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

Abstract

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 (T kin ≈ 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 (T kin ≈ 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 H 2 O as they are far more dependent on the model assumed.

Submillimeter-wave emission of three Galactic red novae: cool molecular outflows produced by stellar mergers

“…They are indicated in Table 1. Earlier far-infrared observations on Herschel revealed the presence of thermal lines of H 2 O, CO, and SiO in V838 Mon (Exter et al 2016). While we do not cover any strong lines of water, identifying spectral features of CO and SiO in the SMA spectra was straightforward.…”

The evolution of luminous red nova AT 2017jfs in NGC 4470

“…As an additional feature, GROND (Greiner et al 2008) observations reveal a moderate rebrightening of the NIR light curves from ∼170 to 220 d. Although we do not have very late spectroscopic observations to support this (Sect. 4), a latetime NIR luminosity excess can be associated with the formation of new dust or IR echoes, occasionally observed in LRNe at late phases (see, e.g., Banerjee et al 2015;Exter 2016). The late NIR brightening may also be a consequence of the transition to the brown (L-type) supergiant stage, as happened for V838 Mon (Evans et al 2003;Munari et al 2007), although this scenario does not comfortably explain the late blue-shift of the Hα emission observed in the late spectra of AT 2017jfs (see Sect.…”

V838 Monocerotis: the central star and its environment a decade after outburst

“…V838 Mon is embedded in a dense, large scale environment (Tylenda & Kamiński 2012;Kamiński et al 2011;Exter et al 2014), potentially contaminating observations of the central star. High angular resolution studies with a field-of-view (FOV) of a few arcsec are an asset in that domain to isolate the central regions from the extended dusty cloud.…”