Impact angle influence in high velocity dust collisions during planetesimal formation

We have examined the influence of impact angle in collisions between small dust aggregates and larger dust targets through laboratory experiments. Targets consisted of μm-sized quartz dust and had a porosity of about 67%; the projectiles, between 1 and 5 mm in diameter, were slightly more compact (64% porosity). The collision velocity was centered at 20 m/s and impact angles range from 0° to 45°. At a given impact angle, the target gained mass for projectiles smaller than a threshold size, which decreases with increasing angle from about 3 mm to 1 mm. The fact that growth is possible up to the largest angles studied supports the idea of planetesimal formation by sweep-up of small dust aggregates.     

Feeding Monsters – A Study of Active Galaxies

We present new interferometric observations of the molecular gas distribution and kinematics in the nuclei of different active galaxies at high angular resolution and high sensitivity carried out with the IRAM Plateau de Bure interferometer (PdBI). The observations cover galaxies in a redshift range of 0.03–1.4. We have so far observed five different active galaxies: NGC3718, NGC1068, HE1029–1831, 3C48 and Q0957+561. The first two objects belong to the NUGA (NUclei of GAlaxies) project – an international collaboration mainly between Spain, France and Germany – containing about 30 Seyfert and LINER galaxies. Both are at the same distance of 14Mpc and show a warped gas and dust disk. The new mosaic map of NGC3718 corrected for short-spacing effects with IRAM 30 m observations well demonstrates the existence of the warped gas disk with several secondary maxima in the projected gas distribution caused by orbit crowding effects. Based on these new data we have improved recent simulations of the warped disk in NGC3718. HE1029–1831 and 3C48 are nearby QSOs. HE1029–1831 is taken out of the Cologne nearby QSO sample. The maps of the integrated CO(1–0) and CO(2–1) emission clearly show that the molecular gas is mostly related to the central bulge with a non-negligible fraction distributed along the bar known from optical observations. Our new CO data of 3C48 unveil new information about the kinematics of its molecular gas complementing and improving further studies based on previous infrared observations and detailed multi-particle simulations. Finally, new measurements of the CO(1–0) line in Q0957+561 – a highly-red-shifted, gravitationally lensed quasar – will be presented as a link to earlier evolutionary stages of active galaxies and their hosts.     

The Qso Hosts I Zw 1 and 3C 48: Prototypes of a Merger-Driven Quasar Evolution?

I Zw 1 and 3C 48 are two neighboring template objects at a later stage of the hypothesized merger-driven evolutionary sequence from ultra-luminous infrared galaxies (ULIRGs) to quasi-stellar objects (QSOs). Since galaxy mergers are assumed to trigger the evolution, it is important to confirm the merger properties of transitionary objects. Using multi-wavelength observations and N-body simulations, the merger histories of I Zw 1 and 3C 48 have been investigated in two separate case studies. Here, the results from both studies are compared and their relevance for the evolutionary hypothesis is discussed.This research is partly based on observations with ISAAC at the Very Large Telescope (VLT) of the European Southern Observatory (ESO) under projects 67.B-0009 and 67.B-0019.     

Eclipsing Binaries in Open Clusters

The study of detached eclipsing binaries in open clusters can provide stringent tests of theoretical stellar evolutionary models, which must simultaneously fit the masses, radii, and luminosities of the eclipsing stars and the radiative properties of every other star in the cluster. We review recent progress in such studies and discuss two unusually interesting objects currently under analysis. GV Carinae is an A0 m + A8 m binary in the Southern open cluster NGC 3532; its eclipse depths have changed by 0.1 mag between 1990 and 2001, suggesting that its orbit is being perturbed by a relatively close third body. DW Carinae is a high-mass unevolved B1 V + B1 V binary in the very young open cluster Collinder 228, and displays double-peaked emission in the centre of the Hα line which is characteristic of Be stars. We conclude by pointing out that the great promise of eclipsing binaries in open clusters can only be satisfied when both the binaries and their parent clusters are well-observed, a situation which is less common than we would like.     

GETEMME—a mission to explore the Martian satellites and the fundamentals of solar system physics

GETEMME (Gravity, Einstein??s Theory, and Exploration of the Martian Moons?? Environment), a mission which is being proposed in ESA??s Cosmic Vision program, shall be launched for Mars on a Soyuz Fregat in 2020. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive Laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine Laser range measurements to the reflectors on Phobos and Deimos. Also, asynchronous two-way Laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellite system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter ?? as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame.     

