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Chemical tracers of a highly eccentric AGB–main-sequence star binary

Nature Astronomy volume 8, pages 308–327 (2024)Cite this article

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Abstract

Binary interactions have been proposed to explain a variety of circumstellar structures seen around evolved stars, including asymptotic giant branch (AGB) stars and planetary nebulae. Studies resolving the circumstellar envelopes of AGB stars have revealed spirals, disks and bipolar outflows, with shaping attributed to interactions with a companion. Here we use a combined chemical and dynamical analysis to reveal a highly eccentric and long-period orbit for W Aquilae, a binary system containing an AGB star and a main-sequence companion. Our results are based on anisotropic SiN emission, the detections of irregular NS and SiC emission towards the S-type star, and density structures observed in the CO emission. These features are all interpreted as having formed during periastron interactions. Our astrochemistry-based method can yield stringent constraints on the orbital parameters of long-period binaries containing AGB stars, and will be applicable to other systems.

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Fig. 1: Observed SiN emission towards W Aql.
Fig. 2: Plots of the orbit of the W Aql system as seen in the plane of the sky.
Fig. 3: Observed SiO, SiS, CS and HCN emission towards W Aql.
Fig. 4: Observed emission of CN-bearing molecules towards W Aql.
Fig. 5: Observations and simulations of CO emission towards W Aql.

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Data availability

The observational data used here are openly available through the data archives for ALMA (https://almascience.nrao.edu/aq/), ESO for the APEX and SPHERE data (http://archive.eso.org), and HST (https://hla.stsci.edu). Custom ALMA data products that were produced for this study are available from T.D. or A.M.S.R. (a.m.s.richards@manchester.ac.uk) upon reasonable request. The Phantom input and output files from our main model can be downloaded from https://doi.org/10.26180/24240001.v1.

Code availability

Phantom is open source under the GPLv3 license and can be downloaded via https://github.com/danieljprice/phantom. MCFOST is open source under the GPLv3 license and can be downloaded via https://mcfost.readthedocs.io/en/latest/overview.html. ALI, the one-dimensional radiative transfer code, is available from the corresponding author upon reasonable request.

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Acknowledgements

We thank S.-H. Cho of the Korean VLBI Network for KVN observations of W Aql to confirm consistency with our ALMA results. T.D. is supported in part by the Australian Research Council through a Discovery Early Career Researcher Award (DE230100183). T.D., F.D.C. and S.H.J.W. acknowledge support from the Research Foundation Flanders (FWO) through grants 12N9920N, 1253223N and 1285221N, respectively. J.M. and S.M. acknowledge support from the Research Foundation Flanders (FWO) grant G099720N. M.V.d.S. acknowledges support from European Union’s Horizon 2020 Research and Innovation programme under the Marie Skłodowska-Curie grant agreement number 882991. M.M. acknowledges funding form the Programme Paris Region fellowship supported by the Région Ile-de-France. P.K. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation programme (synergy grant project UniverScale, grant agreement 951549). T.J.M. is grateful to the STFC for support through grant ST/P000312/1 and thanks the Leverhulme Trust for the award of an Emeritus Fellowship. J.M.C.P. was supported by STFC grant number ST/T000287/1. L.D., J.M.C.P., S.H.J.W., S.M. and D.G. acknowledge support from ERC consolidator grant 646758 AEROSOL. E.D.B. acknowledges support from the Swedish National Space Agency. D.G. was funded by the project grant ‘The Origin and Fate of Dust in Our Universe’ from the Knut and Alice Wallenberg Foundation. K.T.W. acknowledges support from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation programme (grant agreement number 883867, project EXWINGS). F.H., A.B. and L.M. acknowledge funding from the French National Research Agency (ANR) project PEPPER (ANR-20-CE31-0002). H.S.P.M. acknowledges support by the Deutsche Forschungsgemeinschaft through the collaborative research grant SFB 956 (project ID 184018867). R.S.’s contribution to the research described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA, and funded in part by NASA via ADAP awards, and multiple HST GO awards from the Space Telescope Science Institute. A.Z. is funded by STFC/UKRI through grant ST/T000414/1. This research was supported in part by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. This project has received funding from the Framework Program for Research and Innovation ‘Horizon 2020’ under the convention Marie Skłodowska-Curie No 945298. Computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation Flanders (FWO) and the Flemish Government, department EWI. This research was undertaken with the assistance of resources and services from the National Computational Infrastructure (NCI), which is supported by the Australian Government. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2018.1.00659.L. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 0103.D-0772(A). We acknowledge excellent support from the UK ALMA Regional Centre (UK ARC), which is hosted by the Jodrell Bank Centre for Astrophysics (JBCA) at the University of Manchester. The UK ARC Node is supported by STFC Grant ST/P000827/1.

