An infrared study of the remarkable dusty M star HR 3126

HR 3126 is a unique M giant star embedded in the bipolar reflection nebula IC 2220. Its evolutionary status is uncertain, and both the composition of the dust shell and the mechanism responsible for its ejection have proved controversial. In this paper we present new photometric and spectroscopic observations of HR 3126 and combine them with existing data from the literature in an extensive reappraisal of the star's properties at infrared wavelengths. The spectral energy distribution is consistent with an optical classification of M0-3 II with infrared excess. The dust shell cannot be fitted by a single-temperature blackbody: at least three components are required, with temperatures in the range 35-1300 K