arXiv subjects

Noam Soker

Publications and source records attributed to Noam Soker.

At least 145 records · Page 8Linked to original sources

arXiv2021

A red giant branch common envelope evolution scenario for the exoplanet WD 1856 b

We propose a common envelope evolution (CEE) scenario where a red giant branch (RGB) star engulfs a planet during its core helium flash to explain the puzzling system WD 1856+534 where a planet orbits a white dwarf (WD) of mass 0.52Mo with an orbital period of 1.4 day. At the heart of the scenario is the recently proposed assumption that the vigorous convection that core helium flash of RGB stars drive in the core excite waves that propagate and deposit their energy in the envelope. Using the binary-MESA stellar evolution code we show that this energy deposition substantially reduces the binding energy of the envelope and causes its expansion. We propose that in some cases RGB stars might engulf massive planets of ~0.01Mo during their core helium flash phase, and that the planet can unbind most of the mass of the bloated envelope. We show that there is a large range of initial orbital radii for which this scenario might take place under our assumptions. This scenario is relevant to other systems of close sub-stellar objects orbiting white dwarfs, like the brown dwarf-WD system ZTFJ003855.0+203025.5.

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arXiv2021

Binary neutron star merger in common envelope jet supernovae

I explore a triple-star scenario where a tight neutron star (NS) - NS binary system enters the envelope of a red supergiant (RSG) star and spirals-in towards its core. The two NSs accrete mass through accretion disks and launch jets that power a very luminous and long transient event, a common envelope jets supernova (CEJSN) event. Dynamical friction brings the two NSs to merge either in the RSG envelope or core. The total energy of the event, radiation and kinetic, is >10^{52}erg. The light curve stays luminous for months to years and a signal of gravitational waves might be detected. The ejecta contains freshly synthesized r-process elements not only from the NS-NS merger as in kilonova events, but possibly also from the pre-merger jets that the NSs launch inside the core, as in the r-process CEJSN scenario. This scenario shortens the time to NS-NS merger compared with that of kilonovae, and might somewhat ease the problem of the NS-NS r-process scenario to account for r-process nucleosynthesis in the early Universe. I estimate the ratio of NS-NS merger in CEJSN events to core collapse supernova (CCSN) events to be <10^{-6}-2x10^{-5}. However, because they are much more luminous I expect their detection fraction to that of CCSNe to be much larger than this number. This study calls for considering this and similar CEJSN scenarios in binary and in triple star systems when explaining peculiar and puzzling super luminous supernovae.

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arXiv2021

The future influence of six exoplanets on the envelope properties of their parent stars on the giant branches

We study the evolution of six exoplanetary systems with the stellar evolutionary code MESA and conclude that they will likely spin-up the envelope of their parent stars on the red giant branch (RGB) or later on the asymptotic giant branch (AGB) to the degree that the mass loss process might become non-spherical. We choose six observed exoplanetary systems where the semi-major axis is ~1-2AU, and use the binary mode of MESA to follow the evolution of the systems. In four systems the star engulfs the planet on the RGB, and in two systems on the AGB, and the systems enter a common envelope evolution (CEE). In two systems where the exoplanet masses are Mp~10MJ, where MJ is Jupiter mass, the planet spins-up the envelope to about 10% of the break-up velocity. Such envelopes are likely to have significant non-spherical mass loss geometry. In the other four systems where Mp~MJ the planet spins-up the envelope to values of ~1-2% of break-up velocity. Magnetic activity in the envelope that influences dust formation might lead to a small departure from spherical mass loss even in these cases. In the two cases of CEE on the AGB the planet deposits energy to the envelope that amounts to >10% of the envelope binding energy. We expect this to cause a non-spherical mass loss that will shape an elliptical planetary nebula in each case.

