Periodic Reporting for period 1 - SANDS (Stars, plANets, and Discs in multiple Systems)
Periodo di rendicontazione: 2020-04-01 al 2022-03-31
The main objective of the SANDS project was to study disc dynamics and planet formation in multiple stellar systems. Three main goals were foreseen in the context of multiple stellar systems: i) develop hydrodynamical tools to model these discs (WP1); ii) model recently imaged discs in such systems and create synthetic observations at different wavelengths (WP2); iii) study the secular behaviour of perturbed discs (WP3). The detailed study of stellar binaries, triples and flybys – both theoretically and observationally – shed light on the way protoplanetary discs evolve and the resulting impact on planet formation. As a matter of fact, the three WPs of the SANDS project led to 24 articles scientific articles in total, published in peer-reviewed journals (NB: 5 currently under review). Understanding the way discs form planets around young stars is key to reveal how planets (as the ones in our own Solar System) form in our Galaxy and in the Universe in general. Moreover, since most stars are born in systems composed of more than one star, it is of crucial importance to extend our current protoplanetary disc models to multiple stellar systems. This was at the very core of the SANDS projects. The results obtained constitute the foundation of the more ambitious ERC Starting Grant Stellar-MADE project that will start in October 2022 (PI: N. Cuello).
WP1: Disc dynamics in multiple systems
I developed new tools for the code Phantom (Price et al. 2018b) together with my collaborators. Thanks to these new algorithms – available online on the public repository of the code on GitHub – it is now possible to easily setup discs within multiple stellar systems with 2, 3 or 4 stars (in hierarchical configuration or not). Based on this work, I extensively studied the morphology of circumtertiary discs as a function the stellar orbital configuration (semi-major axis, eccentricity, mass ratio). This comprehensive and preliminary work, showed that for hierarchical configurations as the ones often found in Nature, triple stellar systems affect the surrounding disc in a very similar manner as binaries with similar orbital parameters. I worked together with Simone Ceppi on extending this approach to stellar accretion in triples. We found that triples feed from the available disc material in a different manner compared to binaries (see Figure 1), which has profound implications both for planet formation and stellar populations. All these results were recently published in MNRAS (Ceppi, Cuello, Lodato et al., 2022). Regarding the inclusion of radiative effects in Phantom simulations, I developed and tested new methods to take the stellar radiation into account in collaboration with my collaborators in Monash University. In particular, we considered the case of disc-penetrating stellar flybys, which create the most extreme heating events for discs. This work showed that, besides significantly heating the disc, such events lead to dramatic accretion events which are naturally connected to luminosity outburst as the one observed in the archetypical system FU Orionis. We reported the first simulations using the hybrid code Phantom-mcfost and our proposed dynamical scenario in Borchert, Price, Pinte & Cuello (2022).
WP2: Modelling of recently imaged discs in multiple systems.
Thanks to the developed numerical setups and my previous experience in modelling discs in stellar binaries, I participated to observational programmes to image protoplanetary discs in multiple stellar systems. For this specific part of project, I worked closely with Prof. François Ménard at my host institution CNRS/IPAG who is a recognised expert in ALMA and VLT observations. More specifically, we combined several data sets obtained with last-generation telescopes at different wavelengths (from µm to mm emission). During the project, I modelled together with my collaborators the 13 multiple stellar systems with discs. Thanks to the results obtained and the expertise developed, I was invited to become a member of two ALMA Large Programme: exoALMA led by R. Teague (CfA/Harvard, USA) and FAUST led by S. Yamamoto (Tokyo, Japan). Within the FAUST consortium, I am currently leading a project regarding the modelling of L1551 IRS 5 (Cuello et al., in prep.). This binary stellar system is of particular interest due to its young age (Class I star) and the disc over-density observed. Thanks to my hydrodynamical models we were able to show how binary-induced dust traps can already form at early disc evolutionary stages.
WP3: Secular behaviour of perturbed discs in multiple systems.
In March 2021, Damien Latafi (a student from Grenoble) started working on this project under my supervision. We mainly focused on N-body integrations of circumbinary (P-type) planets in binary and triple stellar systems. The goal was to establish the regions of stability in these systems on secular timescales. The N-body approach allowed us to explore which are the most stable orbits in binary and triple stellar systems. To do so, we used the code Rebound (Rein & Liu, 2012) to perform N-body integrations. To test our approach, we first reproduced previous results for S- and P-type orbits in binaries. Then, we extended our exploration to triple stellar systems with different orbital parameters (semi-major axis, mass ratio, and eccentricity). We found new regions of planet stability close to the inner binary for different inclinations of the third (outer) star. In fact, for small enough separations, planets are able to avoid Kozai-Lidov oscillations without being too close to the binary, which would render the orbits unstable (Cuello & Giuppone, in prep.).
Scientific publications
During the project, I published 19 articles in total in prestigious peer-review journals such as Nature Astronomy, MNRAS, A&A, and ApJ. Recently, I submitted 5 other articles to be published in the next months. I presented my work in 6 conferences (1 invited review talk and 5 contributed talks) and seminars (4 in France, 1 in UK).
