Cosmic-ray production of deuterium,He3, lithium,beryllium, and boron in the Galaxy

The production of deuterium, He³, lithium, beryllium, and boron by galactic cosmic rays in the interstellar medium, over the life of the Galaxy, is calculated. It is found that high-energy - reactions contribute in an essential way to the observed lithium. When allowance is made for the interchange of material between stars and the interstellar gas and for the change of cosmic-ray intensity with time, the Li⁶, Be⁹, and boron produced turn out to be ample to explain the observed abundances, and with remarkable internal consistency. Deuterium and He³ arenot produced in significant amounts, nor Li⁷ in sufficient amount, however. To explain the Li⁷/Li⁶ ratio measured terrestrially and in chondritic meteorites, we invoke cosmological production of Li⁷. This implies the production of deuterium, He³, and He⁴ as well, in amounts consistent with observation. The theory in its present form cannot explain a solar-system Li⁷/Li⁶ ratio of 12and stellar ratios as low as 3, but additional processes can be adduced to reconcile them. The consistency of the numbers when cosmological production is included lends additional support to the big-bang hypothesis. An incidental result is that the mean luminosity of the Galaxy over its lifetime has been about 3 times its present luminosity.     

The orbit and exposure history of the Piplia Kalan eucrite

Abstract— Cosmogenic radionuclides, particle tracks and rare gases have been measured in two fragments of the Piplia Kalan eucrite that fell in Rajasthan, India on 1996 June 20. The cosmic-ray exposure age of the meteorite is calculated to be 23 Ma, which is similar to ages of some other eucrites. The track density in feldspars and pyroxenes varies between 0.2 × 10⁶ to ～4.5 × 10⁶ cm^?2. The mass ablation of the meteorite, based on the distribution of track density in near-surface samples of the two fragments, is calculated to be ～75%, which corresponds to an entry velocity of ～17 km/s. The orbital parameters of the eucrite have been computed from the radiant of the meteor trail and the geocentric velocity. The best estimates are a = 2.47 AU, e = 0.62 and i = 7.54°, which is similar to the orbital elements of other meteorites, most of which have been inferred to originate within 2.6 AU of the Sun. The activity of the radionuclide ²⁶Al agrees with the expected production rate; whereas the shortlived radionuclides ²²Na, ⁵⁴Mn, ⁴⁶Sc etc. have levels that are consistent with the galactic cosmic-ray fluxes that are expected during the solar minimum period before the time of fall. All the cosmogenic effects (i.e., radio- and stable- nuclides and particle tracks) are consistent with the meteoroid having had a simple, one-stage exposure history in interplanetary space. Lower radio genic ages of U, Th-He (0.7 Ga) and K-Ar (3.6 Ga) indicate severe losses of ⁴He and ⁴⁰Ar, as observed in most eucrites. A Pu-Xe age, concordant with Angra dos Reis, shows that Piplia belongs to the “old” eucrite group.     

The production of lithium in the solar chromosphere and photosphere during white light flares

Recently new values of the lithium formation rate in low energy flares have been reported in the literature. These values are applied to the white light flare phenomenon on the Sun. It is found that the formation rate in the chromosphere is much larger than in the upper photosphere and that the ratio between the time integrated flare created abundance and the initial photospheric abundance is modest in the chromosphere and small in the upper photosphere. The yield of Li⁶ in the upper photosphere is, however, comparable to the upper limit of Li⁶ there.     

Fission Track Age of the Brahin Pallasite

The results of the determination of the fission track age of the Brahin pallasite are presented. Crystals of phosphates (stanfieldites), with an enhanced uranium concentration, were found directly in the investigated samples. Fossil tracks in them are represented by two generations. The distribution and partial annealing of first-generation track lengths point to a shock/thermal event at an early stage in the cosmic history of the pallasite. The value of the fission track age, registering the time of its passage, was computed from second-generation tracks. It was shown that the second generation is represented mainly by tracks of the spontaneous fission of ²³⁸U and ²⁴⁴Pu nuclei (_Pu/_U 4). The calculations performed made it possible to establish that the last intensive thermal event in the cosmic history of the Brahin pallasite occurred 4.26–4.20 billion years ago. The temperature of the reheating of its parent body did not rise above 500°C. The excellently preserved character of the second-generation tracks provides evidence that the pallasite underwent subsequent cosmic evolution in mild conditions.     