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arXiv2021

The X-ray properties of Eta Carinae during its 2020 X-ray minimum

The massive binary system Eta Carinae is characterized by intense colliding winds that form shocks and emit X-rays. The system is highly eccentric ($e\simeq0.9$), resulting in modulated X-ray emission during its 5.54 year orbit. The X-ray flux increases in the months prior to periastron passage, exhibiting strong flares, then rapidly declines to a flat minimum lasting a few weeks, followed by a gradual recovery. We present Neutron Star Interior Composition Explorer (NICER) telescope spectra obtained before, during, and after the 2020 X-ray minimum, and perform spectral analysis to establish the temporal behavior of X-ray flux and X-ray-absorbing column density ($N_{\rm H}(t)$) for the 2-10 keV and 5-10 keV energy ranges. The latter range is dominated by the stellar wind collision region and, therefore, these spectral parameters - in particular, $N_{\rm H}(t)$ - serves as a potentially stringent constraint on the binary orientation. We compare the observed $N_{\rm H}(t)$ results to the behavior predicted by a simple geometrical model in an attempt to ascertain which star is closer to us at periastron: the more massive primary ($ω\simeq 240$-$270^\circ$), or the secondary ($ω\simeq 90^\circ$). We find that the variations in column density, both far from periastron and around periastron passage, support the latter configuration ($ω\simeq 90^\circ$). The 2020 X-ray minimum showed the fastest recovery among the last five minima, providing additional evidence for a recent weakening of the primary star's wind.

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arXiv2021

Rare events of a peculiar thermonuclear supernova that precedes a core collapse supernova

We study stellar binary evolution that leads to the formation of a white dwarf (WD) that explodes in a thermonuclear supernova at the termination of a common envelope evolution (CEE) shortly before the core of its companion explodes as a core-collapse supernova (CCSN). The CCSN explosion of the core, which is the remnant of a red supergiant (RSG) star, might take place few months to several years after the explosion of the WD as a thermonuclear supernova, i.e., a type Ia peculiar supernova (peculiar SN Ia). Using the evolutionary code MESA-binary we simulate evolution of binary systems with stars of initial masses of 6-7.5Mo. The more massive star, the primary, transfers mass to the secondary star and leaves a CO WD remnant. The secondary becomes massive enough to end in a CCSN. As the secondary evolves to the RSG phase it engulfs the WD and the system experience a CEE that ends with a WD-core binary system at an orbital separation of a_f ~ 1-5Ro. Our simulations show that the core explodes as a CCSN at t_{CEE-CCSN} ~ 3000 - 10^5 yr after the CEE. We assume that if the WD accretes helium-rich gas from the core it might explode as a SN Ia in the frame of the double detonation scenario for SNe Ia and peculiar SNe Ia. We predict the very rare occurrence of a peculiar SN Ia followed within months to years by a CCSN.

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arXiv2021

Rapid expansion of red giant stars during core helium flash by waves propagation to the envelope and implications to exoplanets

We assume that the strong convection during core helium flash of low mass red giant branch (RBG) stars excite waves that propagate to the envelope, and find that the energy that these waves deposit in the envelope causes envelope expansion and brightening. We base our assumption and the estimate of the wave energy on studies that explored such a process due to the vigorous core convection of massive stars just before they experience a core collapse supernova explosion. Using the stellar evolutionary code MESA we find that the wave energy causes an expansion within few years by tens to hundreds solar radii. Despite the large brightening, we expect the increase in radius and luminosity to substantially enhance mass loss rate and dust formation. The dust shifts the star to become much redder (to the infrared), and the star might actually become fainter in the visible. The overall appearance is of a faint red transient event that lasts for months to few years. We suggest that in some cases envelope expansion might lead stars that are about to leave the RGB to engulf exoplanets. The extended envelope has a smaller binding energy to a degree that allows planets of several Jupiter masses or more and brown dwarfs to survive the common envelope evolution. We suggest this scenario to account for the planet orbiting the white dwarf (WD) WD1856+534 (TIC 267574918) and for the WD - brown dwarf binary system ZTFJ003855.0+203025.5.

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arXiv2021

Parasite common envelope evolution by triple-star systems

We study a scenario by which a giant wide tertiary star engulfs and forces a tight binary system of a white dwarf (WD) and a main sequence (MS) star to enter a common envelope evolution (CEE) with each other, and then unbinds the WD-MS common envelope. The WD-MS binary system, now with the WD inside the MS envelope, does not have sufficient orbital energy to unbind their common envelope. However, as they approach the center of the giant star Roche lobe overflow to the core of the giant star and/or merger of the WD with the core remove a large fraction of the WD-MS common envelope or all of it. Namely, the energy source for unbinding the WD-MS tight common envelope is the triple-star CEE. For that we term this scenario a parasite CEE. Overall, the destruction of the MS star absorbs energy from the triple-star system, a process that might lead to WD-core merger during the triple-star CEE. The parasite CEE leaves behind either one massive WD that in some cases might explode as a peculiar type Ia supernova or two close WDs that at later time might explode as a type Ia supernova. We very crudely estimate the rate of the parasite CEE to be a fraction of ~0.001 out of all evolved triple stars.

