Evolution of binary seeds in collapsing protostellar gas clouds

Abstract

We perform three dimensional smoothed particle hydrodynamics (SPH) simulations of gas accretion onto the seeds of binary stars to investigate their short-term evolution. Our simulation setup is more realistic compared to the previous works by taking into account of dynamically evolving envelope with non-uniform distribution of gas density and angular momentum of accreting flow. Our initial condition includes a seed binary and a surrounding gas envelope, modelling the phase of core collapse of gas cloud when the fragmentation has already occurred. We assume that the seed binary has no eccentricity and no growth by gas accretion. The envelope is assumed to be an isothermal gas with no self-gravity. We run multiple simulations with different values of initial mass ratio $q_0$ (the ratio of secondary over primary mass) and gas temperature, and find a critical value of $q_{\mathrm{c}}=0.25$ which distinguishes the later evolution of mass ratio $q$ as a function of time. If $q_0$ >~ $q_{\mathrm{c}}$, the secondary seed grows faster and $q$ increases monotonically towards unity. If $q_0$ <~ $q_{\mathrm{c}}$, on the other hand, the primary seed grows faster and $q$ is lower than $q_0$ at the end of the simulation. Based on our numerical results, we analytically calculate the long-term evolution of the seed binary including the growth of binary by gas accretion. We find that the seed binary with $q_0$ >~ $q_{\mathrm{c}}$ evolves towards an equal-mass binary star, and that with $q_0$ <~ $q_{\mathrm{c}}$ evolves to a binary with an extreme value of $q$. Binary separation is a monotonically increasing function of time for any $q_0$, suggesting that the binary growth by accretion does not lead to the formation of close binaries.

12 pages, 9 figures, MNRAS accepted

References in corpus (6)

• SPLASH: An interactive visualisation tool for Smoothed Particle Hydrodynamics simulations
• The Effects of Radiative Transfer on Low-Mass Star Formation
• The Importance of Radiative Feedback for the Stellar Initial Mass Function
• Precession and accretion in circumbinary discs: The case of HD 104237
• The evolution of the mass ratio of accreting binaries: the role of gas temperature
• Simulating star formation in molecular cloud cores IV. The role of turbulence and thermodynamics

Cited by in corpus (2)

• The binary mass ratios of circumbinary planet hosts
• Study of the mass-ratio distribution of spectroscopic binaries. I. A novel algorithm