ALMA OBSERVATIONS of HD 141569's CIRCUMSTELLAR DISK

We present ALMA band 7 (345 GHz) continuum and ¹²CO(J = 3-2) observations of the circumstellar disk surrounding HD 141569. At an age of about 5 Myr, the disk has a complex morphology that may be best interpreted as a nascent debris system with gas. Our 870 μm ALMA continuum observations resolve a dust disk out to approximately 56 au from the star (assuming a distance of 116 pc) with 0.″38 resolution and 0.07 mJy beam^-1 sensitivity. We measure a continuum flux density for this inner material of 3.8 ±0.4 mJy (including calibration uncertainties). The ¹²CO(3-2) gas is resolved kinematically and spatially from about 30 to 210 au. The integrated ¹²CO(3-2) line flux density is 15.7 ±1.6 Jy km s^-1. We estimate the mass of the millimeter debris and ¹²CO(3-2) gas to be gap 0.04 M _⊕ and ∼2 ×10^-3 M _⊕, respectively. If the millimeter grains are part of a collisional cascade, then we infer that the inner disk (<50 au) has ∼160 M _⊕ contained within objects less than 50 km in radius, depending on the planetesimal size distribution and density assumptions. Markov Chain Monte Carlo modeling of the system reveals a disk morphology with an inclination of 53.°4 centered around an M = 2.39 M _o host star (Msin(i) = 1.92 M _o). We discuss whether the gas in HD 141569's disk may be second generation. If it is, the system can be used to study the clearing stages of planet formation.