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arXiv2021

Double common envelope jets supernovae (CEJSNe) by triple-star systems

I propose a new type of common envelope jets supernova (CEJSN) events where instead of a single neutron star (NS; or a black hole; BH) a tight binary system of a NS and a main sequence star enters a common envelope evolution (CEE) with a red supergiant. The NS and the main sequence star of the tight binary system merge inside the red supergiant envelope and enter a CEE of their own. The NS accretes some mass through an accretion disk and launches jets that explodes the main sequence star. I estimate that the two jets that the NS launches at this phase carry an energy of ~10^{52} erg, about the same order of magnitude as the energy that the jets will carry when the NS or its BH remnant will enter the core in a later phase. For that, I term the entire event a double CEJSN. The outcome of the double CEJSN is a very long, months to years, and very energetic event, a total energy of ~10^{52} - 10^{53} erg, that will be observationally classified as a peculiar super-energetic event. I crudely estimate that new transient surveys should detect about one CEJSN event from a triple star system per year.

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arXiv2021

The circumstellar matter of type II intermediate luminosity optical transients (ILOTs)

I find that a 0.1-1Mo outflowing equatorial dusty disk (torus) that the binary system progenitor of an intermediate luminosity optical transient (ILOT) ejects several years to several months before and during the outburst can reduce the total emission to an equatorial observer by two orders of magnitude and shifts the emission to wavelengths of mainly >10mum. This is termed a type II ILOT (ILOT II). To reach this conclusion I use calculations of type II active galactic nuclei and apply them to the equatorial ejecta (disk/torus) of ILOTs II. This reduction in emission can last for tens of years after outburst. Most of the radiation escapes along the polar directions. The attenuation of the emission for wavelengths of <5mum can be more than three orders of magnitudes, and the emission at <2mum is negligible. Jets that the binary system launches during the outburst can collide with polar CSM and emit radiation above the equatorial plane and dust in the polar outflow can reflect emission from the central source. Therefore, during the event itself the equatorial observer might detect an ILOT. I strengthen the previously suggested ILOT II scenario to the event N6946-BH1, where a red giant star disappeared in the visible.

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arXiv2021

Shaping `Ears' in planetary nebulae by early jets

We conduct three dimensional hydrodynamical numerical simulations of planetary nebula (PN) shaping and show that jets that precede the ejection of the main PN shell can form the morphological feature of ears. Ears are two opposite protrusions from the main nebula that are smaller than the main nebula and with a cross section that decreases monotonically from the base of an ear at the shell to its far end. Only a very small fraction of PNe has ears. The short-lived jets, about a year in the present simulations, interact with the regular asymptotic giant branch (AGB) wind to form the ears, while the later blown dense wind forms the main PN dense shell. Namely, the jets are older than the main PN shell. We also find that for the jets to inflate ears they cannot be too energetic, cannot be too wide, and cannot be too slow. A flow structure where short-lived jets precede the main phase of nebula ejection by a few years or less can result from a system that enters a common envelope evolution. The low mass companion accretes mass through an accretion disk and launches jets just before it enters the envelope of the giant progenitor star of the PN. Shortly after that the companion enters the envelope and spirals-in to eject the envelope that forms the main PN shell.

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arXiv2020

Simulating the inflation of bubbles by late jets in core collapse supernova ejecta

We conducted three-dimensional hydrodynamical simulations to study the interaction of two late opposite jets with the ejecta of a core collapse supernova (CCSN), and study the bipolar structure that results from this interaction as the jets inflate hot-low-density bubbles. The newly born central object, a neutron star (NS; or a black hole), launches these jets at about 50 to 100 days after explosion. The bubbles cross the photosphere in the polar directions at much earlier times than the regions at the same radii near the equatorial plane. The hot bubbles releases more radiation and the photosphere recedes more rapidly in the tenuous bubble. Our results strengthen earlier claims that were based on toy models that such an interaction might lead to a late peak in the light curve, and that an equatorial observer might see a rapid drop in the light curve. Our results might have implications to much earlier jets that explode the star, either jets that the newly born NS launches in a CCSN, or jets that a NS companion that merges with the core of a massive star launches in a common envelope jets supernova (CEJSN) event. Our results add indirect support to the CEJSN scenario for fast blue optical transients, e.g., AT2018cow, ZTF18abvkwla, and CSS161010.

