2022MNRAS.515.2646R

We present the first results of a pilot program to conduct an Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (211-275 GHz) spectral line study of young stellar objects (YSOs) that are undergoing rapid accretion episodes, i.e. FU Ori objects (FUors). Here, we report on molecular emission line observations of the FUor system, V883 Ori. In order to image the FUor object with a full coverage from ∼0.5 arcsec to the map size of ∼30 arcsec, i.e. from disc to outflow scales, we combine the ALMA main array (the 12-m array) with the Atacama Compact Array (7-m array) and the Total Power (TP) array. We detect HCN, HCO⁺, CH₃OH, SO, DCN, and H₂CO emission with most of these lines displaying complex kinematics. From position-velocity (PV) diagrams, the detected molecules HCN, HCO⁺, CH₃OH, DCN, SO, and H₂CO probe a Keplerian rotating disc in a direction perpendicular to the large-scale outflow detected previously with the ¹²CO and ¹³CO lines. Additionally, HCN and HCO⁺ reveal kinematic signatures of infall motion. The north outflow is seen in HCO⁺, H₂CO, and SO emission. Interestingly, HCO⁺ emission reveals a pronounced inner depression or 'hole' with a size comparable to the radial extension estimated for the CH₃OH and 230 GHz continuum. The inner depression in the integrated HCO⁺ intensity distribution of V883 Ori is most likely the result of optical depth effects, wherein the optically thick nature of the HCO⁺ and continuum emission towards the innermost parts of V883 Ori can result in a continuum subtraction artefact in the final HCO⁺ flux level.