scholarly journals Speaking with one voice: simulations and observations discuss the common envelope α parameter

2019 ◽  
Vol 490 (2) ◽  
pp. 2550-2566 ◽  
Author(s):  
Roberto Iaconi ◽  
Orsola De Marco
Keyword(s):  
Binary Interaction ◽  
Agb Stars ◽  
Recombination Energy ◽  
Intermediate Mass ◽  
Data Set ◽  
Hydrodynamic Simulations ◽  
Common Envelope ◽  
Upper Limits ◽  
Low Mass ◽  
The Common

ABSTRACT We present a comparative study between the results of most hydrodynamic simulations of the common envelope binary interaction to date and observations of post-common envelope binaries. The goal is to evaluate whether this data set indicates the existence of a formula that may predict final separations of post-common envelope systems as a function of pre-common envelope parameters. Some of our conclusions are not surprising while others are more subtle. We find that: (i) Values of the final orbital separation derived from common envelope simulations must at this time be considered upper limits. Simulations that include recombination energy do not seem to have systematically different final separations; these and other simulations imply αCE < 0.6–1.0. At least one simulation, applicable to double-degenerate systems, implies αCE < 0.2. (ii) Despite large reconstruction errors, the post-RGB observations reconstructed parameters are in agreement with some of the simulations. The post-AGB observations behave instead as if they had a systematically lower value of αCE. The lack of common envelope simulations with low-mass AGB stars leaves us with no insight as to why this is the case. (iii) The smallest mass companion that survives the common envelope with intermediate mass giants is 0.05–0.1 M⊙. (iv) Observations of binaries with separations larger than ∼10 R⊙, tend to have high M2/M1 mass ratios and may go through a relatively long phase of unstable Roche lobe mass transfer followed by a weakened common envelope (or with no common envelope at all). (v) The effect of the spatial resolution and of the softening length on simulation results remains poorly quantified.

scholarly journals Properties of the post-inspiral common envelope ejecta – I. Dynamical and thermal evolution

2019 ◽  
Vol 489 (3) ◽  
pp. 3334-3350 ◽  
Author(s):  
Roberto Iaconi ◽  
Keiichi Maeda ◽  
Orsola De Marco ◽  
Takaya Nozawa ◽  
Thomas Reichardt
Keyword(s):  
Thermal Evolution ◽  
Kinematic Model ◽  
Numerical Approach ◽  
Binary Interaction ◽  
Recombination Energy ◽  
Compact Binaries ◽  
Common Envelope ◽  
Type Ia ◽  
The Common ◽  
Ia Supernovae

ABSTRACT We investigate the common envelope binary interaction, that leads to the formation of compact binaries, such as the progenitors of Type Ia supernovae or of mergers that emit detectable gravitational waves. In this work, we diverge from the classic numerical approach that models the dynamic inspiral. We focus instead on the asymptotic behaviour of the common envelope expansion after the dynamic inspiral terminates. We use the SPH code phantom to simulate one of the set-ups from Passy et al., with a 0.88 M⊙, 83 R⊙ RGB primary and a 0.6 M⊙ companion, then we follow the ejecta expansion for 50 yr. Additionally, we utilize a tabulated equation of state including the envelope recombination energy in the simulation (Reichardt et al.), achieving a full unbinding. We show that, as time passes, the envelope’s radial velocities dominate over the tangential ones, hence allowing us to apply an homologous expansion kinematic model to the ejecta. The external layers of the envelope become homologous as soon as they are ejected, but it takes 5000 d (14 yr) for the bulk of the unbound gas to achieve the homologously expanding regime. We observe that the complex distribution generated by the dynamic inspiral evolves into a more ordered, shell-like shaped one in the asymptotic regime. We show that the thermodynamics of the expanding envelope are in very good agreement with those expected for an adiabatically expanding sphere under the homologous condition and give a prediction for the location and temperature of the photosphere assuming dust to be the main source of opacity. This technique ploughs the way to determining the long-term light behaviour of common envelope transients.

scholarly journals The impact of recombination energy on simulations of the common-envelope binary interaction

2020 ◽  
Vol 494 (4) ◽  
pp. 5333-5349 ◽  
Author(s):  
Thomas A Reichardt ◽  
Orsola De Marco ◽  
Roberto Iaconi ◽  
Luke Chamandy ◽  
Daniel J Price
Keyword(s):  
Equation Of State ◽  
Comparative Study ◽  
Binary Interaction ◽  
Recombination Energy ◽  
Common Envelope ◽  
Hydrogen Recombination ◽  
The Common ◽  
The Impact

