Constraining the physical structure of the circumstellar environment of V838 Monocerotis remnant

Abstract

V838 Monocerotis (V838 Mon) erupted in 2002 as a luminous red nova after which it cooled and began to form dust. The remnant is predicted to become a blue straggler. Interferometric observations in the HKLM bands have uncovered a stable bipolar feature in the closest vicinity of the remnant star. We aim to constrain the physical structure and nature of the circumstellar material immediately surrounding V838 Mon. Using the radiative-transfer code RADMC3D we managed to constrain the dust density distribution that best represents recent VLTI and CHARA interferometric imaging experiments. We also present recent SAAO-HIPPO polarimetric measurements which further test dust distribution models. We find that a multi-component model consisting of jets, a torus, and an ellipsoid provides an adequate fit to H band interferometric observables, however, it struggles to reproduce the extremely small closure phase deviations in the K band. The jets in our model are vital to produce nonzero closure phases, as they help to produce a gap in the torus, which is the sole source of asymmetry. The polarimetric measurements show that the intrinsic linear polarization is currently very low, with degree of polarization < 2%, consistent with our model. Although not unique, our dust model suggests a persistent torus-like structure and jet or jets in the remnant, in agreement with several predictions for an intermediate-mass merger product. However, even though these features may be important signposts of the evolution of V838 Mon to the blue straggler phase, the origin of these features, remains largely unclear.