The gaseous Halo of the Virgo Cluster Galaxy 45

Observations of the Virgo Cluster galaxy NGC 4569 in soft X-rays and in Hα reveal both an asymmetrically distributed hot gaseous halo and a giant filament of diffuse emission, respectively, extending from the same side of the disk, the latter one to at least 8.8 kpc. A deep longslit spectrum along the filament shows velocities systematically different from the systemic velocity of NGC 4569. With the inclination of the disk one can determine the Hα spur as a giant outflow in NGC 4569. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of bi-orthogonal modes in magnetic butterflies

We present a bi-orthogonal decomposition of the temporal and latitudinal distribution of solar magnetic fields from synoptic magnetograms. Results are compared with a similar decomposition of the distribution of sunspots since 1874. We show that the butterfly diagrams can be interpreted as the result of approximately constant amplitudes and phases of two oscillations with periods close to 22 years. A clear periodicity of 7 years can also be identified in the most energetic modes of both spatio-temporal series. These results can be used to obtain relevant information concerning the physics of the solar dynamo.     

Close encounters in young stellar clusters: implications for planetary systems in the solar neighbourhood

The stars that populate the solar neighbourhood were formed in stellar clusters. Through N -body simulations of these clusters, we measure the rate of close encounters between stars. By monitoring the interaction histories of each star, we investigate the singleton fraction in the solar neighbourhood. A singleton is a star which formed as a single star, has never experienced any close encounters with other stars or binaries, or undergone an exchange encounter with a binary. We find that, of the stars which formed as single stars, a significant fraction is not singletons once the clusters have dispersed. If some of these stars had planetary systems, with properties similar to those of the Solar System, the planets' orbits may have been perturbed by the effects of close encounters with other stars or the effects of a companion star within a binary. Such perturbations can lead to strong planet–planet interactions which eject several planets, leaving the remaining planets on eccentric orbits. Some of the single stars exchange into binaries. Most of these binaries are broken up via subsequent interactions within the cluster, but some remain intact beyond the lifetime of the cluster. The properties of these binaries are similar to those of the observed binary systems containing extrasolar planets. Thus, dynamical processes in young stellar clusters will alter significantly any population of Solar System-like planetary systems. In addition, beginning with a population of planetary systems exactly resembling the Solar System around single stars, dynamical encounters in young stellar clusters may produce at least some of the extrasolar planetary systems observed in the solar neighbourhood.     

Mutual Potential of Homogeneous Polyhedra

The mutual gravitational potential between a pair of homogeneous polyhedra is expressed using an infinite series. The nested volume integrals are evaluated analytically and result in simple tensor expressions containing no special functions. However, complexity increases as O(6 ⁿ ), where n is the term degree. An alternate formulation due to Liebenthal is also presented.     

A map series of the Southern East Pacific Rise and its flanks, 15° S to 19° S

Four large-scale bathymetric maps of the Southern East Pacific Rise and its flanks between 15° S and 19° S display many of the unique features of this superfast spreading environment including abundant seamounts (the Rano Rahi Field), axial discontinuities, discontinuity migration, and abyssal hill variation. Along with a summary of the regional geology, these maps will provide a valuable reference for other sea-going programs on-and off-axis in this area, including the Mantle ELectromagnetic and Tomography (MELT) experiment.     

The STAGES view of red spirals and dusty red galaxies: mass-dependent quenching of star formation in cluster infall

We investigate the properties of optically passive spirals and dusty red galaxies in the A901/2 cluster complex at redshift ∼0.17 using rest-frame near-ultraviolet–optical spectral energy distributions, 24-μm infrared data and Hubble Space Telescope morphologies from the STAGES data set. The cluster sample is based on COMBO-17 redshifts with an rms precision of  σ _cz ≈ 2000 km s⁻¹  . We find that 'dusty red galaxies' and 'optically passive spirals' in A901/2 are largely the same phenomenon, and that they form stars at a substantial rate, which is only four times lower than that in blue spirals at fixed mass. This star formation is more obscured than in blue galaxies and its optical signatures are weak. They appear predominantly in the stellar mass range of  log  M _*/M_⊙=[10, 11]  where they constitute over half of the star-forming galaxies in the cluster; they are thus a vital ingredient for understanding the overall picture of star formation quenching in clusters. We find that the mean specific star formation rate (SFR) of star-forming galaxies in the cluster is clearly lower than in the field, in contrast to the specific SFR properties of blue galaxies alone, which appear similar in cluster and field. Such a rich red spiral population is best explained if quenching is a slow process and morphological transformation is delayed even more. At  log  M _*/M_⊙ < 10  , such galaxies are rare, suggesting that their quenching is fast and accompanied by morphological change. We note that edge-on spirals play a minor role; despite being dust reddened they form only a small fraction of spirals independent of environment.     

