Detection of a Molecular Disk Orbiting the Nearby, "Old," Classical T Tauri Star MP Mus

We have used the Atacama Pathfinder Experiment 12 m telescope to detect circumstellar CO emission from MP Mus (K1 IVe), a nearby (D ~ 100 pc), actively accreting, ~7 Myr-old pre-main sequence (pre-MS) star. The CO emission line profile measured for MP Mus is indicative of an orbiting disk with radius ~120 AU, assuming the central star mass is 1.2 solar masses and the disk inclination is ~30 degrees, and the inferred disk molecular gas mass is ~3 Earth masses. MP Mus thereby joins TW Hya and V4046 Sgr as the only late-type (low-mass), pre-MS star systems within ~100 pc of Earth that are known to retain orbiting, molecular disks. We also report the nondetection (with the Institut de Radio Astronomie Millimetrique 30 m telescope) of CO emission from another ten nearby (D ~ 100 pc or less), dusty, young (age ~10-100 Myr) field stars of spectral type A-G. We discuss the implications of these results for the timescales for stellar and Jovian planet accretion from, and dissipation of, molecular disks around young stars.