The outer turbulence scale in the interstellar plasma

The structure function for phase fluctuations on spatial scales from 10⁶ to 10¹⁷ m is constructed using data on diffractive and refractive scintillation of pulsars, scattering angles, variations in pulse arrival times, and differences in dispersion measures observed for close pairs of pulsars in globular clusters. For distances R>1 kpc (a sample of pulsars with DM≥30 pc/cm³), the fluctuations in the interstellar electron density on scales from 10⁶ to 10¹⁴ m are well described by a Kolmogorov spectrum with index 11/3. Analysis of variations in the dispersion measures for close pairs of pulsars in globular clusters indicates an outer turbulence scale of L ₀=10¹⁵ m. The relative level of turbulent fluctuations is determined for the interstellar plasma, and the important role of turbulence in the energy balance is demonstrated.     

Cobalt in stars and the galaxy

An analysis of the abundance of cobalt in atmospheres of red giants, indicates they can be divided into two groups: stars with the normal [Co/Fe] abundance and those with a small [Co/Fe] excess. A comparative analysis of the spectrograms taking into account the effect of superfine splitting provides evidence for a [Co/Fe] excess in some stars. We have also detected physical and kinematical differences between these groups. Stars with a [Co/Fe] excess are related to the thick-disk population of the Galaxy. These stars are older and less massive, display lower metallicities, and have Galactic velocities corresponding to those of thick-disk objects. It is suggested that the observed pattern of a [Co/Fe] excess in the halo and thick disk reflects the chemical composition of the Galaxy at a very early stage of its evolution, when Population III objects existed. The lower abundance excess in the thick disk compared to the halo and the absence of an excess in the thin disk are due to the contributiuon from Type I supernovae at later stages of the Galaxy’s evolution. We have found that the thick disk of the Galaxy displays gradients of its cobalt and iron abundances, possibly providing evidence that the thick disk formed as a result of the collapse of a protogalactic cloud.     

Globular cluster subsystems in the galaxy

Data from the literature are used to construct a homogeneous catalog of fundamental astrophysical parameters for 145 globular clusters of the Milky Way Galaxy. The catalog is used to analyze the relationships between chemical composition, horizontal-branch morphology, spatial location, orbital elements, age, and other physical parameters of the clusters. The overall globular-cluster population is divided by a gap in the metallicity function at [Fe/H]=?1.0 into two discrete groups with well-defined maxima at [Fe/H]=?1.60±0.03 and ?0.60±0.04. The mean spatial-kinematic parameters and their dispersions change abruptly when the metallicity crosses this boundary. Metal-poor clusters occupy a more or less spherical region and are concentrated toward the Galactic center. Metal-rich clusters (the thick disk subsystem), which are far fewer in number, are concentrated toward both the Galactic center and the Galactic plane. This subsystem rotates with an average velocity of V _rot=165±28 km/s and has a very steep negative vertical metallicity gradient and a negligible radial gradient. It is, on average, the youngest group, and consists exclusively of clusters with extremely red horizontal branches. The population of spherical-subsystem clusters is also inhomogeneous and, in turn, breaks up into at least two groups according to horizontal-branch morphology. Clusters with extremely blue horizontal branches occupy a spherical volume of radius ～9 kpc, have high rotational velocities (V _rot=77±33 km/s), have substantial and equal negative radial and vertical metallicity gradients, and are, on average, the oldest group (the old-halo subsystem). The vast majority of clusters with intermediate-type horizontal branches occupy a more or less spherical volume ≈18 kpc in radius, which is slightly flattened perpendicular to the Z direction and makes an angle of ≈30° to the X-axis. On average, this population is somewhat younger than the old-halo clusters (the young-halo subsystem), and exhibits approximately the same metallicity gradients as the old halo. As a result, since their Galactocentric distance and distance from the Galactic plane are the same, the young-halo clusters have metallicities that are, on average, Δ[Fe/H] ≈0.3 higher than those for old-halo clusters. The young-halo subsystem, which apparently consists of objects captured by the Galaxy at various times, contains many clusters with retrograde orbits, so that its rotational velocity is low and has large errors, V _rot=?23±54 km/s. Typical parameters are derived for all the subsystems, and the mean characteristics of their member globular clusters are determined. The thick disk has a different nature than both the old and young halos. A scenario for Galactic evolution is proposed based on the assumption that only the thick-disk and old-halo subsystems are genetically associated with the Galaxy. The age distributions of these two subsystems do not overlap. It is argued that heavy-element enrichment and the collapse of the proto-Galactic medium occurred mainly in the period between the formation of the old-halo and thick-disk subsystems.     

