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Ealeal Bear

Publications and source records attributed to Ealeal Bear.

At least 37 records · Page 2Linked to original sources

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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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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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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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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Jet-driven active galactic nucleus feedback in galaxy formation before black hole formation

We propose a scenario where during galaxy formation an active galactic nucleus (AGN) feedback mechanism starts before the formation of a supermassive black hole (SMBH). The supermassive star (SMS) progenitor of the SMBH accretes mass as it grows and launches jets. We simulate the evolution of SMSs and show that the escape velocity from their surface is approximately several 10^3 km/s, with large uncertainties. We could not converge with the parameters of the evolutionary numerical code MESA to resolve the uncertainties for SMS evolution. Under the assumption that the jets carry about ten percent of the mass of the SMS, we show that the energy in the jets is a substantial fraction of the binding energy of the gas in the galaxy/bulge. Therefore, the jets that the SMS progenitor of the SMBH launches carry sufficient energy to establish a feedback cycle with the gas in the inner zone of the galaxy/bulge, and hence, set a relation between the total stellar mass and the mass of the SMS. As the SMS collapses to form the SMBH at the center, there is already a relation (correlation) between the newly born SMBH mass and the stellar mass of the galaxy/bulge. During the formation of the SMBH it rapidly accretes mass from the collapsing SMS and launches very energetic jets that might unbind most of the gas in the galaxy/bulge.

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On the role of reduced wind mass-loss rate in enabling exoplanets to shape planetary nebulae

We use the stellar evolution code MESA-binary and follow the evolution of three exoplanets and two brown dwarfs (BDs) to determine their potential role in the future evolution of their parent star on the red giant branch (RGB) and on the asymptotic giant branch (AGB). We limit this study to exoplanets and BDs with orbits that have semi-major axis of 1AU 0.25, and having a parent star of mass M>1Mo. We find that the star HIP 75458 will engulf its planet HIP 75458 b during its RGB phase. The planet will remove the envelope and terminate the RGB evolution, leaving a bare helium core of mass 0.4Mo that will evolve to form a helium white dwarf. Only in one system out of five, the planet beta Pic c will enter the envelope of its parent star during the AGB phase. For that to occur, we have to reduce the wind mass-loss rate by a factor of about four from its commonly used value. This strengthens an early conclusion, which was based on exoplanets with circular orbits, that states that to have a non-negligible fraction of AGB stars that engulf planets we should consider lower wind mass-loss rates of isolated AGB stars (before they are spun-up by a companion). Such an engulfed planet might lead to the shaping of the AGB mass-loss geometry to form an elliptical planetary nebula.

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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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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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Forming H-shaped and barrel-shaped nebulae with interacting jets

We conduct three-dimensional hydrodynamical simulations of two opposite jets launched from a binary stellar system into a previously ejected shell and show that the interaction can form barrel-like and H-like shapes in the descendant nebula. Such features are observed in planetary nebulae and supernova remnants. Under our assumption the dense shell is formed by a short instability phase of the giant star as it interacts with a stellar companion, and the jets are then launched by the companion as it accretes mass through an accretion disk from the giant star. We find that the H-shaped and barrel-shaped morphological features that the jets form evolve with time, and that there are complicated flow patterns, such as vortices, instabilities, and caps moving ahead along the symmetry axis. We compare our numerical results with images of 12 planetary nebulae, and show that jet-shell interaction that we simulate can account for the barrel-like or H-like morphologies that are observed in these PNe.

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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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The imprints of the last jets in core collapse supernovae

We analyze the morphologies of three core collapse supernova remnants (CCSNRs) and the energy of jets in other CCSNRs and in Super Luminous Supernovae (SLSNe) of type Ib/Ic/IIb, and conclude that these properties are well explained by the last jets' episode as expected in the jet feedback explosion mechanism of core collapse supernovae (CCSNe). The presence of two opposite protrusions, termed ears, and our comparison of the CCSNR morphologies with morphologies of planetary nebulae strengthen the claim that jets play a major role in the explosion mechanism of CCSNe. We crudely estimate the energy that was required to inflate the ears in two CCSNRs, and assume that the ears were inflated by jets. We find that the energies of the jets that inflated ears in 11 CCSNRs span a range that is similar to that of jets in some energetic CCSNe (SLSNe), and that this energy, only of the last jets' episode, is much less than the explosion energy. This finding is compatible with the jet feedback explosion mechanism of CCSNe, where only the last jets, that carry a small fraction of the total energy carried by earlier jets, are expected to influence the outer parts of the ejecta. We reiterate our call for a paradigm shift from neutrino-driven to jet-driven explosion models of CCSNe.

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Planetary nebulae that cannot be explained by binary systems

We examine the images of hundreds of planetary nebulae (PNe) and find that for about one in six PNe the morphology is too `messy' to be accounted for by models of stellar binary interaction. We speculate that interacting triple stellar systems shaped these PNe. In this preliminary study we qualitatively classify PNe by one of four categories. (1) PNe that show no need for a tertiary star to account for their morphology. (2) PNe whose structure possesses a pronounced departure from axial-symmetry and/or mirror-symmetry. We classify these, according to our speculation, as `having a triple stellar progenitor'. (3) PNe whose morphology possesses departure from axial-symmetry and/or mirror-symmetry, but not as pronounced as in the previous class, and are classified as `likely shaped by triple stellar system'. (4) PNe with minor departure from axial-symmetry and/or mirror symmetry that could have been as well caused by an eccentric binary system or the inter-stellar medium. These are classified as `maybe shaped by a triple stellar system'. Given a weight eta_t=1, eta_l=0.67, eta_m=0.33 to classes 2, 3 and 4, respectively, we find that according to our assumption about 13 - 21% of PNe have been shaped by triple stellar systems. Although in some evolutionary scenarios not all three stars survive the evolution, we encourage the search for a triple stellar systems at the center of some PNe.

