77 research outputs found
Sample Preparation Techniques for the Analysis of Microplastics in Soil-A Review
Although most plastic pollution originates on land, current research largely remains focused on aquatic ecosystems. Studies pioneering terrestrial microplastic research have adapted analytical methods from aquatic research without acknowledging the complex nature of soil. Meanwhile, novel methods have been developed and further refined. However, methodical inconsistencies still challenge a comprehensive understanding of microplastic occurrence and fate in and on soil. This review aims to disentangle the variety of state-of-the-art sample preparation techniques for heterogeneous solid matrices to identify and discuss best-practice methods for soil-focused microplastic analyses. We show that soil sampling, homogenization, and aggregate dispersion are often neglected or incompletely documented. Microplastic preconcentration is typically performed by separating inorganic soil constituents with high-density salt solutions. Not yet standardized but currently most used separation setups involve overflowing beakers to retrieve supernatant plastics, although closed-design separation funnels probably reduce the risk of contamination. Fenton reagent may be particularly useful to digest soil organic matter if suspected to interfere with subsequent microplastic quantification. A promising new approach is extraction of target polymers with organic solvents. However, insufficiently characterized soils still impede an informed decision on optimal sample preparation. Further research and method development thus requires thorough validation and quality control with well-characterized matrices to enable robust routine analyses for terrestrial microplastics
Subsidy Quality Affects Common Riparian Web-Building Spiders: Consequences of Aquatic Contamination and Food Resource
Anthropogenic stressors can affect the emergence of aquatic insects. These insects link aquatic and adjacent terrestrial food webs, serving as high-quality subsidy to terrestrial consumers, such as spiders. While previous studies have demonstrated that changes in the emergence biomass and timing may propagate across ecosystem boundaries, the physiological consequences of altered subsidy quality for spiders are largely unknown. We used a model food chain to study the potential effects of subsidy quality: Tetragnatha spp. were exclusively fed with emergent Chironomus riparius cultured in the absence or presence of either copper (Cu), Bacillus thuringiensis var. israelensis (Bti), or a mixture of synthetic pesticides paired with two basal resources (Spirulina vs. TetraMin (R)) of differing quality in terms of fatty acid (FA) composition. Basal resources shaped the FA profile of chironomids, whereas their effect on the FA profile of spiders decreased, presumably due to the capacity of both chironomids and spiders to modify (dietary) FA. In contrast, aquatic contaminants had negligible effects on prey FA profiles but reduced the content of physiologically important polyunsaturated FAs, such as 20:4n-6 (arachidonic acid) and 20:5n-3 (eicosapentaenoic acid), in spiders by approximately 30% in Cu and Bti treatments. This may have contributed to the statistically significant decline (40%-50%) in spider growth. The observed effects in spiders are likely related to prey nutritional quality because biomass consumption by spiders was, because of our experimental design, constant. Analyses of additional parameters that describe the nutritional quality for consumers such as proteins, carbohydrates, and the retention of contaminants may shed further light on the underlying mechanisms. Our results highlight that aquatic contaminants can affect the physiology of riparian spiders, likely by altering subsidy quality, with potential implications for terrestrial food webs. (c) 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC
Constraints on the Galactic bar from the Hercules stream as traced with RAVE across the Galaxy
Non-axisymmetries in the Galactic potential (spiral arms and bar) induce kinematic groups such as the Hercules stream. Assuming that Hercules is caused by the effects of the outer Lindblad resonance of the Galactic bar, we model analytically its properties as a function of position in the Galaxy and its dependence on the bar's pattern speed and orientation. Using data from the RAVE survey we find that the azimuthal velocity of the Hercules structure decreases as a function of Galactocentric radius, in a manner consistent with our analytical model. This allows us to obtain new estimates of the parameters of the Milky Way's bar. The combined likelihood function of the bar's pattern speed and angle has its maximum for a pattern speed of Omega(b) = (1.89 +/- 0.08) x Omega(0), where Omega(0) is the local circular frequency. Assuming a solar radius of 8.05 kpc and a local circular velocity of 238 km s(-1), this corresponds to Omega(b) = 56 +/- 2km s(-1) kpc(-1). On the other hand, the bar's orientation phi(b) cannot be constrained with the available data. In fact, the likelihood function shows that a tight correlation exists between the pattern speed and the orientation, implying that a better description of our best fit results is given by the linear relation Omega(b)/Omega(0) = 1.91+0.0044 (phi(b)(deg) - 48), with standard deviation of 0.02. For example, for an angle of phi(b) = 30 deg the pattern speed is 54.0 +/- 0.5 km s(-1) kpc(-1). These results are not very sensitive to the other Galactic parameters such as the circular velocity curve or the peculiar motion of the Sun, and are robust to biases in distance
Bayesian analysis to identify new star candidates in nearby young stellar kinematic groups
We present a new method based on a Bayesian analysis to identify new members
of nearby young kinematic groups. The analysis minimally takes into account the
position, proper motion, magnitude and color of a star, but other observables
can be readily added (e.g. radial velocity, distance). We use this method to
find new young low-mass stars in the \beta Pictoris (\beta PMG) and AB Doradus
(ABDMG) moving groups and in the TW Hydrae (TWA), Tucana-Horologium (THA),
Columba, Carina and Argus associations. Starting from a sample of 758 mid-KM
(K5V-M5V) stars showing youth indicators such as H\alpha\ and X-ray emission,
our analysis yields 215 new highly probable low-mass members of the kinematic
groups analyzed. One is in TWA, 37 in \beta PMG, 17 in THA, 20 in Columba, 6 in
Carina, 50 in Argus, 33 in ABDMG, and the remaining 51 candidates are likely
young but have an ambiguous membership to more than one association. The false
alarm rate for new candidates is estimated to be 5% for \beta PMG and TWA, 10%
for THA, Columba, Carina and Argus, and 14% for ABDMG. Our analysis confirms
the membership of 58 stars proposed in the literature. Firm membership
confirmation of our new candidates will require measurement of their radial
velocity (predicted by our analysis), parallax and lithium 6708 {\AA}
equivalent width. We have initiated these follow-up observations for a number
of candidates and we have identified two stars (2MASSJ0111+1526,
2MASSJ0524-1601) as very strong candidate members of the \beta PMG and one
strong candidate member (2MASSJ0533-5117) of the THA; these three stars have
radial velocity measurements confirming their membership and lithium detections
consistent with young age. Finally, we proposed that six stars should be
considered as new bona fide members of \beta PMG and ABDMG, one of which being
first identified in this work, the others being known candidates from the
literature.Comment: Accepted for publication in Ap
Chemical gradients in the Milky Way from the RAVE data
Aims. We aim at measuring the chemical gradients of the elements Mg, Al, Si, and Fe along the Galactic radius to provide new constraints on the chemical evolution models of the Galaxy and Galaxy models such as the Besancon model. Thanks to the large number of stars of our RAVE sample we can study how the gradients vary as function of the distance from the Galactic plane.
