ALMA Observations of HD141569's Circumstellar Disk

We present ALMA band 7 (345 GHz) continuum and $^{12}$CO(J = 3-2) observations of the circumstellar disk surrounding HD141569. 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 $870\rm~\mu m$ ALMA continuum observations resolve a dust disk out to approximately $56 ~\rm au$ from the star (assuming a distance of 116 pc) with $0."38$ resolution and $0.07 ~ \rm mJy~beam^{-1}$ sensitivity. We measure a continuum flux density for this inner material of $3.8 \pm 0.4 ~ \rm mJy$ (including calibration uncertainties). The $^{12}$CO(3-2) gas is resolved kinematically and spatially from about 30 to 210 au. The integrated $^{12}$CO(3-2) line flux density is $15.7 \pm 1.6~\rm Jy~km~s^{-1}$. We estimate the mass of the millimeter debris and $^{12}$CO(3-2) gas to be $\gtrsim0.04~\rm M_{\oplus}$ and $\sim2\times 10^{-3}~\rm M_{\oplus}$, respectively. If the millimeter grains are part of a collisional cascade, then we infer that the inner disk ($<50$ au) has $\sim 160~\rm M_{\oplus}$ contained within objects less than 50 km in radius, depending on the planetesimal size distribution and density assumptions. MCMC modeling of the system reveals a disk morphology with an inclination of $53.4^{\circ}$ centered around a $\rm M=2.39~ M_{\odot}$ host star ($\rm Msin(i)=1.92~ M_{\odot}$). We discuss whether the gas in HD141569's disk may be second generation. If it is, the system can be used to study the clearing stages of planet formation.