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What planetary nebulae can tell us about jets in core collapse supernovae

We compare the morphology of the core collapse supernova remnant (CCSNR) W49B with the morphology of many planetary nebulae (PNe), and deduce the orientation of the jets that shaped this CCSNR and estimate their energy. We find morphological features that are shared by some PNe and by the CCSNR W49B. In PNe these features, such as a barrel-shaped main body, are thought to be shaped by jets. We use these morphological similarities to deduce that the jets that shaped SNR W49B were launched along the symmetry axis of the `barrel', and to speculate that this CCSNR has two opposite lobes (or ears), that are too faint to be observed. We crudely estimate that the jets that shaped the CCSNR into a barrel shape had a kinetic energy that amounts to about one quarter to one third of the energy of the entire CCSNR. The morphological similarities strengthen the suggestion that jets play a central role in the explosion of massive stars.

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Using Intermediate-Luminosity Optical Transients (ILOTs) to reveal extended extra-solar Kuiper belt objects

We suggest that in the rare case of an Intermediate-Luminosity Optical Transient (ILOTs) event, evaporation of extra-solar Kuiper belt objects (ExtraKBOs) at distances of d ~ 500 - 10000AU from the ILOT can be detected. If the ILOT lasts for 1 month to a few years, enough dust might be ejected from the ExtraKBOs for the IR emission to be detected. Because of the large distance of the ExtraKBOs, tens of years will pass before the ILOT wind disperses the dust. We suggest that after an ILOT outburst there is a period of months to several years during which IR excess emission might hint at the existence of a Kuiper belt analog (ExtraK-Belt).

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Planetary systems and real planetary nebulae from planet destruction near white dwarfs

We suggest that tidal destruction of Earth-like and icy planets near a white dwarf (WD) might lead to the formation of one or more low-mass - Earth-like and lighter - planets in tight orbits around the WD. The formation of the new WD planetary system starts with a tidal break-up of the parent planet to planetesimals near the tidal radius of about 1Rsun. Internal stress forces keep the planetesimal from further tidal break-up when their radius is less than about 100km. We speculate that the planetesimals then bind together to form new sub-Earth - daughter-planets at a few solar radii around the WD. More massive planets that contain hydrogen supply the WD with fresh nuclear fuel to reincarnate its stellar-giant phase. Some of the hydrogen will be inflated in a large envelope. The envelope blows a wind to form a nebula that is later (after the entire envelope is lost) ionized by the hot WD. We term this glowing ionized nebula that originated from a planet a real planetary nebula (RPN). This preliminary study of daughter-planets from a planet (DPP) and the RPN scenarios are of speculative nature. More detail studies must follow to establish whether the suggested scenarios can indeed take place.

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First versus second generation planet formation in post common envelope binary (PCEB) planetary systems

We examine planets orbiting post-common envelope binaries (PCEBs) from the perspective of angular momentum evolution, and conclude that the planets are more likely to be first generation (FG) planets than second generation (SG) planets. FG planets were born together with the parent stars, while SG planets form later from a SG proto-planetary disk formed by mass-loss from the evolved primary star during its red giant branch (RGB) phase or asymptotic giant branch (AGB) phase. We find that in some systems the SG scenario requires that more than twenty percent of the SG proto-planetary disk mass ends in planets. Although we cannot rule out SG planet formation in these systems, this fraction of mass that ends in planets is much higher than the value commonly used in planet formation theories. On the other hand, we find that for each of the systems we can build a progenitor system composed of a main-sequence binary system orbited by the appropriate planets. This can be done if the secondary star was in a resonance with the inner planet. To account for the progenitor properties we suggest that in cases where the secondary star has a mass of ~ 0.1-0.2Msun, it was formed in the same way planets are formed, i.e., from a disk.

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Planetary influences on photometric variation of the extreme helium subdwarf KIC10449976

We propose that the unstable 3.9days photometric periodicity of the hot subdwarf (sdO) KIC10449976 results from a tidally locked planet that is heated to 5000K by the UV radiation from the hot sdO star. Although the bolometric radiation from the planet is very small relative to that of the star, in the visible band the planet contributes 0.07% of the light, sufficient to explain the observed periodic behavior. In our proposed scenario the stochastic variations in period and light amplitude are attributed to weather on the planet. Namely, streams on the surface and thermal variations in the planet's atmosphere that are driven by the heating and by the planet rotation lead to stochastic changes in the amount of radiation emitted by the planets. We predict that a careful monitoring will reveal a gas giant planet at an orbital separation of 8.3Rsun from KIC10449976.

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Transient outburst events from tidally disrupted asteroids near white dwarfs

We discuss the possibility of observing the transient formation event of an accretion disk from the tidal destruction process of an asteroid near a white dwarf (WD). This scenario is commonly proposed as the explanation for dusty disks around WDs. We find that the initial formation phase lasts for about a month and material that ends in a close orbit near the WD forms a gaseous disk rather than a dusty disk. The mass and size of this gaseous accretion disk is very similar to that of Dwarf Novae (DNe) in quiescence. The bolometric luminosity of the event at maximum is estimated to be 0.001-0.1Lsun. Based on the similarity with DNe we expect that transient outburst events such as discussed here will be observed at wavelengths ranging from visible to the X-ray, and be detected by present and future surveys.

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