Formation of massive close binaries I. Detached evolution

Abstract

We explore the initial conditions that lead to detached binary evolution of massive pre-MS binaries and ask how large a fraction of the observed binary systems may have been initially formed as low-mass protobinaries and later undergone a significant accretion phase while remaining detached. We develop a family of analytic models to describe the orbital separation, $a$, and mass ratio, $q$, evolution. For a given mass accretion rate onto the binary system, we define a recipe for distributing this mass between the two components. For this we introduce a parameter $\eta$, such that $\frac{{\dot{M}}_2}{{\dot{M}}_1}=q^{\eta }$ at any time, to determine the binary mass ratio evolution. Depending on the choice of $\eta$, any type of mass ratio evolution is possible. Furthermore, we use MESA, a detailed stellar structure code, to calculate an extensive grid of binary sequences where a protobinary undergoes accretion, and we identify the initial conditions that separates detached from non-detached pre-MS binary evolution. A value of $\eta$ around 2 allows accretion growth in detached systems to form close massive binaries on the Zero Age Main-Sequence with minimum orbital periods down to about 1.2 days for $M_{1,\mathrm{ZAMS}}=20-30M_{\odot }$ twin-binaries. $\eta =2$ can also reproduce the observed population of binary systems with primary stars above $6M_{\odot }$. The whole observed range of massive close binaries can form via accretion growth in detached systems, making the binary formation channel of accretion growth a strong contender to explain the formation of massive close binaries, including progenitors of coalescing binary black holes.

arXiv comment27 pages, 19 figures, 3 tables, submitted to A&A. Abstract context removed to to fit arXiv

References in corpus (19)

• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• Pre-Supernova Evolution of Massive Single and Binary Stars
• Ten eclipsing binaries in the Small Magellanic Cloud: fundamental parameters and SMC distance
• Circumventing the radiation pressure barrier in the formation of massive stars via disk accretion
• Accretion in stellar clusters and the IMF
• Fragmentation of Massive Protostellar Disks
• Formation of massive stars by growing accretion rate
• WR 20a is an Eclipsing Binary: Accurate Determination of Parameters for an Extremely Massive Wolf-Rayet System
• Binary systems and stellar mergers in massive star formation
• Structure and evolution of high-mass stellar mergers
• WR20a: a massive cornerstone binary system comprising two extreme early-type stars
• Discovery of the massive overcontact binary VFTS 352: Evidence for enhanced internal mixing
• Binary accretion rates: dependence on temperature and mass-ratio
• Towards an Accurate Determination of Parameters for Very Massive Stars: the Eclipsing Binary LMC-SC1-105
• Formation of Wide Binaries by Turbulent Fragmentation
• The role of stellar collisions for the formation of massive stars
• Mass Transfer in Close, Rapidly Accreting Protobinaries: An Origin for Massive Twins?
• The evolution of the mass ratio of accreting binaries: the role of gas temperature
• Pre-mainsequence stellar evolution in N-body models

Cited by in corpus (1)

• BRITE observations of $\nu$ Centauri and $\gamma$ Lupi, the first non-eclipsing members of the new class of nascent binaries