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

¹ Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133 Milano, Italy
e-mail: pietro.curone@unimi.it
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
³ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁵ School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliams Place, Dublin 2, Ireland
⁶ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany
⁷ Unidad Mixta Internacional Franco-Chilena de Astronomía, CNRS, UMI 3386. Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
⁸ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁰ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
¹¹ Freie Universität Berlin, Institute of Geological Sciences, Malteserstr. 74-100, 12249 Berlin, Germany
¹² Department of Physics and Astronomy, California State University Northridge, 18111 Nordhoff Street, Northridge, CA 91130, USA

Received: 25 November 2021
Accepted: 17 May 2022

Abstract

Context. Exoplanetary research has provided us with exciting discoveries of planets around very low-mass (VLM) stars (0.08 M_⊙ ≲ M_* ≲ 0.3 M_⊙; 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 ¹²CO (J = 3−2) and ¹³CO (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 ~1.4 M_Jup orbiting at a distance of ~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 ~10⁻². We are able to reproduce the low spectral index (~2) observed where the dust ring is detected, with a ~40−50% fraction of optically thick emission. Assuming a ¹²CO abundance of 5 × 10⁻⁵ and a ¹³CO abundance 70 times lower, our synthetic images reproduce the morphology of the ¹²CO (J = 3−2) and ¹³CO (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_⊙ and a systemic velocity v_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 ~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.