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

Olivier Chesneau (1) , Florentin Millour (1) , Orsola de Marco (2) , S.N. Bright (1, 2) , Alain Spang (1) , D. P. K. Banerjee (3) , N. M. Ashok (3) , T. Kaminski (4) , John P. Wisniewski (5) , Anthony Meilland (1) , Eric Lagadec (1)

1 LAGRANGE - Joseph Louis LAGRANGE
2 Macquarie University
3 PRL - Physical Research Laboratory [Ahmedabad]
4 MPIFR - Max-Planck-Institut für Radioastronomie
5 OU - University of Oklahoma

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≤35m) in April 2013 and the long array (B≤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 ± 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◦, 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∗ = 750 ± 200 R⊙ (3.5 ± 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.

Domaines: Astrophysique stellaire et solaire [astro-ph.SR]; Astrophysique stellaire et solaire [astro-ph.SR]

Olivier Chesneau, Florentin Millour, Orsola de Marco, S.N. Bright, Alain Spang, et al.. V838 Monocerotis: the central star and its environment a decade after outburst. Astronomy and Astrophysics - A&A, 2014, Will be set by the publisher. ⟨hal-01035453⟩