arXiv subjects

Noam Soker

Publications and source records attributed to Noam Soker.

At least 199 records · Page 11Linked to original sources

arXiv2018

Counteracting Tidal Circularization with the Grazing Envelope Evolution

We show that substantially enhanced mass loss at periastron passages, as is expected in the grazing envelope evolution (GEE), can compensate for the circularization effect of the tidal interaction in binary systems composed of an asymptotic giant branch (AGB) star and a main sequence secondary star. By numerically integrating the equations of motion we show that under our assumptions the binary system can maintain its high eccentricity as the AGB star evolves toward the post-AGB phase. Our results can explain the high eccentricity of some post-AGB intermediate binaries (post-AGBIBs), i.e., those with an orbital periods in the range of several months to few years. In the framework of the GEE, the extra energy to sustain a high mass loss rate comes from the accretion of mass from the giant envelope or its slow wind onto a more compact secondary star. The secondary star energizes the outflow from the AGB outer envelope by launching jets from the accretion disk.

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arXiv2018

Possible white dwarf progenitors of type Ia supernovae

We examine catalogs of white dwarfs (WDs) and find that there are sufficient number of massive WDs, M_WD > 1.35Mo, that might potentially explode as type Ia supernovae (SNe Ia) in the frame of the core degenerate scenario. In the core degenerate scenario a WD merges with the carbon-oxygen core of a giant star, and they form a massive WD that might explode with a time delay of years to billions of years. If the core degenerate scenario accounts for all SNe Ia, then we calculate that about 0.2 per cent of the present WDs in the Galaxy are massive. Furthermore, we find from the catalogs that the fraction of massive WDs relative to all WDs is about 1-3 per cent, with large uncertainties. Namely, five to ten times the required number. If there are many SNe Ia that result from lower mass WDs, M_WD < 1.3Mo, for which another scenario is responsible for, and the core degenerate scenario accounts only for the SNe Ia that explode as massive WDs, then the ratio of observed massive WDs to required is larger even. Our finding leaves the core degenerate scenario as a viable and promising SN Ia scenario.

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arXiv2018

Oxygen-neon rich merger during common envelope evolution

We conduct a population synthesis study of the common envelope evolution (CEE) of a white dwarf (WD) and an asymptotic giant branch (AGB) star and find that the potential number of type Ia supernovae (SNe Ia) from the core degenerate (CD) and from the double degenerate (DD) scenarios are of the same order of magnitude. For the CD scenario we consider cases where a carbon oxygen rich (CO) AGB core and a CO WD merge during the CEE and leave a WD remnant with a mass of >1.35Mo, and for the DD scenario we count surviving CO WD binary systems that merge within a time of 10 Gyr. When either the AGB core or the WD are oxygen neon rich (ONe) we assume that the outcome might be a peculiar SN Ia. We find that the number of potential peculiar SNe Ia in the channels we study, that do not include peculiar SNe Ia that involve helium WDs or helium donors, is non-negligible, but less than the number of normal SNe Ia. If a SN Ia or a peculiar SN Ia explosion takes place within about million year after CEE, whether in the CD scenario or in the DD scenario, a massive circumstellar matter is present at explosion time. Our results are compatible with the suggestion that Chandrasekhar-mass SNe Ia mostly come from the CD scenario, and sub-Chandrasekhar SNe Ia mostly come from the DD scenario.

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arXiv2018

Radiating the hydrogen recombination energy during common envelope evolution

By using the stellar evolution code MESA we show that most of the hydrogen recombination energy that is released as the envelope expands during a regular common envelope evolution (CEE), namely, the initial dynamical phase or plunge-in phase, is radiated, and hence increases substantially the stellar luminosity. Only about ten per cent of the hydrogen recombination energy might be used to remove the envelope. We show that the key property of energy transport is that when convection becomes inefficient in the outer parts of the envelope, where the ionization degree of hydrogen falls below about 30 per cent, photon diffusion becomes very efficient and removes the recombination energy. The expanding envelope absorbs most of the gravitational energy that is released by the spiraling-in process of the secondary star inside the common envelope, and so it is the hydrogen recombination energy that is behind most of the luminosity increase of the system. The recombination energy of hydrogen adds only a small fraction of the energy required to remove the common envelope, and hence does not play a significant role in the ejection of the envelope.

