [3.6]-[4.5] vs. [5.8]-[8.0] and [3.6]-[8.0] vs. [8.0] planes are nicely fit by carbon stars models; it results to be an evolutionary sequence with the reddest objects being at the final stages of their AGB evolution. The most extreme stars, with [3.6]-[4.5] $>$ 1.5 and [3.6]-[8.0] $>$ 3, are 2.5-3 $M_{\odot }$ stars surrounded by solid carbon grains. In higher mass ($>3M_{\odot }$) models dust formation is driven by the extent of Hot Bottom Burning (HBB) - most of the dust formed is in the form of silicates and the maximum obscuration phase by dust particles occurs when the HBB experienced is strongest, before the mass of the envelope is considerably reduced.

5 pages, 2 figures, accepted for publication in MNRAS Letters

References in corpus (8)

• Spitzer SAGE survey of the Large Magellanic Cloud II: Evolved Stars and Infrared Color Magnitude Diagrams
• Rubidium-Rich Asymptotic Giant Branch Stars
• AGB stars in the Magellanic Clouds. II. The rate of star formation across the LMC
• Lithium and zirconium abundances in massive Galactic O-rich AGB stars
• The Mass-Loss Return From Evolved Stars to the LMC: Empirical Relations for Excess Emission at 8 and 24 μm
• Dust-driven Winds and Mass Loss of C-rich AGB Stars with subsolar Metallicities
• The Mass-Loss Return from Evolved Stars to the Large Magellanic Cloud IV: Construction and Validation of a Grid of Models for Oxygen-Rich AGB Stars, Red Supergiants, and Extreme AGB Stars
• Discovery of Extreme Carbon Stars in the Large Magellanic Cloud

Cited by in corpus (13)

• Circumstellar Dust Around AGB Stars and Implications for Infrared Emission from Galaxies
• Studying the evolution of AGB stars in the Gaia epoch
• The evolution of Galactic planetary nebula progenitors through the comparison of their nebular abundances with AGB yields
• Understanding the evolution and dust formation of carbon stars in the LMC with a look at the JWST
• AGB dust and gas ejecta in extremely metal-poor environments
• New Post-AGB star models as tools to understand AGB evolution and nucleosynthesis
• Understanding dust production and mass loss on the AGB phase using post-AGB stars in the Magellanic Clouds
• The Infrared Massive Stellar Content of M83
• Discovery of stars surrounded by iron dust in the LMC
• The intense production of silicates during the final AGB phases of intermediate mass stars
• Characterization of M-stars in the LMC in the JWST era
• A study of oxygen-rich post-AGB stars in the Milky Way to understand the production of silicates from evolved stars
• Gas and dust from extremely metal-poor AGB stars