Chemical condensation sequences in supernova ejecta

The mineralogical composition of grains produced in supernova ejecta is explored via chemical equilibrium condensation computations. These calculations are carried out for chemical compositions characteristic of each of several supernova zones, taking into account the pressure decrease due to adiabatic expansion and condensation. The distributions of the major elements among the various gaseous species and solid phases are graphically displayed. These computations reveal that many of the major condensates from supernova ejecta are also stable against evaporation in a gas of solar composition at high temperatures. This is especially true for minerals containing the elements O, Mg, Al, Si, Ca, Fe and Ti. Grains which form in supernova ejecta are less likely to become homogenized with solar nebular gas than SN gas and are thus potential sources of exotic isotopic compositions in the early solar system. The calculated elemental distributions of supernova condensates are applied to problems concerning isotopic anomalies and large mass-dependent isotopic fractionations discovered in the meteorite Allende. The order in which the major elements become totally condensed is found to be nearly independent of the supernova zone considered, being the same as that for a solar gas. The consequence of this may be that some of the observed depletions of heavy elements in the interstellar gas are due to supernova-produced dust.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978.     

Dust formation and survival in supernova ejecta

The presence of dust at high redshift requires efficient condensation of grains in supernova (SN) ejecta, in accordance with current theoretical models. Yet observations of the few well-studied supernovae (SNe) and supernova remnants (SNRs) imply condensation efficiencies which are about two orders of magnitude smaller. Motivated by this tension, we have (i) revisited the model of Todini & Ferrara for dust formation in the ejecta of core collapse SNe, and (ii) followed, for the first time, the evolution of newly condensed grains from the time of formation to their survival – through the passage of the reverse shock – in the SNR. We find that  0.1–0.6  M_⊙  of dust form in the ejecta of 12–40 M_⊙ stellar progenitors. Depending on the density of the surrounding interstellar medium, between 2 and 20 per cent of the initial dust mass survives the passage of the reverse shock, on time-scales of about  4–8 × 10⁴  yr  from the stellar explosion. Sputtering by the hot gas induces a shift of the dust size distribution towards smaller grains. The resulting dust extinction curve shows a good agreement with that derived by observations of a reddened QSO at   z = 6.2  . Stochastic heating of small grains leads to a wide distribution of dust temperatures. This supports the idea that large amounts (∼0.1 M_⊙) of cold dust  ( T ∼ 40   K)  can be present in SNRs, without being in conflict with the observed infrared emission.     

Nucleosynthesis in neutron rich supernova ejecta

A nuclear reaction network of 903 different, strong and electromagnetic reactions, linking 107 chemical constituents is used to study the elements synthesized in the neutron rich material, ejected in supernova explosions. A large number of three body reactions virtually eliminates the usual bottle neck at theA=5 mass gap.For initially high temperatures and densities,T=10¹⁰K and =7×10⁸ gm/cm³, with expansion time scales of 10^–3–10^–2 sec, three differentn top ratios,n/p=4,n/p=3/2, andn/p1, are considered for the ejected matter. In all three cases, the material synthesized is preponderantly heavy. For then/p=4 model, the conditions at the charged particle freeze-out are ideal for the r-process. The onset of this rapid neutron capture phase is explicitly shown with a sequence of time lapse abundance plots.     

Grain formation in the ejecta of a supernova: the nucleation rate of grains heated by radiation

In the ejecta of a supernova, the temperature of the created grains differs from that of the gas due to the radiation from the star. We investigated the grain formation in the supernova using a developed new nucleation rate where the temperature difference between the gas and the grains is taken into account. If the temperature of the grains is higher than that of the gas, the nucleation process does not occur when the gaseous temperature attains the condensation temperature. As a result we found that the temperature difference between the gas and the grains in SN1987A is about 50–200K which leads that the nucleation is delayed for about 20–100 days.     