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arXiv2018

The Class of Jsolated Stars and Luminous Planetary Nebulae in old stellar populations

We suggest that stars whose angular momentum (J) does not increase by a companion, star or planet, along their post-main sequence evolution have much lower mass loss rates along their giant branches. Their classification to a separate group can bring insight on their late evolution stages. We here term these Jsolated stars. We argue that the mass loss rate of Jsolated stars is poorly determined because the mass loss rate expressions on the giant branches are empirically based on samples containing stars that experience strong binary interaction, with stellar or sub-stellar companions, e.g., planetary nebula (PN) progenitors. We use our earlier claim for a low mass loss rate of asymptotic giant branch (AGB) stars that are not spun-up by a stellar or substellar companion to show that we can account for the enigmatic finding that the brightest PNe in old stellar populations reach the same luminosity as the brightest PNe in young populations. It is quite likely that the best solution to the existence of bright PNe in old stellar populations is the combination of higher AGB luminosities, as obtained in some new stellar models, and the lower mass loss rates invoked here.

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arXiv2018

Orbital radius during the grazing envelope evolution

We use the binary module of the MESA code to study the evolution of an evolved binary system where we assume that a main sequence companion removes the outskirts of the envelope of an asymptotic giant branch (AGB) star by launching jets, and explore the characteristics of this grazing envelope evolution (GEE). We base our assumption that jets launched by the secondary star remove a substantial fraction of the outskirts of the envelope of an AGB star on earlier hydrodynamical simulations. We find that in many cases that we study, but not in all cases, the binary system experiences the GEE rather than entering the common envelope phase, under our assumptions of jet-driven mass removal. To prevent the common envelope phase, we assume the secondary star may accrete a large amount of mass in a short time while avoiding rapid inflation, the feasibility of which requires further study. Because of our simplifying assumptions we cannot yet present the parameter space for the GEE. Although the incorporation of the GEE into population synthesis numerical codes requires further studies of the GEE, we conclude that analyses of population synthesis studies of evolved binary stars should include the GEE.

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arXiv2018

Planets, Planetary Nebulae, and Intermediate Luminosity Optical Transients (ILOTs)

I review some aspects related to the influence of planets on the evolution of stars before and beyond the main sequence. Some processes include the tidal destruction of a planet on to a very young main sequence star, on to a low mass main sequence star, and on to a brown dwarf. This process releases gravitational energy that might be observed as a faint intermediate luminosity optical transient (ILOT) event. I then summarize the view that some elliptical planetary nebulae are shaped by planets. When the planet interacts with a low mass upper asymptotic giant branch (AGB) star it both enhances the mass loss rate and shapes the wind to form an elliptical planetary nebula, mainly by spinning up the envelope and by exciting waves in the envelope. If no interaction with a companion, stellar or sub-stellar, takes place beyond the main sequence, the star is termed a Jsolated star, and its mass loss rates on the giant branches are likely to be much lower than what is traditionally assumed.

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arXiv2018

The limited role of recombination energy in common envelope removal

We calculate the outward energy transport time by convection and photon diffusion in an inflated common envelope and find this time to be shorter than the envelope expansion time. We conclude therefore that most of the hydrogen recombination energy ends in radiation rather than in kinetic energy of the outflowing envelope. We use the stellar evolution code MESA and inject energy inside the envelope of an asymptotic giant branch star to mimic energy deposition by a spiraling-in stellar companion. During 1.7 years the envelope expands by a factor of more than 2. Along the entire evolution the convection can carry the energy very efficiently outwards, to the radius where radiative transfer becomes more efficient. The total energy transport time stays within several months, shorter than the dynamical time of the envelope. Had we included rapid mass loss, as is expected in the common envelope evolution, the energy transport time would have been even shorter. It seems that calculations that assume that most of the recombination energy ends in the outflowing gas might be inaccurate.

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arXiv2018

Simulating a binary system that experiences the grazing envelope evolution

We conduct three-dimensional hydrodynamical simulations, and show that when a secondary star launches jets while performing spiral-in motion into the envelope of a giant star, the envelope is inflated, some mass is ejected by the jets, and the common envelope phase is postponed. We simulate this grazing envelope evolution (GEE) under the assumption that the secondary star accretes mass from the envelope of the asymptotic giant branch (AGB) star and launches jets. In these simulations we do not yet include the gravitational energy that is released by the spiraling-in binary system. Neither do we include the spinning of the envelope. Considering these omissions, we conclude that our results support the idea that jets might play a crucial role in the common envelope evolution, or in preventing it.

