Search for shower's duplicates at the IAU MDC. Methods and general results

Observers submit both new and known meteor shower parameters to the database of the IAU Meteor Data Center (MDC). It may happen that a new observation of an already known meteor shower is submitted as a discovery of a new shower. Then, a duplicate shower appears in the MDC. On the other hand, the observers may provide data which, in their opinion, is another set of parameters of an already existing shower. However, if this is not true, we can talk about a shower that is a false-duplicate of a known meteor shower. We aim to develop a method for objective detection of duplicates among meteor showers and apply it to the MDC. The method will also enable us to verify whether various sets of parameters of the same shower are compatible and, thus, reveal the false-duplicates. We suggest two methods based on cluster analyses and two similarity functions among geocentric and heliocentric shower parameters collected in the MDC. 8 new showers represented by two or more parameter sets were discovered. 31 times there was full agreement between our results and those reported in the MDC. 23 times the same duplicates as given in the MDC, were found only by one method. We found 27 multi-solution showers for which the number of the same duplicates found by both method is close to the corresponding number in the MDC database. However for 60 multi-solution showers listed in the MDC no duplicates were found by any of the applied methods. The obtained results confirmed the effectiveness of the proposed approach of identifying duplicates. We have shown that in order to detect and verify duplicate meteor showers, it is possible to apply the objective proposal instead of the subjective approach used so far

Showers with both northern and southern solutions

Meteoroids of a low-inclination stream hit the Earth arriving from a direction near the ecliptic. The radiant area of stream like this is often divided into two parts: one is situated northward and the other southward of the ecliptic. In other words, two showers are caused by such a stream. Well-known examples of such showers are the Northern Taurids, #17, and Southern Taurids, #2, or the Northern $\delta$-Aquariids, #26, and Southern $\delta$-Aquariids, #5. While the meteoroids of the northern shower collide with the Earth in the descending node, those of the southern shower collide with our planet in the ascending node of their orbits. Because of this circumstance and tradition, the northern and southern showers must be distinguished. Unfortunately, this is not always the case with meteor showers listed in the IAU Meteor Data Center (MDC). For the same shower, some authors reported a set of its mean parameters corresponding to the northern shower and other authors to the southern shower. We found eleven such cases in the MDC. In this paper, we propose corrections of these mis-identifications.Comment: Submitted: Planetary and Space Scienc

On the stable configuration of ultra-relativistic material spheres. The solution for the extremely hot gas

During the last stage of collapse of a compact object into the horizon of events, the potential energy of its surface layer decreases to a negative value below all limits. The energy-conservation law requires an appearance of a positive-valued energy to balance the decrease. We derive the internal-state properties of the ideal gas situated in an extremely strong, ultra-relativistic gravitational field and suggest to apply our result to a compact object with the radius which is slightly larger than or equal to the Schwarzschild's gravitational radius. On the surface of the object, we find that the extreme attractivity of the gravity is accompanied with an extremely high internal, heat energy. This internal energy implies a correspondingly high pressure, the gradient of which has such a behavior that it can compete with the gravity. In a more detail, we find the equation of state in the case when the magnitude of the potential-type energy of constituting gas particles is much larger than their rest energy. This equation appears to be identical with the general-relativity condition of the equilibrium between the gravity and pressure gradient. The consequences of the identity are discussed.Comment: 12 pages (no figure, no table) Changes in 3-rd version: added an estimate of neutrino cooling and relative time-scale of the final stage of URMS collaps

Meteor showers of comet C/1917 F1 Mellish

December Monocerotids and November Orionids are weak but established annual meteor showers active throughout November and December. Analysis of a high quality orbits subset of the SonotaCo video meteor database shows that the distribution of orbital elements, geocentric velocity and also the orbital evolution of the meteors and potential parent body may imply a common origin for these meteors coming from the parent comet C/1917 F1 Mellish. This is also confirmed by the physical properties and activity of these shower meteors. An assumed release of meteoroids at the perihelion of the comet in the past and the sky-plane radiant distribution reveal that the December Monocerotid stream might be younger than the November Orionids. A meteoroid transversal component of ejection velocity at the perihelion must be larger than 100 m/s. A few authors have also associated December Canis Minorids with the comet C/1917 F1 Mellish. However, we did not find any connection.Comment: 11 pages, 11 figures and 5 table

Barkhausen noise emission of AISI 304 stainless steel originating from strain induced martensite by shot peening

This study deals with magnetic Barkhausen noise emission produced by strain-induced martensite generated during shot peening of austenitic AISI 304 stainless steel. The transformation from the paramagnetic to ferromagnetic state and the corresponding birth of the magnetic domain structure are important with respect to irreversible motion of domain walls and the corresponding Barkhausen noise emission. Barkhausen noise is investigated and explained with respect to the residual stress state as well as the micro-structure expressed in terms of the martensite fraction, its crystallite size, preferred orientation, surface topography, and microhardness. The strength of the Barkhausen noise is mainly linked with the number of shot peening cycles, corresponding Almen intensity, and the associated volume fraction of strain-induced martensite as well as the extent of its depth. The role of the residual stress state in the martensite phase is minor. Surface strengthening expressed in terms of the microhardness in the near-surface region is very high for the medium shot peening intensity. A remarkable decrease in the near-surface microhardness as well as the presence of heavily thinned folds indicate over shot peen-ing and surface microcracking in the case of a longer shot peening time and the corre-sponding higher Almen intensity.Web of Science2076274

