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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

Dan McLachlan, Christian Ginski, Jake Byrne, Chloe Lawlor, Justyn Campbell-White, Rik Claes, Bin Ren, Anibal Sierra

Abstract

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. Aided by a collection of visual and spectroscopic data available for this system, this paper aims to infer the possibility of embedded planets existing within the disk and how the system's environment may affect its disk morphology. Using data from the VLT's instruments XSHOOTER, ESPRESSO and - most prominently - SPHERE along with data from ALMA, we make 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 is 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. The disk is found to be eccentric 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. Measurement of the velocities associated with nearby globule cloud material returns reasonable velocities for a late-stage infall event. We estimate far-ultraviolet 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. 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.

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

Abstract

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. Aided by a collection of visual and spectroscopic data available for this system, this paper aims to infer the possibility of embedded planets existing within the disk and how the system's environment may affect its disk morphology. Using data from the VLT's instruments XSHOOTER, ESPRESSO and - most prominently - SPHERE along with data from ALMA, we make 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 is 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. The disk is found to be eccentric 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. Measurement of the velocities associated with nearby globule cloud material returns reasonable velocities for a late-stage infall event. We estimate far-ultraviolet 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. 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.
Paper Structure (30 sections, 24 equations, 21 figures, 3 tables)

This paper contains 30 sections, 24 equations, 21 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Observations
  3. XSHOOTER/spectroscopic observations
  4. ALMA
  5. Millimetre dust continuum emission
  6. 12CO (J=2-1) emission
  7. SPHERE/scattered light
  8. Methods
  9. Gas velocity analysis
  10. Spiral modelling
  11. Spiral arm contrast
  12. Spiral arm structure and distribution
  13. Eccentricity
  14. Results
  15. Spiral modelling
  16. ...and 15 more sections

Figures (21)

  • Figure 1: Characteristic stellar spectra for AT Pyx. Black indicates the observed spectrum, yellow the best fit photospheric template, red the slab model, light blue the best fit. Top: 2023 September 25 spectrum. Bottom: 2023 November 06 spectrum.
  • Figure 2: ALMA 1.3 mm dust continuum image. The grey ellipse indicates beam size and angle.
  • Figure 3: ALMA images of the AT Pyx system in 12CO (J=2-1) line emission. Left: Total intensity image (Moment 0). Middle: Intensity-weighted velocity (Moment 1). The major (dashed) and minor (dotted) axes are overplotted in black. Right: Peak intensity (moment 8).
  • Figure 4: SPHERE H-band Q$_\phi$ images from 2017 (left) and 2024 (right). All disk features are identical between epochs; the only difference is the better signal-to-noise ratio in the 2024 observation.
  • Figure 5: AT Pyx disk features in H-band scattered light SPHERE Q$_\phi$ image. The spiral features are numbered in order of decreasing apparent length. North is up and east is to the left.
  • ...and 16 more figures