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arXiv2018

The orientation of Eta Carinae and the powering mechanism of intermediate luminosity optical transients (ILOTs)

Contrary to recent claims, we argue that the orientation of the massive binary system Eta Carinae is such that the secondary star is closer to us at periastron passage, and it is on the far side during most of the time of the eccentric orbit. The binary orientation we dispute is based on problematic interpretations of recent observations. Among these observations are the radial velocity of the absorption component of He I P-Cyg lines, of the He II $\lambda4686$ emission line, and of the Br$γ$ line emitted by clumps close to the binary system. We also base our orientation on observations of asymmetric molecular clumps that were recently observed by ALMA around the binary system, and were claimed to compose a torus with a missing segment. The orientation has implications for the modeling of the binary interaction during the nineteenth century Great Eruption (GE) of Eta Carinae that occurred close to periastron passage. The orientation where the secondary is closer to us at periastron leads us to suggest that the mass-missing side of the molecular clumps is a result of accretion onto the secondary star during the periastron passage when the clumps were ejected, probably during the GE. The secondary star accreted a few solar masses during the GE and the energy from the accretion process consists the majority of the GE energy. This in turn strengthens the more general model according to which many intermediate-luminosity optical transients (ILOTs) are powered by accretion onto a secondary star.

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arXiv2018

Explaining the morphology of supernova remnant (SNR) 1987A with the jittering jets explosion mechanism

We find that the remnant of supernova (SN) 1987A share some morphological features with four supernova remnants (SNRs) that have signatures of shaping by jets, and from that we strengthen the claim that jets played a crucial role in the explosion of SN 1987A. Some of the morphological features appear also in planetary nebulae where jets are observed. The clumpy ejecta bring us to support the claim that the jittering jets explosion mechanism can account for the structure of the remnant of SN 1987A, i.e., SNR 1987A. We conduct a preliminary attempt to quantify the fluctuations in the angular momentum of the mass that is accreted on to the newly born neutron star via an accretion disk or belt. The accretion disk/belt launches the jets that explode core collapse supernovae (CCSNe). The relaxation time of the accretion disk/belt is comparable to the duration of a typical jet-launching episode in the jittering jets explosion mechanism, and hence the disk/belt has no time to relax. We suggest that this might explain unequal two opposite jets that later lead to unequal sides of the elongated structures in SNR of CCSNe. We reiterate our earlier call for a paradigm shift from neutrino-driven explosion to a jet-driven explosion of CCSNe.

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arXiv2018

Uplifted cool gas and heating by mixing in cooling flows

We analyze our earlier three-dimensional hydrodynamical numerical simulation of jet-inflated bubbles in cooling flow clusters, and find that dense gas that was not heated by the jets' activity and that resides around the hot jet-inflated bubbles can be identified as uplifted gas as observed in some clusters. During the build up of the dense gas around the hot bubble, mixing of hot bubble gas with other regions of the intracluster medium (ICM) heats the ICM. The vortices that mix the ICM with the hot bubble gas also excite shock waves, sound waves, and turbulence. Sound waves, shocks, turbulence, and uplifted gas, might be easier to detect than the mixing process and hence attract more attention, but we argue that the contributions of these processes to the heating of the ICM do not add up to the level of contribution of the mixing-heating process.

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arXiv2018

A mixed helium-oxygen shell in some core-collapse supernova progenitors

We evolve models of rotating massive stars up to the stage of iron core collapse using the MESA code and find a shell with a mixed composition of primarily helium and oxygen in some cases. In the parameter space of initial masses of 13-40 Mo and initial rotation velocities of 0-450 km/s that we investigate, we find a mixed helium-oxygen shell with a significant mass only for a small fraction of the models. While the shell is formed due to rotational mixing, the pre-collapse rotation rate is not very high, as required for an energetic collapse-induced thermonuclear explosion. Our results suggest that the collapse-induced thermonuclear explosion mechanism that was revisited recently can account for at most a small fraction of core-collapse supernovae. The presence of such a mixed helium-oxygen shell still might have some implications for core-collapse supernovae, such as some nucleosynthesis processes when jets are present, or might result in peculiar sub-luminous core-collapse supernovae.

