A search for extended disks around weak-lined T Tauri stars

We present the results of a search for dust and gas emission around T Tauri stars in the Taurus-Auriga region, conducted with the IRAM interferometer in CO, HCO+ and the adjacent continua at 1.3 and 3.4 mm. We studied a sampl e of young stars with and without the near-infrared spectral signature of d isks, to learn whether young stars with little or no evidence of inner accr etion disks are surrounded by extensive outer disks providing reservoirs of cold gas and dust. Our sample comprises 3 classical T Tauris (TTs) and 12 weak-lined T Tauris (WTs). We detect the thermal emission indicative of the presence of a disk around the TTs: IPTau, LkCa 15 and HP Tau. We resolve the continuum emissio n of the dust disk of LkCa 15. We also resolve the CO and HCO+ emission of a large rotating disk at LkCa 15. We do not detect any millimeter continuum or CO emission from the WTs. with the notable exception of V 836 Tau, a bo rderline WT presenting evidence of accretion activity. Our detection limits place stringent upper bounds on the amount of circumst ellar gas and dust left around the WTs. Our detection of all the TTs and no n-detection of all the WTs indicate that the disappearance of disks in TTs, and the corresponding time scale for this disappearance, customarily deriv ed from infrared observations that sample the hot inner part of circumstell ar disks (R less than or equal to 5 AU), concerns in reality the entire dis k, including the outer regions (R greater than or equal to 50 - 500 AU) to which our observations are more sensitive.