Fluid inclusions in microstructures of shocked quartz from the Keurusselkä impact site,Central Finland

Granitoid rock samples from the assumed center of the Keurusselkä impact site were subjected to a systematic study of fluid‐inclusion compositions and densities in various microstructures of the shocked quartz. The results are consistent with the following impact‐induced model of formation. After cessation of all major regional tectonic activity and advanced erosional uplift of the Fennoscandian shield, a meteorite impact (approximately 1.1 Ga) caused the formation of planar fractures (PFs) and planar deformation features (PDFs) and the migration of shock‐liberated metamorphic fluid (CO₂ ± H₂O) to the glass in the PDFs. Postimpact annealing of the PDFs led to the formation of CO₂ (±H₂O) fluid‐inclusion decorated PDFs. The scarce fluid‐inclusion implosion textures (IPs) suggest a shock pressure of 7.6–10 GPa. The postimpact pressure release and associated heating initiated hydrothermal activity that caused re‐opening of some PFs and their partial filling by moderate‐salinity/high temperature (>200 °C) H₂O (+ chlorite + quartz) and moderate‐density CO₂. The youngest postimpact endogenic sub‐ and nonplanar microfractures (MFs) are characterized by low‐density CO₂ and low‐salinity/low‐temperature (<200 °C) H₂O.     

I Zwicky 1: Decomposition and dynamics of the nearby QSO host

We address current theories of research on morphology, environment and evolution of active galaxies in the form of a detailed case study of the nearby QSO host I Zw 1. This study is based on sub-kpc resolution ¹²CO(1-0) observations with the BIMA mm-interferometer and on near-infrared imaging with ISAAC at the VLT. The ¹²CO(1-0) maps reveal a circumnuclear molecular gas ring with a radius of 0.9 kpc. The imaging data in the J-band are analyzed with respect to a disk-bulge decomposition. Together with a model of the gas rotation curve, the radial profile of the dynamical J-band mass-to-light ratio (M/L) is discussed. The J-band images give new evidence for an interaction between I Zw 1 and its nearby companion. First results from a sequence of N-body simulations for an extensive test of the parameter space of the interaction are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analytical solutions for saturated P cygni type profiles II: General case

As in the first part of the present study (Sapar et al., 2002) we use the β-law for velocity of stellar wind and the Sobolev approximation for radiative transfer. Here we have succeeded to derive general and relatively simple analytical formulae in elementary functions for saturated P Cygni type line profiles if parameter 2β is arbitrary positive integer (in the first part we studied the cases 2β ≤ 4). The four terms obtained describe contributions to the line profile due to isotropic and anisotropic parts of optical thickness in the source function of the light-scattering layer followed by isotropic and anisotropic parts of multiple scattering. The limits of acceptability of the Sobolev approximation for β-law have been discussed and specified. This revised version was published online in July 2006 with corrections to the Cover Date.     

Total flux density radio observations as a tool for understanding AGN behaviour

A wealth of information on the properties of jets in Active Galactic Nuclei (AGNs) can be derived from total flux density observations at high radio frequencies. This includes, for example, the Doppler factor, the Lorentz factor, and the viewing angle of the jet. We have earlier calculated these parameters for a sample of ～80 sources of different AGN types using almost 20 years of 22 and 37 GHz data from Metsähovi Radio Observatory. We have now gathered data for an additional ten years, and studied the long term characteristic variability time scales of a large sample of AGNs using the first order structure function, the discrete autocorrelation function and the Lomb-Scargle periodogram. Some of the results will be presented in this paper. We also stress the importance of long term observations of AGNs, the main reason for this being misinterpretations of source properties due to insufficient time coverage. Only a few observing epochs will too easily lead to incorrect conclusions about variability, continuum spectra, and the general detectability of the source, not to mention the exclusion of interesting objects from further studies. This is particularly important when considering, for example, the Planck satellite for which the quality of the main mission product, the accurate cosmic microwave background anisotropy maps, depends heavily on the elimination of foreground sources such as AGNs.     