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arXiv2020

Modelling light curves of bipolar core collapse supernovae from the equatorial plane

We use the two-components bipolar toy model of core collapse supernova (CCSN) ejecta to fit the rapid decline from maximum luminosity in the light curve of the type IIb CCSN SN 2018gk (ASASSN-18am). In this toy model we use a template light curve from a different CCSN that is similar to SN 2018gk, but that has no rapid drop in its light curve. The bipolar morphology that we model with a polar ejecta and an equatorial ejecta increases the maximum luminosity and causes a steeper decline for an equatorial observer, relative to a similar spherical explosion. The total energy and mass of our toy model for SN 2018gk are E=5e51 erg and M=2.7Mo. This explosion energy is more than what a neutrino-driven explosion mechanism can supply, implying that jets exploded SN 2018gk. These energetic jets likely shaped the ejecta to a bipolar morphology, as our toy model requires. We crudely estimate that f=2-5% of all CCSNe show this behavior, most being hydrogen deficient (stripped-envelope) CCSNe, as we observe them from the equatorial plane. We estimate the overall fraction of CCSNe that have a pronounced bipolar morphology to be 5-15% of all CCSNe.

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arXiv2020

A pre-explosion extended effervescent zone around core collapse supernova progenitors

I propose a scenario according to which the dense compact circumstellar matter (CSM) that the ejecta of many core collapse supernovae (CCSNe) collide with within several days after explosion results from a dense zone where in addition to the stellar wind there is gas that does not reach the escape velocity. In this effervescent zone around red supergiant (RSG) stars, there are dense clumps that are ejected from the vicinity of the RSG surface, rise to radii of tens of astronomical units, and then fall back. I consider two simple velocity distributions of the ejected clumps. I find that the density of the bound mass can be tens of times that of the escaping wind, and therefore can mimic a very high mass loss rate. The dense effervescent compact CSM zone can (1) explain the collision of the ejecta of many CCSNe with a dense compact CSM days after explosion, (2) facilitate very high mass loss rate if the star experiences powerful pre-explosion activity, (3) form dust that obscures the progenitor in the visible band, and (4) lead to an efficient mass transfer to a stellar companion at separations of tens of astronomical units, if exists. The effervescent zone might exist for thousands of years and more, and therefore the effervescent CSM model removes the requirement from many type II CCSN progenitors to experience a very strong outburst just years to months before explosion.

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arXiv2020

On rare core collapse supernovae inside planetary nebulae

We conduct simulations using MESA of the reverse formation of a white dwarf (WD)-neutron star (NS) binary system in which the WD forms before the NS. We conclude that a core collapse supernova (CCSN) explosion might occur inside a planetary nebula (PN) only if a third star forms the PN. In this WD-NS reverse binary evolution, the primary star evolves and transfers mass to the secondary star, forms a PN, and leaves a WD remnant. If the mass-transfer brings the secondary star to have a mass of >8Mo before it develops a helium core, and if the secondary does not suffer an enhanced mass-loss before it develops a massive helium core, e.g., by mass-transfer, it explodes as a CCSN and leaves a NS remnant. The time period from the formation of the PN by the primary to the explosion of the secondary is >10^6 year. By that time the PN has long dispersed into the interstellar medium. In a binary system with nearly equal mass components, the first mass-transfer episode takes place after the secondary star has developed a helium core and it ends its life forming a PN and a WD. The formation of a CCSN inside a PN (CCSNIP) requires the presence of a third star. The third star should be less massive than the secondary star but by no more than few times 0.01Mo. We estimate that the rate of CCSNIP is ~10^{-4} times the rate of all CCSNe.

