摘要：Aims. We aim to probe the close and distant circumstellar environments
of the stellar outburst object V838 Mon.
Methods. Herschel far-infrared 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 dust
immediately around V838 Mon, and in the surrounding infrared-bright region. These maps
were fitted in 1d and 2d to measure the temperature, mass, and β of the two dust sources.
PACS and SPIRE spectra were used to detect emission lines from the extended atmosphere of
the star, which were then modelled to study the physical conditions in the emitting
material. HIFI spectra were taken to measure the kinematics of the extended atmosphere but
unfortunately yielded no detections.
Results. Fitting of the far-infrared imaging of V838 Mon reveals
0.5−0.6 M⊙ of
≈19 K dust in the environs
(≈2.7 pc) surrounding
V838 Mon. The surface-integrated infrared flux (signifying the thermal light echo), and
derived dust properties do not vary significantly between the different epochs. We
measured the photometry of the point source. As the peak of the SED (Spectral Energy
Distribution) lies outside the Herschel spectral range, it is only by
incorporating data from other observatories and previous epochs that we can usefully fit
the SED; with this we explicitly assume no evolution of the point source between the
epochs. We find that warm dust with a temperature ~ 300 K distributed over a radius of
150–200 AU. 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 ≈
18 K) that could be associated with the ISM or possibly with a cold
layer in the outermost part of the shell, and a warm (Tkin ≈ 400 K)
zone that is associated with the extended environment of V838 Mon within a region of
radius of ≈210 AU. 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.