Infrared spectroscopy of Wild 2 particle hypervelocity tracks in Stardust aerogel: Evidence for the presence of volatile organics in cometary dust

Abstract— Infrared spectroscopy maps of some tracks made by cometary dust from 81P/Wild 2 impacting Stardust aerogel reveal an interesting distribution of organic material. Out of six examined tracks, three show presence of volatile organic components possibly injected into the aerogel during particle impacts. When particle tracks contained volatile organic material, they were found to be ‐CH₂‐rich, while the aerogel is dominated by the ‐CH₃‐rich contaminant. It is clear that the population of cometary particles impacting the Stardust aerogel collectors also includes grains that contained little or none of this organic component. This observation is consistent with the highly heterogeneous nature of collected grains, as seen by a multitude of other analytical techniques.     

Photo-electric study of the eclipsing binary RU Eridani

B andV observations of the eclipsing binary RU Eridani made on 23 nights during 1974–76 are reported. An improved period of 0^d.63219951 is derived. After rectification ofB andV light curves, new elements are derived using Russel-Merrill method. The system is classified as semidetached.     

Tachocline Confinement by an Oscillatory Magnetic Field

Helioseismic measurements indicate that the solar tachocline is very thin, its full thickness not exceeding 4% of the solar radius. The mechanism that inhibits differential rotation to propagate from the convective zone to deeper into the radiative zone is not known, though several propositions have been made. In this paper we demonstrate by numerical models and analytic estimates that the tachocline can be confined to its observed thickness by a poloidal magnetic field B _p of about one kilogauss, penetrating below the convective zone and oscillating with a period of 22 years, if the tachocline region is turbulent with a diffusivity of η∼10¹⁰ cm² s⁻¹ (for a turbulent magnetic Prandtl number of unity). We also show that a similar confinement may be produced for other pairs of the parameter values (B _p, η). The assumption of the dynamo field penetrating into the tachocline is consistent whenever η≳10⁹ cm² s⁻¹. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1013389631585     

On the UV-excesses of cepheid variables

On the basis of the intrinsic (U – B)₀ colours of the cepheid variables, found by the authors, the UV-excesses in the maximum and minimum light δ(U – B)^max and δ(U – B)^min are defined. It is found out that the UV-excesses in the maximum light δ(U – B)^min increase with the period P (Fig. 2), but there is no correlation between δ(U – B)^min and log P. A correlation between δ(U – B)^max and the “amplitude defects” f_B is also determined. These results in connection with some other considerations, as well as the possible causes of the UV-excesses, are discussed.     

Chemical and isotopic characteristics of the Didwana‐Rajod (H5) chondrite

Abstract— The mineralogical and chemical characteristics of the Didwana‐Rajod chondrite are described. The mean mineral composition is found to be olivine (Fo_83.2) and pyroxene (En_83.5Wo_0.7Fs_15.8), and feldspar is mainly oligoclase. Oxygen isotopic analysis shows δ¹⁸O = +3.8%0 and δ¹⁷O = +2.59%0. The nitrogen content of Didwana‐Rajod is ～2 ppm with δ¹⁵N ? 3.4%0. Based on microscopic, chemical, isotopic and electron probe microanalysis, the meteorite is classified as an H5 chondrite. Cosmogenic tracks, radionuclides and the isotopic composition of rare gases were also measured in this meteorite. The track density in olivines varies in a narrow range with an average value of (6.5 ± 0.5) × 10⁵/cm² for four spot samples taken at the four corners of the stone. The cosmic‐ray exposure age based on neon and argon is 9.8 Ma. ²²Na/²⁶Al ? 0.94 is lower than the solar‐cycle average value of ～1.5 and is consistent with irradiation of the meteoroid to lower galactic cosmic‐ray fluxes as expected at the solar maximum. The track density, rare gas isotopic ratios, ⁶⁰Co activity and other radionuclide data are consistent with a preatmospheric radius of ～15 cm, corresponding to a mass of ～50 kg. The cosmogenic properties are consistent with a simple exposure history in interplanetary space.     

