Radiation shielding of protoplanetary discs in young star-forming regions

Protoplanetary discs spend their lives in the dense environment of a star forming region. While there, they can be affected by nearby stars through external photoevaporation and dynamic truncations. We present simulations that use the AMUSE framework to couple the Torch model for star cluster formation from a molecular cloud with a model for the evolution of protoplanetary discs under these two environmental processes. We compare simulations with and without extinction of photoevaporation-driving radiation. We find that the majority of discs in our simulations are considerably shielded from photoevaporation-driving radiation for at least 0.5 Myr after the formation of the first massive stars. Radiation shielding increases disc lifetimes by an order of magnitude and can let a disc retain more solid material for planet formation. The reduction in external photoevaporation leaves discs larger and more easily dynamically truncated, although external photoevaporation remains the dominant mass loss process. Finally, we find that the correlation between disc mass and projected distance to the most massive nearby star (often interpreted as a sign of external photoevaporation) can be erased by the presence of less massive stars that dominate their local radiation field. Overall, we find that the presence and dynamics of gas in embedded clusters with massive stars is important for the evolution of protoplanetary discs.Comment: 23 pages, 22 figures, 1 table, accepted for publication in MNRA

Implementing Primordial Binaries in Simulations of Star Cluster Formation with a Hybrid MHD and Direct N-Body Method

The fraction of stars in binary systems within star clusters is important for their evolution, but what proportion of binaries form by dynamical processes after initial stellar accretion remains unknown. In previous work, we showed that dynamical interactions alone produced too few low-mass binaries compared to observations. We therefore implement an initial population of binaries in the coupled MHD and direct N-body star cluster formation code Torch. We compare simulations with, and without, initial binary populations and follow the dynamical evolution of the binary population in both sets of simulations, finding that both dynamical formation and destruction of binaries take place. Even in the first few million years of star formation, we find that an initial population of binaries is needed at all masses to reproduce observed binary fractions for binaries with mass ratios above the $q \geq 0.1$ detection limit. Our simulations also indicate that dynamical interactions in the presence of gas during cluster formation modify the initial distributions towards binaries with smaller primary masses, larger mass ratios, smaller semi-major axes and larger eccentricities. Systems formed dynamically do not have the same properties as the initial systems, and systems formed dynamically in the presence of an initial population of binaries differ from those formed in simulations with single stars only. Dynamical interactions during the earliest stages of star cluster formation are important for determining the properties of binary star systems.Comment: 15 pages, 14 figures, submitted to MNRAS and edited to address positive referee's repor

A new framework for feedback from massive binaries in simulations of cluster formation

Massive stars are born in clusters embedded within giant molecular clouds, which they in turn influence via radiative and momentum feedback. Most massive stars are also born in binaries or higher-order systems, with companions close enough to trigger mass loss in excess of what is expected for single stars. Those interactions shape the feedback coming from massive stars, by increasing the amount of ionizing radiation and delaying some of the first core-collapse supernovae. It is therefore crucial to model concurrently those massive interacting binaries and the giant molecular cloud in which they form to reach a more comprehensive understanding of cluster formation. I will present a new model for the implementation of feedback from massive binaries in simulations of cluster formation. This model couples hydrodynamics, stellar dynamics, stellar evolution, and star and binary formation, and innovates by modelling the feedback from both massive single stars and massive binaries. I will discuss our first results and highlight future outlooks for this novel framework.This work was started during a research visit at the Max Planck Institute for Astrophysics, supported by a Michael Smith Foreign Studies Supplement from the Natural Sciences and Engineering Research Council of Canada (NSERC). This work is further supported by a Canada Graduate Scholarship – Doctoral from NSERC

Early-forming Massive Stars Suppress Star Formation and Hierarchical Cluster Assembly

Feedback from massive stars plays an important role in the formation of star clusters. Whether a very massive star is born early or late in the cluster formation timeline has profound implications for the star cluster formation and assembly processes. We carry out a controlled experiment to characterize the effects of early-forming massive stars on star cluster formation. We use the star formation software suite Torch , combining self-gravitating magnetohydrodynamics, ray-tracing radiative transfer, N -body dynamics, and stellar feedback, to model four initially identical 10 ^4 M _⊙ giant molecular clouds with a Gaussian density profile peaking at 521.5 cm ^−3 . Using the Torch software suite through the AMUSE framework, we modify three of the models, to ensure that the first star that forms is very massive (50, 70, and 100 M _⊙ ). Early-forming massive stars disrupt the natal gas structure, resulting in fast evacuation of the gas from the star-forming region. The star formation rate is suppressed, reducing the total mass of the stars formed. Our fiducial control model, without an early massive star, has a larger star formation rate and total efficiency by up to a factor of 3, and a higher average star formation efficiency per freefall time by up to a factor of 7. Early-forming massive stars promote the buildup of spatially separate and gravitationally unbound subclusters, while the control model forms a single massive cluster