Modeling extinction and reddening effects by circumstellar dust in the Betelgeuse envelope in the presence of radiative torque disruption

TL;DR

This study models how radiative torque disruption alters circumstellar dust grain sizes around Betelgeuse, affecting observed extinction and flux, and provides insights into dust evolution in evolved star envelopes.

Contribution

It introduces a model incorporating RAT-D effects on dust grain size distribution, explaining observed extinction and flux variations in Betelgeuse's circumstellar environment.

Findings

Large grains are disrupted into smaller grains by RAT-D.

Extinction decreases in near-UV, optical, and IR, increases in far-UV.

Model reproduces observed flux from near-UV to near-IR.

Abstract

Circumstellar dust is formed and evolved within the envelope of evolved stars, including Asymptotic Giant Branch (AGB) and Red Supergiant (RSG). The extinction of stellar light by circumstellar dust is vital for interpreting RSG/AGB observations and determining high-mass RSG progenitors of core-collapse supernovae. Nevertheless, circumstellar dust properties are not well understood. Modern understanding of dust evolution suggests that intense stellar radiation can radically change the dust properties across the circumstellar envelope through the RAdiative Torque Disruption (RAT-D) mechanism. In this paper, we study the impacts of RAT-D on the grain size distribution (GSD) of circumstellar dust and model its effects on photometric observations of $\alpha$ Orionis (Betelgeuse). Due to the RAT-D effects, large grains formed in the dust formation zone are disrupted into smaller species of size $a < 0.5\,\rm\mu m$. Using the GSD constrained by the RAT-D effects, we model the visual extinction of background stars and Betelgeuse. We find that the extinction decreases at near-UV, optical, and infrared wavelengths while increasing at far-UV wavelengths. The resulting flux potentially reproduces the observation from the near-UV to near-IR range. Our results can be used to explain dust extinction and photometric observations toward other RSG/AGB stars.