Water and titanium oxide in late-type M dwarfs

Despite the identification of brown dwarf candidates the lack of understanding of M dwarfs has meant that it has not been possible to unambiguously distinguish these candidates from cool M dwarfs. Unlike hotter stars their atmospheres are dominated by a variety of species of molecules, many with billions of line transitions modulating their energy output. We have recently examined water vapour and titanium oxide opacities which are the most important sources of opacity in cool low-mass stars.