We present Atacama Large Millimeter/submillimeter Array ( ALMA ) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region .
The continuum images at wavelengths of 2.9 , 1.3 , and 0.87 mm have unprecedented angular resolutions of 0 \farcs 075 ( 10 AU ) to 0 \farcs 025 ( 3.5 AU ) , revealing an astonishing level of detail in the circumstellar disk surrounding the young solar analogue HL Tau , with a pattern of bright and dark rings observed at all wavelengths .
By fitting ellipses to the most distinct rings , we measure precise values for the disk inclination ( 46.72 \arcdeg \pm 0.05 \arcdeg ) and position angle ( +138.02 \arcdeg \pm 0.07 \arcdeg ) .
We obtain a high-fidelity image of the 1.0 mm spectral index ( \alpha ) , which ranges from \alpha \sim 2.0 in the optically-thick central peak and two brightest rings , increasing to 2.3-3.0 in the dark rings .
The dark rings are not devoid of emission , and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings , consistent with some degree of grain growth and evolution .
Additional clues that the rings arise from planet formation include an increase in their central offsets with radius and the presence of numerous orbital resonances .
At a resolution of 35 AU , we resolve the molecular component of the disk in HCO ^ { + } ( 1-0 ) which exhibits a pattern over LSR velocities from 2-12 km s ^ { -1 } consistent with Keplerian motion around a \sim 1.3M _ { \odot } star , although complicated by absorption at low blue-shifted velocities .
We also serendipitously detect and resolve the nearby protostars XZ Tau ( A/B ) and LkH \alpha 358 at 2.9 mm .