2018ApJ...859..111H

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations at 0.''3 resolution of EX Lup, the prototype of the EXor class of outbursting pre-main-sequence stars. The circumstellar disk of EX Lup is resolved for the first time in 1.3 mm continuum emission and in the J = 2-1 spectral line of three isotopologues of CO. At the spatial resolution and sensitivity achieved, the compact dust continuum disk shows no indications of clumps, fragments, or asymmetries above the 5σ level. Radiative transfer modeling constrains the characteristic radius of the dust disk to 23 au and the total dust mass to 1.0 x 10^–4 M_☉ (33 M_⊕), similar to other EXor sources. The ¹³CO and C¹⁸O line emissions trace the disk rotation and are used to constrain the disk geometry, kinematics, and a total gas disk mass of 5.1 x 10^–4 M_☉. The ¹²CO emission extends out to a radius of 200 au and is asymmetric, with one side deviating from Keplerian rotation. We detect blueshifted, ¹²CO arc-like emission located 0.''8 to the northwest and spatially disconnected from the disk emission. We interpret this extended structure as the brightened walls of a cavity excavated by an outflow, which are more commonly seen in FUor sources. Such outflows have also been seen in the borderline FU/EXor object V1647 Ori, but not toward EXor objects. Our detection provides evidence that the outflow phenomenon persists into the EXor phase, suggesting that FUor and EXor objects are a continuous population in which outflow activity declines with age, with transitional objects such as EX Lup and V1647 Ori.