Young system development in a cometary globule

An investigation into the eccentric disk around AT Pyx^* in terms of planet formation and interaction with its surrounding environment

¹ Charles University, Faculty of Mathematics and Physics, Astronomical Institute, V Holešovičkách 2, 18000 Praha 8, Czechia
² School of Natural Sciences, Center for Astronomy, University of Galway, Galway, H91 CF50, Ireland
³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁴ P.E.S., Observatoire de la Côte d’Azur, Nice 06304, France
⁵ Universidad Nacional Autónoma de México, Instituto de Astronomía, A.P. 70-264, Ciudad de México 04510, Mexico
⁶ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 4 November 2025
Accepted: 13 February 2026

Abstract

Context. To understand the formation of planetary systems, it is necessary to observe and study systems at different evolutionary stages and in different environments. This paper presents new data and analyses of the AT Pyx system, a disk-hosting young star located in a cometary globule in the Gum Nebula. This radiation-driven structure is an unusual environment for observations of planet formation, and differs greatly from the low-mass star-forming regions disks are most commonly observed in.

Aims. Aided by a collection of visual and spectroscopic data available for this system, our aim is to infer the possibility of embedded planets existing within the disk and how the system’s environment may affect its disk morphology.

Methods. Using data from the VLT’s instruments XSHOOTER, ESPRESSO, and most prominently SPHERE, along with data from ALMA, we made a variety of measurements (geometric, photometric, and otherwise) to characterise the observed disk features and attributes such as spiral arms and eccentricity. Mapping of the velocity components was also undertaken using the ALMA gas line data to characterise disk orientation and determine the likelihood that the system is experiencing a late-stage infall event.

Results. The disk is measured to have a position angle of 28.06 ± 0.02^° and an inclination of 42.5 ± 0.5^°. The disk is found to be eccentric with measured e ≈ 0.626 when deprojected. Under the assumption that the formation of a planet is wholly responsible for the primary and secondary spiral arms, we find the mass of such a planet can range between 0.004 and 3 Jupiter masses. Measurements of the velocities associated with nearby globule cloud material return reasonable velocities for a late-stage infall event. We estimate the far-ultraviolet (FUV) field strength at AT Pyx’s location to be low in comparison to other surveyed disks. We also find that AT Pyx is possibly a binary system.

Conclusions. AT Pyx is the first disk within a cometary globule to be spatially resolved, and is now the first such disk to be investigated to this extent. The work of this paper could potentially be a first step into the further study of disks in the moderate FUV environment of the Gum Nebula and its globules.