A red supergiant nebula at 25 micron: arcsecond scale mass-loss asymmetries of mu Cep

TL;DR

This study uses high-resolution infrared imaging to reveal a circumstellar nebula around mu Cep, showing asymmetries and suggesting a steady mass-loss process over the past millennium.

Contribution

First detailed infrared imaging of mu Cep's circumstellar environment revealing asymmetries and modeling its mass-loss history.

Findings

Detected a 6" radius nebula at 25 microns not seen at shorter wavelengths.

Model indicates constant mass-loss rate of a few times 10^(-7) Msun/yr over 1000 years.

Nebula morphology transitions from spherical at large scales to asymmetric closer in.

Abstract

We present diffraction limited (0.6") 24.5micron Subaru/COMICS images of the red supergiant mu Cep. We report the detection of a circumstellar nebula, that was not detected at shorter wavelengths. It extends to a radius of at least 6" in the thermal infrared. On these angular scales, the nebula is roughly spherical, in contrast, it displays a pronounced asymmetric morphology closer in. We simultaneously model the azimuthally averaged intensity profile of the nebula and the observed spectral energy distribution using spherical dust radiative transfer models. The models indicate a constant mass-loss process over the past 1000 years, for mass-loss rates a few times 10^(-7) Msun/yr. This work supports the idea that at least part of the asymmetries in shells of evolved massive stars and supernovae may be due to the mass-loss process in the red supergiant phase.