L. Neslušan

Meteor-shower complex of asteroid 2003 EH1 compared with that of comet 96P/Machholz

Aims. We studied the structure of the meteoroid particle complexes released from asteroid 196 256 (2003 EH1) to reveal the relationship to the meteor showers observed in Earth’s atmosphere that belong to this complex as well. In addition, we studied the relationship between the asteroid and comet 96P/Machholz, which is situated in the same orbital phase space. Methods. For nine perihelion passages of the parent asteroid in the past, we modeled the associated theoretical streams and followed their dynamical evolution until the present. Subsequently, we analyzed the orbital characteristics of the modeled streams, especially of the parts that approach Earth’s orbit. Results. We confirm the filamentary structure of the complex, which is qualitatively identical to the complex of 96P. Six wellestablished and two minor filaments approach the orbit of the Earth, producing four well-known meteor showers, daytime Arietids, Southern δ-Aquarids, Quadrantids, and Northern δ-Aquarids. The filaments corresponding to the Arietids and δ-Aquarids S and N constitute the ecliptical component, and those corresponding to the Quadrantids and their southern counterpart constitute the toroidal component of the complex.

The meteor-shower complex of 96P/Machholz revisited

Aims. The structure of the complex of meteoroid particles released from comet 96P/Machholz is studied to reveal a relationship among the meteor showers observed in the Earth’s atmosphere that belong to this complex. Methods. For eight perihelion passages of the parent comet in the past, we model theoretical streams associated with comet 96P and follow their dynamical evolution until the present. Subsequently, we analyze the orbital characteristics of the streams, especially of their parts approaching the Earth’s orbit. Results. The dynamics of the stream is controlled by Jupiter, which changes the initial orbits of the particles into the orbits situated within several specific corridors. It thus creates a filamentary structure of the complex. Six filaments approach the orbit of the Earth producing four well-known meteor showers and two showers, whose identification with κ -Velids and α -Cetids is not certain. The known showers, in order of the predicted abundance of meteors, are daytime Arietids, Southern δ -Aquarids, Quadrantids, and Northern δ -Aquarids. The filaments corresponding to the Arietids, δ -Aquarids S and N, and possibly α -Cetids constitute the ecliptical component and those corresponding to the Quadrantids and possibly κ -Velids constitute the toroidal component of the complex.

A procedure of selection of meteors from major streams for determination of mean orbits

A procedure of selection of meteoroids from major streams is suggested and applied to the IAU Lund photographic database modified by a check for internal consistency among orbital elements (3411 orbits). Limits for choice of stream members were defined by break points on the plots of the cumulative numberNC vs. the Southworth-HawkinsD discriminant. For the break points were considered the points from which the dependenceNC vs.D changes to a quasi-linear one, and with the increasingD, NC changes only moderately. Except for the Taurids which desire a separate analysis, theNC vs.D diagrams are presented for the following major meteoroid streams: Quadrantids, Lyrids,η Aquarids,α Capricornids, N and Sδ Aquarids, Perseids, Orionids, Leonids and Geminids. The mean orbits, velocities and radiants of the streams are derived and compared with the osculating orbits of their parent bodies. The limitingDB was found to be a function of the number of the stream membersNCB. Omitting the exceptionally concentrated Geminids, the relation is in the formDB = 0.058 *ln(NCB) − 0.04.

