arXiv subjects

Noam Soker

Publications and source records attributed to Noam Soker.

At least 307 records · Page 17Linked to original sources

arXiv2012

A tidally destructed massive planet as the progenitor of the two light planets around the sdB star KIC 05807616

We propose that the two newly detected Earth-size planets around the hot B subdwarf star KIC 05807616 are remnant of the tidally destructed metallic core of a massive planet. A single massive gas-giant planet was spiralling-in inside the envelope of the red giant branch star progenitor of the extreme horizontal branch (EHB) star KIC 05807616. The released gravitational energy unbound most of the stellar envelope, turning it into an EHB star. The massive planet reached the tidal destruction radius of ~Ro from the core, where the planet's gaseous envelope was tidally removed. In our scenario the metallic core of the massive planet was tidally destructed into several Earth-like bodies immediately after the gaseous envelope of the planet was removed. Two, and possibly more, Earth-size fragments survived at orbital separations of >Ro within the gaseous disk. The bodies interact with the disk and among themselves and migrated to reach orbits close to a 3:2 resonance. These observed planets can have a planetary magnetic field about ten times as strong as that of Earth. This strong magnetic field can substantially reduce the evaporation rate from the planets and explain their survivability against the strong UV radiation of the EHB star.

astro-ph.SR↗

arXiv2011

Nucleosynthesis of r-Process Elements by Jittering Jets in Core-Collapse Supernovae

We calculate the nucleosynthesis inside the hot bubble formed in the jittering-jets model for core collapse supernovae (CCSNe) explosions, and find the formation of several times 10^-4 M_\odot of r-process elements. In the jittering-jets model fast jets launched from a stochastic accretion disk around the newly formed neutron star are shocked at several thousands km, and form hot high-pressure bubbles. These bubbles merge to form a large bubble that explode the star. In the current study we assume a spherically symmetric homogenous bubble, and follow its evolution for about one second during which nuclear reactions take place. The jets last for about one second, their velocity is v_j=0.5c, and their total energy is 10^51 erg. We use jets' neutron enrichment independent on time, and follow the nuclear reactions to the formation of the seed nuclei up to $Z \leq 50$, on which more neutrons will be absorbed to form the r-process elements. Based on the mass of the seed nuclei we find the r-process element mass in our idealized model to be several times 10^-4 M_\odot, which is slightly larger than the value deduced from observations. More realistic calculations that relax the assumptions of a homogenous bubble and constant jets composition might lead to agreement with observations.

astro-ph.HE↗

arXiv2011

Formation of Bipolar Planetary Nebulae by Intermediate-Luminosity Optical Transients

We present surprising similarities between some bipolar planetary nebulae (PNe) and eruptive objects with peak luminosity between novae and supernovae. The later group is termed ILOT for intermediate luminosity optical transients (other terms are intermediate luminosity red transients and red novae). In particular we compare the PN NGC 6302 and the pre-PNe OH231.8+4.2, M1-92 and IRAS 22036+5306 with the ILOT NGC 300 OT2008-1. These similarities lead us to propose that the lobes of some (but not all) PNe and pre-PNe were formed in an ILOT event (or several close sub-events). We suggest that in both types of objects the several months long outbursts are powered by mass accretion onto a main-sequence companion from an AGB (or extreme-AGB) star. Jets launched by an accretion disk around the main-sequence companion shape the bipolar lobes. Some of the predictions that result from our comparison is that the ejecta of some ILOTs will have morphologies similar to those of bipolar PNe, and that the central stars of the PNe that were shaped by ILOTs should have a main-sequence binary companion with an eccentric orbit of several years long period.

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arXiv2011

The core-degenerate scenario for type Ia supernovae

In the core-degenerate (CD) scenario for the formation of Type Ia supernovae (SNe) the Chandrasekhar or super-Chandrasekhar mass white dwarf (WD) is formed at the termination of the common envelope phase or during the planetary nebula phase, from a merger of a WD companion with the hot core of a massive asymptotic giant branch (AGB) star. The WD is destructed and accreted onto the more massive core. In the CD scenario the rapidly rotating WD is formed shortly after the stellar formation episode, and the delay from stellar formation to explosion is basically determined by the spin-down time of the rapidly rotating merger remnant. The spin-down is due to the magneto-dipole radiation torque. Several properties of the CD scenario make it attractive compared with the double-degenerate (DD) scenario. (1) Off-center ignition of carbon during the merger process is not likely to occur. (2) No large envelope is formed. Hence avoiding too much mass loss that might bring the merger remnant below the critical mass. (3) This model explains the finding that more luminous SNe Ia occur preferentially in star forming galaxies.

