A Red Supergiant Nebula at 25 μm: Arcsecond-Scale Mass-Loss Asymmetries of μ Cephei

Abstract

We present diffraction-limited (0.6'') 24.5 μm Subaru COMICS images of the red supergiant μ Cep. We report the detection of a circumstellar nebula, which 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 (SED) using spherical dust radiative transfer models. The models indicate a constant mass-loss process over the past 1000 years, for mass-loss rates of a few × 10−7 M☉ yr−1. 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.