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

Abstract

Aims. V838 Monocerotis erupted in 2002, brightened in a series of outbursts, and eventually developed a spectacular light echo. A very red star emerged a few months after the outburst. The whole event has been interpreted as the result of a merger. Methods. We obtained near-IR and mid-IR interferometric observations of V838 Mon with the AMBER and MIDI recombiners located at the Very Large Telescope Interferometer (VLTI) array. The MIDI two-beam observations were obtained with the 8m Unit Telescopes between October 2011 and February 2012. The AMBER three-beam observations were obtained with the compact array (B$\le$m) in April 2013 and the long array (B$\le$140m) in May 2014, using the 1.8m Auxiliary Telescopes. Results. A significant new result is the detection of a compact structure around V838 Mon, as seen from MIDI data. The extension of the structure increases from a FWHM of 25 mas at 8 μm to 70 mas at 13 μm. At the adopted distance of D = 6.1 $\pm$ 0.6 kpc, the dust is distributed from about 150 to 400 AU around V838 Mon. The MIDI visibilities reveal a flattened structure whose aspect ratio increases with wavelength. The major axis is roughly oriented around a position angle of -10 degrees, which aligns with previous polarimetric studies reported in the literature. This flattening can be interpreted as a relic of the 2002 eruption or by the influence of the currently embedded B3V companion. The AMBER data provide a new diameter for the pseudo-photosphere, which shows that its diameter has decreased by about 40% in 10yrs, reaching a radius R${}_{\ast }$ = 750 $\pm$ 200 R${}_{\odot }$ (3.5 $\pm$ 1.0 AU). Conclusions. After the 2002 eruption, interpreted as the merging of two stars, it seems that the resulting source is relaxing to a normal state. The nearby environment exhibits an equatorial over-density of dust up to several hundreds of AU.

Astronomy and Astrophysics (2014) Will be set by the publisher

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• Interferometric data reduction with AMBER/VLTI.Principle,estimators and illustration
• V838 Monocerotis: A Geometric Distance from Hubble Space Telescope Polarimetric Imaging of its Light Echo
• Spitzer Observations of V838 Monocerotis: Detection of a Rare Infrared Light Echo
• High Spatial Resolution Mid-IR Imaging of V838 Monocerotis: Evidence of New Circumstellar Dust Creation
• Infrared spectroscopy of carbon monoxide in V838 Mon during 2002--2006

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• On the properties of dust and gas in the environs of V838 Monocerotis
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• Two-Dimensional Radiation-Hydrodynamic Simulations of Luminous Red Novae
• V838 Mon: A slow waking up of Sleeping Beauty?
• V838 Monocerotis as seen by ALMA: a remnant of a binary merger in a triple system
• The Infrared Evolution of Dust in V838 Monocerotis