Measurement of the lunar neutron density profile

Anin situ measurement of the lunar neutron density from 20 to 400 g cm^?2 depth below the lunar surface was made by the Apollo 17 Lunar Neutron Probe Experiment (LNPE) using particle tracks produced by the¹⁰B (n,α)⁷Li reaction. Both the absolute magnitude and the depth profile of the neutron density are in good agreement with theoretical calculations by Lingenfelter, Canfield, and Hampel. However, relatively small deviations between experiment and theory in the effect of Cd absorption on the neutron density and in the relative¹⁴⁹Sm to¹⁵⁷Gd capture rates reported previously (Russet al., 1972) imply that the true lunar¹⁵⁷Gd capture rate is about one half of that calculated theoretically.     

The rotation,color, phase coefficient,and diameter of 1915 quetzalcoatl

Photoelectric observations of 1915 Quetzalcoatl on March 2, 1981 show that this asteroid has a rotational period of 4.9 ± 0.3 hr and a lightcurve amplitude of 0.26 magnitudes. B-V and U-B colors are found to be 0.83 ± 0.04 and 0.43 ± 0.03, respectively, consistent with Quetzalcoatl being an S-type asteroid. Additional observations from March 31, 1981 give a linear phase coefficient of 0.033 mag deg^?1 and a mean B(1,0) magnitude of 20.10. The resulting estimated mean diameter for Quetzalcoatl is only 0.37 km, making it one of the smallest asteroids for which physical observations have yet been made.     

On the temperature and emission measure of thermal radio bursts

Once the area of a thermal burst region has been determined, it is possible to obtain the temperature and emission measure of the burst by examination of the flux spectrum. Such determinations have been made for three events. Temperatures in the range 2 to 6 × 10⁶K and emission measures in the area of 2.6 to 5.4 × 10⁴⁹ cm^–3 are consistent with radio observations. Electron densities are estimated to be of the order of 1 to 5 ]x 10¹⁰ electrons cm^–3.This work was supported by the U.S. Air Force under Contract No. F04701-70-C-0059.     

Fall,classification and cosmogenic records of the Sabrum (LL6) chondrite

Abstract— The petrographic and chemical characteristics of a fresh Indian meteorite fall at Sabrum are described. Its mean mineral composition is defined by olivine (Fa_31.4), orthopyroxene (Fs_25.1,Wo_2.0), clinopyroxene (Wo₄₅En_45.6Fs_9.4) and plagioclase (An_10.6Ab_83.6Or_5.8). The meteorite shows moderate shock features, which indicate that it belongs to the S4 category. Based on mineralogical and chemical criteria the meteorite is classified as an LL6 brecciated veined chondrite. Several cosmogenic radioisotopes (⁴⁶Sc, ⁷Be, ⁵⁴Mn, ²²Na and ²⁶Al), noble gas (He, Ne, Ar, Kr and Xe), nitrogen isotopes, and particle tracks density have been measured. Concentrations of cosmogenic ²¹Ne and ³⁸Ar indicate that its cosmic‐ray exposure age is 24.8 Ma. Small amounts of trapped Kr and Xe, consistent with petrologic class 5/6, are present. The track density in olivines is found to be (1.3 ± 0.3) × 10⁶/cm². Activities of most of the short‐lived isotopes are lower than those expected from solar cycle variation. ²²Na/²⁶Al (1.12 ± 0.02) is found to be significantly anomalous, being ?25% lower than expected from the Climax neutron monitor data. These results indicate that the cosmic‐ray flux during the terminal segment of the meteoroid orbit was low. The activities of ²⁶Al and ⁶⁰Co and the track density indicate small meteoroid size with a radius ?15 cm.     

On the presence of electric currents in the solar atmosphere

An elementary analysis based on Ampére's Law is given to separate the general magnetic field above the photosphere into two parts B=B ₁+B ^*. The field B ₁ is a potential field due to electric currents below the photosphere. The field B ^* is produced by electric currents above the photosphere combined with the induced mirror currents. By symmetry, B ^* has a set of field lines lying entirely in the plane z = 0 taken to be the photosphere. This set of field lines can be constructed from given vector magnetograph measurements and represents all the information on the electric currents above the photosphere that a magnetograph can provide. Theoretical illustrations are given and the implications for data analysis are discussed.     

