New abundance determinations in z < 1.5 QSO absorbers: seven sub-DLAs and one DLA

We present chemical abundance measurements from high-resolution observations of seven subdamped Lyα (sub-DLA) absorbers and one DLA system at   z < 1.5  . Three of these objects have high metallicity, with near or supersolar Zn abundance. Grids of cloudy models for each system were constructed to look for possible ionization effects in these systems. For the systems in which we could constrain the ionization parameter, we find that the ionization corrections as predicted by the cloudy models are generally small and within the typical error bars (∼0.15 dex), in general agreement with previous studies. The Al  iii to Al  ii ratio for these and other absorbers from the literature are compared, and we find that while the sub-DLAs have a larger scatter in the Al  iii to Al  ii ratios than the DLAs, there appears to be little correlation between the ratio and   N _{H  i}   . The relationship between the metallicity and the velocity width of the profile for these systems is investigated. We show that the sub-DLAs that have been observed to date follow a similar trend as DLA absorbers, with the more metal rich systems exhibiting large velocity widths. We also find that the systems at the upper edge of this relationship with high metallicities and large velocity widths are more likely to be sub-DLAs than DLA absorbers, perhaps implying that the sub-DLA absorbers are more representative of massive galaxies.     

What properties of star and galaxy evolution depend on metallicity Z?

The purpose of this discussion was twofold. On one side, we would like to establish a kind of catalogue of as many as possible effects of metallicity in stellar evolution, in the spectral evolution of galaxies and in the chemical evolution of galaxies. The other goal is to critically discuss some of the effects mentioned. Although the project was ambitious, it turned out to be successful and a relatively extensive list of metallicity effects could be established. The lively discussion was mainly focused on a few most critical effects. The conclusion is that the devil of the Z-effects enters everywhere in Astrophysics. This revised version was published online in September 2006 with corrections to the Cover Date.     

Star formation history up to z= 7.4: implications for gamma-ray bursts and cosmic metallicity evolution

The current Swift sample of gamma-ray bursts (GRBs) with measured redshifts allows us to test the assumption that GRBs trace star formation in the Universe. Some authors have claimed that the rate of GRBs increases with cosmic redshift faster than the star formation rate, whose cause is not yet known. In this paper, I investigate the possibility of interpreting the observed discrepancy between the GRB rate history and the star formation rate history using cosmic metallicity evolution. I am motivated by the observation that cosmic metallicity evolves with redshift and GRBs tend to occur in low-metallicity galaxies. First, I derive a star formation history up to redshift   z = 7.4  from an updated sample of star formation rate densities. This is obtained by adding the new ultraviolet measurements of Bouwens et al. and the new ultraviolet and infrared measurements of Reddy et al. to the existing sample compiled by Hopkins & Beacom. Then, adopting a simple model for the relation between GRB production and the cosmic metallicity history as proposed by Langer & Norman, I show that the observed redshift distribution of the Swift GRBs can be reproduced with good accuracy. Although the results are limited by the small size of the GRB sample and the poorly understood selection biases in detection and localization of GRBs and in redshift determination, they suggest that GRBs trace both star formation and metallicity evolution. If the star formation history can be accurately measured with other approaches, which is presumably achievable in the near future, it will be possible to determine the cosmic metallicity evolution using the study of the redshift distribution of GRBs.     

A near-infrared and optical photometric study of the Sculptor dwarf spheroidal galaxy: implications for the metallicity spread

The Sculptor dwarf spheroidal galaxy has a giant branch with a significant spread in colour, symptomatic of an intrinsic age–metallicity spread. We present here a detailed study of the Sculptor giant branch and horizontal branch (HB) morphology, combining new near-infrared photometry from the Cambridge Infrared Survey Instrument (CIRSI), with optical data from the European Southern Observatory Wide Field Imager. For a Sculptor-like old and generally metal-poor system, the position of red giant branch (RGB) and asymptotic giant branch (AGB) stars on the colour–magnitude diagram (CMD) is mainly metallicity dependent. The advantage of using optical–near-infrared colours is that the position of the RGB locus is much more sensitive to metallicity than with optical colours alone. In contrast the HB morphology is strongly dependent on both metallicity and age. Therefore a detailed study of both the RGB in optical–near-infrared colours and the HB can help break the age–metallicity degeneracy. Our measured photometric width of the Sculptor giant branch corresponds to a range in metallicity of 0.75 dex. We detect the RGB and AGB bumps in both the near-infrared and the optical luminosity functions, and derive from them a mean metallicity of  [M/H]=−1.3 ± 0.1  . From isochrone fitting we derive a mean metallicity of  [Fe/H]=−1.42  with a dispersion of 0.2 dex. These photometric estimators are for the first time consistent with individual metallicity measurements derived from spectroscopic observations. No spatial gradient is detected in the RGB morphology within a radius of 13 arcmin, twice the core radius. On the other hand, a significant gradient is observed in the HB morphology index, confirming the 'second parameter problem' present in this galaxy. These observations are consistent with an early extended period of star formation continuing in time for a few Gyr.     

