V-type asteroids in the middle main belt Roig, F.; Nesvorný, D.; Gil-Hutton, R. ...
Icarus (New York, N.Y. 1962),
03/2008, Volume:
194, Issue:
1
Journal Article
Peer reviewed
V-type asteroids are bodies whose surfaces are constituted of basalt. In the Main Asteroid Belt, most of these asteroids are assumed to come from the basaltic crust of Asteroid (4) Vesta. This idea ...is mainly supported by (i) the fact that almost all the known V-type asteroids are in the same region of the belt as (4) Vesta, i.e., the inner belt (semi-major axis
2.1
<
a
<
2.5
AU), (ii) the existence of a dynamical asteroid family associated to (4) Vesta, and (iii) the observational evidence of at least one large craterization event on Vesta's surface. One V-type asteroid that is difficult to fit in this scenario is (1459) Magnya, located in the outer asteroid belt, i.e., too far away from (4) Vesta as to have a real possibility of coming from it. The recent discovery of the first V-type asteroid in the middle belt (
2.5
<
a
<
2.8
AU), (21238) 1995WV7 Binzel, R.P., Masi, G., Foglia, S., 2006. Bull. Am. Astron. Soc. 38, 627; Hammergren, M., Gyuk, G., Puckett, A., 2006. ArXiv e-print, astro-ph/0609420, located at ∼2.54 AU, raises the question of whether it came from (4) Vesta or not. In this paper, we present spectroscopic observations indicating the existence of another V-type asteroid at ∼2.53 AU, (40521) 1999RL95, and we investigate the possibility that these two asteroids evolved from the Vesta family to their present orbits by a semi-major axis drift due to the Yarkovsky effect. The main problem with this scenario is that the asteroids need to cross the 3/1 mean motion resonance with Jupiter, which is highly unstable. Combining
N-body numerical simulations of the orbital evolution, that include the Yarkovsky effect, with Monte Carlo models, we compute the probability that an asteroid of a given diameter
D evolves from the Vesta family and crosses over the 3/1 resonance, reaching a stable orbit in the middle belt. Our results indicate that an asteroid like (21238) 1995WV7 has a low probability (∼1%) of having evolved through this mechanism due to its large size (
D
∼
5
km
), because the Yarkovsky effect is not sufficiently efficient for such large asteroids. However, the mechanism might explain the orbits of smaller bodies like (40521) 1999RL95 (
D
∼
3
km
) with
∼
70
–
100
%
probability, provided that we assume that the Vesta family formed
≳
3.5
Gy
ago. We estimate the debiased population of V-type asteroids that might exist in the same region as (21238) and (40521) (
2.5
<
a
≲
2.62
AU
) and conclude that about 10 to 30% of the V-type bodies with
D
>
1
km
may come from the Vesta family by crossing over the 3/1 resonance. The remaining 70–90% must have a different origin.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•A dynamical mechanism to disperse ancient main asteroid belt families is proposed.•Most of the dispersions occur during the instability phase of a 5 giant planet model.•(a; ecc, I) are displaced by ...close encounters; mean motion and/or secular resonances.
