The Infrared Continuum Spectrum of VY CMa

Abstract

We combine spectra of VY CMa obtained with the short- and long-wavelength spectrometers, SWS and LWS, on the Infrared Space Observatory to provide a first detailed continuum spectrum of this highly luminous star. The circumstellar dust cloud through which the star is observed is partially self-absorbing, which makes for complex computational modeling. We review previous work and comment on the range of uncertainties about the physical traits and mineralogical composition of the modeled disk. We show that these uncertainties significantly affect the modeling of the outflow and the estimated mass loss. In particular, we demonstrate that a variety of quite diverse models can produce good fits to the observed spectrum. If the outflow is steady, and the radiative repulsion on the dust cloud dominates the star's gravitational attraction, we show that the total dust mass-loss rate is $\sim 4\times 10^{-6}M_{\odot}$ yr$^{-1}$, assuming that the star is at a distance of 1.5 kpc. Several indications, however, suggest that the outflow from the star may be spasmodic. We discuss this and other problems facing the construction of a physically coherent model of the dust cloud and a realistic mass-loss analysis.