An analysis of a spectrum of V838 Monocerotis in October 2005

摘要

Context. V838 Mon erupted at the beginning of 2002 becoming an extremely luminous star with L = 10~6L_⊙. Among various scenar-ios 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, pre-sented in detail in Paper I, are analysed and discussed. Modelling of the observed line profiles has been used to constrain the physicalparameters 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 pro-files of atomic lines shows that the object loses matter with a velocity of up to 215 km s~(-1)and a rate of 10~(-6)-5)M_⊙yr_(-1). In theprofiles of some atomic lines, we have, however, found evidence of matter infall. Moreover, a narrow absorption component, whichis 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 Fe lines and an eclipse-like event observed in November/December 2006 was probablycaused 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 Fe II 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 lostin the 2002 eruption. The observed appearance of strong Ha emission, just before and during the eclipse-like event, can be interpretedas 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.