2010ApJ...725.2392M

We present the discovery of an infrared nebula around the Cepheid prototype δ Cephei and its hot companion HD 213307. Large-scale (∼2.1x10⁴ AU) nebulosity is detected at 5.8, 8.0, 24, and 70 µm. Surrounding the two stars, the 5.8 and 8.0 µm emission is largely attributable to polycyclic aromatic hydrocarbon emission swept from the interstellar medium by a wind originating from δ Cephei and/or its companion. Stochastically heated small dust grains are the most likely source of the 24 and 70 µm extended emission. The 70 µm emission, in particular, resembles a bow shock aligned in the direction of the proper motion of δ Cephei. This discovery supports the hypothesis that δ Cephei may be currently losing mass, at a rate in the range of ~5x10^–9 to 6x10^–8 M_☉/yr.