Asymmetry of 56Ni ejecta and polarization in the type-IIP supernova 2004dj

I study the question of whether the asymmetry of ⁵⁶Ni ejecta that results in the asymmetry of the Hα emission line at the nebular epoch of the type-IIP supernova SN 2004dj can account for the recently detected polarization of the supernova radiation. I have developed a model of the Hα profile and luminosity with nonthermal ionization and excitation in a spherically symmetric envelope for an asymmetric bipolar ⁵⁶Ni distribution. I have calculated the polarized radiation transfer against the background of the recovered electron density distribution. The observed polarization is shown to be reproduced at the nebular epoch around day 140 for the same parameters of the envelope, and the ⁵⁶Ni distribution for which the evolution of the Hα luminosity and profile is explained. Yet the model polarization decreases with time more slowly than is observed. The origin of the additional component responsible for the early polarization on day 107 is discussed.     

Hints of a second explosion(a quark nova) in Cassiopeia A supernova

We show that the explosive transition of the neutron star(NS)to a quark star(QS)(a Quark Nova)in Cassiopeia A(Cas A)a few days following the supernova(SN)proper can account for several of the puzzling kinematic and nucleosynthetic features that are observed.The observed decoupling between Fe and44Ti and the lack of Fe emission within44Ti regions is expected in the QN model owing to the spallation of the inner SN ejecta by relativistic QN neutrons.Our model predicts the44Ti to be more prominent to the NW of the central compact object(CCO)than in the SE and little of it along the NE-SW jets,in agreement with Nu Star observations.Other intriguing features of Cas A are addressed,such as the lack of a pulsar wind nebula and the reported few percent drop in the CCO temperature over a period of 10 yr.     

A quark nova in the wake of a core-collapse supernova:a unifying model for long duration gamma-ray bursts and fast radio bursts

By appealing to a quark nova(QN;the explosive transition of a neutron star to a quark star) in the wake of a core-collapse supernova(CCSN) explosion of a massive star,we develop a unified model for long duration gamma-ray bursts(LGRBs) and fast radio bursts(FRBs).The time delay(years to decades)between the SN and the QN,and the fragmented nature(i.e.,millions of chunks) of the relativistic QN ejecta are key to yielding a robust LGRB engine.In our model,an LGRB light curve exhibits the interaction of the fragmented QN ejecta with turbulent(i.e.,filamentary and magnetically saturated) SN ejecta which is shaped by its interaction with an underlying pulsar wind nebula(PWN).The afterglow is due to the interaction of the QN chunks,exiting the SN ejecta,with the surrounding medium.Our model can fit BAT/XRT prompt and afterglow light curves simultaneously with their spectra,thus yielding the observed properties of LGRBs(e.g.,the Band function and the X-ray flares).We find that the peak luminositypeak photon energy relationship(i.e.,the Yonetoku law),and the isotropic energy-peak photon energy relationship(i.e.,the Amati law) are not fundamental but phenomenological.FRB-like emission in our model results from coherent synchrotron emission(CSE) when the QN chunks interact with non-turbulent weakly magnetized PWN-SN ejecta,where conditions are prone to the Weibel instability.Magnetic field amplification induced by the Weibel instability in the shocked chunk frame sets the bunching length for electrons and pairs to radiate coherently.The resulting emission frequency,luminosity and duration in our model are consistent with FRB data.We find a natural unification of high-energy burst phenomena from FRBs(i.e.,those connected to CCSNe) to LGRBs including X-ray flashes(XRFs) and X-ray rich GRBs(XRR-GRBs) as well as superluminous SNe(SLSNe).We find a possible connection between ultra-high energy cosmic rays and FRBs and propose that a QN following a binary neutron star merger can yield a short duration GRB(SGRB) with fits to BAT/XRT light curves.     

Hypervelocity impacts on dry and wet sandstone: Observations of ejecta dynamics and crater growth

Abstract– This study deals with the investigation of highly dynamic processes associated with hypervelocity impacts on porous sandstone. For the impact experiments, two light‐gas accelerators with different calibers were used, capable of accelerating steel projectiles with diameters ranging from 2.5 to 12 mm to several kilometers per second. The projectiles impacted on dry and water‐saturated Seeberger Sandstone targets. The study includes investigations of the influence of pore water on the shape of the ejecta cloud as well as transient crater growth. The results show a significant influence of pore water on ejecta behavior. Steeper ejecta cone angles are observed if the impacts are conducted on wet sandstones. The transient crater grows at a faster rate and reaches a larger diameter if the target is water saturated. In our experiments, target porosity leads to smaller crater sizes compared with nonporous targets. Water within the pore space reduces porosity and counteracts this process. Power law fits were applied to the crater growth curves. The results show an increase in the scaling exponent μ with increasing pore space saturation.     