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arXiv2020

Explaining recently studied intermediate luminosity optical transients (ILOTs) with jet powering

We apply the jet-powered ILOT scenario to two recently studied intermediate luminosity optical transients (ILOTs), and find the relevant shell mass and jets' energy that might account for the outbursts of these ILOTs. In the jet-powered ILOT scenario accretion disk around one of the stars of a binary system launches jets. The interaction of the jets with a previously ejected slow shell converts kinetic energy to thermal energy, part of which is radiated away. We apply two models of the jet-powered ILOT scenario. In the spherical shell model the jets accelerate a spherical shell, while in the cocoon toy model the jets penetrate into the shell and inflate hot bubbles, the cocoons. We find consistent results. For the ILOT (ILRT: intermediate luminosity red transient) SNhunt120 we find the shell mass and jets' energy to be Ms=0.5-1Mo and E2j=5e47erg, respectively. The jets' half opening angle is alpha=30-60 degrees. For the second peak of the ILOT (luminous red nova) AT2014ej we find these quantities to be Ms=1-2Mo and E2j=1.5e48erg, with alpha=20-30 degrees. The models cannot tell whether these ILOTs were powered by a stellar merger that leaves one star, or by mass transfer where both stars survived. In both cases the masses of the shells and energies of the jets suggest that the binary progenitor system was massive, with a combined mass of M1+M2>10Mo.

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arXiv2020

Possible post-kick jets in SN 1987A

I suggest that the recently observed hot-dust elongated structure that likely engulfs the neutron star (NS) remnant of supernova (SN) 1987A was shaped by jets that the NS launched shortly after it acquired its natal kick velocity. I take the axis of the two post-kick jets to be along the long dimension of the hot-dust elongated structure, which I term the bipolar lobe. The jittering jets explosion mechanism accounts for the misalignment of the post-kick jets axis and the main-jets axis of the ejecta. For post-kick jets to shape the bipolar lobe their energy should have been about equal to the energy of the ejecta inner to the outer edge of the lobe, E(2j)~E(ej,lobe)~4.6e48erg. For an efficiency of 0.01-0.1 to convert accretion energy to post-kick jets' energy I estimate that the post-kick accreted mass was Macc~0.0002-0.002Mo. The negative jets feedback mechanism, where jets remove some of the mass that could have been accreted, accounts for the limited amount of accreted mass. This study adds to the growing recognition of the importance of jets in core collapse supernovae, including post-explosion jets.

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arXiv2020

Minutes-delayed jets from a neutron star companion in core collapse supernovae

I study cases where a neutron star (NS; or a black hole) companion to a type Ib or type Ic (stripped-envelope) core collapse supernova (CCSN) accretes mass from the explosion ejecta and launches jets minutes to hours after explosion. The NS orbits at a pre-explosion radius of a=1-5Ro. I find that when the ejecta velocity drops to be <1000-1500km/s the ejecta gas that the NS accretes possesses sufficient specific angular momentum to form an accretion disk around the NS. The NS accretes a fraction of 3e-5 to 3e-4 of the ejecta mass through an accretion disk over a time period of 10min to few hours. If the jets carry about ten per cent of the accretion energy, then their total energy is a fraction of about 0.003-0.03 of the kinetic energy of the ejecta. The implications of these jets from a NS (or a black hole) companion to a CCSN are the shaping the inner ejecta to have a bipolar morphology, energising the light curve of the CCSN, and in some cases the possible enrichment of the inner ejecta with r-process elements.

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arXiv2020

Simulating jets from a neutron star companion hours after a core collapse supernova

We conduct three-dimensional hydrodynamical simulations to explore the interaction of jets that a neutron star (NS) companion to a type Ic or type Ib core collapse supernova (CCSN) launches few hours after explosion with the ejecta of the CCSN. We assume that a NS companion at 5Ro from the exploding star accretes mass from the slower inner ejecta through an accretion disk, and that the disk launches two opposite jets. Although the energy of the jets is only about one per cent of the total energy of the ejecta, it is comparable to the energy of the slower inner part of the ejecta. We find that the jets inflate one low-density hot bubble to one side of the ejecta, and that this bubble expands to influence ejecta gas up to expansion velocities of v=3500 km/s. The post-shock jets' material develops a large meridional flow and small vortexes. The boundary between the ejecta and jets' post-shock gases is unstable. The instabilities and vortexes mix jets' gas with the ejecta. We expect such a hot bubble to contribute to the light curve of CCSNe that are progenitors of binary NS systems, in particular to observers on the side of the bubble.

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