Near infra-red spectroscopy of V838 Monocerotis

Abstract

Near - IR, multi - epoch, spectroscopic and photometric observations of the enigmatic, eruptive variable V838 Mon in the JHK bands are reported. One of the unusual features of the spectra is the detection of several strong neutral TiI lines in emission in the K band. From the strength of these lines, the mass of the ejected envelope is estimated to be in the range 10-7 to 10-5 M⊙. The spectra also show the strong presence of the first and second overtone 12CO bands seen in the K and H bands. The CO bands show a complex evolution. Deep water bands at 1.4 μm and 1.9 μm are also seen later in the object's evolution. Blackbody fits to the JHK photometric data show that V838 Mon has evolved to temperatures between 2400-2600 K by ∼ 130 days after outburst. The spectra at this stage have the general characteristics of a very cool M giant.