The effects of metallicity and grain growth and settling on the early evolution of gaseous protoplanets

Giant protoplanets formed by gravitational instability in the outer regions of circumstellar disks go through an early phase of quasi-static contraction during which radii are large (∼1 AU) and internal temperatures are low (<2000 K). The main source of opacity in these objects is dust grains. We investigate two problems involving the effect of opacity on the evolution of isolated, non-accreting planets of 3, 5, and 7 M_J. First, we pick three different overall metallicities for the planet and simply scale the opacity accordingly. We show that higher metallicity results in slower contraction as a result of higher opacity. It is found that the pre-collapse time scale is proportional to the metallicity. In this scenario, survival of giant planets formed by gravitational instability is predicted to be more likely around low-metallicity stars, since they evolve to the point of collapse to small size on shorter time scales. But metal-rich planets, as a result of longer contraction times, have the best opportunity to capture planetesimals and form heavy-element cores. Second, we investigate the effects of opacity reduction as a result of grain growth and settling, for the same three planetary masses and for three different values of overall metallicity. When these processes are included, the pre-collapse time scale is found to be of order 1000 years for the three masses, significantly shorter than the time scale calculated without these effects. In this case the time scale is found to be relatively insensitive to planetary mass and composition. However, the effects of planetary rotation and accretion of gas and dust, which could increase the timescale, are not included in the calculation. The short time scale we find would preclude metal enrichment by planetesimal capture, as well as heavy-element core formation, over a large range of planetary masses and metallicities.     

Observational evidence for the evolution of nuclear metallicity and star formation rate with the merger stage

We investigate the evolution of nuclear gas-phase oxygen abundance and star formation rate(SFR) of local far-infrared selected star-forming galaxies along the merger sequence, as traced by their optical morphologies. The sample was drawn from a cross-correlation analysis of the IRAS Point Source Catalog Redshift Survey and 1 Jy ultraluminous infrared galaxy sample with the Sloan Digital Sky Survey Data Release 7 database. The investigation is done by comparing our sample to a control sample matched in the normalized redshift distribution in two diagnostics, which are the nuclear gas-phase metallicity vs.stellar mass and the nuclear SFR vs. stellar mass diagrams. Galaxies with different morphological types show different mass-metallicity relations(MZRs). Compared to the MZR defined by the control sample,isolated spirals have comparable metallicities with the control sample at a given stellar mass. Spirals in pairs and interacting galaxies with projected separations of rp 20 kpc show a mild metallicity dilution of0.02–0.03 dex. Interacting galaxies with rp 20 kpc, pre-mergers and advanced mergers are underabundant by～0.06,～0.05 and～0.04 dex, respectively. This shows an evolutionary trend that the metallicity is increasingly depressed as the merging proceeds and it is diluted most dramatically when two galaxies are closely interacting. Afterwards, the interstellar medium(ISM) is enriched when the galaxies coalesce.This is the first time that such ISM enrichment at the final coalescence stage has been observed, which demonstrates the importance of supernova explosions in affecting the nuclear metallicity. Moreover, the central SFR enhancement relative to the control sample evolves simultaneously with the nuclear gas-phase oxygen abundance. Our results support the predictions from numerical simulations.     

The metallicity distribution of G dwarfs in the solar neighbourhood and the chemical evolution of the Galaxy

Based on a new metallicity distribution for G dwarfs within 25 pc of the sun this paper discusses in detail four galactic chemical evolution models in an inhomogeneous interstellar medium. It is shown that both the so-called simple model and the collapse model deviate greatly from the observations, while the two models labelled PIE (Prompt Initial Enrichment) and PPY (Proportional Yield) not only give much better fit, but also alleviate the so-called G-dwarf problem. The indications are that the outer halo has little influence on the chemical evolution near the Sun.     

The evolution of nighttime mid-latitude mesoscale F-region structures: A case study utilizing numerical solution of the Perkins instability equations

