Clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks 94101: evidence for aqueous alteration prior to complex mixing

Clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks (LON) 94101 have been characterized using scanning and transmission electron microscopy and electron microprobe analysis to determine their degrees of aqueous alteration, and the timing of alteration relative to incorporation of clasts into the host. The provenance of the clasts, and the mechanism by which they were incorporated and mixed with their host material are also considered. Results show that at least five distinct types of clasts occur in LON 94101, of which four have been aqueously altered to various degrees and one is largely anhydrous. The fact that they have had different alteration histories implies that the main part of aqueous activity occurred prior to the mixing and assimilation of the clasts with their host. Further, the presence of such a variety of clasts suggests complex mixing in a dynamic environment involving material from various sources. Two of the clasts, one containing approximately 46 vol% carbonate and the other featuring crystals of pyrrhotite up to approximately 1 mm in size, are examples of unusual lithologies and indicate concentration of chemical elements in discrete areas of the parent body(ies), possibly by flow of aqueous solutions

Neural networks for impact parameter determination

Abstract: An accurate impact parameter determination in a heavy ion collision is crucial for almost all further analysis. The capabilities of an artificial neural network are investigated to that respect. A novel input generation for the network is proposed, namely the transverse and longitudinal momentum distribution of all outgoing (or actually detectable) particles. The neural network approach yields an improvement in performance of a factor of two as compared to classical techniques. To achieve this improvement simple network architectures and a 5 × 5 input grid in (pt, pz) space are suffcient

Light Curve Patterns and Seismology of a White Dwarf with Complex Pulsation

The ZZ Ceti star KUV 02464+3239 was observed over a whole season at the mountain station of Konkoly Observatory. A rigorous frequency analysis revealed 6 certain periods between 619 and 1250 seconds, with no shorter period modes present. We use the observed periods, published effective temperature and surface gravity, along with the model grid code of Bischoff-Kim, Montgomery and Winget (2008) to perform a seismological analysis. We find acceptable model fits with masses between 0.60 and 0.70 M_Sun. The hydrogen layer mass of the acceptable models are almost always between 10^-4 and 10^-6 M_*. In addition to our seismological results, we also show our analysis of individual light curve segments. Considering the non-sinusoidal shape of the light curve and the Fourier spectra of segments showing large amplitude variations, the importance of non-linear effects in the pulsation is clearly seen.Comment: 5 pages, 6 figures, in "Stellar Pulsation: Challenges for Theory and Observation", Eds. J. Guzik and P. A. Bradley, AIP

Mineralogy and petrography of the anomalous carbonaceous chondrites Yamato-86720, Yamato-82162, and Belgica-7904

As a part of the consortium study on antarctic meteorites with affinities to CI-chondrites we studied the samples of Yamato (Y)-86720,Y-82162,and Belgica (B)-7904. These carbonaceous chondrites are unique samples and do not perfectly fit in the traditional classification schemes. Therefore, they have to be considered as very important samples to carry distinct information about processes in the early solar system. Y-82162 is a very fine-grained carbonaceous chondrite. Based on the occurrence of abundant clasts (up to several mm in size) we suggest that this sample is a chondritic breccia. The dominating phases are phyllosilicates; abundant sulfide grains are scattered throughout the entire sample. However, the abundances of sulfides vary from clast to clast. Y-86720 contains about 13 vol% of light objects embedded in a fine-grained, phyllosilicate-rich groundmass. Some of these objects appear to be relict chondrules; however, they essentially consist of phyllosilicates. Most light, round to irregularly-shaped components exhibit well-preserved accretionary dust mantles ("dark rims") similar to those found in CM-chondrites. Y-86720 is mineralogically more closely related to the CI-chondrites than to any other chondrite group; texturally, however, it appears to be an intermediate chondrite between CI and CM as also suggested by bulk chemical criteria (G. W. KALLEMEYN; Papers Presented to the 13th symposium on Antarctic Meteorites, June 7-9,1988,Tokyo, NIPR, 132,1988). B-7904 contains 18 vol% of objects larger than about 70μm in size. 42 vol% of these components are chondrules or chondrule fragments. The most abundant constituents are, however, olivine-bearing, fragment-like objects (45.9 vol%) unknown from other chondrites. The olivines within these components are embedded in a fine-grained brownish-grey matrix. Other constituents include fine-grained CAIs, olivine aggregates, and mineral fragments. B-7904 is a new kind of carbonaceous chondrite and we do not like to classify this meteorite as a CM-type chondrite because of the following reasons : a) A great number of chondrules in B-7904 is much larger (0.5-3mm) than measured for the mean size of chondrules in CM-chondrites (0.3mm). b) Many components (olivine-bearing, fragment-like objects, Cr, Al-rich fine-grained particles) are unknown from CM-chondrites. c) The oxygen isotope composition and the low H_2O-contents are untypical for CM-chondrites

Neural Networks for Impact Parameter Determination

An accurate impact parameter determination in a heavy ion collision is crucial for almost all further analysis. The capabilities of an artificial neural network are investigated to that respect. A novel input generation for the network is proposed, namely the transverse and longitudinal momentum distribution of all outgoing (or actually detectable) particles. The neural network approach yields an improvement in performance of a factor of two as compared to classical techniques. To achieve this improvement simple network architectures and a 5 by 5 input grid in (p_t,p_z) space are sufficient.Comment: Phys. Rev. C in print. Postscript-file also available at http://www.th.physik.uni-frankfurt.de/~bass/pub.htm

A New Timescale for Period Change in the Pulsating DA White Dwarf WD 0111+0018

We report the most rapid rate of period change measured to date for a pulsating DA (hydrogen atmosphere) white dwarf (WD), observed in the 292.9 s mode of WD 0111+0018. The observed period change, faster than 10^{-12} s/s, exceeds by more than two orders of magnitude the expected rate from cooling alone for this class of slow and simply evolving pulsating WDs. This result indicates the presence of an additional timescale for period evolution in these pulsating objects. We also measure the rates of period change of nonlinear combination frequencies and show that they share the evolutionary characteristics of their parent modes, confirming that these combination frequencies are not independent modes but rather artifacts of some nonlinear distortion in the outer layers of the star.Comment: 10 pages, 6 figures, accepted for publication in The Astrophysical Journa