ABSTRACT During the common-envelope binary interaction, the expanding layers of the gaseous common envelope recombine and the resulting recombination energy has been suggested as a contributing factor to the ejection of the envelope. In this paper, we perform a comparative study between simulations with and without the inclusion of recombination energy. We use two distinct setups, comprising a 0.88- and 1.8-M⊙ giants, that have been studied before and can serve as benchmarks. In so doing, we conclude that (i) the final orbital separation is not affected by the choice of equation of state (EoS). In other words, simulations that unbind but a small fraction of the envelope result in similar final separations to those that, thanks to recombination energy, unbind a far larger fraction. (ii) The adoption of a tabulated EoS results in a much greater fraction of unbound envelope and we demonstrate the cause of this to be the release of recombination energy. (iii) The fraction of hydrogen recombination energy that is allowed to do work should be about half of that which our adiabatic simulations use. (iv) However, for the heavier star simulation, we conclude that it is helium and not hydrogen recombination energy that unbinds the gas and we determine that all helium recombination energy is thermalized in the envelope and does work. (v) The outer regions of the expanding common envelope are likely to see the formation of dust. This dust would promote additional unbinding and shaping of the ejected envelope into axisymmetric morphologies.

scholarly journals Mixing Uncertainties in Low-Metallicity AGB Stars: The Impact on Stellar Structure and Nucleosynthesis

Universe ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 25
Author(s):  
Umberto Battino ◽  
Claudia Lederer-Woods ◽  
Borbála Cseh ◽  
Pavel Denissenkov ◽  
Falk Herwig
Keyword(s):  
Stellar Structure ◽  
Process Efficiency ◽  
Agb Stars ◽  
Mixing Processes ◽  
Data Set ◽  
Convective Envelope ◽  
Capture Process ◽  
Low Metallicity ◽  
Low Mass ◽  
The Impact

The slow neutron-capture process (s-process) efficiency in low-mass AGB stars (1.5 < M/M⊙ < 3) critically depends on how mixing processes in stellar interiors are handled, which is still affected by considerable uncertainties. In this work, we compute the evolution and nucleosynthesis of low-mass AGB stars at low metallicities using the MESA stellar evolution code. The combined data set includes models with initial masses Mini/M⊙=2 and 3 for initial metallicities Z=0.001 and 0.002. The nucleosynthesis was calculated for all relevant isotopes by post-processing with the NuGrid mppnp code. Using these models, we show the impact of the uncertainties affecting the main mixing processes on heavy element nucleosynthesis, such as convection and mixing at convective boundaries. We finally compare our theoretical predictions with observed surface abundances on low-metallicity stars. We find that mixing at the interface between the He-intershell and the CO-core has a critical impact on the s-process at low metallicities, and its importance is comparable to convective boundary mixing processes under the convective envelope, which determine the formation and size of the 13C-pocket. Additionally, our results indicate that models with very low to no mixing below the He-intershell during thermal pulses, and with a 13C-pocket size of at least ∼3 × 10−4 M⊙, are strongly favored in reproducing observations. Online access to complete yield data tables is also provided.

Magnetic fields in PNe and other evolved low-mass and intermediate-mass stars

2016 ◽  
Vol 12 (S323) ◽  
pp. 136-140
Author(s):  
Laurence Sabin ◽  
Qizhou Zhang ◽  
Gregg A. Wade ◽  
Agnès Lèbre ◽  
Roberto Vázquez
Keyword(s):  
Magnetic Fields ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Efficient Mechanism ◽  
Intermediate Mass Stars ◽  
Low Mass

AbstractMagnetic fields are likely to be an efficient mechanism which can affect evolved intermediate mass stars (i.e. post-AGB stars and planetary nebulae) in different ways such as via the shaping of their envelope. However, observational probes for the presence of those fields are still scarce. I will present a summary of the works, including those from our group, on the detection and measurement of magnetic fields in various evolved objects.

scholarly journals The effect of binding energy and resolution in simulations of the common envelope binary interaction

