Periodic Reporting for period 1 - OSIRIS (Observational Signatures of planet formation in externally IRradiated dIScs)
Reporting period: 2023-10-01 to 2025-09-30
Summary of the context and overall objectives of the project
Most stars—and most planets—form in massive, crowded stellar nurseries. Although planet formation is often assumed to be an isolated process, the reality is far more complex. Star forming regions are often flooded by intense ultraviolet (UV) radiation from nearby massive stars, which drives photoevaporative winds that strip away disc material, potentially halting planet formation before it even begins. These regions are dynamic environments where stars move rapidly and pass close to one another, potentially perturbing the protoplanetary discs of gas and dust from which planets form. Close stellar encounters can truncate discs, stir their contents, or even eject material entirely, altering the conditions under which planets can grow. Compounding this complexity, significant reservoirs of dense gas and dust often remain in the vicinity of young stars. This material can obscure observations and shape the local radiation field, but may also accrete onto discs and stars, replenishing them with new material and extending their lifetimes.
Despite these factors, protoplanetary are often interpreted as isolated objects. This understanding biases our interpretation of observational evidence. The OSIRIS project set to address this issue by uncovering how environmental factors affect the evolution of protoplanetary discs and the observational constraints on their properties. By linking new models with state-of-the-art data from cutting edge instruments such as the Atacama Large Millimeter/submillimeter Array (ALMA), OSIRIS connected theory with observation to answer a fundamental question: how does the birthplace of a planetary system affect the protoplanetary discs of dust and gas that we observe?
To address this question, the project pursued thel key objectives:
-- Develop and apply models that capture how the environment shapes the structure and evolution of protoplanetary discs in dynamically evolving star forming regions;
-- Analyse and interpret the dynamical response of a disc to its external environment;
-- Link theoretical predictions with observational diagnostics, enabling robust interpretation of environmental effects.
The results of OSIRIS contribute to our understanding of the diversity of planetary systems observed today, offering a more complete picture of how and where planets can form. These insights help contextualise the formation of our own Solar System and guide the interpretation of exoplanet demographics. By integrating theoretical and observational approaches, OSIRIS enhances the scientific return of current and future astronomical facilities and strengthens Europe’s leadership in the study of planet formation under realistic, environmentally complex conditions.
Despite these factors, protoplanetary are often interpreted as isolated objects. This understanding biases our interpretation of observational evidence. The OSIRIS project set to address this issue by uncovering how environmental factors affect the evolution of protoplanetary discs and the observational constraints on their properties. By linking new models with state-of-the-art data from cutting edge instruments such as the Atacama Large Millimeter/submillimeter Array (ALMA), OSIRIS connected theory with observation to answer a fundamental question: how does the birthplace of a planetary system affect the protoplanetary discs of dust and gas that we observe?
To address this question, the project pursued thel key objectives:
-- Develop and apply models that capture how the environment shapes the structure and evolution of protoplanetary discs in dynamically evolving star forming regions;
-- Analyse and interpret the dynamical response of a disc to its external environment;
-- Link theoretical predictions with observational diagnostics, enabling robust interpretation of environmental effects.
The results of OSIRIS contribute to our understanding of the diversity of planetary systems observed today, offering a more complete picture of how and where planets can form. These insights help contextualise the formation of our own Solar System and guide the interpretation of exoplanet demographics. By integrating theoretical and observational approaches, OSIRIS enhances the scientific return of current and future astronomical facilities and strengthens Europe’s leadership in the study of planet formation under realistic, environmentally complex conditions.
Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far
The OSIRIS project carried out a coordinated programme of simulations, theoretical analysis, and interpretation of new observational data to assess how the clustered environments of star formation affect the formation and evolution of protoplanetary discs and the planets they host.
The fellow performed numerous activities targeted at establishing the links between observational signatures and environmental effects on protoplanetary discs in both high- and low-mass star-forming regions, as well as supervising student projects on several aspects of this problem:
-- A theoretical study led by the fellow introduced a novel statistical “excursion-set” formalism to track how environmental factors shape the long-term evolution of protoplanetary discs. The work demonstrated that observed disc properties can be directly inherited from their birth environments, providing a statistical framework to connect initial conditions with present-day observations. This study was published in The Astrophysical Journal Letters (ApJL).
-- A second study addressed the role of dynamical interactions in sparse star-forming regions. Using a new method for modelling stellar dynamics, the fellow applied N-body simulations to the Taurus star-forming region and showed that—even in relatively low-density environments—stellar encounters can significantly influence disc evolution. This work delivered the first statistical estimate of encounter rates in Taurus and predicted the observational consequences for ongoing and future ALMA surveys. These findings were published in Astronomy & Astrophysics (A&A).
-- Building on these theoretical insights, the fellow led an observational study revealing spatially correlated accretion rates among young stars in the Lupus region. These results provide strong evidence that discs are not isolated systems, but continue to interact with their environment through ongoing gas accretion. This study was also published in A&A.
