Impact Vaporization and Ionization of Cosmic Dust Particles

We report on theoretical efforts to understand the process of vaporization and ion formation upon hypervelocity impact of small cosmic dust particles on a solid surface. Such collisions occur at the surface of solid bodies within the planetary system, which do not have an atmosphere as well as in various actual and upcoming space missions for in-situ measurements of interplanetary, interstellar and cometary dust. The investigation uses Godunov's method to simulate the impact. For the very high velocitites investigated, the impacting dust particle as well as parts of the target vaporize and some of the vapor cloud may change to partially ionized. Numerical results of the impact process are communicated for an 80 kms^-1impact of a slightly porous SiO₂ particle on a compact SiO₂surface. Values of the amount of vapor and liquid excavated from the target are given. Ionization rates are calculated for the example investigated and an estimate is given how this extrapolates to the highest conceivable velocities in the planetary system (above 100 km s^-1). This revised version was published online in July 2006 with corrections to the Cover Date.     

Multi‐frequency solar observations at Metsähovi Radio Observatory and KAIRA

We describe solar observations carried out for the first time jointly with Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) and Aalto University Metshovi Radio Observatory (MRO). KAIRA is new radio antenna array observing the decimeter and meter wavelength range. It is located near Kilpisjärvi, Finland, and operated by the SodankyläGeophysical Observatory, University of Oulu. We investigate the feasibility of KAIRA for solar observations, and the additional benefits of carrying out multi‐instrument solar observations with KAIRA and the MRO facilities, which are already used for regular solar observations. The data measured with three instruments at MRO, and with KAIRA during time period 2014 April–October were analyzed. One solar radio event, measured on 2014 April 18, was studied in detail. Seven solar flares were recorded with at least two of the three instruments at MRO, and with KAIRA during the chosen time period. KAIRA is a great versatile asset as a new Finnish instrument that can also be used for solar observations. Collaboration observations with MRO instruments and KAIRA enable detailed multi‐frequency solar flare analysis. Flare pulsations, flare statistics and radio spectra of single flares can be investigated due to the broad frequency range observations. The Northern locations of both MRO and KAIRA make as long as 15‐hour unique solar observations possible during summer time. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multi‐epoch time‐resolved photometry of the eclipsing polar CSS081231:071126+440405

The eclipsing polar CSS081231:071126+440405 turned bright (V_max ∼ 14.5) in late 2008 and was subsequently observed intensively with small and medium‐sized telescopes. A homogeneous analysis of this comprehensive dataset comprising 109 eclipse epochs is presented and a linear ephemeris covering the five years of observations, about 24000 orbital cycles, is derived. Formally this sets rather tight constraints on the mass of a hypothetical circumbinary planet, M_pl ≤ 2 M_Jup. This preliminary result needs consolidation by long‐term monitoring of the source. The eclipse lasts 433.08 ± 0.65 s, and the orbital inclination is found to be i = 79.3°–83.7°. The centre of the bright phase displays accretion‐rate dependent azimuthal shifts. No accretion geometry is found that explains all observational constraints, suggesting a complex accretion geometry with possible pole switches and a likely non‐dipolar field geometry. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cosmic ray exposure and pre‐atmospheric size of the Gebel Kamil iron meteorite

Cosmogenic He, Ne, and Ar as well as the radionuclides ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca, ⁵³Mn, and ⁶⁰Fe have been determined on samples from the Gebel Kamil ungrouped Ni‐rich iron meteorite by noble gas mass spectrometry and accelerator mass spectrometry (AMS), respectively. The meteorite is associated with the Kamil crater in southern Egypt, which is about 45 m in diameter. Samples originate from an individual large fragment (“Individual”) as well as from shrapnel. Concentrations of all cosmogenic nuclides—stable and radioactive—are lower by a factor 3–4 in the shrapnel samples than in the Individual. Assuming negligible ³⁶Cl decay during terrestrial residence (indicated by the young crater age <5000 years; Folco et al. 2011 ), data are consistent with a simple exposure history and a ³⁶Cl‐³⁶Ar cosmic ray exposure age (CRE) of approximately (366 ± 18) Ma (systematic errors not included). Both noble gases and radionuclides point to a pre‐atmospheric radius >85 cm, i.e., a pre‐atmospheric mass >20 tons, with a preferred radius of 115–120 cm (50–60 tons). The analyzed samples came from a depth of approximately 20 cm (Individual) and approximately 50–80 cm (shrapnel). The size of the Gebel Kamil meteoroid determined in this work is close to estimates based on impact cratering models combined with expectations for ablation during passage through the atmosphere (Folco et al. 2010 , 2011 ).     

