Massive Compact Dust Disk with a Gap around CW Tau Revealed by ALMA Multiband Observations

Compact protoplanetary disks with a radius of $\lesssim$ 50 au are common around young low-mass stars. We report high resolution ALMA dust continuum observations toward compact disk CW Tau at Band 4 ($\lambda=2.2$ mm), 6 (1.3 7 (0.89 mm) and 8 (0.75 mm). The SED shows the spectral slope $2.0\pm0.24$ between 0.75 1.3 mm, while it is $3.7\pm0.29$ 2.17 3.56 mm. steep mm consistent that optically thin emission from small grains ($\lesssim$ 350 ${\rm \mu m}$). perform parametric fitting data to characterize disk. Interestingly, if dust-to-gas mass ratio 0.01, Toomre's Q parameter reaches $\sim$ 1-3, suggesting might be marginally gravitationally unstable. total estimated as $\sim250M_{\oplus}$ for maximum size 140 m}$ inferred previous polarimetric observation least $80M_{\oplus}$ even larger grain sizes. This result quite massive in spite its smallness. Furthermore, we clearly identify gap structure located $\sim20$ au, which induced by giant planet. In these interesting characteristics, has normal luminosity, index 6, could clue budget problem Class II disks.