Letter to the Editor

The heart of Sakurai’s object revealed by ALMA

¹ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
e-mail: daniel.tafoya@chalmers.se
² Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
³ Instituto de Radioastronomía y Astrofísica, UNAM, Ant. carretera a Pátzcuaro 8701, Ex-Hda. San José de la Huerta, Morelia, 58089 Mich., Mexico
⁴ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstr. 25, 6020 Innsbruck, Austria
⁵ Universidad Católica del Norte, Instituto de Astronomía, Av. Angamos 0610, Antofagasta, Chile
⁶ European Southern Observatory, Karl Schwarzschild str. 2, 85748 Garching, Germany
⁷ Space Radio-Diagnostics Research Centre, University of Warmia and Mazury, Prawocheńskiego 9, 10-720 Olsztyn, Poland
⁸ Facultad de Ingeniería y Arquitectura, Universidad Central de Chile, Av. Francisco de Aguirre 0405, La Serena, Coquimbo, Chile
⁹ Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Manchester M13 9PL, UK

Received: 26 June 2023
Accepted: 16 August 2023

Abstract

We present high-angular-resolution observations of Sakurai’s object using the Atacama Large Millimeter Array, shedding new light on its morpho-kinematical structure. The millimetre continuum emission observed at an angular resolution of 20 milliarcsec (corresponding to 70 AU) reveals a bright compact central component whose spectral index indicates that it is composed of amorphous carbon dust. Based on these findings, we conclude that this emission traces the previously suggested dust disc observed in mid-infrared observations, and therefore our observations provide the first direct imaging of this disc. The H¹²CN(J = 4 → 3) line emission observed at an angular resolution of 300 milliarcsec (corresponding to 1000 AU) displays a bipolar structure with a north–south velocity gradient. From the position–velocity diagram of this emission, we identify the presence of an expanding disc and a bipolar molecular outflow. The inclination of the disc is determined to be i = 72°. The derived values for the de-projected expansion velocity and the radius of the disc are v_exp = 53 km s⁻¹ and R = 277 AU, respectively. On the other hand, the de-projected expansion velocity of the bipolar outflow detected in the H¹²CN(J = 4 → 3) emission is of approximately 1000 km s⁻¹. We propose that the molecular outflow has an hourglass morphology with an opening angle of around 60°. Our observations unambiguously show that an equatorial disc and bipolar outflows formed in Sakurai’s object during the 30 years following the occurrence of the born-again event, providing important constraints for future modelling efforts of this phenomenon.