FAUST - XXVII. The circumbinary disc and the outflow of the L 1551 IRS 5 binary system

Using continuum and (CO)-O-18 (2-1) line data obtained from the large ALMA (Atacama Large Millimeter/submillimeter Array) programme FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar-like protostars), we studied the structure of the protostellar binary system L 1551 IRS 5 at scales between 30 and 3000 au to constrain its properties, from the circumstellar and circumbinary discs up to the envelope and outflow scales, which exhibits complex and entangled structures at the scales of its inner and outer envelopes, presumably caused by the influence of the central binary. Assuming a dust-to-gas ratio of 100, we calculated the dust + gas mass for the circumbinary disc and each circumstellar disc of the binary, obtaining 0.018 M-(R) for the circumbinary disc, 0.004 and 0.002 M-(R) for the northern and southern circumstellar disc, respectively. From the line emission, we retrieved the gas masses for each structure component. With the (CO)-O-18 (2-1) position-velocity diagram along the circumbinary disc, we were able to constrain the centrifugal barrier, r(CB) = 55 au, update the specific angular momentum, j similar to 270 au km s(-1). We built an analytical model that can be used to predict the influence of the morphology of the outflow and a few dynamic features that can reproduce the system emission, allowing us to explain and discern the outflow contribution from the complex emission due to the binary . Additionally , we inferred the density power-law index, alpha = 1 . 7 , and the envelope rotation velocity, v(c) = 2 km s(-1).Finally, the observations gave us the physical constraints to obtain a coherent outflow model for L 1551 IRS 5.