Influence of relative density and stress level on the bearing capacity of sands

A finite element approach is presented to determine the bearing capacity of shallow footings on silica sand deposits. The approach can take into account the effects of relative density and stress level on the shear strength of granular soil and is applicable to a fairly large effective stress range. The strength of sand is characterized by a non-linear Mohr–Coulomb criterion which depends on maximum and critical friction angles, widely used parameters in engineering practice. The results of analysis indicate that this approach yields reliable predictions of bearing capacity and, in particular, it can model the volumetric behaviour of the soil at failure.     

Dust in galaxy clusters

The conditions for the destruction of dust in hot gas in galaxy clusters are investigated. It is argued that extinction measurements can be subject to selection effects, hindering their use in obtaining trustworthy estimates of dust masses in clusters. It is shown, in particular, that the ratio of the dust mass to the extinction M _d /S _d increases as dust grains are disrupted, due to the rapid destruction of small grains. Over long times, this ratio can asymptotically reach values a factor of three higher than the mean value in the interstellar medium in the Galaxy. This lowers dust-mass estimates based on measurements of extinction in galaxy clusters. The characteristic lifetime of dust in hot cluster gas is determined by its possible thermal isolation by the denser medium of gas fragments within which the dust is ejected from galaxies, and can reach 100–300 million years, depending on the kinematics and morphology of the fragments. As a result, the mass fraction of dust in hot cluster gas can reach 1–3% of the Galactic value. Over its lifetime, dust can also be manifest through its far-infrared emission. The emission characteristics of the dust change as it is disrupted, and the ratio of the fluxes at 350 and 850 μm can increase appreciably. This can potentially serve as an indicator of the state of the dust and ambient gas.     

Postglacial uplift and relative sea level changes in Finnmark,northern Norway

The outer coast of Finnmark in northern Norway is where the former Fennoscandian and Barents Sea ice sheets coalesced. This key area for isostatic modelling and deglaciation history of the ice sheets has abundant raised shorelines, but only a few existing radiocarbon dates constrain their chronology. Here we present three Holocene sea level curves based on radiocarbon dated deposits from isolation basins at the outermost coast of Finnmark; located at the islands Sørøya and Rolvsøya and at the Nordkinn peninsula. We analysed animal and plant remains in the basin deposits to identify the transitions between marine and lacustrine sediments. Terrestrial plant fragments from these transitions were then radiocarbon dated. Radiocarbon dated mollusk shells and marine macroalgae from the lowermost deposits in several basins suggest that the first land at the outer coast became ice free around 14,600 cal yr BP. We find that the gradients of the shorelines are much lower than elsewhere along the Norwegian coast because of substantial uplift of the Barents Sea. Also, the anomalously high elevation of the marine limit in the region can be attributed to uplift of the adjacent seafloor. After the Younger Dryas the coast emerged 1.6–1.0 cm per year until about 9500–9000 cal yr BP. Between 9000 and 7000 cal yr BP relative sea level rose 2–4 m and several of the studied lakes became submerged. At the outermost locality Rolvsøya, relative sea level was stable at the transgression highstand for more than 3000 years, between ca 8000 and 5000 cal yr BP. Deposits in five of the studied lakes were disturbed by the Storegga tsunami ca 8200–8100 cal yr BP.     

A catalog of star-forming regions in the galaxy

This Catalog of Star-Forming Regions in the Galaxy contains coordinates and fluxes of young objects in the radio and infrared, as well as data on the radial velocities of recombination and molecular lines, for more than three thousand star-forming regions. In addition to photometric and kinematic data, we present information on diffuse and reflecting nebulae, dark and molecular clouds, and other objects related to young stars. The catalog consists of two parts. The main catalog lists star-forming regions in order of Galactic longitude and is supplemented by analogous information for star-forming regions in complexes of dark clouds with large angular sizes that are closest to the Sun. The main catalog is located at http://www.strasbg.-u.fr/pub/cats. In our preliminary study of the catalog data using a formal classification of the star-forming regions, we subdivided these objects into several classes and characterized them as being populated primarily by massive or low-mass stars at early or late stages of the star-formation process. We also distinguish between relatively nearby and distant complexes.     