Optical observations of type-IIP supernova 2004dj: Evidence for asymmetry of the <Superscript>56</Superscript>Ni ejecta

Photometric and spectroscopic observations of the nearby type-IIP supernova 2004dj are presented. The ⁵⁶Ni mass in the envelope of SN 2004dj was estimated from the light curve to be ≈0.02M_⊙. This estimate is confirmed by modeling the Hα luminosity. The Hα emission line exhibits a strong asymmetry characterized by the presence of a blue component in the line with a shift of ?1600 km s^?1 at the early nebular phase. A similar asymmetry was found in the Hβ, [O I], and [Ca II] lines. The line asymmetry is interpreted as being the result of asymmetric ⁵⁶Ni ejecta. The Hα profile and its evolution are reproduced in the model of an asymmetric bipolar ⁵⁶Ni structure for a spherical hydrogen distribution. The mass of the front ⁵⁶Ni jet is comparable to that of the central component and twice that of the rear ⁵⁶Ni jet. We point out that the asymmetric bipolar structure of ⁵⁶Ni ejecta is also present in SN 1999em, a normal type-IIP supernova.     

A dwarf nova in Taurus

In searchs for flare stars in the vicinity of the Pleiades cluster, three flares were detected in 1970,1972, and 1977 in a star with the coordinates α ₁₉₅₀ = 3 ^h 48 ^m ·9, δ _l950 = 25‡15’.8. The star’s brightness at a minimum is >21 ^m ·5. The star was tentatively assigned to the U Gem type. To confirm this assumption, we examined photographic plates for the period of 1947–1987. As a result, we found 12 more flares. The average recurrence time based on the 1963–1977 observations is about 330 days, and the maximum flare amplitude is >6 ^m .Narrow superflares and steady-state flares lasting over 40 days have been observed in the star. The results show that this is a dwarf nova of the UGSU subtype. Translated from Astrofizika, Vol. 42, No. 1, pp. 47–52, January–March, 1999.     

Dust processing in nova winds

We have radically re-assessed the conditions required for the formation and growth of carbon grains in the ejecta of novae. The stability and hence the ultimate fate of the grains is primarily determined by the degree to which they are annealed by the nova's ultraviolet radiation field.     

Dust formation in nova winds

We review the properties of classical novae, with particular emphasison their dust formation. Recent observational and theoretical workindicates that CO formation in nova winds does not go to saturation,so that both oxygen- and carbon-rich condensates can appearsimultaneously in the ejected material. The UIR carrier in novaeappears to be near-unique to novae, although whether this is due toenvironmental, excitation or abundance effects is not yet clear.     

Mercurian impact ejecta: Meteorites and mantle

Abstract— We have examined the fate of impact ejecta liberated from the surface of Mercury due to impacts by comets or asteroids, in order to study 1) meteorite transfer to Earth, and 2) reaccumulation of an expelled mantle in giant‐impact scenarios seeking to explain Mercury's large core. In the context of meteorite transfer during the last 30 Myr, we note that Mercury's impact ejecta leave the planet's surface much faster (on average) than other planets in the solar system because it is the only planet where impact speeds routinely range from 5 to 20 times the planet's escape speed; this causes impact ejecta to leave its surface moving many times faster than needed to escape its gravitational pull. Thus, a large fraction of Mercurian ejecta may reach heliocentric orbit with speeds sufficiently high for Earth‐crossing orbits to exist immediately after impact, resulting in larger fractions of the ejecta reaching Earth as meteorites. We calculate the delivery rate to Earth on a time scale of 30 Myr (typical of stony meteorites from the asteroid belt) and show that several percent of the high‐speed ejecta reach Earth (a factor of 2–3 less than typical launches from Mars); this is one to two orders of magnitude more efficient than previous estimates. Similar quantities of material reach Venus. These calculations also yield measurements of the re‐accretion time scale of material ejected from Mercury in a putative giant impact (assuming gravity is dominant). For Mercurian ejecta escaping the gravitational reach of the planet with excess speeds equal to Mercury's escape speed, about one third of ejecta reaccretes in as little as 2 Myr. Thus collisional stripping of a silicate proto‐Mercurian mantle can only work effectively if the liberated mantle material remains in small enough particles that radiation forces can drag them into the Sun on time scale of a few million years, or Mercury would simply re‐accrete the material.     