Considerations on the accretion of Uranus and Neptune by mutual collisions of planetary embryos in the vicinity of Jupiter and Saturn

Modeling the formation of the ice giants Uranus and Neptune is a long-lasting problem in planetary science. Due to gas-drag, collisional damping, and resonant shepherding, the planetary embryos repel the planetesimals away from their reach and thus they stop growing (Levison et al. 2010). This problem persists independently of whether the accretion took place at the current locations of the ice giants or closer to the Sun. Instead of trying to push the runaway/oligarchic growth of planetary embryos up to 10-15 Earth masses, we envision the possibility that the planetesimal disk could generate a system of planetary embryos of only 1-3 Earth masses. Then we investigate whether these embryos could have collided with each other and grown enough to reach the masses of current Uranus and Neptune. Our results point to two major problems. First, there is typically a large difference in mass between the first and the second most massive core formed and retained beyond Saturn. Second, in many simulations the final planetary system has more than two objects beyond Saturn. The growth of a major planet from a system of embryos requires strong damping of eccentricities and inclinations from the disk of gas. But strong damping also favors embryos and cores to find a stable resonant configuration, so that systems with more than two surviving objects are found. In addition to these problems, in order to have substantial mutual accretion among embryos, it is necessary to assume that the surface density of the gas was several times higher than that of the minimum-mass solar nebula. However this contrasts with the common idea that Uranus and Neptune formed in a gas-starving disk, which is suggested by the relatively small amount of hydrogen and helium contained in the atmospheres of these planets. Only one of our simulations "by chance" successfully reproduced the structure of the outer Solar System.Comment: 16 pages; 15 color figures; accepted in Astronomy & Astrophysics; shortened abstrac

Constraining the electric charges of some astronomical bodies in Reissner-Nordstrom spacetimes and generic r^-2-type power-law potentials from orbital motions

We put model-independent, dynamical constraints on the net electric charge Q of some astronomical and astrophysical objects by assuming that their exterior spacetimes are described by the Reissner-Nordstroem metric, which induces an additional potential U_RN \propto Q^2 r^-2. Our results extend to other hypothetical power-law interactions inducing extra-potentials U_pert = r^-2 as well (abridged).Comment: LaTex2e, 16 pages, 3 figures, no tables, 128 references. Version matching the one at press in General Relativity and Gravitation (GRG). arXiv admin note: substantial text overlap with arXiv:1112.351

Extrasolar enigmas: from disintegrating exoplanets to exoasteroids

Thousands of transiting exoplanets have been discovered to date, thanks in great part to the {\em Kepler} space mission. As in all populations, and certainly in the case of exoplanets, one finds unique objects with distinct characteristics. Here we will describe the properties and behaviour of a small group of `disintegrating' exoplanets discovered over the last few years (KIC 12557548b, K2-22b, and others). They evaporate, lose mass unraveling their naked cores, produce spectacular dusty comet-like tails, and feature highly variable asymmetric transits. Apart from these exoplanets, there is observational evidence for even smaller `exo-'objects orbiting other stars: exoasteroids and exocomets. Most probably, such objects are also behind the mystery of Boyajian's star. Ongoing and upcoming space missions such as {\em TESS} and PLATO will hopefully discover more objects of this kind, and a new era of the exploration of small extrasolar systems bodies will be upon us.Comment: Accepted for publication in the book "Reviews in Frontiers of Modern Astrophysics: From Space Debris to Cosmology" (eds Kabath, Jones and Skarka; publisher Springer Nature) funded by the European Union Erasmus+ Strategic Partnership grant "Per Aspera Ad Astra Simul" 2017-1-CZ01-KA203-03556

The fading problem and the population of the Oort cloud

Context.The discovery efficiency of the dynamically new comets has been assumed to be approximately the same as that of all long-period (LP) comets when estimating the population of the Oort cloud. On the other hand, studies of the so-called fading problem have implied a strong difference in the discovery efficiencies of both new and old comets. Some authors have attempted to explain this discrepancy by suggesting that old comets disappeared due to the extinction or disintegration of their nuclei. Aims.We attempt to answer the question of whether the absolute brightness of old comets steeply decreases in time or whether their nuclei become extinct, dormant, or disintegrated. Moreover, we analyse the impact of the highly different discovery efficiencies on an estimate of the Oort-cloud population. Methods.The dominance of the fading over the extinction, dormant-phase, or disintegration is demonstrated with the help of the distributions of the reciprocal semi-major axes of the original orbits of the LP comets and a more moderate decrease in discoveries of new comets with increasing perihelion distance. The comet discoveries within the LINEAR sky survey are also used to support our conclusion. Results.The demonstrated dominance of the fading implies the relatively higher discovery efficiency of new comets. Its ignorance causes an overestimation of the actual intrinsic flux of new comets through the zone of visibility compared to the corresponding intrinsic flux of all LP comets. This overestimate is also documented by a significantly smaller amount of new comets with perihelia q \loa 3\,AU discovered within the LINEAR. Conclusions.The actual intrinsic flux of new comets must be about one order of magnitude lower than has been derived before. Its reduction implies a one-order-of-magnitude less numerous population for the Oort cloud. Moreover, such the reduction also solves (or, at least, weakens) the problem of too high a mass of the comet cloud, as well as the problem of too numerous a population of predicted Halley-type objects or too high a space density of interstellar comets