I developed new tools for the code Phantom (Price et al. 2018b) together with my collaborators. Thanks to these new algorithms – available online on the public repository of the code on GitHub – it is now possible to easily setup discs within multiple stellar systems with 2, 3 or 4 stars (in hierarchical configuration or not). Based on this work, I extensively studied the morphology of circumtertiary discs as a function the stellar orbital configuration (semi-major axis, eccentricity, mass ratio). This comprehensive and preliminary work, showed that for hierarchical configurations as the ones often found in Nature, triple stellar systems affect the surrounding disc in a very similar manner as binaries with similar orbital parameters. I worked together with Simone Ceppi on extending this approach to stellar accretion in triples. We found that triples feed from the available disc material in a different manner compared to binaries (see Figure 1), which has profound implications both for planet formation and stellar populations. All these results were recently published in MNRAS (Ceppi, Cuello, Lodato et al., 2022). Regarding the inclusion of radiative effects in Phantom simulations, I developed and tested new methods to take the stellar radiation into account in collaboration with my collaborators in Monash University. In particular, we considered the case of disc-penetrating stellar flybys, which create the most extreme heating events for discs. This work showed that, besides significantly heating the disc, such events lead to dramatic accretion events which are naturally connected to luminosity outburst as the one observed in the archetypical system FU Orionis. We reported the first simulations using the hybrid code Phantom-mcfost and our proposed dynamical scenario in Borchert, Price, Pinte & Cuello (2022).
WP2: Modelling of recently imaged discs in multiple systems.
Thanks to the developed numerical setups and my previous experience in modelling discs in stellar binaries, I participated to observational programmes to image protoplanetary discs in multiple stellar systems. For this specific part of project, I worked closely with Prof. François Ménard at my host institution CNRS/IPAG who is a recognised expert in ALMA and VLT observations. More specifically, we combined several data sets obtained with last-generation telescopes at different wavelengths (from µm to mm emission). During the project, I modelled together with my collaborators the 13 multiple stellar systems with discs. Thanks to the results obtained and the expertise developed, I was invited to become a member of two ALMA Large Programme: exoALMA led by R. Teague (CfA/Harvard, USA) and FAUST led by S. Yamamoto (Tokyo, Japan). Within the FAUST consortium, I am currently leading a project regarding the modelling of L1551 IRS 5 (Cuello et al., in prep.). This binary stellar system is of particular interest due to its young age (Class I star) and the disc over-density observed. Thanks to my hydrodynamical models we were able to show how binary-induced dust traps can already form at early disc evolutionary stages.
WP3: Secular behaviour of perturbed discs in multiple systems.
In March 2021, Damien Latafi (a student from Grenoble) started working on this project under my supervision. We mainly focused on N-body integrations of circumbinary (P-type) planets in binary and triple stellar systems. The goal was to establish the regions of stability in these systems on secular timescales. The N-body approach allowed us to explore which are the most stable orbits in binary and triple stellar systems. To do so, we used the code Rebound (Rein & Liu, 2012) to perform N-body integrations. To test our approach, we first reproduced previous results for S- and P-type orbits in binaries. Then, we extended our exploration to triple stellar systems with different orbital parameters (semi-major axis, mass ratio, and eccentricity). We found new regions of planet stability close to the inner binary for different inclinations of the third (outer) star. In fact, for small enough separations, planets are able to avoid Kozai-Lidov oscillations without being too close to the binary, which would render the orbits unstable (Cuello & Giuppone, in prep.).
Scientific publications
During the project, I published 19 articles in total in prestigious peer-review journals such as Nature Astronomy, MNRAS, A&A, and ApJ. Recently, I submitted 5 other articles to be published in the next months. I presented my work in 6 conferences (1 invited review talk and 5 contributed talks) and seminars (4 in France, 1 in UK).
The SANDS project successfully addressed the topic of discs dynamics in multiple stellar systems. The results obtained unambiguously show that stellar multiplicity has a dramatic impact on the way discs evolve around young stars. This in turn drastically modifies the conditions under which the first solids and planets form. The detailed study I performed through last-generation hydrodynamical simulations goes beyond the state-of-the-art. By developing new tools (e.g. the hybrid hydrodynamical code with live transfer called Phantom-mcfost) and by robustly connecting hydrodynamical models with telescope observations, the results obtained in WP1 and WP2 constitute a valuable legacy for the community working on planet formation and exoplanets. The results obtained in WP3 on planet stability in multiple stellar systems opened new scientific perspectives in order to connect disc dynamics to (exo)planetary architectures. This aspect will be further explored in the upcoming Stellar-MADE project (ERC Starting Grant 2021, October 2022 - September 2027). It is worth noting that this ERC grant application was submitted in April 2021, directly relying on the results obtained during the SANDS project. The impact of this MSCA-IF is clear: it demonstrated the relevance of multiple stellar systems for planet formation theories and it opened new avenues for future research in the field.