Stellar evolution theories predict that as the protoplanetary disc evolves, the gas component disappears as it photoevaporates or is accreted onto the star. Therefore, gas should not be present in stars older than few Myr, leaving a disc composed by dust, planetesimals and maybe, newly-formed planets. But a number of main sequence stars with debris disc have been detected either in far infra-red (FIR) or sub-milimiter (sub-mm) atomic and molecular lines, showing the presence of cold gaseous component in the outskirts of the disc. Since the prevalence of the gas for long periods is very unlikely, a secondary origin has been proposed in most cases, such as major collisions between planetesimals, grain-grain collisions, or exocomet evaporation.
We present here the spectroscopical detection of hot gas in cold gas-bearing discs, that seems to be located in the inner parts of the disc and that could reinforce the idea that the gas has secondary origin furthermore providing a physical link for the existence of both components (hot and cold).