Main stages of evolution of matter in the universe. II

A possible scenario for the evolution of the universe following the big bang at t > 10^-5 sec is considered. The necessary conditions that must be present for the formation of stars and stellar systems to be possible are formulated. As a condition for the formation of stars we take kT_s≤ GM_sm_p(3R), and for stellar systems HR ? (GM/R)^1/2, where T_s is the temperature of the cosmic plasma, m_p is the mass of a proton, M_s is the mass of a star, M is the mass of a stellar cluster, R is the radius of these celestial bodies, and H is the bubble parameter for the corresponding time. In accordance with these criteria, we assume that in the course of cosmological expansion, neutron stars should have been formed first (times 2.10^-4 ? t ? 1 sec, densities 0.07 ? ρ_B? 2.10⁴ g/cm³) and then, in chronological order, appeared white dwarfs (t ≈ 10² sec, ρ_B ? 5.10^-3 g/cm³), ordinary stars (t ≈ 4.10⁶ sec, ?_B ≈ 10^-11 g/cm³), galactic nuclei (t ≈ 3.10¹¹ sec, ?_B ≈ 5.10^-19 g/cm³, globular clusters (t ≈ 10¹³ sec, ?_B ≈ 4.10^-21 g/cm³), and galaxies (t ≈ 10¹⁵ sec, ?_B ≈ 10^-24 g/cm³), where ?_B is the average density of ordinary (baryon) matter in the universe. It is shown that a galactic nucleus is a stellar system in statistical equilibrium and consists mainly of neutron stars and white dwarfs. The formation of some pulsars (neutron stars with angular rotation rates 1 < Ω < 200 sec^-1) may occur in a galactic nucleus. Observed pulsars should therefore contain some fraction of neutron stars from the nucleus of the Galaxy that were able to escape it over the relaxation time (the tail of the Maxwell distribution, with star velocities v > v₀, where v₀ is the velocity corresponding to the work function 2GMM_s/R, M being the mass and R the radius of the Galaxy’s nucleus.     

Solar flare track densities in interplanetary dust particles: The determination of an asteroidal versus cometary source of the zodiacal dust cloud

Dust particles that are larger than 1 μm, when injected into the Solar System from comets and asteroids, will spiral into the Sun due to the Poynting-Robertson effect. During the process of spiraling in, such dust particles accumulate solar flare tracks in their component minerals. The accumulated track density for a given dust grain is a function of the duration of its space exposure and its distance from the Sun. Using a computer model, it was determined that the expected track density distributions from grains produced by comets are very different from those produced by asteroids. Individual asteroids produce populations of particles that arrive at 1 AU with scaled track density distributions containing “spikes,” while comets supply particles with a flatter and wider distribution of track densities. Particles with track densities above 3 × 10⁷ (sϱA/v) tracks/cm² have probably been exposed to solar flare tracks prior to injection into the interplanetary medium and are therefore likely to be asteroidal. Particles with track densities below 0.7 × 10⁷(sϱA/v) tracks/cm² must be derived from comets or Earth-crossing asteroids. Earth-crossing asteroids are not responsible for all the dust collected at 1 AU since they cannot produce the large track densities observed in some of the interplanetary dust particles collected in the stratosphere. The track densities observed in the stratospheric dust fall within the predicted range, but there is at present an insufficient number of carefully determined densities to make strong statements about the sources of the present dust population.     

Physical, Chemical, and Mineralogical Properties of Comet 81P/Wild 2 Particles Collected by Stardust

