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Dust formation in common envelope binary interactions – II: 3D simulations with self-consistent dust formation

Abstract (Expand)

We performed numerical simulations of the common envelope (CE) interaction between thermally-pulsing asymptotic giant branch (AGB) stars of 1.7 M⊙ and 3.7 M⊙, respectively, and a 0.6 M⊙ compact companion. … We use tabulated equations of state to take into account recombination energy. For the first time, formation and growth of dust is calculated explicitly, using a carbon dust nucleation network with a C/O abundance ratio of 2.5 (by number). The first dust grains appear within ∼1–3 yrs after the onset of the CE, forming an optically thick shell at ∼10–20 au, growing in thickness and radius to values of ∼400–500 au over ∼40 yrs, with temperatures around 400 K. Most dust is formed in unbound material, having little effect on mass ejection or orbital evolution. By the end of the simulations, the total dust yield is ∼8.4 × 10−3 M⊙ and ∼2.2 × 10−2 M⊙ for the CE with a 1.7 M⊙ and a 3.7 M⊙ AGB star, respectively, corresponding to a nucleation efficiency close to 100%, if no dust destruction mechanism is considered. Despite comparable dust yields to single AGB stars, in CE ejections the dust forms a thousand times faster, over tens of years as opposed to tens of thousands of years. This rapid dust formation may account for the shift in the infrared of the spectral energy distribution of some optical transients known as luminous red novae. Simulated dusty CEs support the idea that extreme carbon stars and ‘water fountains’ may be objects observed after a CE event.

Authors: Luis C Bermúdez-Bustamante, Orsola De Marco, Lionel Siess, Daniel J Price, Miguel González-Bolívar, Mike Y M Lau, Chunliang Mu, Ryosuke Hirai, Taïssa Danilovich, Mansi M Kasliwal

Date Published: 30th Jul 2024

Publication Type: Journal

Expansion of Accreting Main-sequence Stars during Rapid Mass Transfer

Abstract (Expand)

Accreting main-sequence stars expand significantly when the mass accretion timescale is much shorter than their thermal timescales. This occurs during mass transfer from an evolved giant star onto a … main-sequence companion in a binary system and is an important phase in the formation of compact binaries including X-ray binaries, cataclysmic variables, and gravitational-wave sources. In this study, we compute 1D stellar models of main-sequence accretors with different initial masses and accretion rates. The calculations are used to derive semianalytical approximations to the maximum expansion radius. We assume that mass transfer remains fully conservative as long as the inflated accretor fits within its Roche lobe, leading stars to behave like hamsters, stuffing excess material behind their expanding cheeks. We suggest a physically motivated prescription for the mass growth of such "hamstars," which can be used to determine mass-transfer efficiency in rapid binary population synthesis models. With this prescription, we estimate that progenitors of high-mass X-ray binaries and gravitational-wave sources may have experienced highly nonconservative mass transfer. In contrast, for low-mass accretors, the accretion timescale can exceed the thermal timescale by a larger factor without causing significant radial expansion.

Authors: Mike Lau, Ryosuke Hirai, Ilya Mandel, Christopher A. Tout

Date Published: 24th Apr 2024

Publication Type: Journal

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