Many asteroid families are identified and well characterized all over the main asteroid belt. Interestingly, however, none of them are older than 4Gyr. Many mechanisms have been proposed to disperse such old primordial asteroid families that presumably have existed, but only very few have really worked. Here we present a plausible mechanism for dispersing primordial asteroid families that is based on the 5-planet instability model known as jumping Jupiter. Using two different evolutions for the jumping-Jupiter model, we have numerically integrated orbits of eight putative primordial families. Our results show that the most important effect on the asteroid families’ eccentricity and inclination dispersal is that of the secular resonances, in some cases associated with the mean motion resonances. As for the semimajor axes spreading we find that the principal effect is that of close encounters with the fifth giant planet whose orbit briefly overlaps with (part of) the main belt. Therefore, the existence of a fifth giant planet with the mass comparable with that of Uranus’ or Neptune’s could contribute in important ways to dispersal of the primordial asteroid families. To have that effect, the interloper planet should go into and considerably interact with the asteroids during the instability phase.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The taxonomic properties of the main asteroid families are analyzed and discussed in the light of an updated definition of the families using a large proper elements database and the asteroids ...taxonomy derived from reflectance spectra recently obtained by two large visible spectroscopic surveys: the SMASS II and the S3OS2. Our analysis indicates that most families are quite homogeneous taxonomically and mineralogically—whenever there exists a mineralogical constraint—, being probably originated from homogeneous parent bodies. The exceptions are the Nysa family, that should likely be considered a clan, and the Eos family that encompasses a broad range of taxonomies, whose mineralogical relations cannot be completely ruled out. Only in a few cases the families may be taxonomically distinguished from the background population. That is the case of the Minerva/Gefion, Adeona, Dora, Merxia, Hoffmeister, Koronis, Eos, and Veritas families. Some of the families presented in this work show a larger spectral diversity than previously reported, as it is the case for the Maria and Koronis families. On the other hand, the Veritas family is found to be homogeneous, in sharp contrast with previous works. Mineralogical relations are reported whenever they could be found in the literature and we examine the possible constraints posed by the presence of different taxonomies in certain families.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Recent years have seen a consolidation and expansion of tree-ring sample collection across South America. Most collections are concentrated in the temperate forests along the eastern and western ...slopes of the Southern Andes (32°S to 55°S). However, important advances in the reconnaissance and collection of new woody species useful for dendrochronology have recently been documented in new regions. The development of chronologies in tropical and subtropical arid regions of the Cordillera, and in particular the Bolivian Altiplano, is probably one of the most important recent advances in South American dendrochronology.
Polylepis tarapacana, growing at 4000–4500 m elevation on the Altiplano, has yielded more than ten chronologies spanning the past 700 years. These records are highly correlated with summer variations in climate. The development of chronologies in the humid subtropics and tropics remains a major challenge. The number of tree-ring chronologies built up using species from these regions (ca. 40) is comparatively low in relation to the extent of tropical forests. The recognition of strong climate signals in tree rings from
Cedrela species provides a unique opportunity to develop a tree-ring network in subtropical and tropical South America. The future of dendroclimatology in South American tropical regions is perceived as extremely promising.
Reconstructions of temperature, rainfall, streamflow, snow and regional atmospheric circulation based on ring width, density and stable isotopes, have been conducted using tree-ring chronologies from subtropical and temperate forests. These chronologies have also been used in studies relating South American tree rings to high-resolution proxies from other continents, and studies analyzing past changes in atmospheric circulation. The comparison of climatic reconstructions based on tree rings with projected atmospheric circulation patterns provides a useful bridge between past and future trends in global climate change, and its implications for human welfare and socio-economic development. Some examples of this bridging are presented in this review.
Future research should continue the development of long tree-ring chronologies to improve detection of decadal to centennial climatic variations and to distinguish between natural and human-induced climatic changes in South America. Efforts to develop new tree-ring chronologies in the tropical lowlands should also be encouraged. Collaboration among South American countries in training young scholars is crucial to maintain and increase the progress of dendroclimatology in the region. Initiatives facilitating the interaction between scientists from the Americas and overseas, such as done by the IAI and PAGES projects, should be broadened and their long-term continuation assured.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Context. High-velocity halo stars provide important information about the properties of the extreme Galactic halo. The study of Population II unbound and bound stars enables us better estimate the ...mass of the halo. Aims. We carried out a detailed spectroscopic and kinematic study of two red horizontal branch stars, CD-41°15048 and HD 214362. Methods. The atmospheric parameters, chemical abundances, and kinematical properties were determined using high-resolution optical spectroscopy and employing the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code moog. Results. We found that CD-41°15048 and HD 214362 are metal-poor red horizontal branch stars. Their abundance patterns are similar to other metal-poor halo stars already investigated. Our kinematic analysis of the 3D space motions shows that HD 214362 has a highly eccentric (e = 0.95) orbit and passes at 2 kpc from the Galactic center. CD-41°15048, for an adopted distance of 1.3 kpc, has an extreme retrograde motion and travels with very high velocity relative to the Galactocentric reference frame (VGRF = 583 km s-1). Conclusions. CD-41°15048 is a bound or an unbound star, depending on the adopted Galactic potential. We also show that the red horizontal branch star BD+09°3223 is another example of a hypervelocity star. Whether it is bound or unbound to the Galaxy depends on the assumed mass and adopted Galactic potential. Possible origins of these two high-velocity stars are briefly discussed. CD-41°15048 and BD+09°3223 are further examples of evolved stars to join the restricted group of hypervelocity stars. Finally, our results seem to contradict the idea that a passage of a star very close to the Galactic center is the only possible origin of hypervelocity stars.
