Resolving the circumbinary dust disk surrounding HH 30

Context.The jet-disk connection is an important part of the star formation process. HH 30 is a rare and beautiful example of a system exhibiting a flared edge-on disk, an optical jet and a CO molecular outflow. A recent analysis of the jet wiggling has revealed that the central star is in reality a binary object. Therefore, the dust and gas disk observed around HH 30 is circumbinary. Aims.In this paper, we attempt to better constrain the system (disk + stars) properties, as well as the system age. Methods.We obtained very high angular resolution ($\sim 0.4''$) observations in continuum at 1.3 mm with the IRAM interferometer. A standard disk model is used to fit the continuum and line data in the Fourier-plane and derive the disk properties. Results.We find that the disk of HH 30 is truncated at an inner radius 37 ± 4 AU. The simplest explanation is tidal truncation in a binary system. This confirms the binarity of the HH 30 system, which consists of two stars on a low eccentricity, 15 AU semi-major axis orbit. The jet wiggling is due to orbital motion. The mass ratio is poorly constrained. The system age may be less than 2 Myr. The disk is optically thin at 1.3 mm and the dust opacity index, $\beta \approx 0.4$, indicates the presence of cm size grains. Conclusions.These observations confirm that HH 30, often presented as an archetypal example of the jet-disk paradigm, is a binary star, with one of the components at the origin of the optical jet. This suggests that many other objects similar to HH 30 may be unknown binary or multiple systems. These new data confirm that high angular resolution observations at millimeter wavelengths are powerful tools to unveil the inner dust disk properties. In this domain, ALMA will likely change our observational vision of these objects