Cratering and modification of wet‐target craters: Projectile impact experiments and field observations of the Lockne marine‐target crater (Sweden)

Abstract— Marine impacts are one category of crater formation in volatile targets. At target water depths exceeding the diameter of the impactor, the zones of vaporization, melting, and excavation of the standard land‐target cratering model develop partially or entirely in the water column. The part of the crater that has a potential of being preserved (seafloor crater) may to a great extent be formed by material emplacement and excavation processes that are very different from land‐target craters. These processes include a high‐energy, water‐jet‐driven excavation flow. At greater water depths, the difference in strength of the target layers causes a concentric crater to evolve. The crater consists of a wide water cavity with a shallow excavation flow along the seabed surrounding a nested, deeper crater in the basement. The modification of the crater is likewise influenced by the water through its forceful resurge to fill the cavity in the water mass and the seafloor. The resurge flow is strongly erosive and incorporates both ejecta and rip‐up material from the seabed surrounding the excavated crater. A combination of field observations and impact experiments has helped us analyze the processes affecting the zone between the basement crater and the maximum extent of the water cavity. The resurge erosion is facilitated by fragmentation of the upper parts of the solid target caused by a) spallation and b) vibrations from the shallow excavation flow and, subsequently, c) the vertical collapse of the water cavity rim wall. In addition, poorly consolidated and saturated sediments may collapse extensively, possibly aided by a violent expansion of the pore water volume when it turns into a spray during passage of the rarefaction wave. This process may also occur at impacts into water‐saturated targets without an upper layer of seawater present. Our results have implications for impacts on both Earth and Mars, and possibly anywhere in the solar system where volatiles exist/have existed in the upper part of the target.     

Intersex in feral marine and freshwater fish from northeastern Germany

A histopathological assessment of the gonad of male fish was performed as part of biological field studies carried out in coastal waters and small rivers in Mecklenburg-Western Pomerania, northeastern Germany. In the marine environment the eelpout (Zoarces viviparus) was selected as sentinel species. The three spined stickleback (Gasterosteus aculeatus) and perch (Perca fluviatilis) were chosen at freshwater locations. Histopathology of the testis revealed the presence of intersexuality in specimens of all three species. The intersex condition was defined by the simultaneous presence of primary oocytes within the apparently normal testis tissue. In comparison to stickleback and perch the eelpout exhibited the highest intersex prevalence and the most severe histological alterations. Fish with intersex were found at contaminated marine and freshwater stations as well as at sites with apparently little pollution. The findings suggest that feminised male fish were exposed to endocrine disrupting substances in the aquatic environment.     

Effects of Dredging Activities on Growth of Laminaria saccharina

Abstract. The possible effects of fine-grained deposits on the photosynthesis, growth, and nutrient uptake of Laminaria have been studied in field and laboratory experiments. Some of the plants were treated with fine-grained material for two hours and then transplanted in rows together with untreated plants. At two-week intervals the treatment was repeated and samples collected. The macroalgae were analyzed for growth as well as chlorophyll a , nitrogen, and phosphorus content. In the laboratory experiments, plants of a uniform size were incubated in Plexiglas containers after leaf-marking and treatment in a sediment suspension. At weekly intervals, photosynthesis, growth, chlorophyll a , and nutrients were analyzed.
The field study showed that Laminaria growth was significantly affected by the fine-grained material. The growth in the control experiment was 20% higher than in the treated plants. The chlorophyll a concentrations in the treated plants were significantly lower than in the control experiment, and the results indicated a reduced nutrient uptake in the treated plants. In the laboratory experiments the growth of the treated plants was only 30% of the controls, but no differences in photosynthetic capacities were detected. Nitrogen uptake was reduced in the treated plants, but no effects were observed on phosphorus uptake. Thick layers of fine-grained material caused direct harmful effects and rotting.
The results are discussed in relation to dredging activities; it is concluded that in heavy sedimentation areas, Laminaria growth may be significantly reduced beyond the indirect effect of shading from suspended material in the water.     

Heat flow in the southern Chile forearc controlled by large-scale tectonic processes

Between 33°S and 47°S, the southern Chile forearc is affected by the subduction of the aseismic Juan Fernandez Ridge, several major oceanic fracture zones on the subducting Nazca Plate, the active Chile Ridge spreading centre, and the underthrusting Antarctic Plate. The heat flow through the forearc was estimated using the depth of the bottom simulating reflector obtained from a comprehensive database of reflection seismic profiles. On the upper and middle continental slope along the whole forearc, heat flow is about 30–60 mW m^–2, a range of values common for the continental basement and overlying slope sediments. The actively deforming accretionary wedge on the lower slope, however, in places shows heat flow reaching about 90 mW m^–2. This indicates that advecting pore fluids from deeper in the subduction zone may transport a substantial part of the heat there. The large size of the anomalies suggests that fluid advection and outflow at the seafloor is overall diffuse, rather than being restricted to individual fault structures or mud volcanoes and mud mounds. One large area with very high heat flow is associated with a major tectonic feature. Thus, above the subducting Chile Ridge at 46°S, values of up to 280 mW m^–2 indicate that the overriding South American Plate is effectively heated by subjacent zero-age oceanic plate material.