NASA’s Stardust spacecraft collected dust from the coma of Comet 81P/Wild 2 by impact into aerogel capture cells or into Al-foils. The first direct, laboratory measurement of the physical, chemical, and mineralogical properties of cometary dust grains ranging from <10⁻¹⁵ to ∼10⁻⁴ g were made on this dust. Deposition of material along the entry tracks in aerogel and the presence of compound craters in the Al-foils both indicate that many of the Wild 2 particles in the size range sampled by Stardust are weakly bound aggregates of a diverse range of minerals. Mineralogical characterization of fragments extracted from tracks indicates that most tracks were dominated by olivine, low-Ca pyroxene, or Fe-sulfides, although one track was dominated by refractory minerals similar to Ca–Al inclusions in primitive meteorites. Minor mineral phases, including Cu–Fe-sulfide, Fe–Zn-sulfide, carbonate and metal oxides, were found along some tracks. The high degree of variability of the element/Fe ratios for S, Ca, Ti, Cr, Mn, Ni, Cu, Zn, and Ga among the 23 tracks from aerogel capture cells analyzed during Stardust Preliminary Examination is consistent with the mineralogical variability. This indicates Wild 2 particles have widely varying compositions at the largest size analyzed (>10 μm). Because Stardust collected particles from several jets, sampling material from different regions of the interior of Wild 2, these particles are expected to be representative of the non-volatile component of the comet over the size range sampled. Thus, the stream of particles associated with Comet Wild 2 contains individual grains of diverse elemental and mineralogical compositions, some rich in Fe and S, some in Mg, and others in Ca and Al. The mean refractory element abundance pattern in the Wild 2 particles that were examined is consistent with the CI meteorite pattern for Mg, Si, Cr, Fe, and Ni to 35%, and for Ca, Ti and Mn to 60%, but S/Si and Fe/Si both show a statistically significant depletion from the CI values and the moderately volatile elements Cu, Zn, Ga are enriched relative to CI. This elemental abundance pattern is similar to that in anhydrous, porous interplanetary dust particles (IDPs), suggesting that, if Wild 2 dust preserves the original composition of the Solar Nebula, the anhydrous, porous IDPs, not the CI meteorites, may best reflect the Solar Nebula abundances. This might be tested by elemental composition measurements on cometary meteors.     

How bright is the [Si X] 1431 nm coronal emission line?

Airborne eclipse observations of the [Six] 1430.5 nm coronal emission line are reviewed, and new ground-based out-of-eclipse coronagraph observations obtained at NSO/Sacramento Peak are reported. We find that the [Six] 1430.5 nm coronal emission line brightness is less than 8 × 10⁻⁶ B⊙ in small active region corona which showed [Fexiii] 1074.7 nm emission (corrected for sky background) of about 20 × 10⁻⁶ B⊙. Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.     

Solar and galactic cosmic‐ray records of the Fermo (H) chondrite regolith breccia

Abstract— ‐We demonstrate the presence of solar flare as well as neutron capture effects in the isotopic composition of rare gases in the Fermo regolith breccia acquired on its parent body based on the measurements of tracks, rare gases and radionuclides. The track density along a 3.2 cm long core decreases by a factor of about 6 and by more than a factor of 13 within the meteorite, indicating small (2–9 cm) and asymmetrical ablation. Rare gases show a large trapped component; the isotopic ratios, particularly ²⁰Ne/²²Ne ? 11 and ²⁰Ne/³⁶Ar = 10 are indicative of a solar component. The galactic cosmic‐ray exposure age is determined to be 8.8 Ma. Activities of a dozen radionuclides ranging in half‐life from 16 day ⁴⁸V to 0.73 Ma ²⁶Al are consistent with their expected production rates. Track, rare gas and radionuclide data show that the meteoroid was a small body (≤ 120 kg) and had a simple, one‐stage exposure history to cosmic rays in the interplanetary space. However, ⁸²Kr and ¹²⁸Xe show an excess due to neutron irradiation on the parent body of the meteorite. The presence of solar gases and the neutron capture effects indicate several stages of irradiation on the parent asteroid. The chemical composition of Fermo confirms that it belongs to the H group of ordinary chondrites with lithic clasts having varying compositions. δ¹⁵N is found to be 8.3 ± 1.2%0, close to the typical values observed in H chondrites.     

Difference between the optical flickering colours of cataclysmic variables and symbiotic recurrent novae

We performed simultaneous observations in 3 bands (U BV) of the flickering variability of the recurrent novae RS Oph and T CrB at quiescence. Using new and published data, we compare the colours of the flickering in cataclysmic variables and symbiotic recurrent novae. We find a difference between the colours of the flickering source in these two types of accreting white dwarfs. The detected difference is highly significant with p ‐values ≈2 x 10^–6 for the distributions of (U – B)₀ colour and p ≈ 3 x 10^–5 on an (U – B) versus (B – V) diagram. The possible physical reasons are briefly discussed. The data are available upon request from the authors. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)