2018 ◽  
Vol 477 (2) ◽  
pp. 2349-2365 ◽  
Author(s):  
Roberto Iaconi ◽  
Orsola De Marco ◽  
Jean-Claude Passy ◽  
Jan Staff
Keyword(s):  
Binding Energy ◽  
Binary Interaction ◽  
Common Envelope ◽  
The Common

scholarly journals HST's hunt for intermediate-mass black holes in star clusters

2009 ◽  
Vol 5 (S266) ◽  
pp. 231-237 ◽  
Author(s):  
Julio Chanamé ◽  
Justice Bruursema ◽  
Rupali Chandar ◽  
Jay Anderson ◽  
Roeland van der Marel ◽  
...  
Keyword(s):  
Black Holes ◽  
Globular Clusters ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Dynamical Analysis ◽  
Intermediate Mass ◽  
Data Set ◽  
Upper Limits ◽  
Intermediate Mass Black Holes

AbstractEstablishing or ruling out, either through solid mass measurements or upper limits, the presence of intermediate-mass black holes (IMBHs; with masses of 102 − 105 M⊙) at the centers of star clusters would profoundly impact our understanding of problems ranging from the formation and long-term dynamical evolution of stellar systems, to the nature of the seeds and the growth mechanisms of supermassive black holes. While there are sound theoretical arguments both for and against their presence in today's clusters, observational studies have so far not yielded truly conclusive IMBH detections nor upper limits. We argue that the most promising approach to solving this issue is provided by the combination of measurements of the proper motions of stars at the centers of Galactic globular clusters and dynamical models able to take full advantage of this type of data set. We present a program based on HST observations and recently developed tools for dynamical analysis designed to do just that.

scholarly journals s-Process Enrichment in Low-Mass Agb Stars

1989 ◽  
Vol 106 ◽  
pp. 176-195 ◽  
Author(s):  
R. Gallino
Keyword(s):  
Solar System ◽  
Massive Stars ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Low Mass Stars ◽  
Temporal Behaviour ◽  
Physical Conditions ◽  
Intermediate Mass Stars ◽  
Low Mass ◽  
Main Component

AbstractAfter a brief description of the developments of the theory of s-process nucleosynthesis, the difficulties recently encountered in envisaging reliable astrophysical conditions for obtaining a solar-system distribution of s-isotopes are discussed. In particular, while the reaction 22Ne(α, n)25Mg may account for the nucleosynthesis of the weak s-component in massive stars, it fails to reproduce the main s-component in intermediate mass stars. The efficiency of the alternative reaction 13C(α, n)160 occurring in low mass stars during recurring thermal instabilities of the He shell is then analyzed. It is shown that, contrary to previous expectations, the 13C source well reproduces the main component, provided that realistic physical conditions are assumed for the temporal behaviour of the pulse and the effect of the light n-absorbers (especially 12C) is properly taken into account. The results satisfactorily compare with the constraints of the classical s-analysis. Key observational evidences also appear to be in agreement with this scenario.

scholarly journals Companion-launched jets and their effect on the dynamics of common envelope interaction simulations

2019 ◽  
Vol 488 (4) ◽  
pp. 5615-5632 ◽  
Author(s):  
Sagiv Shiber ◽  
Roberto Iaconi ◽  
Orsola De Marco ◽  
Noam Soker
Keyword(s):  
Three Dimensional ◽  
Gravitational Energy ◽  
Numerical Code ◽  
Binary Interaction ◽  
Giant Star ◽  
Common Envelope ◽  
The Common ◽  
Red Giant ◽  
Set Up ◽  
First Time

Abstract We conduct three-dimensional hydrodynamic simulations of the common envelope binary interaction and show that if the companion were to launch jets while interacting with the giant primary star’s envelope, the jets would remove a substantial fraction of the envelope’s gas. We use the set-up and numerical code of an earlier common envelope study that did not include jets, with a 0.88-M⊙, 83-R⊙ red giant star and a 0.3-M⊙ companion. The assumption is that the companion star accretes mass via an accretion disc that is responsible for launching the jets which, in the simulations, are injected numerically. For the first time we conduct simulations that include jets as well as the gravitational energy released by the inspiralling core-companion system. We find that simulations with jets unbind approximately three times as much envelope mass than identical simulations that do not include jets, though the total fraction of unbound gas remains below 50 per cent for these particular simulations. The jets generate high-velocity outflows in the polar directions. The jets also increase the final core-companion orbital separation and lead to a kick velocity of the core-companion binary system. Our results show that, if able to form, jets could play a crucial role in ejecting the envelope and in shaping the outflow.

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