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arXiv2011

Type IA supernovae from very long delayed explosion of core - WD merger

We study the spinning down time scale of rapidly rotating white dwarfs (WDs) in the frame of the core-degenerate (CD) scenario for type Ia supernovae (SNe Ia). In the CD scenario the Chandrasekhar or super-Chandrasekhar mass WD is formed at the termination of the common envelope phase or during the planetary nebula phase, from a merger of a WD companion with the hot core of a massive asymptotic giant branch star. In the CD scenario the rapidly rotating WD is formed shortly after the stellar formation episode, and the delay from stellar formation to explosion is basically determined by the spin-down time of the rapidly rotating merger remnant. We find that gravitational radiation is inefficient in spinning down WDs, while the magneto-dipole radiation torque can lead to delay times that are required to explain SNe Ia.

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arXiv2011

The energy source of intermediate luminosity optical transients

We argue that transient systems with luminosity between novae and supernovae (SNe) are powered by gravitational energy of mass accreted onto, or a companion merges with, a main-sequence star. These transient events are termed Intermediate-Luminosity Optical Transients (ILOTs; other terms in use are Intermediate-Luminosity Red Transients and Red Novae). We show that despite the wide range of 10^{45}-10^{50} erg, the typical energy released by ILOTs can be expressed as a function of fundamental variables: the planck constant, speed of light, gravitational constant, electron mass, neutron mass, and ignition temperature of hydrogen. This expression explains why ILOTs are located between SNe and novae with respect to their total energy. We also put an upper limit on the power (luminosity) of ILOTs, which explains their lower luminosity than SNe.

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arXiv2011

A Circumbinary Disk in the Final Stages of Common Envelope and the Core-Degenerate Scenario for Type Ia Supernovae

We study the final stages of the common envelope (CE) evolution and find that a substantial fraction of the ejected mass does not reach the escape velocity. To reach this conclusion we use a self-similar solution under simplifying assumptions. Most of the gravitational energy of a companion white dwarf (WD) is released in the envelope of a massive asymptotic giant branch (AGB) or the red giant branch (RGB) star in a very short time. This rapid energy release forms a blast wave in the envelope. We follow the blast wave propagation from the center of the AGB outwards, and show that ~1-10 per cent of the ejected envelope remains bound to the remnant binary system. We suggest that due to angular momentum conservation and further interaction with the binary system, the fallback material forms a circumbinary disk around the post-AGB Core and the companion WD. The interaction of the circumbinary disk with the binary system will reduce the orbital separation much more than expected from the dynamical phase (where the envelope is ejected) of the CE alone. The smaller orbital separation favors a merger at the end of the CE phase or a short time after, while the core is still hot. This is another channel to form a massive WD with super-Chandrasekhar mass that might explode as a type Ia supernova. We term this the core-degenerate (CD) scenario.

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arXiv2011

Mergerburst Transients of Brown Dwarfs with Exoplanets

We explore the properties of an optical transient event formed by the destruction of a planet by a brown dwarf (BD) -- a BD-planet mergerburst. When a massive planet approaches a BD towards a merging process it will be tidally destroyed and will form an accretion disk around the BD. The viscosity in the disk sets the characteristic time for the event -- several days. We suggest that BD-planet mergerburst events have light curves resembling those of other intermediate luminosity optical transient (ILOT) events, such as V838 Mon, but at shorter timescales and lower luminosities. With the high percentage coverage of the sky, we expect that such events will be detected in the near future.

astro-ph.SR↗

arXiv2011

Possible Implications of the Planet Orbiting the Red Horizontal Branch Star HIP 13044

We propose a scenario to account for the surprising orbital properties of the planet orbiting the metal poor red horizontal branch star HIP 13044. The orbital period of 16.2 days implies that the planet went through a common envelope phase inside the red giant branch (RGB) stellar progenitor of HIP 13044. The present properties of the star imply that the star maintained a substantial envelope mass of 0.3Mo, raising the question of how the planet survived the common envelope before the envelope itself was lost? If such a planet enters the envelope of an RGB star, it is expected to spiral-in to the very inner region within <100yr, and be evaporated or destructed by the core. We speculate that the planet was engulfed by the star as a result of the core helium flash that caused this metal poor star to swell by a factor of ~3-4. The evolution following the core helium flash is very rapid, and some of the envelope is lost due to the interaction with the planet, and the rest of the envelope shrinks within about a hundred years. This is about equal to the spiraling-in time, and the planet survived.

astro-ph.SR↗

arXiv2011

The N II Lines in Eta Carinae: A Further Evidence for Mass Transfer During the Nineteenth Century Great Eruption

