Paper detail

On the properties of dust and gas in the environs of V838 Monocerotis

Herschel FIR imaging and spectroscopy were taken at several epochs to probe the central point source and the extended environment of V838 Mon. PACS and SPIRE maps were used to obtain photometry of the near and far dust around V838 Mon. Fitting reveals 0.5-0.6 solar masses of ~19K dust in the environs (~2.7pc) surrounding the star. The surface-integrated infrared flux (signifying the thermal light echo) and derived dust properties do not vary significantly between the epochs. We also fit the SED of the point source. As the peak of the SED lies outside the Herschel spectral range, it is only by incorporating data from other observatories and epochs that we can perform useful fitting; with this we explicitly assume no evolution of the point source between the epochs. We find warm dust with a temperature of ~300K distributed over a radius of 150-200AU. PACS and SPIRE spectra were also used to detect emission lines from the extended environment around the star. We fit the far-infrared lines of CO arising from the point source, from an extended environment around V838 Mon. Assuming a model of a spherical shell for this gas, we find that the CO appears to arise from two temperature zones: a cold zone (Tkin ~18K) that could be associated with the ISM or possibly with a cold layer in the outermost part of the shell, and a warm (Tkin ~400K) zone that is associated with the extended environment of V838 Mon within a region of radius of ~210AU. The SiO lines arise from a warm/hot zone. We did not fit the lines of H2O as they are far more dependent on the model assumed.