On the properties of dust and gas in the environs of V838 Monocerotis⋆
1 Institute of Astronomy,
KU Leuven, Celestijnenlaan 200D, BUS
2 Herschel Science Centre, European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Spain
3 ISDEFE, Beatriz de Bobadilla 3, 28040 Madrid, Spain
4 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
5 RAL Space, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK
6 School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK
7 Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
8 Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
9 Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
10 Astronomical Institute Anton Pannekoek, Universiteit van Amsterdam, Science Park 904, 1090 GE Amsterdam, The Netherlands
Accepted: 28 July 2016
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.
Key words: novae, cataclysmic variables / stars: individual: V838 Monocerotis / ISM: clouds / dust, extinction
© ESO, 2016