We argue that the emission and the absorption components of he N II lines recently observed in Eta Carinae can originate in the secondary's wind acceleration zone. We base this claim in part on the presence of these lines in hot nitrogen rich stars, such as WN 8 stars, and on the expected clumpy nature of such winds. The envelope of the secondary star in Eta Carinae is expected to be nitrogen rich due to accretion of few solar masses of the primary luminous blue variable's nitrogen rich material during the nineteenth century Great Eruption. Another argument in support of N II lines origin in the acceleration zone of the secondary wind is the behavior of the emission components. The emission components of the lines show the same Doppler shift variation as that of the absorption components. The secondary's-wind origin of the N II lines is compatible with the binary orientation in which the secondary is closer to us near periastron passage.

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arXiv2011

Exploding Core-Collapse Supernovae with Jittering Jets

We argue that jittering jets, i.e., jets that have their launching direction rapidly change, launched by the newly formed neutron star in a core collapse supernova can explode the star. We show that under a wide range of parameters the fast narrow jets deposit their energy inside the star via shock waves, and form two hot bubbles, that eventually merge, accelerate the rest of the star and lead to the explosion. To prevent the jets from penetrating through the collapsing stellar core and escape with their energy, instead of forming the hot bubbles, the jets should be prevented from drilling a hole through the star. This condition can be met if the jets' axis rapidly changes its direction. This process of depositing jets' energy into the ambient medium is termed the it penetrating jet feedback mechanism. The feedback exists in that the neutron star (or a black hole) at the center of the core collapse supernova shuts off its own growth by exploding the star. The jets deposit their energy at a distance of 1000 km from the center and expel the mass above that radius. In our model, the material near the stalled shock at several hundreds kilometers from the center is not expelled, but it is rather accreted and feed the accretion disk that blows the jets. The neutrinos might influence the accretion flow, but in the proposed model their role in exploding the star is small.

astro-ph.HE↗

arXiv2011

Evaporation of Jupiter like planets orbiting extreme horizontal branch stars

We study the evaporation of planets orbiting close to hot (extreme) horizontal branch (EHB) stars. These planets survived the common envelope phase inside the envelope of the reg giant star progenitor. We find that Jupiter-like planets orbiting within 10Ro from an EHB star suffers a non-negligible mass-loss during their 10^8 yr evolution on the horizontal branch. The evaporated gas is ionized and becomes a source of Balmer lines. Such planets might be detected by the periodic variation of the Doppler shift of the Balmer lines.

astro-ph.SR↗

arXiv2011

The role of planets in shaping planetary nebulae

In 1997 Soker laid out a framework for understanding the formation and shaping of planetary nebulae (PN). Starting from the assumption that non-spherical PN cannot be formed by single stars, he linked PN morphologies to the binary mechanisms that may have formed them, basing these connections almost entirely on observational arguments. In light of the last decade of discovery in the field of PN, we revise this framework, which, although simplistic, can still serve as a benchmark against which to test theories of PN origin and shaping. Within the framework, we revisit the role of planets in shaping PN. Soker invoked a planetary role in shaping PN because there are not enough close binaries to shape the large fraction of non-spherical PN. In this paper we adopt a model whereby only ~20% of all 1-8 solar mass stars make a PN. This reduces the need for planetary shaping. Through a propagation of percentages argument, and starting from the assumption that planets can only shape mildly elliptical PN, we conclude, like in Soker, that ~20% of all PN were shaped via planetary and other substellar interactions but we add that this corresponds to only ~5% of all 1-8 solar mass stars. This may be in line with findings of planets around main sequence stars. PN shaping by planets is made plausible by the recent discovery of planets that have survived interactions with red giant branch (RGB) stars. Finally, we conclude that of the ~80% of 1-8 solar mass stars that do not make a PN, about one quarter do not even ascend the AGB due to interactions with stellar and substellar companions, while three quarters ascend the AGB but do not make a PN. Once these stars leave the AGB they evolve normally and can be confused with post-RGB, extreme horizontal branch stars. We propose tests to identify them.

