A search for remnant molecular disks around young nearby stars

Sensitive 12 CO J=1−0 (115 GHz) millimeter-wave observations of eight Ursa Major stream stars (age ∼ 3 × 10 8 yr, d ∼ 25 pc) ranging in spectral type from A7 to K3 reval no detectable emission arising from gaseous remnants of circumstellar disks. If the precursor disks are sufficiently large (r > 350 AU) then the total mass remaining at large radii must be < 3 × 10 −5 M ⊙ if the CO/H 2 ratio is characteristic of the molecular interstellar medium