Material ejecta in a disturbed solar filament

H observations, using the Multichannel Subtractive Double Pass (MSDP) spectrograph operating on the Meudon Solar Tower, have been made of an active region filament which undergoes a disparition brusque. The period of observation was from 10 45 to 13 30 UT on 22 June, 1981. Velocity and intensity fluctuations in H were measured. The proper motions of ejecta were followed allowing their trajectories and vector velocities to be determined. To model the dynamics of ejecta several models using thermal or magnetic driving forces are compared. The most promising model explains the motion as the consequence of magnetic stresses acting on an isolated magnetized plasmoïd in a diverging flux tube.     

Material ejecta in a disturbed solar filament

Hα observations, using the Multichannel Subtractive Double Pass (MSDP) spectrograph operating on the Meudon Solar Tower, have been made of an active region filament which undergoes a ‘disparition brusque’. The period of observation was from 10 ∶ 45 to 13 ∶ 30 UT on 22 June, 1981. Velocity and intensity fluctuations in Hα were measured. The proper motions of ejecta were followed allowing their trajectories and vector velocities to be determined. To model the dynamics of ejecta several models using thermal or magnetic driving forces are compared. The most promising model explains the motion as the consequence of magnetic stresses acting on an isolated magnetized plasmoïd in a diverging flux tube.     

Interacting winds in classical nova outbursts

Classical nova outbursts occur in binary systems containing a white dwarf accretor and a Roche-lobe-filling main-sequence star. The outburst is due to a thermonuclear runaway in the accreted material on the surface of the white dwarf, and results in the ejection of up to 10^–4 M of material at velocities of several hundred to a few thousand kilometres per second. There is now strong evidence that the mass ejection takes place via a wind with secularly increasing velocity. The fast ejecta catches up with slower moving material ejected earlier in the outburst, forming a layer of shock-heated gas which gives rise to a short burst of soft X-ray emission. This emission was observed in V838 Her (Nova Herculis 1991), and was succesfully accounted for by the interacting winds model. In this paper, we present 2.5-D numerical hydrodynamics calculations of interacting winds in novae which consider the effects of the binary system on shaping the mass-loss, and show that many of the features seen in the optical shells of novae many years after outburst can be accounted for.This author is supported by a PPARC research assistantship     

Generation and emplacement of fine-grained ejecta in planetary impacts

We report here on a survey of distal fine-grained ejecta deposits on the Moon, Mars, and Venus. On all three planets, fine-grained ejecta form circular haloes that extend beyond the continuous ejecta and other types of distal deposits such as run-out lobes or ramparts. Using Earth-based radar images, we find that lunar fine-grained ejecta haloes represent meters-thick deposits with abrupt margins, and are depleted in rocks ?1 cm in diameter. Martian haloes show low nighttime thermal IR temperatures and thermal inertia, indicating the presence of fine particles estimated to range from ∼10 μm to 10 mm. Using the large sample sizes afforded by global datasets for Venus and Mars, and a complete nearside radar map for the Moon, we establish statistically robust scaling relationships between crater radius R and fine-grained ejecta run-out r^* for all three planets. On the Moon, r^* ∼ R^−0.18 for craters 5-640 km in diameter. For Venus, radar-dark haloes are larger than those on the Moon, but scale as r^* ∼ R^−0.49, consistent with ejecta entrainment in Venus’ dense atmosphere. On Mars, fine-ejecta haloes are larger than lunar haloes for a given crater size, indicating entrainment of ejecta by the atmosphere or vaporized subsurface volatiles, but scale as R^−0.13, similar to the ballistic lunar scaling. Ejecta suspension in vortices generated by passage of the ejecta curtain is predicted to result in ejecta run-out that scales with crater size as R^1/2, and the wind speeds so generated may be insufficient to transport particles at the larger end of the calculated range. The observed scaling and morphology of the low-temperature haloes leads us rather to favor winds generated by early-stage vapor plume expansion as the emplacement mechanism for low-temperature halo materials.