Letter to the Editor

A kinematically detected planet candidate in a transition disk^⋆

¹ Laboratoire Lagrange, Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
e-mail: jochen.stadler@oca.eu
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁴ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
⁵ Universitá degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
⁶ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁷ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁸ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
⁹ Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
¹⁰ NASA Headquarters, 300 E Street SW, Washington, DC 20546, USA
¹¹ National Radio Astronomy Observatory, Charlottesville, VA 22903, USA
¹² The Graduate University for Advanced Studies, SOKENDAI, Shonan Village, Hayama, Kanagawa 240-0193, Japan
¹³ Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
¹⁴ Núcleo Milenio de Formación Planetaria (NPF), Avenida España 1680, Valparaíso, Chile

Received: 4 November 2022
Accepted: 2 January 2023

Abstract

Context. Transition disks are protoplanetary disks with inner cavities possibly cleared by massive companions. Observing them at high resolution is ideal for mapping their velocity structure and probing companion–disk interactions.

Aims. We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 dust and gas observations of the transition disk around RXJ1604.3–2130 A, known to feature nearly symmetric shadows in scattered light, and aim to search for non-Keplerian features.

Methods. We studied the ¹²CO line channel maps and moment maps of the line-of-sight velocity and peak intensity. We fitted a Keplerian model of the channel-by-channel emission to study line profile differences and produced deprojected radial profiles for all velocity components.

Results. The ¹²CO emission is detected out to R ∼ 1.8″ (265 au). It shows a cavity inward of 0.39″ (56 au) and within the dust continuum ring (at ∼0.56″, i.e., 81 au). Azimuthal brightness variations in the ¹²CO line and dust continuum are broadly aligned with the shadows detected in scattered-light observations. We find a strong localized non-Keplerian feature toward the west within the continuum ring (at R = 41 ± 10 au and PA = 280 ± 2°). It accounts for Δv_ϕ/v_kep ∼ 0.4 or Δv_z/v_kep ∼ 0.04, depending on if the perturbation is in the rotational or vertical direction. A tightly wound spiral is also detected and extends over 300° in azimuth, possibly connected to the localized non-Keplerian feature. Finally, a bending of the iso-velocity contours within the gas cavity indicates a highly perturbed inner region, possibly related to the presence of a misaligned inner disk.

Conclusions. While broadly aligned with the scattered-light shadows, the localized non-Keplerian feature cannot be solely due to changes in temperature. Instead, we interpret the kinematical feature as tracing a massive companion located at the edge of the dust continuum ring. We speculate that the spiral is caused by buoyancy resonances driven by planet–disk interactions. However, this potential planet at ∼41 au cannot explain the gas-depleted cavity, the low accretion rate, and the misaligned inner disk, which suggests the presence of another companion closer in.