-- A student-led project, supervised and co-developed by the fellow, produced a catalogue of far-ultraviolet (FUV) radiation fields experienced by discs in local star-forming regions. Using a new method to estimate the FUV flux from nearby massive stars, this work provides a foundation for interpreting disc structure and evolution in UV-rich environments. The results were published in A&A.
-- As part of the XUE collaboration, the fellow contributed to the interpretation of JWST spectra of protoplanetary discs exposed to intense radiation fields. These efforts have resulted in two published studies, with more in progress.
-- As a member of the exoALMA collaboration, the fellow contributed to theoretical modelling and interpretation of ALMA observations of CO molecular lines in discs. These studies span a wide range of physical conditions and focus on recovering disc substructures, kinematics, and turbulence. Seventeen papers from the collaboration were published in ApJL during the fellowship period.
-- The fellow also contributed theoretical expertise to the interpretation of VLT/MUSE observations of externally irradiated discs in the Orion Nebula Cluster. These studies identified new observational tracers of photoevaporative winds and provided physical constraints on the interplay between disc structure and external UV fields. Results were published in A&A.
-- In parallel, the fellow played a key role in designing and motivating new observational campaigns. This included contributing to successful proposals for ALMA, VLT, and two JWST programmes focused on discs in irradiated environments.
-- Finally, the fellow co-led a large collaborative effort to synthesise the current state of knowledge on externally irradiated discs. This culminated in a comprehensive review article, now published, that will serve as a guide for the next generation of observational and theoretical work.
Together, these activities delivered new theoretical tools, simulation frameworks, observational catalogues, and physical insights that significantly advance our understanding of planet formation in realistic, environmentally complex settings.
The fellow performed numerous activities targeted at establishing the links between observational signatures and environmental effects on protoplanetary discs in both high- and low-mass star-forming regions, as well as supervising student projects on several aspects of this problem:
-- A theoretical study led by the fellow introduced a novel statistical “excursion-set” formalism to track how environmental factors shape the long-term evolution of protoplanetary discs. The work demonstrated that observed disc properties can be directly inherited from their birth environments, providing a statistical framework to connect initial conditions with present-day observations. This study was published in The Astrophysical Journal Letters (ApJL).
-- A second study addressed the role of dynamical interactions in sparse star-forming regions. Using a new method for modelling stellar dynamics, the fellow applied N-body simulations to the Taurus star-forming region and showed that—even in relatively low-density environments—stellar encounters can significantly influence disc evolution. This work delivered the first statistical estimate of encounter rates in Taurus and predicted the observational consequences for ongoing and future ALMA surveys. These findings were published in Astronomy & Astrophysics (A&A).
-- Building on these theoretical insights, the fellow led an observational study revealing spatially correlated accretion rates among young stars in the Lupus region. These results provide strong evidence that discs are not isolated systems, but continue to interact with their environment through ongoing gas accretion. This study was also published in A&A.
-- A student-led project, supervised and co-developed by the fellow, produced a catalogue of far-ultraviolet (FUV) radiation fields experienced by discs in local star-forming regions. Using a new method to estimate the FUV flux from nearby massive stars, this work provides a foundation for interpreting disc structure and evolution in UV-rich environments. The results were published in A&A.
-- As part of the XUE collaboration, the fellow contributed to the interpretation of JWST spectra of protoplanetary discs exposed to intense radiation fields. These efforts have resulted in two published studies, with more in progress.
-- As a member of the exoALMA collaboration, the fellow contributed to theoretical modelling and interpretation of ALMA observations of CO molecular lines in discs. These studies span a wide range of physical conditions and focus on recovering disc substructures, kinematics, and turbulence. Seventeen papers from the collaboration were published in ApJL during the fellowship period.
-- The fellow also contributed theoretical expertise to the interpretation of VLT/MUSE observations of externally irradiated discs in the Orion Nebula Cluster. These studies identified new observational tracers of photoevaporative winds and provided physical constraints on the interplay between disc structure and external UV fields. Results were published in A&A.
-- In parallel, the fellow played a key role in designing and motivating new observational campaigns. This included contributing to successful proposals for ALMA, VLT, and two JWST programmes focused on discs in irradiated environments.
-- Finally, the fellow co-led a large collaborative effort to synthesise the current state of knowledge on externally irradiated discs. This culminated in a comprehensive review article, now published, that will serve as a guide for the next generation of observational and theoretical work.
Together, these activities delivered new theoretical tools, simulation frameworks, observational catalogues, and physical insights that significantly advance our understanding of planet formation in realistic, environmentally complex settings.
Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)
The OSIRIS project has produced multiple advances beyond the state of the art in the field of planet formation, particularly in the context of externally influenced protoplanetary discs. These include new theoretical tools, improved interpretive frameworks for observations, and novel observational diagnostics, many of which lay the groundwork for future scientific and technological developments.