Salt marshes as archives of recent relative sea level change in West Greenland

Temperate latitude salt marshes are a proven environment from which high precision (±0.10–0.20 m) relative sea level (RSL) records can be developed over recent decades and centuries. Such records provide an important link between millennial histories of RSL change and instrumental records. The high latitude salt marshes in Greenland have not previously been explored as potential archives of recent RSL change. Here we develop four diatom-based transfer functions using contemporary diatom data collected from three salt marshes located 40 km south of the coastal town of Sisimiut, West Greenland. Our preferred model has a good fit between observed and predicted elevations (r² = 0.94) and a root mean square error prediction of ±0.19 m. We apply the four models to a short sediment profile collected from one of the marshes that formed between c. 600 cal. year BP and the present. Three of the four models predict the same trend in which RSL rose from ?0.55 ±0.19 m mean tide level (MTL) to ?0.05 ± 0.19 m MTL between c. 600 and 400 cal. year BP at a rate of c. 2.7 mm year^?1. After 400 cal. year BP RSL slowed and remained stable until the present day. The results of this study demonstrate that Greenland salt marshes are potentially valuable archives of data for developing quantitative estimates of RSL change during the last few centuries, thereby bridging the gap between existing millennial-scale approaches and more recent direct observations of ice sheet behaviour and associated vertical land motions.     

Measurement of the inner turbulence scale of the interstellar plasma toward the pulsar PSR B2111+46

The pulsar PSR B2111+46 has been observed at 112 MHz, and a new approach to analyzing pulsar pulses scattered in turbulent interstellar plasma applied. This method is based on the dependence of the normalized energy in the trailing part of a pulse on the intrapulse time. Since the trailing edge of a pulse follow exponential law to high accuracy, the inner turbulence scale of the interstellar plasma exceeds the field coherence scale. The measured scattering parameter is τ _sc = 147 ± 1 ms. Analysis of the parameters of diffractive and refractive scintillations of the pulsar at 610 MHz together with the 112 MHz data shows that the spectrum of the interstellar plasma toward PSR B2111+46 is a piecewise power law: on scales of 10¹³–10¹⁴ cm, the exponent of the turbulence spectrum is n ≃ 4, whereas n = 3.5 on scales of 2 × 10⁸−10¹³ cm. The spectrum flattens with approach to the inner turbulence scale l: n = 3–3.2. The obtained inner turbulence scale is l = (3.5 ± 1.5) × 10⁷ cm. The distribution of the interstellar plasma toward the pulsar is close to statistically homogeneous. The local density (N _e = 0.4 cm⁻³) and filling factor (F = 0.04) of the interstellar plasma have been estimated. The similarity of N _e estimates obtained from the inner scale of the inhomogeneities and the ratio of the emission measure to the dispersion measure provides evidence that the inner turbulence scale corresponds to the ion inertial length.     

Late Holocene relative sea level rise and the Neoglacial history of the Greenland ice sheet

In West Greenland, early and mid Holocene relative sea level (RSL) fall was replaced by late Holocene RSL rise during the Neoglacial, after 4–3 cal. ka BP (thousand calibrated years before present). Here we present the results of an isolation basin RSL study completed near to the coastal town of Sisimiut, in central West Greenland. RSL fell from 14 m above sea level at 5.7 cal. ka BP to reach a lowstand of ?4.0 m at 2.3–1.2 cal. ka BP, before rising by an equivalent amount to present. Differences in the timing and magnitude of the RSL lowstand between this and other sites in West and South Greenland record the varied interplay of local and non‐Greenland RSL processes, notably the reloading of the Earth's crust caused by a Neoglacial expansion of the Greenland Ice Sheet (GIS) and the subsidence associated with the collapse of the Laurentide Ice Sheet forebulge. This means that the timing of the sea level lowstand cannot be used to infer directly when the GIS advanced during the Neoglacial. The rise in Late Holocene RSL is contrary to recently reported bedrock uplift in the Sisimiut area, based on repeat GPS surveys. This indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late Holocene, and that there has been a switch from subsidence to uplift at some point in the last thousand years or so. Copyright © 2008 John Wiley & Sons, Ltd.     

