The dusty envelopes of asymptotic giant branch stars with ultraviolet excesses

TL;DR

This study characterizes the dust and gas components of circumstellar envelopes around 29 UV-excess AGB stars, analyzing their properties and effects on UV emission to enhance understanding of their mass-loss processes.

Contribution

It provides a combined analysis of dust and gas in AGB star envelopes, including modeling spectral energy distributions and assessing dust attenuation effects on UV emission.

Findings

Mass-loss rates and gas-to-dust ratios are typical for AGB stars.

An anticorrelation exists between gas-to-dust ratio and UV emission.

Dust attenuation significantly affects observed UV emission.

Abstract

Aims. In a first study, we characterised the properties of the gas component in the circumstellar envelopes surrounding a sample of 29 AGB stars with UV excesses. Now we intend to complement this information with an analysis of the dust component and compare the estimated parameters with those previously inferred from larger samples of AGB stars. Methods. We modelled the spectral energy distributions of the sample using dust radiative transfer models. In some cases, we complemented the analysis with Herschel/PACS radial surface brightness profiles. Results. We derived mass-loss rates and gas-to-dust ratios, which are in the typical ranges for AGB stars. We found that the stellar and mass-loss parameters follow similar trends than those presented in the literature. There is an anticorrelation between the gas-to-dust ratio and the UV emission, although it is weaker than its correlations with pulsation and mass-loss. We also estimated the dust attenuation produced by the dust at UV wavelengths and describe its effects on the intrinsic UV emission. Conclusions. Stellar and mass-loss parameters of UV emitting AGB stars follow similar trends as found for larger samples of AGB stars. High-angular resolution observations are required to explore the dust forming regions and identify the presence of stellar companions. Circumstellar dust attenuation might play a dominant role in the observed UV emission, and needs to be accounted to estimate the intrinsic UV emission.