Resolving the dusty circumstellar environment of the A[e] supergiant HD 62623 with the VLTI/MIDI

TL;DR

This study used VLTI/MIDI observations and radiative transfer modeling to resolve and characterize the dusty circumstellar disk of the B[e] supergiant HD 62623, providing new constraints on its inner rim and environment.

Contribution

First detailed modeling of the dusty disk inner rim of a supergiant B[e] star using interferometric data and radiative transfer analysis.

Findings

The dusty environment is partially resolved and consists of a compact disk and an extended component.

The disk has an inner radius of approximately 3.85 AU and is inclined at about 60 degrees.

The gaseous inner envelope contributes significantly to the IR flux and influences the disk structure.

Abstract

B[e] stars are hot stars surrounded by circumstellar gas and dust responsible for the presence of emission lines and IR-excess in their spectra. How dust can be formed in this highly illuminated and diluted environment remains an open issue. HD 62623 is one of the very few A-type supergiants showing the B[e] phenomenon. We obtained nine calibrated visibility measurements using the VLTI/MIDI instrument in SCI-PHOT mode and PRISM spectral dispersion mode with projected baselines ranging from 13 to 71 m and with various position angles. We used geometrical models and physical modeling with a radiative transfer code to analyze these data. The dusty circumstellar environment of HD 62623 is partially resolved by the VLTI/MIDI even with the shortest baselines. The environment is flattened and can be separated into two components: a compact one whose extension grows from 17 mas at 8 microns to 30 mas at 9.6 microns and stays almost constant up to 13 microns, and a more extended one that is over-resolved even with the shortest baselines. Using the radiative transfer code MC3D, we managed to model HD 62623's circumstellar environment as a dusty disk with an inner radius of 3.85+-0.6 AU, an inclination angle of 60+-10 deg, and a mass of 2x10^-7Mo. It is the first time that the dusty disk inner rim of a supergiant star exhibiting the B[e] phenomenon is significantly constrained. The inner gaseous envelope likely contributes up to 20% to the total N band flux and acts like a reprocessing disk. Finally, the hypothesis of a stellar wind deceleration by the companion's gravitational effects remains the most probable case since the bi-stability mechanism does not seem to be efficient for this star.