An analysis of a spectrum of V838 Monocerotis in October 2005

Department for Astrophysics, N. Copernicus Astronomical Center, Rabiańska 8, 87-100 Toruń, Poland e-mail: [tylenda;tomkam;schmidt]@ncac.torun.pl

Received: 9 April 2009
Accepted: 30 May 2009

Abstract

Context. V838 Mon erupted at the beginning of 2002 becoming an extremely luminous star with . Among various scenarios proposed to explain the nature of the outburst, the most promising is a stellar merger event.

Aims. We attempt to obtain information about the structure and evolution of the object in the decline from the 2002 eruption.

Methods. The results of spectroscopic observations of the object obtained in October 2005 with the Keck/HIRES instrument, presented in detail in Paper I, are analysed and discussed. Modelling of the observed line profiles has been used to constrain the physical parameters of the system.

Results. The kinematics of the atmosphere of V838 Mon is very complex. Our analysis of the molecular bands and the P-Cyg profiles of atomic lines shows that the object loses matter with a velocity of up to 215 km s^-1 and a rate of   yr^-1. In the profiles of some atomic lines, we have, however, found evidence of matter infall. Moreover, a narrow absorption component, which is particularly strong in some P-Cyg profiles, may indicate that a jet-like outflow has also been formed.
We show that the observed emission in the [] lines and an eclipse-like event observed in November/December 2006 was probably caused by interactions of the expanding matter, ejected by V838 Mon in 2002, with radiation from the B3V companion. In particular, the observed profiles of the [] lines can be easily modelled in this scenario and allow us to estimate parameters of the system, such as the position of the B3V companion relative to V838 Mon and the line of sight, density in the outflowing matter, and mass lost in the 2002 eruption. The observed appearance of strong Hα emission, just before and during the eclipse-like event, can be interpreted as a result of the accretion of the outflowing matter onto the B3V companion: the accreted matter, shocked above the stellar surface, can be a source of extreme-UV and soft X-ray radiation capable of ionizing and exciting H in the outflow.