Massive identification of asteroids in three-body resonances

An essential role in the asteroidal dynamics is played by the mean motion resonances. Two-body planet–asteroid resonances are widely known, due to the Kirkwood gaps. Besides, so-called three-body mean motion resonances exist, in which an asteroid and two planets participate. Identification of asteroids in three-body (namely, Jupiter–Saturn–asteroid) resonances was initially accomplished by Nesvorný and Morbidelli (Nesvorný D., Morbidelli, A. [1998]. Astron. J. 116, 3029–3037), who, by means of visual analysis of the time behaviour of resonant arguments, found 255 asteroids to reside in such resonances. We develop specialized algorithms and software for massive automatic identification of asteroids in the three-body, as well as two-body, resonances of arbitrary order, by means of automatic analysis of the time behaviour of resonant arguments. In the computation of orbits, all essential perturbations are taken into account. We integrate the asteroidal orbits on the time interval of 100,000 yr and identify main-belt asteroids in the three-body Jupiter–Saturn–asteroid resonances up to the 6th order inclusive, and in the two-body Jupiter–asteroid resonances up to the 9th order inclusive, in the set of ～250,000 objects from the “Asteroids – Dynamic Site” (AstDyS) database. The percentages of resonant objects, including extrapolations for higher-order resonances, are determined. In particular, the observed fraction of pure-resonant asteroids (those exhibiting resonant libration on the whole interval of integration) in the three-body resonances up to the 6th order inclusive is ≈0.9% of the whole set; and, using a higher-order extrapolation, the actual total fraction of pure-resonant asteroids in the three-body resonances of all orders is estimated as ≈1.1% of the whole set.     

Poststack diffraction imaging using reverse‐time migration

We propose a method for imaging small‐scale diffraction objects in complex environments in which Kirchhoff‐based approaches may fail. The proposed method is based on a separation between the specular reflection and diffraction components of the total wavefield in the migrated surface angle domain. Reverse‐time migration was utilized to produce the common image gathers. This approach provides stable and robust results in cases of complex velocity models. The separation is based on the fact that, in surface angle common image gathers, reflection events are focused at positions that correspond to the apparent dip angle of the reflectors, whereas diffracted events are distributed over a wide range of angles. The high‐resolution radon‐based procedure is used to efficiently separate the reflection and diffraction wavefields. In this study, we consider poststack diffraction imaging. The advantages of working in the poststack domain are its numerical efficiency and the reduced computational time. The numerical results show that the proposed method is able to image diffraction objects in complex environments. The application of the method to a real seismic dataset illustrates the capability of the approach to extract diffractions.     

Is the additional increase of star luminosity due to partial mixing real?

The partial mixing of matter between the radiative envelope and convective core in an early Btype star produces an additional increase of star luminosity during main sequence evolution. High quality data on stellar mass and luminosity defined from studies of detached double-lined eclipsing binaries are used to check the existence of such additional increase. It is shown that the additional luminosity increase does not contradict observed high quality data, if the intensity of partial mixing is restricted by the observed increase in surface helium content.     

Non-sinusoidal transit timing variations for the exoplanet HAT-P-12b

Considering the importance of investigating the transit timing variations(TTVs) of transiting exoplanets,we present a follow-up study of HAT-P-12 b.We include six new light curves observed between2011 and 2015 from three different observatories,in association with 25 light curves taken from the published literature.The sample of the data used thus covers a time span of ～10.2 years with a large coverage of epochs(1160) for the transiting events of the exoplanet HAT-P-12 b.The light curves are utilized to determine the orbital parameters and conduct an investigation of possible TTVs.The new linear ephemeris shows a large value of reduced χ~2,i.e.X~2_(red)(23)=7.93,and the sinusoidal fitting using the prominent frequency coming from a periodogram shows a reduced χ~2 around 4.Based on these values and the corresponding O-C diagrams,we suspect the presence of a possible non-sinusoidal TTV in this planetary system.Finally,we find that a scenario with an additional non-transiting exoplanet could explain this TTV with an even smaller reduced χ~2 value of around 2.     

