Unraveling the Dusty Environment Around RT Vir

TL;DR

This study models the dusty environment of RT Vir, an oxygen-rich AGB star, revealing two distinct dust shells with different compositions and temperatures, shedding light on dust formation processes in such stars.

Contribution

First detailed radiative transfer modeling of RT Vir's circumstellar dust shells using multi-source infrared data, identifying two distinct dust formation epochs.

Findings

Two distant, cool dust shells with different compositions identified

Inner shell contains silicates, Al2O3, FeO, Fe; outer shell mainly crystalline Al2O3

Dust formation influenced by stellar pressure-temperature conditions or C/O ratio changes

Abstract

Infrared studies of asymptotic giant branch (AGB) stars are critical to our understanding of the formation of cosmic dust. In this investigation, we explore the mid-to-far-infrared emission of oxygen rich AGB star RT Virginis. This optically thin dusty environment has unusual spectral features when compared to other stars in its class. To explore this enigmatic object we use the 1-D radiative transfer modeling code DUSTY. Modeled spectra are compared with observations from the Infrared Space Observatory (ISO), InfraRed Astronomical Satellite (IRAS), the Herschel Space Observatory and a host of other sources to determine the properties of RT Vir's circumstellar material. Our models suggest a set of two distant and cool dust shells at low optical depths (tauV,inner = 0.16, tauV,outer = 0.06), with inner dust temperatures: T1 = 330K, T3 = 94K. Overall, these dust shells exhibit a chemical composition consistent with dust typically found around O-rich AGB stars. However, the distribution of materials differs significantly. The inner shell consists of a mixture of silicates, Al2O3, FeO, and Fe, while the outer shell primarily contains crystalline Al2O3 polymorphs. This chemical change is indicative of two distinct epochs of dust formation around RT Vir. These changes in dust composition are driven by either changes in the pressure-temperature conditions around the star, or by a decrease in the C/O ratio due to hot-bottom burning.