TNOs are Cool: A Survey of the Transneptunian Region

Over one thousand objects have so far been discovered orbiting beyond Neptune. These trans-Neptunian objects (TNOs) represent the primitive remnants of the planetesimal disk from which the planets formed and are perhaps analogous to the unseen dust parent-bodies in debris disks observed around other main-sequence stars. The dynamical and physical properties of these bodies provide unique and important constraints on formation and evolution models of the Solar System. While the dynamical architecture in this region (also known as the Kuiper Belt) is becoming relatively clear, the physical properties of the objects are still largely unexplored. In particular, fundamental parameters such as size, albedo, density and thermal properties are difficult to measure. Measurements of thermal emission, which peaks at far-IR wavelengths, offer the best means available to determine the physical properties. While Spitzer has provided some results, notably revealing a large albedo diversity in this population, the increased sensitivity of Herschel and its superior wavelength coverage should permit profound advances in the field. Within our accepted project we propose to perform radiometric measurements of 139 objects, including 25 known multiple systems. When combined with measurements of the dust population beyond Neptune (e.g. from the New Horizons mission to Pluto), our results will provide a benchmark for understanding the Solar debris disk, and extra-solar ones as well.     

39Ar‐40Ar “ages” and origin of excess 40Ar in Martian shergottites

Abstract— We report new ³⁹Ar‐⁴⁰Ar measurements on 15 plagioclase, pyroxene, and/or whole rock samples of 8 Martian shergottites. All age spectra suggest ages older than the meteorite formation ages, as defined by Sm‐Nd and Rb‐Sr isochrons. Employing isochron plots, only Los Angeles plagioclase and possibly Northwest Africa (NWA) 3171 plagioclase give ages in agreement with their formation ages. Isochrons for all shergottite samples reveal the presence of trapped Martian ⁴⁰Ar (⁴⁰Ar_xs), which exists in variable amounts in different lattice locations. Some ⁴⁰Ar_xs is uniformly distributed throughout the lattice, resulting in a positive isochron intercept, and other ⁴⁰Ar_xs occurs in association with K‐bearing minerals and increases the isochron slope. These samples demonstrate situations where linear Ar isochrons give false ages that are too old. After subtracting ⁴⁰Ar*that would accumulate by ⁴⁰K decay since meteorite formation and small amounts of terrestrial ⁴⁰Ar, all young age samples give similar ⁴⁰Ar_xs concentrations of ?1–2 × 10^?6cm³/g, but a variation in K content by a factor of ?80. Previously reported NASA Johnson Space Center data for Zagami, Shergotty, Yamato (Y‐) 000097, Y‐793605, and Queen Alexandra Range (QUE) 94201 shergottites show similar concentrations of ⁴⁰Ar_xs to the new meteorite data reported here. Similar ⁴⁰Ar_xs in different minerals and meteorites cannot be explained as arising from Martian atmosphere carried in strongly shocked phases such as melt veins. We invoke the explanation given by Bogard and Park (2008) for Zagami, that this ⁴⁰Ar_xs in shergottites was acquired from the magma. Similarity in ⁴⁰Ar_xs among shergottites may reveal common magma sources and/or similar magma generation and emplacement processes.     

The Canadian Meteor Orbit Radar Meteor Stream Catalogue

The Canadian Meteor Orbit Radar is a multi-frequency backscatter radar which has been in routine operation since 1999, with an orbit measurement capability since 2002. In total, CMOR has measured over 2 million orbits of meteoroids with masses greater than 10 μg, while recording more than 18 million meteor echoes in total. We have applied a two stage comparative technique for identifying meteor streams in this dataset by making use of clustering in radiants and velocities without employing orbital element comparisons directly. From the large dataset of single station echoes, combined radiant activity maps have been constructed by binning and then stacking each years data per degree of solar longitude. Using the single-station mapping technique described in Jones and Jones (Mon Not R Astron Soc 367:1050–1056, 2006) we have identified probable streams from these single station observations. Additionally, using individual radiant and velocity data from the multi-station velocity determination routines, we have utilized a wavelet search algorithm in radiant and velocity space to construct a list of probable streams. These two lists were then compared and only streams detected by both techniques, on multiple frequencies and in multiple years were assigned stream status. From this analysis we have identified 45 annual minor and major streams with high reliability.     

Lensing, reddening and extinction effects of Mg ii absorbers from z= 0.4 to 2

Using a sample of almost 7000 strong Mg  ii absorbers with   W ₀ > 1 Å  and  0.4 < z < 2.2  detected in the SDSS DR4 data set, we investigate the gravitational lensing and dust extinction effects they induce on background quasars. After carefully quantifying several selection biases, we isolate the reddening effects as a function of redshift and absorber rest equivalent width, W ₀. We find the amount of dust to increase with cosmic time as  τ( z ) ∝ (1 + z )^−1.1±0.4  , following the evolution of cosmic star density or integrated star formation rate. We measure the reddening effects over a factor of 30 in E ( B − V ) and we find that  τ∝ ( W ₀)^1.9±0.1  , providing us with an important scaling for theoretical modelling of metal absorbers. We also measure the dust-to-metal ratio and find it similar to that of the Milky Way. In contrast to previous studies, we do not detect any gravitational magnification by Mg  ii systems. We measure the upper limit  μ < 1.10  and discuss the origin of the discrepancy. Finally, we estimate the fraction of absorbers missed due to extinction effects and show that it rises from 1 to 50 per cent in the range  1 < W ₀ < 6 Å  . We parametrize this effect and provide a correction for recovering the intrinsic  ∂ N /∂ W ₀  distribution.