The spectral energy distribution and mass-loss history of IRC + 10420

Abstract

We present a study of the spectral energy distribution of the peculiar hypergiant IRC + 10420. To this end we have collected published photometry of IRC + 10420 and obtained some new data, in order to construct the spectral energy distribution and fit it with a radiative transfer model. In addition high-quality (CO)-C-12 spectra of the rotational J=1-0, 2-1, 3-2 and 4-3 transitions have been obtained to determine the gas outflow velocity and independently estimate the gas mass-loss rate. The main conclusions from this work are that the photometric changes over the last 20 years indicate that the object has increased in temperature by more than 1000 K and that the spectral energy distribution cannot be fitted with a single-shell model without first including a hot component. This hot component is likely to be a circumstellar disc. Finally, we present evidence that IRC + 10420 is nota post-AGE star.