The simulation of the outer Oort cloud formation - The first giga-year of the evolution

Aims. Considering a model of an initial disk of planetesimals that consists of 10 038 test particles, we simulate the formation of distant-comet reservoirs for the first 1 Gyr. Since only the outer part of the Oort cloud can be formed within this period, we analyse the efficiency of the formation process and describe approximately the structure of the part formed. Methods. The dynamical evolution of the particles is followed by numerical integration of their orbits. We consider the perturbations by four giant planets on their current orbits and with their current masses, in addition to perturbations by the Galactic tide and passing stars. Results. In our simulation, the population size of the outer Oort cloud reaches its maximum value at about 210 Myr. After a subsequent, rapid decrease, it becomes almost stable (with only a moderate decrease) from about 500 Myr. At 1 Gyr, the population size decreases to about 40% of its maximum value. The efficiency of the formation is low. Only about 0.3% of the particles studied still reside in the outer Oort cloud after 1 Gyr. The space density of particles in the comet cloud, beyond the heliocentric distance, r ,o f 25 000 AU is proportional to r −s ,w heres = 4.08 ± 0.34. From about 50 Myr to the end of the simulation, the orbits of the Oort cloud comets are not distributed randomly, but high galactic inclinations of the orbital planes are strongly dominant. Among all of the outer perturbers considered, this is most likely caused by the dominant, disk component of the Galactic tide.

The meteor-shower complex of comet C/1917 F1 (Mellish)

Aims. In our overall work, we attempt to predict some new meteor showers associated with as many as possible known periodic comets and to find the generic relationship of some already known showers with these comets. In this paper, we focus our attention on the meteor-shower complex of the long-period comet C/1917 F1 (Mellish), which is the known parent body of the December Monocerotids. Some other showers have also been suggested to be associated with this comet. We map its whole complex here. Methods. For five perihelion passages of the parent comet in the past, we model associated theoretical streams, with each consisting of 10 000 test particles and follow their dynamical evolution until the present. Subsequently, we analyze the orbital characteristics of the parts of found streams that approach the Earth’s orbit. Results. We confirm the generic relationship between the studied parent comet and December Monocerotids. The comet is probably also the parent body of the April ρ-Cygnids. The evolution of meteoroids to the orbits of April ρ-Cygnids is very long at about 20 millennia. If we follow even a longer evolutionary period, which is up to 50 millennia, then two diffuse showers with the radiant situated symmetrically to both the December Monocerotids and April ρ-Cygnids showers with respect to the apex of the Earth’s motion occur. Our simulation does not confirm any relationship between C/1917 F1 and the November Orionids, although this shower was found in all three databases of observed orbits.

A search for streams and associations in meteor databases. Method of Indices

Abstract A new method of searching for minor meteor streams and associations is presented and discussed. The procedure, based only on mathematical statistics, enables a parallel separation of major and minor streams or associations. The approach utilizes a division of the ranges of examined parameters into equidistant intervals. The method is tested on the IAU Meteor Data Center Lund catalogue of precise photographic orbits representing the most extensive set of photographic meteor orbits. Besides the five orbital elements incorporated in the Southworth–Hawkins D-criterion, we have also included in the procedure the coordinates of the radiant which belong to the most accurately known parameters and the geocentric velocity as a significant parameter characteristic for physically related orbits. The basic idea of the procedure is a division of the observed ranges of parameters into a number of equidistant intervals and assignment of indices to a meteor according to the intervals pertinent to its parameters. The meteors with equal indices are regarded as mutually related. Since various parameters listed in the catalogue contain various relative errors, it is necessary to use several intervals in the division of each parameter to obtain a good fit with the real orbital distribution. The relative ratios, approximated by small integers, corresponding to the reciprocal values of the relative errors, were applied as the basic numbers for the division of the parameters. To test the quality of this method, the first step presented in this paper is aimed at wider intervals providing a less detailed classification (a smaller branching). In this step all the major streams (except of the northern branch of δ-Aquarids) were identified, confirming the efficiency of the procedure. After combining the related groups, 16 streams were identified. The search program also identifies widely spread Taurids. There are separated orbits pertinent to some minor streams such as the o-Draconids, κ-Cygnids, October Draconids, Pegasids and December Monocerotids. Rather surprisingly, even at this strict level, a pair of meteors in orbits similar to the Lyrids with the maximum on April 8 (Arter and Williams, 1995. Earth, Moon, Planets 68, 141–153) are identified. In the next steps the search will be concentrated on the separation of minor streams and eventually some so far unknown associations.