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Authors and Affiliations

  1. Institute of Astronomy, KU Leuven, Leuven, Belgium

    T. Danilovich, J. Malfait, F. De Ceuster, A. Coenegrachts, L. Decin, J. Bolte, A. de Koter, S. Maes & S. H. J. Wallström

  2. School of Physics and Astronomy, Monash University, Clayton, Victoria, Australia

    T. Danilovich, C. Pinte & D. J. Price

  3. ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Clayton, Victoria, Australia

    T. Danilovich

  4. School of Physics and Astronomy, University of Leeds, Leeds, UK

    M. Van de Sande

  5. LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, Meudon, France

    M. Montargès & P. Kervella

  6. Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast, UK

    T. J. Millar

  7. JBCA, Department Physics and Astronomy, University of Manchester, Manchester, UK

    A. M. S. Richards, S. Etoka, M. Gray, I. McDonald, B. Pimpanuwat & A. Zijlstra

  8. School of Chemistry, University of Leeds, Leeds, UK

    L. Decin & J. M. C. Plane

  9. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA

    C. A. Gottlieb

  10. Université Grenoble Alpes, CNRS, IPAG, Grenoble, France

    C. Pinte

  11. Department of Space, Earth and Environment, Chalmers University of Technology, Gothenburg, Sweden

    E. De Beck

  12. Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden

    K. T. Wong

  13. Institut de Radioastronomie Millimétrique, Saint-Martin-d’Hères, France

    K. T. Wong

  14. Department of Mathematics, Kiel University, Kiel, Germany

    J. Bolte

  15. Max-Planck-Institut für Radioastronomie, Bonn, Germany

    K. M. Menten & M. Jeste

  16. Laboratoire d’Astrophysique de Bordeaux, Université de Bordeaux, Pessac, France

    A. Baudry, F. Herpin & L. Marinho

  17. Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands

    A. de Koter

  18. Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden

    D. Gobrecht

  19. National Astronomical Research Institute of Thailand, Chiangmai, Thailand

    M. Gray & B. Pimpanuwat

  20. Laboratoire Lagrange, Observatoire de la Côte d’Azur, Université Côte d’Azur, Nice, France

    E. Lagadec

  21. School of Physical Sciences, The Open University, Milton Keynes, UK

    I. McDonald

  22. I. Physikalisches Institut, Universität zu Köln, Cologne, Germany

    H. S. P. Müller

  23. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

    R. Sahai

  24. Department of Computer Science, University College London, London, UK

    J. Yates

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  1. T. Danilovich
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  2. J. Malfait
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  35. A. Zijlstra
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Contributions

T.D. conceived of and led this publication, analysed and interpreted data, performed the radiative transfer models, wrote the paper, and created most of the figures. J.M. performed and interpreted the hydrodynamics model and made Fig. 5c, and Supplementary Figs. 9a,b and 10. M.V.d.S. led the chemical interpretation and made Supplementary Figs. 7 and 8. M.M. and P.K. contributed the analysis of the resolved imaging. A.M.S.R. performed the ALMA data reduction. F.D.C. and A.C. contributed to the three-dimensional interpretation of the data. T.J.M. and J.M.C.P. contributed to the chemical interpretation. C.A.G. contributed to the line identifications and interpretation. C.P. assisted in the MCFOST modelling. D.J.P. assisted in the Phantom modelling and interpretation. E.D.B. contributed the fully reduced APEX data. The ALMA proposal was led by L.D. and C.A.G., with contributions from M.M., T.D., A.d.K., K.M.M., R.S., A.M.S.R., J.M.C.P., H.S.P.M., E.D.B., P.K., A.B., K.T.W., M.V.d.S., E.L., D.G., J.Y. and D.J.P. All authors contributed to discussions of the results, and commented on the paper and analysis.

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Correspondence to T. Danilovich.

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Extended data

Extended Data Fig. 1 A series of sketches illustrating the formation of SiN during the periastron passage of the W Aql system.

The orbit (black line) is shown face on in the frame of the AGB star and the F9 star is assumed to be moving clockwise. Relative to our observations, the observer is located to the left, represented by the radio dish. (a) The F9 star (yellow) approaches the AGB star (red) and enters the dense inner wind region (\({n}_{{{{{\rm{H}}}}}_{2}} \sim 1{0}^{8}\) to 1010 cm−3). (b) The rapid periastron passage is completed and SiN (and, similarly, SiC and NS) has formed in the wake of the F9 star (cyan region), with formation initiated by the F9 UV flux (see ‘Chemical modelling’ in the Methods). (c) As the F9 star continues on its orbit, the arc of SiN expands away from the AGB star, along with the stellar wind in which it is embedded. The present-day configuration of SiN can be seen in Fig. 1, where the PV diagram is a good approximation of the final arc shape that would be seen around the AGB star were the orbit viewed face-on.

Extended Data Fig. 2 Observed SiC emission towards W Aql.

(a) Zeroth moment map of SiC towards W Aql with contours at levels of 3 and 5σ. Transition details are given in Table 1. North is up and east is to the left. The position of the AGB star is indicated by the red star at (0,0) and the location of the F9 companion is indicated by the yellow star to the south-west. North is up and east is left. The white ellipse in the bottom left corner indicates the size of the synthesized beam. (b) Position-velocity diagram of SiC towards W Aql, taken with the same wide slit as used for SiN (Fig. 1), with a position angle of north 33∘ east. Dashed black contours are at levels of 3 and 5σ, a dotted white parabola is fit to the data (see ‘SiN and SiC’ in the ‘Data reduction’ section in the Methods), and a dash-dotted pink ellipse is plotted to emphasize the shape of the emission in the PV diagram. The position and LSR velocity of the AGB star is indicated by the red star and the horizontal yellow dotted line indicates the present offset of the F9 star.