Linear kinetic theory of instabilities of a gravitatingstellar disk

Linear kinetic theory is developed to describe collective oscillations (and their instabilities) propagating in a rapidly rotating disk of stars, representing a highly flattened galaxy. The analysis is carried out for the special case of a self-gravitating, infinitesimally thin, and spatially inhomogeneous system, taking into account the effects both of thermal movements of stars and of gravitational encounters between stars and giant molecular clouds of an interstellar medium. The star–cloud encounters are described with the use of the Landau collision integral. The dynamics of gravity perturbations with rare interparticle encounters is considered. Such a disk is treated by employing the well elaborated mathematical formalisms from plasma perturbation theory using normal-mode analysis. In particular, the method of solving the Boltzmann equation is applied by integration along paths, neglecting the influence of star–cloud encounters on the distribution of stars in the zeroth-order approximation. We are especially interested in important kinetic effects due to wave–star resonances, which we have little knowledge about. The kinetic effects are introduced via a minor drift motion of stars which is computed from the equations of stellar motion in an unperturbed central force field of a galaxy. The dispersion laws for two main branches of disk's oscillations, that is the classical Jeans branch and an additional gradient branch, are deduced. The resonant Landau-type instabilities of hydrodynamically stable Jeans and gradient gravity perturbations is considered to be a long-term generating mechanism for propagating density waves, thereby leading to spiral-like and/or ring-like patterns in the flat galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimental shock metamorphism of the L4 ordinary chondrite Saratov induced by spherical shock waves up to 400 GPa

Abstract– We carried out shock experiments on macroscopic spherical samples of the L4 ordinary chondrite Saratov (natural shock stages S2–S3), using explosively generated spherical shock waves with maximum peak pressures of 400 GPa and shock‐induced temperatures >800 °C (up to several thousands °C). The evolution of shock metamorphism within a radius of the spherical samples was investigated using optical and scanning electron microscopy, microprobe and magnetic analyses as well as Mössbauer spectroscopy and X‐ray diffraction techniques. Petrographic analyses revealed a shock‐induced formation of three different concentric petrographic zones within the shocked samples: zone of total melting (I), zone of partial melting (II), and zone of solid‐state shock features (III). We found a progressive pressure‐induced oxidation of Fe‐Ni metal, whose degree increased with increasing shock peak pressure. The amount of FeO within zone I increased the factor of 1.4 with respect to its amount in the unshocked Saratov sample. This suggests that within zone I about 70 wt% of the initial metallic iron was oxidized, whereas magnetic analyses showed that about 10 wt% of it remained intact. This strongly supports the hypothesis that, in addition to oxidation, a migration of metallic iron from the central heavily shocked zone I toward less shocked peripheral zone took place as well (likely through shock veins where metallic droplets were observed). Magnetic analyses also showed a shock‐induced transformation of tetrataenite to taenite within all shocked subsamples, resulting in magnetic softening of these subsamples (decrease in remanent coercivity). These results have important implications for extraterrestrial paleomagnetism suggesting that due to natural impact processes, the buried crustal rocks of heavily cratered solid solar system bodies can have stronger remanent magnetism than the corresponding surface rocks.     

New Taxa of Chrysomelidae (Insecta:Coleoptera)from Rovno Amber,Late Eocene

<正>Leaf beetles Chrysomelidae of Rovno amber,from the Late Eocene,are recorded and described. Chrysomelidae of Rovno amber are represented by three subfamilies:Galerucinae(Alticini),Chrysomelinae,and Eumolpinae.Two new genera and three new species of Alticini:Manobiomorpha Nadein,gen.nov.(type species Manobiomorpha eocenica Nadein,sp.nov.),Psyllototus Nadein,gen.nov.(type species Psyllototus progenitor Nadein,sp.nov.),and Crepidodera decolorata Nadein et Perkovsky,sp.nov.are described.A new chrysomeline genus and species Paleophaedon minutus Nadein gen.nov.et sp.nov.is described.Probable trophic association of Crepidodera decolorata sp.nov.,the taxonomic positions of Manobiomorpha gen.nov.and Psyllototus gen.nov., and the composition of leaf beetle faunas of Middle and Late Eocene of Europe are discussed.     

Community Structure in the Amber Forest: Study of the Arthropod Syninclusia in the Rovno Amber(Late Eocene of Ukraine)

<正>Arthropodan syninclusions in the Late Eocene Rovno amber were examined using x~2 to reveal correlation of the component groups(some taxa of Diptera,ants,aphids,and mites) supposedly indicative of the biocoenotic relationships in the ancient amber forest.Three tightly correlated groups were identified,representing a putative aerial plankton guild(Chironomidae+Ceratopogonidae) and two tree-trunk guilds,one of which (Dolichopodidae+Germaraphis) is possibly connected to more open or/and more hygrophilous habitats than the other(Sciara zone Diptera +"Acarus"rhombeus).The ants were not linked with any of the above components.