The Circumstellar Disk and Asymmetric Outflow of the EX Lup Outburst System

Abstract

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 5-sigma level. Radiative transfer modeling constrains the characteristic radius of the dust disk to 23 au and a total dust mass of 1.0×10 −4 M (33 M ⊕ ), similar to other EXor sources. The 13 CO and C 18 O line emission trace the disk rotation and are used to constrain the disk geometry, kinematics, and a total gas disk mass of 5.1×10 −4 M . The 12 CO emission extends out to a radius of 200 au and is asymmetric, with one side deviating from Keplerian rotation. We detect blue-shifted, 12 CO arc-like emission located 0.8 to the north-west, 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 towards 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.

ALMA observations of the early stages of substellar formation in the Lupus 1 and 3 molecular clouds

“…We note that several disks in Lupus 3 show systemic velocities in that range (e.g. EX Lup at +4.4 km/s Hales et al 2018 or the sources in Ansdell et al 2018). The rest of the ALMA sources were not detected in CO and have an upper limit to their CO(2-1) fluxes of ∼6 mJy/beam (1 σ) in a 0.3 km/s channel.…”

The circumstellar environment of EX Lupi: SPHERE and SINFONI views

“…Paβ in the quiescent spectra might still trace accretion, as also found by Sipos et al (2009), but orders of magnitude lower than in the outburst phase. Hales et al (2018) reported the first spatially resolved observation of the disk around EX Lup, obtained with ALMA at 0.3 resolution in 1.3 mm continuum emission and in the J = 2-1 spectral line of 12 CO, 13 CO, and C 18 O. The compact dust continuum disk does not show indication of clumps or asymmetries in their data and is consistent with a characteristic radius of ∼23 au.…”

“…In Fig. 5, the top panel, we show the radial brightness profile after de-projecting the detected feature, using a position angle of 333 • , as determined through the azimuthal profile (bottom panel of the same figure), and an inclination of 38 • (Hales et al 2018). The feature peaks at around 60 au, with a sharp inner edge at ∼34 au and a shallower outer edge at ∼88 au.…”

“…In order to put both these interpretations into context, we summarize and discuss the recent results found by Hales et al (2018), which employ ALMA observations.…”

“…From the optically thin 13 CO line, they derived a total disk mass of 2.3 × 10 −4 M , which is significantly lower than the one derived from the continuum data (assuming a canonical gas-to-dust ratio of 100) and SEDmodeling. Hales et al (2018) spatially resolved the dust emission from the disk in a 1.3 mm continuum and a more extended Keplerian gas disk in 12 CO(2-1), 13 CO(2-1), and C 18 O(2-1) using ALMA observations. Moreover, they pointed out a more extended and non-Keplerian 12 CO(2-1) emission interpreted as the interaction of a molecular outflow with remnant ambient material.…”