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arXiv2011

Explaining the transient fast blue absorption lines in the massive binary system Eta Carinae

We use recent observations of the He I $\lambda10830 Å$ absorption line and 3D hydrodynamical numerical simulations of the winds collision, to strengthen the case for an orientation of the semimajor axis of the massive binary system Eta Carinae where the secondary star is toward us at periastron passage. Those observations show that the fast blue absorption component exists for only several weeks prior to the periastron passage. We show that the transient nature of the fast blue absorption component supports a geometry where the fast secondary wind, both pre and post-shock material, passes in front of the primary star near periastron passage.

astro-ph.SR↗

arXiv2011

Common Powering Mechanism of Intermediate Luminosity Optical Transients and Luminous Blue Variables

We study recent Intermediate Luminosity Optical Transients (ILOTs) and major eruptions of Luminous Blue Variables (LBVs), and strengthen claims for a similar mechanism powering both. This process is a short duration release of gravitational energy in a binary system. In some ILOTs a merger occurs and one of the stars does not survive the transient event, e.g., V838 Mon and V1309 Sco. In some transient events a rapid and short mass transfer process takes place and the two stars survive the transient event, e.g., the Great Eruption of Eta Carinae. We study new ILOTs and reanalyze known ones in light of new observations and models. We reach our conclusion by analyzing these ILOTs using the Energy-Time Diagram (ETD) where we plot the total energy of the eruption against its eruption timescale. ILOTs and major LBV eruptions occupy the Optical Transient Stripe (OTS) in the ETD. The upper boundary of the stripe is explained by our proposed model where a main sequence (or a slightly off-main sequence) star accretes at a very high rate (<~ 1 M_\odot yr^{-1}) from a companion. We identify one LBV, NGC 3432 OT, with two eruptions; one with weak total energy and the other with large total energy. It bridges the regions of the ILOTs and LBVs in the OTS. We further study the ILOT M85 OT2006 and show that it cannot be a nova, even not an extreme one. We build a model where ILOTs can become optically thin in a timescale of few years and the inflated envelope collapses into an accretion disk around the star. Such an ILOT will evolve blue-ward after few years.

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arXiv2010

Magnetic Fields in Cooling Flow Clusters: A Critical View

Shortly after the first results of Chandra and XMM-Newton appeared, many researchers in the field abandoned the term "cooling flow clusters" in favor of the name "cool core clusters". This change, I argue, has been causing damage by promoting the view that there is no substantial cooling in these clusters. In this contribution I discuss the following points, with emphasize on the last one that deals with magnetic fields in cooling flow clusters. (1) Both AGN-feedback and hot-gas cooling to form stars occur during galaxy formation as well as in cooling flow clusters. Ignoring cooling of the intra-cluster medium, as implied by the term "cool core", does not encourage comparative study of AGN feedback in cooling flow clusters with that of galaxy formation. (2) The line of thought that there is no cooling might lead to wrong questions and research directions. (3) A key question in both cooling flow clusters and during galaxy formation is the mode of accretion by the super massive black hole (SMBH). When cooling is neglected only accretion from the hot phase remains. Accretion from the hot phase, such as the Bondi accretion, suffers from some severe problems. (4) When it is accepted that moderate quantities of gas are cooling, it becomes clear that global heat conduction must be substantially suppressed. This does not favor a globally ordered magnetic field. As well, it makes global heat conduction unattractive.

astro-ph.CO↗

arXiv2010

Planets around extreme horizontal branch stars

We review three main results of our recent study: * We show that a proper treatment of the tidal interaction prior to the onset of the common envelope (CE) leads to an enhance mass loss. This might increase the survivability of planets and brown dwarfs that enter a CE phase. * From the distribution of planets around main sequence stars, we conclude that around many sdB/sdO stars more than one planet might be present. One of these might have a close orbit and the others at about orbital periods of years or more. * We show that the intense ionizing flux of the extreme horizontal branch star might evaporate large quantities of a very close surviving substellar object. Balmer emission lines from the evaporated gas can be detected via their Doppler shifts.

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arXiv2010

Comparing shocks in planetary nebulae with the solar wind termination shock

We show that suprathermal particles, termed pick-up ions (PUIs), might reduce the postshock temperature of the fast wind and jets in some planetary nebulae (PNs) and in symbiotic systems. The goal is to explain the finding that the temperature of the hot bubble formed by the post-shock gas in some PNs and symbiotic nebulae is lower, sometimes by more than an order of magnitude, than the value expected from simple hydrodynamical calculations. Although various explanations have been proposed, there is as yet no prefered solution for this low tempeature problem. PUIs have been invoked to explain the low temperature behind the termination shock of the solar wind. While in the case of the solar wind the neutral atoms that turn into PUIs penetrate the pre-shock solar wind region from the interstellar medium (ISM), in PNs the PUI source is more likely slowly moving clumps embedded in the fast wind or jets. These clumps are formed by instabilities or from backflowing cold gas. Our estimates indicate that in young PNs these PUIs will thermalize before leaving the system. Only in older PNs whose sizes exceed ~5000 AU and for which the fast-wind mass loss rate is below ~10^{-7} Mo/yr do we expect the PUIs to be an efficient carrier of energy out of the postshock region (the hot bubble).

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