Radio-induced activity in galaxy pairs

The close proximity of a radio-loud active galactic nucleus (AGN) can trigger star formation in nearby objects containing gas if they are hit by a radio jet emerging from the active nucleus (as is observed, for example, in the case of Minkowski’s Object). The predicted frequency of such events is modest for close pairs of galaxies—of the order of several percent of all close (with separations of the order of several tens of parsec) pairs containing a radio AGN. A statistical study of this effect is carried out using the SDSS and FIRST surveys, by searching for spatially close pairs (projected separations <150 kpc, relative radial velocities <600 km/s) containing AGNs with radio jets. The frequency of galaxies with bursts of star formation, f _SF, and active nuclei f _AGN, in pairs either containing or not containing an AGN with radio jets are evaluated as functions of the separation of the galaxies in the pair. It is concluded that (1) the predicted effect should be of the order of 5%, falling off with increasing separation between the galaxies in the pair; (2) the observed values of f _SF and f _AGN and their dependences on the galaxy separation are consistent withmodel predictions, but the large uncertainties associated with the limited size of the studied sample hinders firm conclusions about the existence of radio-induced activity in close galaxy pairs; (3) further investigations using a larger volume of observational material are required, for example, using only photometric redshifts.     

New dwarf galaxy candidates in the Leo-I Group

We have carried out a search for low-surface-brightness dwarf galaxies in the region of the Leo-I Group (M96) in images of the second Palomar Sky Survey. We found a total of 36 likely dwarf members of the group with typical magnitudes B _t ～18^m–19^m in an area of sky covering 120 square degrees. Half of these galaxies are absent from known catalogs and lists of galaxies. The radial-velocity dispersion calculated for 19 galaxies is 130 km/s. The Leo-I Group has a mean distance from the Sun of 10.4 Mpc, a mean projected radius of 352 kpc, an integrated luminosity of 6.7 × 10¹⁰L_⊙, a virial mass-to-luminosity ratio of 107 M_⊙/L_⊙, and a mean crossing time of 2.7 Gyr. The group shows evidence for a radial segregation of the galaxies according to morphological type and luminosity, suggesting that the group is in a state of dynamical relaxation. The subsystem of bright galaxies in the Leo-I Group is smaller in size (250 kpc) and has a lower velocity dispersion (92 km/s), resulting in a lower virial mass-to-luminosity ratio (34 M_⊙/L_⊙), as is typical of the Local Group and other nearby groups of galaxies.     

The age-metallicity relation in the thin disk of the galaxy

HST trigonometric distances, photometric metallicities, isochronic ages from the second revised version of the Geneva-Copenhagen survey, and uniform spectroscopic Fe and Mg abundances from our master catalog are used to construct and analyze the age-metallicity and age-relative Mg abundance relations for stars of the thin disk. The influences of selection effects are discussed in detail. It is demonstrated that the radial migration of stars does not lead to appreciable distortions in the age dependence of the metallicity. During the first several billion years of the formation of the thin disk, the interstellarmaterial in this disk was, on average, fairly rich in heavy elements (〈[Fe/H]〉 ≈ −0.2) and poorly mixed. However, the metallicity dispersion continuously decreased with age, from σ _[Fe/H] ≈ 0.22 to ≈0.13. All this time, the mean relative abundance of Mg was somewhat higher than the solar value (〈[Mg/Fe]〉 ≈ 0.1). Roughly four to five billion years ago, the mean metallicity began to systematically increase, while retaining the same dispersion; the mean relative Mg abundance began to decrease immediately following this. The number of stars in this subsystem increased sharply at the same time. These properties suggest that the star-formation rate was low in the initial stage of formation of the thin disk, but abruptly increased about four to five billion years ago.     

Postglacial relative sea‐level rise in the Limfjord region,northern Jutland,Denmark

A new core drilled at Nørrekær Enge, Løgstør, Denmark, shows terrestrial lake and bog sediments lying beneath 10 m of marine sediments. Pollen analysis, ¹⁴C dating and sedimentary observations show that these sediments relate to an ancient lake basin that was flooded when the rising sea levels reached 8.0 m b.s.l. This new study has allowed a review of previous data relating to shoreline displacement from the Limfjord region of northern Jutland, Denmark. Here we present a new shoreline displacement curve spanning the period between c. 11 700 and 7700 cal. a BP and built upon the Nørrekær Enge data and data from seven other boreholes and excavations from the Limfjord region. A previous shoreline displacement curve for this region suggested a very rapid relative sea‐level rise of 3 to 5 m 100 a^?1 whereas this new curve suggests a much slower rise of around 1 m 100 a^?1, similar to global rates.     

Stellar subsystems of the galaxy NGC 2366

Hubble Space Telescope archive data are used to perform photometry of stars in seven fields at the center and periphery of the galaxy NGC 2366. The variation of the number density of stars of various ages with galactocentric radius and along the minor axis of the galaxy are determined. The boundaries of the thin and thick disks of the galaxy are found. The inferred sizes of the subsystems of NGC 2366 (Z _thin = 4 kpc and Z _thick = 8 kpc for the thin and thick disks, respectively) are more typical for spiral galaxies. Evidence for a stellar halo is found at the periphery of NGC 2366 beyond the thick disk of the galaxy.     