Extended Data Fig. 3 Plots of NS towards W Aql.

(a) Zeroth moment map of NS towards W Aql with contours at levels of 3 and 5σ. North is up and east is to the left. The position of the AGB star is indicated by the red star at (0,0) and the location of the F9 companion is indicated by the yellow star to the south-west. The white ellipse in the bottom left corner indicates the size of the synthesized beam. (b) Position-velocity diagram of NS taken with the same wide slit as used for SiN (Fig. 1). The position and LSR velocity of the AGB star is indicated by the red star and the horizontal dotted yellow line indicates the present offset of the F9 star. (c) Spectra of the NS, SiN and SiC lines given in Table 1. All lines were extracted for circular apertures with radii 0.25″, centred on the continuum peak. The flux of the SiC spectrum is multiplied by 5 to allow for a more direct comparison to SiN and NS.

Extended Data Fig. 4 Central channels of molecular emission towards W Aql.

A channel of SiS (left) and CS (right) are plotted, showing the asymmetric distribution of these molecules caused by the flux from the F9 star. The positions of the AGB and F9 stars are indicated by the red and yellow stars, respectively. The channel velocities are given in the top right corners and the beam is shown in the bottom left corner. Contours are plotted for levels of 3, 5, and 10σ. North is up and east is left.

Extended Data Fig. 5 A comparison of spectral lines at different locations in the AGB wind.

Plots are shown of CS, HCN, SiO and H13CN emission extracted from circular apertures with 100 mas radii centred on the F9 star (blue), on the AGB star (orange) and at the same separation as the F9 star but on the opposite side of the AGB (Opp. F9, brown, dashed). (See Table 1 for line frequencies.) The AGB and Opp. F9 line profiles are scaled by the factor given in the legend to facilitate comparison with the F9 line profiles. The vertical grey line indicates υLSR = − 23km s−1.

Extended Data Fig. 6 Zeroth moment maps of HC3N towards W Aql.

The transition for each map is given in the top right, with further details given in Table 1. Contours are plotted at levels of 3 and 5σ. North is up and east is to the left. The position of the AGB star is indicated by the red star at (0,0), also corresponding to the continuum peak, and the location of the F9 companion is indicated by the yellow star to the south-west. The white ellipse in the bottom left corner indicates the size of the synthesized beam.

Extended Data Fig. 7 CO emission towards W Aql.

Channel maps of CO (J = 2 → 1) are shown towards W Aql, obtained by combining observations from three configurations of ALMA. The AGB star is located at (0,0) and is marked by a red cross. The LSR velocity of each channel is given in the top right hand corner and the three channels closest to the W Aql υLSR = − 23km s−1 are highlighted with red borders and summed for Fig. 5. The synthetic beam is given by the white ellipse in the bottom left corner of each channel. North is up and east is left.

Extended Data Fig. 8 Variations in the radial emission of CO with angle.

The plots show the radial emission distribution against angle for the summed central three channels of CO (Fig. 5) with a full revolution shown in the centre (0 to 2π) and half a revolution is shown on either side ( − π to 0 and 2π to 3π) to show how the structures extend onwards. The location of the F9 star is indicated by the yellow star and a yellow dotted line which passes through both stars is plotted in the central winding to guide the eye. The black, red and white curves correspond to the same features highlighted in Fig. 5. The top plot shows the full observed extent of the CO emission (out to 15″) and the bottom plot focuses on the regions out to 5″ from the AGB star. These plots are reproduced without the additional curves in Supplementary Figure 4.

Extended Data Fig. 9 Observations and models of blue and red CO emission towards W Aql.

The plots show that blue (a and c) and red (b and d) channels equidistant from the stellar LSR velocity (υLSR = − 23km s−1) in velocity space do not exhibit identical CO emission patterns. The ALMA observations (a and b) show an elongated emission region on the blue side (a) and an approximately round emission region on the red side (b). The same pattern is mimicked in the red (c) and blue (d) channels of the hydrodynamic model processed with MCFOST. The red and black crosses correspond to the locations of the AGB and F9 stars. Note that the modelled and observed positions do not exactly correspond. Details are given in ‘Hydrodynamic simulations’ in the Methods.

Extended Data Table 1 Possible orbital solutions for the W Aql system
Full size table

Supplementary information

Supplementary Information

Supplementary Discussion (‘Radiation pressure on dust’ and ‘Anisotropic mass loss’), Table 1 and Figs. 1–13.

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Danilovich, T., Malfait, J., Van de Sande, M. et al. Chemical tracers of a highly eccentric AGB–main-sequence star binary. Nat Astron 8, 308–327 (2024). https://doi.org/10.1038/s41550-023-02154-y

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