arXiv subjects

R. Kuruwita

Publications and source records attributed to R. Kuruwita.

2 recordsLinked to original sources

arXiv2023

The contribution of binary star formation via core-fragmentation on protostellar multiplicity

Observations of young multiple star systems find a bimodal distribution in companion frequency and separation. The origin of these peaks has often been attributed to binary formation via core and disc fragmentation. However, theory and simulations suggest that young stellar systems that form via core fragmentation undergo significant orbital evolution. We investigate the influence of the environment on the formation and orbital evolution of multiple star systems, and how core fragmentation contributes to the formation of close (20-100AU) binaries. We use multiple simulations of star formation in giant molecular clouds and compare them to the multiplicity statistics of the Perseus star-forming region. Simulations were run with the adaptive mesh refinement code RAMSES with sufficient resolution to resolve core fragmentation beyond 400AU and dynamical evolution down to 16.6AU, but without the possibility of resolving disc fragmentation. The evolution of the resulting stellar systems was followed over millions of years. We find that star formation in lower gas density environments is more clustered; however, despite this, the fractions of systems that form via dynamical capture and core fragmentation are broadly consistent at ~40\% and ~60\%, respectively. We then compared the simulation with the conditions most similar to the Perseus star-forming region to determine whether the observed bimodal distribution can be replicated. We find that it can be replicated, but it is sensitive to the evolutionary state of the simulation. Our results indicate that a significant number of low-mass close binaries with separations from 20-100AU can be produced via core fragmentation or dynamical capture due to efficient inspiral, without the need for a further contribution from disc fragmentation.

astro-ph.GA↗

arXiv2020

The dependence of episodic accretion on eccentricity during the formation of binary stars

Aims: Our goal is to investigate how the strength of episodic accretion bursts depends on eccentricity. Methods: We investigate the binary trigger hypothesis in longer-period (>20yr) binaries by carrying out three-dimensional magnetohydrodynamical (MHD) simulations of the formation of low-mass binary stars down to final separations of $\sim$10$\au$, including the effects of gas turbulence and magnetic fields. We ran two simulations with an initial turbulent gas core of one solar mass each and two different initial turbulent Mach numbers, M = 0.1 and M=0.2, for 6500yr after protostar formation. Results: We observe bursts of accretion at periastron during the early stages when the eccentricity of the binary system is still high. We find that this correlation between bursts of accretion and passing periastron breaks down at later stages because of the gradual circularisation of the orbits. For eccentricities greater than e=0.2, we observe episodic accretion triggered near periastron. However, we do not find any strong correlation between the strength of episodic accretion and eccentricity. The strength of accretion is defined as the ratio of the burst accretion rate to the quiescent accretion rate.We determine that accretion events are likely triggered by torques between the rotation of the circumstellar disc and the approaching binary stars. We compare our results with observational data of episodic accretion in short-period binaries and find good agreement between our simulations and the observations. Conclusions: We conclude that episodic accretion is a universal mechanism operating in eccentric young binary-star systems, independent of separation, and it should be observable in long-period binaries as well as in short-period binaries. Nevertheless, the strength depends on the torques and hence the separation at periastron.

astro-ph.SR↗