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FMFMET, NUK, UL, UM, UPUK
We study the dynamics of the group of Atira asteroids, characterized by aphelion distance Q < 0.983 au. This group has a significant observational bias, and their number is expected to be an order of ...magnitude larger than is known today. Due to their orbital configuration, these asteroids may represent a potential danger to the Earth. Here, we construct dynamical maps of the region between 0.2 and 0.98 au using a simple chaos indicator, the mean standard deviation in semimajor axis, and also analyse the behaviour of the real Atira orbits by means of the diffusion coefficient in semimajor axis. Our results indicate that Atira asteroids are located in the most unstable regions of the inner Solar system, and their stability is determined by close encounters and collisions with Mercury, Venus, and the Earth. A fraction of the known Atiras may represent a potential threat to the Earth over a few 105 yr of evolution. We found two islands of low-eccentricity stable orbits that might harbour a long-lasting sub-population of Atiras not yet observed.
In this paper we develop a semianalytical model to describe the long-term motion of Trojan asteroids located in tadpole orbits around the L
4 and L
5 jovian Lagrangian points. The dynamical model is ...based on the spatial elliptic three-body problem, including the main secular variations of Jupiter's orbit and the direct perturbations of the remaining outer planets. Based on ideas introduced by A. H. Jupp (1969,
Astron. J.
74, 35–43), we develop a canonical transformation which allows the transformation of the tadpole librating orbits into circulating orbits. The disturbing function is then explicitly expanded around each libration point by means of a Taylor–Fourier asymmetric expansion.
Making use of the property in which the different degrees of freedom in the Trojan problem are well separated with regard to their periods of oscillation, we are able to find approximate action-angle variables combining Hori's method with the theory of adiabatic invariants. This procedure is applied to estimate proper elements for the sample of 533 Trojans with well determined orbits at December 2000. The errors of our semianalytical estimates are about 2–3 times larger than those previously obtained with numerical approaches by other authors.
Finally, we use these results to search for asteroidal families among the Trojan swarms. We are able to identify and confirm the existence of most of the families previously detected by Milani (1993,
Celest. Mech. Dynam. Astron.
57, 59–94). The families of
Menelaus and
Epeios, both around L
4, are the most robust candidates to be the by-product of catastrophic disruption of larger asteroids. On the other hand, no significant family is detected around L
5.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Hydrothermal synthesis of TiO2-Ni(SO4)0.3(OH)1.4 nanocomposite.•Use of Graphite|TiO2-Ni(SO4)0.3(OH)1.4 as electrocatalytic anode in alkaline medium.•Electrochemical determination of kinetic ...parameters for meglumine oxidation.•Facile meglumine electrooxidation revealed by UHPLC-ESI-Q-TOF-MS analysis.•Effective electrooxidation of meglumine also in a commercial formulation.
The electrocatalytic oxidation of meglumine and gadoterate meglumine (Gd-DOTA) on a TiO2-Ni(SO4)0.3(OH)1.4 composite anode was investigated in alkaline medium (5 M KOH) using cyclic voltammetry and chronoamperometry. The composite was prepared by hydrothermal method and the morphology and structure of the produced nanoparticles were studied by scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, atomic force microscopy, BET surface area analysis and Fourier transform infrared spectroscopy. The characterization revealed the formation of Ni(SO4)0.3(OH)1.4 nanobelts dispersed on TiO2 nanoaggregates. The composite was coated onto a porous graphite rod, showing good adherence without requiring any binder (according to their anodic and cathodic charges). The supported composite was electrocatalytic, allowing the oxidation of meglumine, either as pure reagent or contained in gadoterate meglumine solutions. Electrochemical methods allowed determining the kinetic parameters, such as the electron transfer coefficient α, the total number of electrons n and the standard heterogeneous rate constant k0 for the reaction of meglumine. The chronoamperometric tests informed about the good stability of the composite anode upon meglumine oxidation at +0.6 V for 10 h. The electrochemical oxidation of meglumine in a commercial pharmaceutical formulation (Dotarem®) was corroborated via ultra-high performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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