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arXiv2018

Jittering jets in cooling flow clusters

I put forth a scenario of jet-driven jittering-jets in cooling flows in galaxies and clusters of galaxies. By uplifting cool gas from the center of the cluster jets and the bubbles they inflate cause the direction of later jets to substantially change. Some uplifted cool clumps fall back to feed the active galactic nucleus, in what is termed the cold feedback mechanism, but with an average angular momentum that is largely inclined to that of the original jets. The proposed jittering jets scenario allows, over the cooling time of the intracluster medium (ICM), the heating by the mixing of hot jet-inflated bubble gas with the ICM to operate in all directions. The proposed scenario further supports the heating by mixing mechanism of the ICM. The feedback heating mechanism of the ICM chiefly refers to the energy cycle. The cold feedback mechanism introduces mass as another ingredient of the feedback cycle, as the mass accretion of future activity cycles is determined by the formation of perturbations by the present activity cycle. The jittering jets scenario that I propose here brings angular momentum to be another ingredient of the feedback cycle.

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arXiv2017

Explaining iPTF14hls as a common envelope jets supernova

We propose a common envelope jets supernova scenario for the enigmatic supernova iPTF14hls where a neutron star that spirals-in inside the envelope of a massive giant star accretes mass and launches jets that power the ejection of the circumstellar shell and a few weeks later the explosion itself. To account for the kinetic energy of the circumstellar gas and the explosion, the neutron star should accrete a mass of approximately 0.3 solar masses. The tens of solar masses of circumstellar gas that accounts for some absorption lines is ejected while the neutron star orbits for about one to several weeks inside the envelope of the giant star. In the last hours of the interaction the neutron star merges with the core, accretes mass, and launches jets that eject the core and the inner envelope to form the explosion itself and the medium where the supernova photosphere resides. The remaining neutron star accretes fallback gas and further powers the supernova. We attribute the 1954 pre-explosion outburst to an eccentric orbit and temporary mass accretion by the neutron star at periastron passage prior to the onset of the common envelope phase.

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arXiv2017

Neutron star natal kick and jets in core collapse supernovae

We measure the angle between the neutron star (NS) natal kick direction and the inferred direction of jets according to the morphology of 12 core collapse supernova remnants (SNR), and find that the distribution is almost random, but missing small angles. The 12 SNRs are those for which we could both identify morphological features that we can attribute to jets and for which the direction of the NS natal kick is given in the literature. Unlike some claims for spin-kick alignment, here we rule out jet-kick alignment. We discuss the cumulative distribution function of the jet-kick angles under the assumption that dense clumps that are ejected by the explosion accelerate the NS by the gravitational attraction, and suggest that the jet feedback explosion mechanism might in principle account for the distribution of jet-kick angles.

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arXiv2017

Supernovae Ia in 2017: a long time delay from merger/accretion to explosion

I use recent observational and theoretical studies of type Ia supernovae (SNe Ia) to further constrain the viable SN Ia scenarios and to argue that there must be a substantial time delay between the end of the merger of the white dwarf (WD) with a companion or the end of mass accretion on to the WD and its terminal explosion. This merger/accretion to explosion delay (MED) is required to allow the binary system to lead to a more or less spherical explosion and to prevent a pre-explosion ionizing radiation. Considering these recent results and the required MED, I conclude that the core degenerate scenario is somewhat more favorable over the other scenarios, followed by the double degenerate scenario. Although the single degenerate scenario is viable as well, it is less likely to account for common (normal) SN Ia. As all scenarios require substantial MED, the MED has turned from a disadvantage of the core degenerate scenario to a challenge that theory should overcome. I hope that the requirement for a MED will stimulate the discussion of the different SN Ia scenarios and the comparison of the scenarios to each other.

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arXiv2017

Magnetar-powered superluminous supernovae must first be exploded by jets

We analyze recent magnetar light-curve modeling of 38 hydrogen-poor superluminous supernovae (SLSNe), and find that the energies of the explosions themselves, that take place before the magnetar energy is released, are more than what the neutrino-driven explosion mechanism can supply for about half of the systems. These SLSNe must have been exploded by a different process than the delayed neutrino mechanism, most likely the jet feedback mechanism (JFM). The conclusion for magnetar modeling of SLSNe is that jets launched at magnetar birth cannot be ignored, not at the explosion itself and not later when mass fall-back might occur. More generally, the present analysis strengthens the call for a paradigm shift from neutrino-driven to jet-driven explosion models of all core collapse supernovae.

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