The post-outburst photometric behaviour of V838 Mon

The unusual eruptive variable discovered in Monoceros in 2002 January underwent dramatic photometric and spectroscopic changes in the months prior to its 2002 June–August conjunction with the Sun. Optical and infrared (IR) photometry obtained at the SAAO between 2002 January and June (JD 245 2280–440) is presented here in an analysis of the post-outburst behaviour of the star. The light curve indicated that three eruptions took place in 2002 January, February and March. South African Astronomical Observatory (SAAO) echelle spectra obtained in the week prior to the March maximum indicated the ejection of a new shell of material. JHKL photometry obtained during 2002 April showed the development of an IR excess owing to the formation of a dust shell. The shell appears to be largely responsible for the rapid fade in the optical flux during 2002 April–May (ΔV > 6 mag within 3 weeks). Blueing of the optical colours during the decline is probably due either to the revealing of an emission-line region surrounding V838 Mon, or to the unveiling of the progenitor or a spatially close early-type star.