A key theoretical advancement is the development of an “excursion-set” statistical formalism for tracking the evolution of discs embedded in dynamically evolving star-forming environments. This approach, adapted from cosmological structure formation, allows for rapid and robust predictions of how disc populations respond to varying levels of stellar density, external radiation, and dynamical interactions. It enables a self-consistent treatment of the link between large-scale environment and disc-scale physics, and provides a new way to interpret disc demographics across different star-forming regions. The results demonstrated that the properties of observed protoplanetary discs could be interpreted as being directly inherited from the surroundings. This has broad consequences for the field, and the approach may be adapted in future for diverse applications to interpret populations of protoplanetary discs.
The project also introduced a novel simulation framework for modelling stellar dynamics in observed regions, successfully applying this to the Taurus region to infer encounter statistics and their impact on disc structure . This approach allows environmental effects to be reconstructed from current stellar positions and motions, without needing full hydrodynamical simulations of star forming region. This opens a path toward connecting astrometric surveys (e.g. Gaia) with disc evolution studies in specific regions.
Observationally, OSIRIS has helped define new diagnostics of environmental influence. The project demonstrated, for the first time, spatial correlations in stellar accretion rates that likely reflect ongoing gas flows from the local environment . This challenges the conventional view of discs as closed systems and underscores the importance of environmental inflows in regulating disc longevity and planet formation. If the environment affects gas all the way down to the scale of the stellar radius, this is a radical departure from the canonical picture of planet formation.
In terms of data products, a student-led component of OSIRIS produced a catalogue of FUV radiation fields affecting discs in local star-forming regions, using a new photometric estimation technique. This publicly accessible dataset enables statistical comparisons across star-forming regions and improves the interpretive power of ALMA and JWST surveys. The novel method applied here makes calculations of distances between stars far more accurate than can be achieved by e.g. Gaia data alone, and therefore has broad applications beyond the immediate goals of the OSIRIS project.
The project also delivered new physical interpretation tools for molecular line observations. Through contributions to the exoALMA collaboration, OSIRIS helped build and interpret a major observational database of CO kinematics, substructure, and turbulence in discs. These studies connect observed features such as pressure maxima and spiral arms to underlying physical processes including planet-disc interactions and magnetic turbulence .
The results of OSIRIS have direct implications for the interpretation of data from major facilities (ALMA, JWST, VLT) and guide the selection of targets and tracers in future surveys.
A key theoretical advancement is the development of an “excursion-set” statistical formalism for tracking the evolution of discs embedded in dynamically evolving star-forming environments. This approach, adapted from cosmological structure formation, allows for rapid and robust predictions of how disc populations respond to varying levels of stellar density, external radiation, and dynamical interactions. It enables a self-consistent treatment of the link between large-scale environment and disc-scale physics, and provides a new way to interpret disc demographics across different star-forming regions. The results demonstrated that the properties of observed protoplanetary discs could be interpreted as being directly inherited from the surroundings. This has broad consequences for the field, and the approach may be adapted in future for diverse applications to interpret populations of protoplanetary discs.
The project also introduced a novel simulation framework for modelling stellar dynamics in observed regions, successfully applying this to the Taurus region to infer encounter statistics and their impact on disc structure . This approach allows environmental effects to be reconstructed from current stellar positions and motions, without needing full hydrodynamical simulations of star forming region. This opens a path toward connecting astrometric surveys (e.g. Gaia) with disc evolution studies in specific regions.
Observationally, OSIRIS has helped define new diagnostics of environmental influence. The project demonstrated, for the first time, spatial correlations in stellar accretion rates that likely reflect ongoing gas flows from the local environment . This challenges the conventional view of discs as closed systems and underscores the importance of environmental inflows in regulating disc longevity and planet formation. If the environment affects gas all the way down to the scale of the stellar radius, this is a radical departure from the canonical picture of planet formation.
In terms of data products, a student-led component of OSIRIS produced a catalogue of FUV radiation fields affecting discs in local star-forming regions, using a new photometric estimation technique. This publicly accessible dataset enables statistical comparisons across star-forming regions and improves the interpretive power of ALMA and JWST surveys. The novel method applied here makes calculations of distances between stars far more accurate than can be achieved by e.g. Gaia data alone, and therefore has broad applications beyond the immediate goals of the OSIRIS project.
The project also delivered new physical interpretation tools for molecular line observations. Through contributions to the exoALMA collaboration, OSIRIS helped build and interpret a major observational database of CO kinematics, substructure, and turbulence in discs. These studies connect observed features such as pressure maxima and spiral arms to underlying physical processes including planet-disc interactions and magnetic turbulence .
The results of OSIRIS have direct implications for the interpretation of data from major facilities (ALMA, JWST, VLT) and guide the selection of targets and tracers in future surveys.