Analysis of energetic electron drop-outs in the upper atmosphere of Titan during flybys in the dayside magnetosphere of Saturn

We discuss the high energy electron absorption signatures at Titan during the Cassini dayside magnetospheric encounters. We use the electron measurements of the Low Energy Measurement System of the Magnetospheric Imaging Instrument. We also examine the mass loading boundary based on the ion data of the Ion Mass Spectrometer sensor of the Cassini Plasma Spectrometer. The dynamic motion of the Kronian magnetopause and the periodic charged particle flux and magnetic field variations – associated with the magnetodisk of Saturn – of the subcorotating magnetospheric plasma creates a unique and complex environment at Titan. Most of the analysed flybys (like T25–T33 and T35–T51) cluster at similar Saturn Local Time positions. However the instantaneous direction of the incoming magnetospheric particles may change significantly from flyby to flyby due to the very different magnetospheric field conditions which are found upstream of Titan within the sets of encounters.The energetic magnetospheric electrons gyrate along the magnetic field lines of Saturn, and at the same time bounce between the mirror points of the magnetosphere. This motion is combined with the drift of the magnetic field lines. When these flux tubes interact with the upper atmosphere of Titan, their content is depleted over approximately an electron bounce period. These depletion signatures are observed as sudden drop-outs of the electron fluxes. We examined the altitude distribution of these drop-outs and concluded that these mostly detected in the exo-ionosphere of Titan and sometimes within the ionosphere.However there is a relatively significant scatter in the orbit to orbit data, which can be attributed to the which can be attributed to the variability of the plasma environment and as a consequence, the induced magnetosphere of Titan. A weak trend between the incoming electron fluxes and the measured drop-out altitudes has also been observed.     

On the occurrence and origin of anthropogenic radionuclides found in a fragment of the Chelyabinsk (LL5) meteorite

A piece of the 2013 Chelyabinsk meteorite was investigated for its content of anthropogenic radionuclides. In addition to traces of cesium‐137 that had been previously reported for this particular fragment, we found an unusually high amount of strontium‐90, which indicates that the source of this contamination was the Kyshtym accident (1957). A high Sr‐90/Cs‐137 activity ratio is characteristic for Kyshtym‐derived contaminations. Based on the cesium‐137 content in the soil from the finding site, it is estimated that the fragment was contaminated with soil particles in the milligram range upon impact. Investigation of the soil revealed very unusual ferromagnetic characteristics and an iron‐rich chemical composition. Mössbauer spectroscopy indicated the presence of steel components in this soil, suggesting that the investigated meteorite fragment was found in an industrial dumping site rather than natural soil.     

The Solar Connection of Enhanced Heavy Ion Charge States in the Interplanetary Medium: Implications for the Flux-Rope Structure of CMEs

We investigated a set of 54 interplanetary coronal mass ejection (ICME) events whose solar sources are very close to the disk center (within ±?15^° from the central meridian). The ICMEs consisted of 23 magnetic-cloud (MC) events and 31 non-MC events. Our analyses suggest that the MC and non-MC ICMEs have more or less the same eruption characteristics at the Sun in terms of soft X-ray flares and CMEs. Both types have significant enhancements in ion charge states, although the non-MC structures have slightly lower levels of enhancement. The overall duration of charge-state enhancement is also considerably smaller than that in MCs as derived from solar wind plasma and magnetic signatures. We find very good correlation between the Fe and O charge-state measurements and the flare properties such as soft X-ray flare intensity and flare temperature for both MCs and non-MCs. These observations suggest that both MC and non-MC ICMEs are likely to have a flux-rope structure and the unfavorable observational geometry may be responsible for the appearance of non-MC structures at 1 AU. We do not find any evidence for an active region expansion resulting in ICMEs lacking a flux-rope structure because the mechanism of producing high charge states and the flux-rope structure at the Sun is the same for MC and non-MC events.