宇宙线分布、氢分布和宇宙γ射线

本文利用几种典型的银河系宇宙线分布律和星际氢分布律计算单漏模式和双漏模式中的弥散宇宙γ射线谱。结果表明,几种典型的宇宙线分布中,李惕碚的分布律优于其他作者的分布律;星际氢分子数量的取值应当比Gordon值除以1.7更小;只要适当地选择宇宙线分布和氢分布就可得到与观测γ谱相近的理论谱,宇宙线分布和氢分布均可在一定范围里选取。     

Cosmic Lithium-Beryllium-Boron Story

Light element nucleosynthesis is an important chapter of nuclear astrophysics. Specifically, the rare and fragile light nuclei Lithium, Beryllium and Boron (LiBeB) are not generated in the normal course of stellar nucleosynthesis (except ⁷Li) and are, in fact, destroyed in stellar interiors. This characteristic is reflected in the low abundance of these simple species. Up to recently, the most plausible interpretation was that Galactic Cosmic Rays (GCR) interact with interstellar CNO to form LiBeB. Other origins have been also identified: primordial and stellar (⁷Li) and supernova neutrino spallation (⁷Li and ¹¹B). In contrast, ⁹Be, ¹⁰B and ⁶Li are pure spallative products. This last isotope presents a special interest since the ⁶Li/⁷Li ratio has been measured recently in a few halo stars offering a new constraint on the early galactic evolution of light elements. Optical measurements of the beryllium and boron abundances in halo stars have been achieved by the 10 meter KECK telescope and the Hubble Space Telescope. These observations indicate a quasi linear correlation between Be and B vs Fe, at least at low metallicity, which, at first sight, is contradictory to a dominating GCR origin of the light elements which predicts a quadratic relationship. As a consequence, the theory of the origin and evolution of LiBeB nuclei has to be refined. Aside GCRs, which are accelerated in the general interstellar medium (ISM) and create LiBeB through the break up of CNO by fast protons and alphas, Wolf-Rayet stars (WR) and core collapse supernovae (SNII) grouped in superbubbles could produce copious amounts of light elements via the fragmentation in flight of rapid carbon and oxygen nuclei colliding with H and He in the ISM. In this case, LiBeB would be produced independently of the interstellar medium chemical composition and thus a primary origin is expected. These different processes are discussed in the framework of a galactic evolutionary model. More spectroscopic observations (specifically of O, Fe, Li, Be, B) in halo stars are required for a better understanding of the relative contribution of the various mechanisms. Future tests on the injection and acceleration of nuclei by supernovae and Wolf Rayet relying on gamma-ray line astronomy will be invoked in the perspective of the European INTEGRAL satellite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cosmic Gamma-Ray Bursts

Since their discovery in 1973, Gamma-Ray Bursts (GRBs) have remained for many years one of the most elusive mysteries in High Energy-Astrophysics. Despite the fact that ∼800 GRBs are detected every year in the full sky, only a few of them can be localized accurately to less than half a degree. Thus the main problem regarding the nature of GRBs has usually been the lack of knowledge of their distance scale. For many years, follow-up observations by other satellites and ground-based telescopes were conducted, but no counterparts at other wavelengths were found. The breakthrough took place in 1997, thanks to the observation by BSAX and RXTE of the fading X-ray emission that follows the more energetic gamma-ray photons once the GRB event has ended. This emission (the afterglow) extends at longer wavelengths, and the good accuracy in the position determination has led to the discovery of the first counterparts at other wavelengths, greatly improving our understanding of these puzzling sources. Now it is widely accepted that GRBs originate at cosmological distances but the central engines that power these extraordinary events remain still unknown. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cosmic ray acceleration

This review describes the basic theory of cosmic ray acceleration by shocks including the plasma instabilities confining cosmic rays near the shock, the effect of the magnetic field orientation, the maximum cosmic ray energy and the shape of the cosmic ray spectrum. Attention is directed mainly towards Galactic cosmic rays accelerated by supernova remnants.     

