On the Eccentricity Excitation in Post-Main-Sequence Binaries

Rafikov, Roman R.

doi:10.3847/0004-637x/830/1/8

Cited by 41 publications

(35 citation statements)

References 49 publications

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“…By taking typical values for a post-AGB binary with L * = 5000 L , a b = 2 AU, and M b = 1.7 M (Oomen et al 2018), and assuming a disc mass of 10 −2 M Kluska et al 2018), we can derive the typical accretion rate onto a post-AGB binary. Here, we take ζ = 0.1, η = 2, α = 0.01, and I L = 1 (see Rafikov 2016b). We find a typical accretion rate of ∼ 10 −7 M /yr, which is in agreement with the accretion rate in the model of Izzard & Jermyn (2018).…”

Section: Accretionsupporting

confidence: 75%

“…Consequently, since we expect post-AGB stars that start their evolution in small orbits with high T eff never to become depleted in the first place, the models that are favourable for explaining the observed post-AGB sample are those with initial disc masses in the range 3 × 10 −3 -10 −2 M . These findings could provide interesting constraints on the accretion model of (Rafikov 2016b) in Eq. 3.…”

Section: Constraints On Accretion Parametersmentioning

confidence: 81%

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Modelling depletion by re-accretion of gas from a dusty disc in post-AGB stars

Oomen

Winckel

Pols

et al. 2019

A&A

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Many disc-type post-asymptotic giant branch (post-AGB) stars are chemically peculiar, showing underabundances of refractory elements in their photospheres that correlate with condensation temperature. The aim of this paper is to investigate how accretion from a circumbinary disc can cause this phenomenon of depletion and how this impacts the evolution of post-AGB stars. We used the MESA code to evolve stars in the post-AGB phase, while including accretion of metal-poor gas. We compared the models to a sample of 58 observed disc-type post-AGB stars with chemical abundance data. For each of these stars, we estimated the luminosity and the mass using the Gaia distance. We modelled the accretion rate onto the binary from a viscously evolving disc for a range of initial accretion rates and disc masses. We find that large initial accretion rates ( 3 × 10 −7 M /yr) and large initial disc masses (∼ 10 −2 M ) are needed to reproduce the observed depleted post-AGB stars. Based on these high accretion rates, the evolution timescale of post-AGB stars can be significantly extended by a factor between two and five. We distinguish depletion patterns that are unsaturated (plateau profile) from those that are saturated, and we expect that post-red giant branch (post-RGB) stars are much more likely to show an unsaturated abundance pattern compared to post-AGB stars. Finally, because of the slower evolution of the low-mass post-RGB stars, we find that these systems can become depleted at lower effective temperatures (< 5000 K). We conclude that accretion from a circumbinary disc successfully accounts for the chemical peculiarity of post-AGB stars.

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Section: Accretionsupporting

confidence: 75%

Section: Constraints On Accretion Parametersmentioning

confidence: 81%

Modelling depletion by re-accretion of gas from a dusty disc in post-AGB stars

Oomen

Winckel

Pols

et al. 2019

A&A

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“…To our knowledge, this theory has only been developed for post-main-sequence stars (see, e.g. Verbunt & Phinney 1995;Rafikov 2016). It is not obvious that this theory would apply to WASP-12 and be compatible with e ∼ 10 −3 .…”

Section: Prior Probabilitiesmentioning

confidence: 99%

The Apparently Decaying Orbit of WASP-12b

et al. 2017

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We present new transit and occultation times for the hot Jupiter WASP-12b. The data are compatible with a constant period derivative:Ṗ = −29 ± 3 ms yr −1and P/Ṗ = 3.2 Myr. However, it is difficult to tell whether we have observed orbital decay or a portion of a 14-year apsidal precession cycle. If interpreted as decay, the star's tidal quality parameter Q ⋆ is about 2 × 10 5 . If interpreted as precession, the planet's Love number is 0.44 ± 0.10. Orbital decay appears to be the more parsimonious model: it is favored by ∆χ 2 = 5.5 despite having two fewer free parameters than the precession model. The decay model implies that WASP-12 was discovered within the final ∼0.2% of its existence, which is an unlikely coincidence but harmonizes with independent evidence that the planet is nearing disruption. Precession does not invoke any temporal coincidence, but it does require some mechanism to maintain an eccentricity of ≈0.002 in the face of rapid tidal circularization. To distinguish unequivocally between decay and precession will probably require a few more years of monitoring. Particularly helpful will be occultation timing in 2019 and thereafter.

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“…With our chosen torque prescription, our discs' inner radii are typically around twice the orbital separation, as assumed in other works (e.g. [12]).…”

Section: Circumbinary Disc Modelmentioning

confidence: 99%

Post-AGB Discs from Common-Envelope Evolution

Izzard

Jermyn

2018

Galaxies

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Post-asymptotic giant branch (post-AGB) stars with discs are all binaries. Many of these binaries have orbital periods between 100 and 1000 days so cannot have avoided mass transfer between the AGB star and its companion, likely through a common-envelope type interaction. We report on preliminary results of our project to model circumbinary discs around post-AGB stars using our binary population synthesis code binary_c. We combine a simple analytic thin-disc model with binary stellar evolution to estimate the impact of the disc on the binary, and vice versa, fast enough that we can model stellar population and hence explore the rather uncertain parameter space involved with disc formation. We find that, provided the discs form with sufficient mass and angular momentum, and have an inner edge that is relatively close to the binary, they can both prolong the life of their parent post-AGB star and pump the eccentricity of orbits of their inner binaries.

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On the Eccentricity Excitation in Post-Main-Sequence Binaries

Cited by 41 publications

References 49 publications

Modelling depletion by re-accretion of gas from a dusty disc in post-AGB stars

Modelling depletion by re-accretion of gas from a dusty disc in post-AGB stars

The Apparently Decaying Orbit of WASP-12b

Post-AGB Discs from Common-Envelope Evolution

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