Macromolecules in the galaxy and the cosmic microwave background

A deep search for the predicted Galactic microwave dipole emission of spinning interstellar fullerene-type molecules has been conducted using the RATAN-600 radio telescope. This effect is of interest both in its own right and as a new form of Galactic screen between the cosmic microwave background (CMB) and the observer. The power of this noise component on angular scales of about 0.1° (l=1000) is estimated. These scales are of primary interest for the “Cosmological Gene of the Universe” (RATAN-600), PLANCK Surveyor Mission, and other projects. At the frequencies of the expected emission peak of this dust component, the small-scale noise is a factor of 20 weaker than the predicted noise. It is shown that the role of this dust component is negligible, at least at the main PLANCK frequencies. The first estimates of the contribution from Galactic polarization noise are given for λ=3.9 cm, where the theory predicts a maximum in the CMB polarization (l～1000). At wavelengths of ～1 cm and shorter, macromolecules contribute less than 1 µK, and should not hinder CMB polarization studies. Galactic synchrotron polarization, likewise, should not prevent CMB polarization experiments at the main PLANCK frequencies.     

Polycyclic aromatic hydrocarbons in the dwarf galaxy IC 10

Archival infrared Spitzer Space Telescope observations are used to study the dust component of the ISM in the irregular galaxy IC 10. The dust distribution in the galaxy is compared to the distributions of the Hα and [S II] emission, neutral gas and CO clouds, and ionizing radiation sources. The distribution of polycyclic aromatic hydrocarbons (PAHs) in the galaxy is shown to be highly non-uniform, with the fraction of these particles in total dust mass reaching 4%. On the whole, PAHs avoid bright H II regions and correlate with the atomic and molecular gas. This pattern suggests that they form in the dense interstellar gas. It is suggested that the observed metallicity dependence of the PAH abundance shows up not only globally (at the level of the entire galaxy), but also locally (at least, at the level of individual H II regions). No conclusive evidence for shock destruction of PAHs in the IC 10 galaxy has been found.     

Impacts of relative sea level rise on the shoreface deposition,Shuidong Bay,South China

The influence of relative sea level rise on shoreface deposition helps to elucidate changes in beach and nearshore geomorphology in response to different forcing factors. In this study, two sets of sediment samples, one from 1982 and one from 2004, from the Shuidong Bay of South China were analyzed to determine the changes in shoreface depositions. An EOF (Empirical orthogonal function) method was used to examine how these depositions changed based on the relative sea level rise. The results show that shoreface sediments of Shuidong Bay are mainly composed of sand. Fine-grained sediments are distributed in the lower shoreface/offshore area, and coarse-grained sediments are mainly found in the upper shoreface/nearshore area. Due to the altered hydrological forcing caused by relative sea level rise, the sand fraction in sediments increased from 84.7 % in 1982 to over 90 % in 2004, and the clay and silt fractions decreased from 11.8 % in 1982 to 5.6 % in 2004. Grain-size parameters in sediments in 2004 became coarser, slightly more well sorted, less skewed and had lower kurtosis than those in 1982. In addition, the shoreface deposition of Shuidong in 1982 and 2004 is distinctly different: a polarized mode was described by the first eigenfunctions, and a homogenized mode was described by the second eigenfunctions. The former means that the sediment components developed towards the two opposite poles, undergoing both coarsening and refining processes. The second mode indicates that the secondary variation in sediment components was mostly in the three intermediate-grained sand components. In the future, the Shuidong Bay shoreface may be subjected to even further erosion because of increases in the energy of the environment resulting from rapid relative sea level rise.     

Distribution of the potential and concentration of electrons in low-temperature plasma with hollow microparticles

Using approximation of a uniform background (the jellium model) for a condensed dispersed phase, the analytical expressions describing a spatial distribution of the potential of the electric field and electron concentration in the low-temperature plasma at equilibrium which contains hollow spherical microparticles are obtained. The influence of heating temperature of plasma on the above distributions is studied, and the dependencies of the charge on microparticle radius, the size of the microparticle cavity and the absolute temperature of plasma are calculated. It is shown that electrons can be emitted not only into the surrounding plasma but also into the cavity of the particles.