Spectroscopic Discovery of Brown Dwarf-like Secondary Stars in the Cataclysmic Variables LL And and EF Eri

摘要

Infrared spectroscopic observations of LL Andromedae and EF Eridani arepresented. Our K band spectrum of LL Andromedae reveals the presence of methaneabsorption in the secondary star indicating an effective temperature less than1300K, similar to a "T" type methane brown dwarf. The secondary star in EFEridani is seen to be warmer with an effective temperature of ~1650K and aspectroscopic classification consistent with an L4-5 star. Both secondarieshave theoretical mass estimates of 0.04-0.055 solar masses (40-55 Jupitermasses). Our IR spectroscopic observations of LL And and EF Eri provide thefirst direct proof of the theoretical prediction that post-period minimumcataclysmic variables contain brown dwarf-like secondary stars.