Evolution of V838 Monocerotis during and after the 2002 eruption

Department for Astrophysics, N. Copernicus Astronomical Centre, Rabiańska 8, 87-100 Toruń, Poland e-mail: tylenda@ncac.torun.pl

Received: 1 February 2005
Accepted: 20 February 2005

Abstract

By fitting the available photometric data on V838 Mon with standard supergiant spectra we have derived principal stellar parameters, i.e. effective temperature, radius and luminosity, and followed the evolution of the object since its discovery in early January 2002. Our analysis shows that the 2002 outburst of V838 Mon consisted of two major phases: pre-eruption, which was observed in January 2002 and a major outburst, the eruption, which started in the beginning of February 2002. During pre-eruption the object seemed to be relaxing after an initial event which had presumably taken place in last days of December 2001. The eruption phase, which lasted until mid-April 2002, resulted from a very strong energy burst, which presumably took place in last days of January at the base of the stellar envelope inflated in pre-eruption. The burst produced an energy wave, which was observed as a strong luminosity flash in the beginning of February, followed by a strong mass outflow in the form of two shells, which was observed as an expanding photosphere in later epochs. In mid-April, when the outflow became optically transparent and most of its energy radiated away, the object entered the decline phase during which V838 Mon was evolving along the Hayashi track. This we interpret as evidence that the main energy source during decline was gravitational contraction of the object envelope inflated in eruption. Late in 2002, dust formation started in the expanding shells which gave rise to a strong infrared excess observed in 2003.