The Origin of Highest Energy Cosmic Rays and Cosmic Magnetic Fields

We summarize the status of the search for the origin of the highest energy cosmic rays. We briefly mention several competing proposals, such as supersymmetric particles, Gamma Ray Bursts also giving rise to energetic protons, interacting high energy neutrinos and cosmological defects, and then concentrate on the possibilities of the propagation of these particles, assuming that they are charged. The distribution of arrival directions of the highest energy particles on the sky ought to reflect the source distribution as well as propagation history. The present status can be summarized as inconclusive. If we were able to confirm any particular theory these particles beyond 10²⁰eV may be turned into tools of high energy physics. This revised version was published online in July 2006 with corrections to the Cover Date.     

宇宙线与奇异滴

奇异滴，即质量较小的奇异夸克物质团块，有关它的研究涉及物理学的多个重要分支．如果存在奇异滴，人们对暗物质组分和致密星体结构的认识将会改变，强相互作用的研究也会有新的途径．已经有若干实验结果表明宇宙线中可能含有奇异滴成分．因此，研究宇宙线奇异滴的产生、传播及其与地球大气作用过程等是非常重要的．将重点围绕上述几个问题，综述目前奇异滴研究的现状。     

Origin of Cosmic Gamma-Bursts

The papers deals with a model of origin of cosmic gamma-bursts (CGB) which appear at cosmological distances from the merging of two compact stars. The process of CGB degeneration is divided into three stages – formation of the initial state, hydrodynamic expansion and free runaway. Theory includes fundamental parameters – a star mass and electron mass. Quantitative predictions of a model agree with the observed characteristics of CGB.     

Active Cosmic Dust Collector

The Stardust mission returned two types of unprecedented extraterrestrial samples: the first samples of material from a known solar system body beyond the moon, the comet 81P/Wild2, and the first samples of contemporary interstellar dust. Both sets of samples were captured in aerogel and aluminum foil collectors and returned to Earth in January 2006. While the analysis of particles from comet Wild 2 yielded exciting new results, the search for and analysis of collected interstellar particles is more demanding and is ongoing.Novel dust instrumentation will tremendously improve future dust collection in interplanetary space: an Active Cosmic Dust Collector is a combination of an in-situ dust trajectory sensor (DTS) together with a dust collector consisting of aerogel and/or other collector materials, e.g. such as those used by the Stardust mission. Dust particles’ trajectories are determined by the measurement of induced electrical signals when charged particles fly through a position sensitive electrode system. The recorded waveforms enable the reconstruction of the velocity vector with high precision.The DTS described here was subject to performance tests at the Heidelberg dust accelerator at the same time as the recording of impact signals from potential collector materials. The tests with dust particles in the speed range from 3 to 40 km/s demonstrate that trajectories can be measured with accuracies of ～1° in direction and ～1% in speed. The sensitivity of the DTS electronics is of the order of 10^?16 C and thus the trajectory of cosmic dust particles as small as 0.4 μm size can be measured. The impact position on the collector can be determined with better than 1 mm precision, which will ease immensely the task of locating sub-micron-sized particles on the collector. Statistically significant numbers of trajectories of interplanetary and interstellar dust particles can thus be collected in interplanetary space and their compositions correlated with their trajectories.     

Cosmic Čerenkov emission

In real intensive cosmic sources it is necessary to take into account the ?erenkov reabsorption which restricts the brightness temperature of ?erenkov emission by energies of emitted relativistic electrons. As ?erenkov optical depth is given by τ_c~N/E, the brightness temperature of emission on frequencies near gyrofrequency is determined by electron energyE _r in which τ_c(E _r)=1. It is shown that most of the synchrotron sources (quasars, pulsars) must be powerful sources of ?erenkov emission. In these sources the high density of low frequency ?erenkov emission can give rise to many parametric effects.     

Cosmic gamma-ray burst spectroscopy

A review is given of the gamma-ray burst energy spectrum measurements on Venera 11 and Venera 12 space probes. The gamma burst continuum approximates in shape thermal brems-strahlung emission of a hot plasma. The radiation temperature varies over a broad range, 50–1000 keV, for different events. Spectra of many bursts contain cyclotron absorption and/or redshifted annihilation lines. Strong variability is typically observed in both continuum and line spectra. These spectral data provide convincing evidence for the gamma-ray bursts being generated by neutron stars with superstrong magnetic fields 10¹²–10¹³ G.     

Cosmic structures, parameters & temperature anisotropies: Status and perspectives

After recalling the current understanding of the formation of the large scale structures of the Universe which the distribution of galaxies revealed, I review what the imprint on the Cosmic Microwave Background (CMB) of the seeds of these structures can tell us, has already told us, and what it should tell us within the next five years.