2000A&A...355..165D

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 3.4mm. We studied a sample of young stars with and without the near-infrared spectral signature of disks, to learn whether young stars with little or no evidence of inner accretion 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: IP Tau, LkCa 15 and HP Tau. We resolve the continuum emission 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 V836 Tau, a borderline WT presenting evidence of accretion activity. Our detection limits place stringent upper bounds on the amount of circumstellar gas and dust left around the WTs. Our detection of all the TTs and non-detection of all the WTs indicate that the disappearance of disks in TTs, and the corresponding time scale for this disappearance, customarily derived from infrared observations that sample the hot inner part of circumstellar disks (R≤5AU), concerns in reality the entire disk, including the outer regions (R≥50-500AU) to which our observations are more sensitive.