High-resolution ALMA observations of V4046 Sgr: a circumbinary disc with a thin ring

Abstract

The nearby V4046 Sgr spectroscopic binary hosts a gas-rich disc known for its wide cavity and dusty ring. We present high resolution (∼20 mas or 1.4 au) ALMA observations of the 1.3 mm continuum of V4046 Sgr which, combined with SPHERE–IRDIS polarised images and a well-sampled spectral energy distribution (SED), allow us to propose a physical model using radiative transfer (RT) predictions. The ALMA data reveal a thin ring at a radius of 13.15±0.42 au (Ring13), with a radial width of 2.46±0.56 au. Ring13 is surrounded by a ∼10 au-wide gap, and it is flanked by a mm-bright outer ring (Ring24) with a sharp inner edge at 24 au. Between 25 and ∼35 au the brightness of Ring24 is relatively flat and then breaks into a steep tail that reaches out to ∼60 au. In addition, central emission is detected close to the star which we interpret as a tight circumbinary ring made of dust grains with a lower size limit of 0.8 mm at 1.1 au. In order to reproduce the SED, the model also requires an inner ring at ∼5 au (Ring5) composed mainly of small dust grains, hiding under the IRDIS coronagraph, and surrounding the inner circumbinary disc. The surprisingly thin Ring13 is nonetheless roughly 10 times wider than its expected vertical extent. The strong near-far disc asymmetry at 1.65 $\rm{\mu m}$ points at a very forward-scattering phase function, and requires grain radii of no less than 0.4 $\rm{\mu m}$.

Constraining giant planet formation with synthetic ALMA images of the Solar System’s natal protoplanetary disk

“…10, middle panel of second row). Observations of the V4046 Sgr circumbinary disk by Martinez-Brunner et al (2022) present features that are very similar to the Spread Solar System observed with a similar resolution (in Fig. 10, top left panel), around a binary, unlike our configuration.…”

Dust dynamics in planet-forming discs in binary systems

“…Common features in these systems are dust cavities surrounded by ring(s), either circular and azimuthally symmetric (e.g. [ 59 , 60 ]) or, more often, eccentric (as in the case of HD 142527, where to 0.44, [ 61 ]) and showing clear asymmetries in the dust and/or CO isotopologues [ 62 – 67 ]. In the latter case, spirals [ 61 , 65 , 68 ], warps (e.g.…”

“…In the latter case, spirals [ 61 , 65 , 68 ], warps (e.g. [ 64 , 65 ]), stream-like filaments [ 63 , 68 ] and shadows cast by misaligned inner disc(s) [ 60 , 64 , 68 , 69 ] are also detected. These features are generally interpreted as due to binary–disc interactions.…”

“…Indeed, there may be a dichotomy in outcomes: disc formation is usually suppressed in binary systems, but some of the longest-lived and most massive known discs turn out to be circumbinary (e.g. V4046 Sgr, with an age of Myr, [ 60 , 76 ]). A larger census of circumbinary discs is needed to address this question.…”

ALMA's view of the M-dwarf GSC 07396-00759's edge-on debris disc: AU Mic's coeval twin

“…V4046 Sgr possesses both a gas-rich circumbinary disc and evidence of ongoing accretion (e.g. Stempels & Gahm 2004;Öberg et al 2011;Rosenfeld et al 2013;Rapson et al 2015;Kastner et al 2018;D'Orazi et al 2019;Martinez-Brunner et al 2022). The survival of the more primordial-like disc of V4046 Sgr may be attributed to its binary nature, as Alexander (2012) find close binaries to possess longer lived discs than single stars.…”