In recent years, all-sky camera airglow observations of evolving nighttime F-region structures have raised questions regarding the formation and apparent motion of these often wave-like structures. We address these issues using a pseudo-spectral method code developed to numerically solve the Perkins (1973. Spread F and ionospheric currents. J. Geophys. Res. 78, 218-226) moment equations modeling F-region electrodynamics. To aid in interpretation of the results, we utilize a Gaussian shape initial condition of the (geomagnetic field, B, parallel) integrated conductivity under the homogeneous TEC (B-parallel total electron content) condition and a northeastward DC electric field (E-field). We find that the initial Gaussian shape conductivity structure gradually evolves into banded structures oriented along the northwest-southeast direction while the amplitude of the banded structures continues growing and the peak of the structure moves to the northwest due to the E×B drift. The potential distribution corresponding to the initial Gaussian conductivity distribution is more complex but also becomes banded with the same orientation and growing trend as the conductivity. Wave vector domain plots show structure growth in approximately the first and third quadrants and damping in the second and fourth quadrants for both the conductivity and potential, as Perkins predicts—this leads to the orientation of the structures. We note that the evolved banded structures in conductivity and potential are oriented perpendicular to the direction given by half the angle between the DC E-field and east—the direction of maximum instability growth rate predicted by Perkins. The polarization (perturbation) E-field is seen mainly perpendicular to the long axis of the banded structures—i.e., no obvious structure-parallel E-field is observed in the simulation. By tracking the maximum point of the conductivity as a function of time, it is found that the localized structures move northwestward at a nearly constant speed that corresponds to the E×B drift velocity (to within relative errors on the direction and magnitude of ?4%). We also note that the E×B drift velocity has a dominant effect on the speed and propagation direction of the wave-like bands. The “wave” velocity is the projection of the E×B drift velocity on the line perpendicular to the wave front. Thus, the movement of a northwest-southeast oriented band can be decomposed into two components—parallel (to the band, northwestward) and perpendicular (southwestward) motions. A preliminary comparison of these results with an Arecibo all-sky camera observations shows good agreement.     

A discussion on metallicity effects on the period-luminosity relations of Cepheids and Miras

We present an automatic, fast, accurate and robust method of classifying astronomical objects. The Self Organizing Map (SOM) as an unsupervised Artificial Neural Network (ANN) algorithm is used for classification of stellar spectra of stars. The SOM is used to make clusters of different spectral classes of Jacoby, Hunter and Christian (JHC) library. This ANN technique needs no training examples and the stellar spectral data sets are directly fed to the network for the classification. The JHC library contains 161 spectra out of which, 158 spectra are selected for the classification. These 158 spectra are input vectors to the network and mapped into a two dimensional output grid. The input vectors close to each other are mapped into the same or neighboring neurons in the output space. So, the similar objects are making clusters in the output map and making it easy to analyze high dimensional data.     

Late Quaternary evolution of fluvial sediment composition: a modeling case study of the River Meuse

This paper addresses the influence of external forcing (changes in tectonics, sea level and climate) on the downstream and long-term (10³–10⁵ years) evolution of sediment composition along a fluvial longitudinal profile. The River Meuse served as a case study for a semi 2-D forward-modelling approach to simulate the downstream sediment transport in the 200- to 0-ka period. This has been related to bulk geochemical properties of the tributary catchments to quantify the bulk composition of the sediment load in the main river. The model was used to test the hypothesis that long-term fluvial dynamics influences sediment composition.The simulation exercise showed that long-term fluvial dynamics can yield systematic temporal changes in fluvial sediment composition, especially in high-relief areas. We tested a scenario of minimal discharges and maximum hillslope erosion during cold glacial periods (weathering-limited sediment supply), alternating with maximal discharges and minimal hillslope erosion during prolonged interstadials or interglacials (transport-limited sediment supply). This scenario largely reproduced the timing and direction of measured changes in the bulk and clay geochemistry of fine-grained sediments, which were deposited in the River Meuse lower reach from 13 to 0 ka. However, it failed to reproduce the measured amplitude of change, which was five to six times larger than the modelled amplitude. This suggests that climate-dependent changes in weathering intensity of rocks and saprolite in the source areas were more important and that aeolian inputs from outside the drainage basin have co-determined the sediment composition.     

Homologous prominence non-radial eruptions: A case study

The present study provides important details on homologous eruptions of a solar prominence that occurred in active region NOAA 10904 on 2006 August 22. We report on the pre-eruptive phase of the homologous feature as well as the kinematics and the morphology of a forth from a series of prominence eruptions that is critical in defining the nature of the previous consecutive eruptions. The evolution of the overlying coronal field during homologous eruptions is discussed and a new observational criterion for homologous eruptions is provided. We find a distinctive sequence of three activation periods each of them containing pre-eruptive precursors such as a brightening and enlarging of the prominence body followed by small surge-like ejections from its southern end observed in the radio 17 GHz. We analyse a fourth eruption that clearly indicates a full reformation of the prominence after the third eruption. The fourth eruption although occurring 11 h later has an identical morphology, the same angle of propagation with respect to the radial direction, as well as similar kinematic evolution as the previous three eruptions. We find an important feature of the homologous eruptive prominence sequence that is the maximum height increase of each consecutive eruption. The present analysis establishes that all four eruptions observed in Hα are of confined type with the third eruption undergoing a thermal disappearance during its eruptive phase. We suggest that the observation of the same direction of the magnetic flux rope (MFR) ejections can be consider as an additional observational criterion for MFR homology. This observational indication for homologous eruptions is important, especially in the case of events of typical or poorly distinguishable morphology of eruptive solar phenomena.