A giant planet shaping the disk around the very low-mass star CIDA 1

Abstract

Context. Exoplanetary research has provided us with exciting discoveries of planets around very low-mass (VLM) stars (0.08 M-circle dot less than or similar to M-*less than or similar to 0.3 M-circle dot ; e.g., TRAPPIST-1 and Proxima Centauri). However, current theoretical models still strive to explain planet formation in these conditions and do not predict the development of giant planets. Recent high-resolution observations from the Atacama Large Millimeter/submillimeter Array (ALMA) of the disk around CIDA 1, a VLM star in Taurus, show substructures that hint at the presence of a massive planet.

Aims. We aim to reproduce the dust ring of CIDA 1, observed in the dust continuum emission in ALMA Band 7 (0.9 mm) and Band 4 (2.1 mm), along with its (CO)-C-12 (J = 3-2) and (CO)-C-13 (J = 3-2) channel maps, assuming the structures are shaped by the interaction of the disk with a massive planet. We seek to retrieve the mass and position of the putative planet, through a global simulation that assesses planet-disk interactions to quantitatively reproduce protoplanetary disk observations of both dust and gas emission in a self-consistent way.

Methods. Using a set of hydrodynamical simulations, we model a protoplanetary disk that hosts an embedded planet with a starting mass of between 0.1 and 4.0 M-Jup and initially located at a distance of between 9 and 11 au from the central star. We compute the dust and gas emission using radiative transfer simulations, and, finally, we obtain the synthetic observations, treating the images as the actual ALMA observations.

Results. Our models indicate that a planet with a minimum mass of similar to 1.4 M-Jup orbiting at a distance of similar to 9-10 au can explain the morphology and location of the observed dust ring in Band 7 and Band 4. We match the flux of the dust emission observation with a dust-to-gas mass ratio in the disk of similar to 10(-2) . We are able to reproduce the low spectral index (similar to 2) observed where the dust ring is detected, with a similar to 40-50% fraction of optically thick emission. Assuming a (CO)-C-12 abundance of 5 x 10(-5) and a (CO)-C-13 abundance 70 times lower, our synthetic images reproduce the morphology of the (CO)-C-12 (J = 3-2) and (CO)-C-13 (J = 3-2) observed channel maps where the cloud absorption allowed a detection. From our simulations, we estimate that a stellar mass M-* = 0.2 M-circle dot and a systemic velocity nu(sys) = 6.25 km s(-1) are needed to reproduce the gas rotation as retrieved from molecular line observations. Applying an empirical relation between planet mass and gap width in the dust, we predict a maximum planet mass of similar to 4-8 M-Jup.

Conclusions. Our results suggest the presence of a massive planet orbiting CIDA 1, thus challenging our understanding of planet formation around VLM stars.