On separation of major meteoroid streams from the sporadic background

The paper deals with a search for chosen photographic meteoroid streams compiled from the IAU Meteor Data Center Lund catalogue from which less than 2% of the orbits had to be removed due to internal inconsistency among the orbit parameters. Additional 35 orbits were removed due to extremely high hyperbolic velocities. The final set consists of 3411 orbits. Members of the Quadrantids, Lyrids, Perseids and Geminids were searched for, firstly, by a stream-search procedure utilizing the Southworth-HawkinsD-criterion. This choice, as a rule, represents the most abundant filament of the stream. Secondly, rate distribution histograms ofD were divided into region of shower meteors and region of sporadic background meteors. The searched database with a relatively low abundance of sporadic meteors in the analyzed periods simplified this choice, and followingly, fitting the obtained values by means of power and exponential functions, the limitingDs for particular showers were derived. The derivedDs appears as the optimum value, as for higherD, the number of sporadic meteors included in the stream sample increases more rapidly than the number of additional shower meteors, and for smallerD, the number of shower meteors decreases quicker than the number of omitted sporadic meteors. The following counts of shower meteorsN and limitingDs were found: Quadrantids (39, 0.22), Lyrids (11, 0.15), Perseids (595, 0.53) and Geminids (224, 0.32). Efficiency of the procedure was tested comparing the number of sporadic meteors in the region of radiant area and the neighbouring regions of the same size.

Creating Gateway Alliances Using WS-PGRADE/gUSE

The STARnet Gateway Federation is a unique example of a federated network of science gateways based on WS-PGRADE/gUSE technologies, and explicitly designed and tuned to the needs of the astronomical and astrophysical (A&A) community in Europe. The use of a federated gateway infrastructure allows scientists to explore new collaboration opportunities and advancing the scientific research activity within A&A. STARnet Gateways share a common authentication system, a distributed computing infrastructure, data archives, portlets, and workflow repositories. Building upon these technologies, a number of challenging applications from different A&A domains have been successfully prototyped and tested.

Probing the relation between the structure of initial proto-planetary disc and the Oort-cloud formation

Aims. The Oort cloud consists of cometary nuclei which were ejected from the once existing proto-planetary disc to large heliocentric distances by the giant planets. The process of the cloud formation depended on the initial structure and mass of the disc. Considering four models of an initial proto-planetary disc, we roughly probe this dependence. Methods. We use the resultant data of our previous simulation of the Oort cloud formation for the first two Gyr. The considered disc models consist of a set of representative test particles. The new models are created subtracting a fraction of the particles from the model considered in our previous work, in a way to obtain the required heliocentric-distance distribution. Specifically, we focus on the situations in which a part of the small bodies in the disc is assumed to be already spent in the previous process of the giant planet formation. We omit the particles from an originally smooth profile in the regions adjacent to the planet orbits. With the reduced data, we construct the comet cloud characteristics we are interested in. Results. We find that it is difficult to construct the proto-planetary disc if (i) the amount of heavy chemical elements in Jupiter and Saturn is as high as currently accepted (≈20 and ≈29 M⊕; respectively) and (ii) the total mass of the minimum-mass solar nebula is assumed to be lower than ≈0.05 M . The behaviour of the Oort cloud formation does not crucially depend on the initial disc model. Some quantitative differences in its structure are obvious: since the cloud is known to be filled mainly by Uranus and Neptune, the efficiency of its formation is higher if the initial amount of particles in the Uranus-Neptune region is relatively higher. The efficiency is also higher in the gapped-disc models because a less amount of particles experience a very close encounter with a planet resulting in their ejection into the interstellar space.

Stable configuration of ultrarelativistic material spheres: The solution for an 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, ultrarelativistic gravitational field and suggest the application of our result to a compact object with a radius that is slightly larger than or equal to the Schwarzschild 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 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.