Methods. We analysed three different samples selected from three independent datasets: a sample of 19 962 dwarf stars selected from the RAVE database, a sample of 10 616 dwarf stars selected from the Geneva-Copenhagen Survey (GCS) dataset, and a mock sample (equivalent to the RAVE sample) created by using the GALAXIA code, which is based on the Besancon model. The three samples were analysed by using the very same method for comparison purposes. We integrated the Galactic orbits and obtained the guiding radii (R-g) and the maximum distances from the Galactic plane reached by the stars along their orbits (Z(max)). We measured the chemical gradients as functions of R-g at different Z(max).
Results. We found that the chemical gradients of the RAVE and GCS samples are negative and show consistent trends, although they are not equal: at Z(max) < 0.4 kpc and 4.5 < R-g(kpc) < 9.5, the iron gradient for the RAVE sample is d[Fe/H]/dR(g) = -0.065 dex kpc(-1), whereas for the GCS sample it is d[Fe/H]/dR(g) = -0.043 dex kpc(-1) with internal errors of +/-0.002 and +/-0.004 dex kpc(-1), respectively. The gradients of the RAVE and GCS samples become flatter at larger Z(max). Conversely, the mock sample has a positive iron gradient of d[Fe/H]/dR(g) = +0.053 +/- 0.003 dex kpc(-1) at Z(max) < 0.4 kpc and remains positive at any Z(max). These positive and unrealistic values originate from the lack of correlation between metallicity and tangential velocity in the Besancon model. In addition, the low metallicity and asymmetric drift of the thick disc causes a shift of the stars towards lower R-g and metallicity which, together with the thin-disc stars with a higher metallicity and R-g, generates a fictitious positive gradient of the full sample. The flatter gradient at larger Z(max) found in the RAVE and the GCS samples may therefore be due to the superposition of thin-and thick-disc stars, which mimicks a flatter or positive gradient. This does not exclude the possibility that the thick disc has no chemical gradient. The discrepancies between the observational samples and the mock sample can be reduced by i) decreasing the density; ii) decreasing the vertical velocity; and iii) increasing the metallicity of the thick disc in the Besancon model
Automatic Determination of Stellar Atmospheric Parameters and Construction of Stellar Spectral Templates of the Guoshoujing Telescope (LAMOST)
A number of spectroscopic surveys have been carried out or are planned to
study the origin of the Milky Way. Their exploitation requires reliable
automated methods and softwares to measure the fundamental parameters of the
stars. Adopting the ULySS package, we have tested the effect of different
resolutions and signal-to-noise ratios (SNR) on the measurement of the stellar
atmospheric parameters (effective temperature Teff, surface gravity log g, and
metallicity [Fe/H]). We show that ULySS is reliable to determine these
parameters with medium-resolution spectra (R~2000). Then, we applied the method
to measure the parameters of 771 stars selected in the commissioning database
of the Guoshoujing Telescope (GSJT). The results were compared with the
SDSS/SEGUE Stellar Parameter Pipeline (SSPP), and we derived precisions of 167
K, 0.34 dex, and 0.16 dex for Teff, log g and [Fe/H] respectively. Furthermore,
120 of these stars are selected to construct the primary stellar spectra
template library (Version 1.0) of GSJT, and will be deployed as basic
ingredients for the GSJT automated parametrization pipeline.Comment: 23 pages, 15 figures, accepted by RA
Structure in the motions of the fastest halo stars
We have analyzed the catalog of 2106 non-kinematically selected metal poor
stars in the solar neighborhood published by Beers et al. (2000), with the goal
of quantifying the amount of substructure in the motions of the fastest halo
stars. We have computed the two-point velocity correlation function for a
subsample of halo stars within 1-2 kpc of the Sun, and found statistical
evidence of substructure, with a similar amplitude to that predicted by high
resolution CDM simulations. The signal is due to a small kinematic group whose
dynamical properties are compared to the stellar "stream", previously
discovered by Helmi et al. (1999). If real, this high velocity moving group
would provide further support to the idea that substructures remain as fossils
from the formation of the Galaxy as expected in the CDM scenario.Comment: 9 pages, 6 figures, accepted for publication in A&
Kinematics of Tycho-2 Red Giant Clump Stars
Based on the Ogorodnikov-Milne model, we analyze the proper motions of 95 633
red giant clump (RGC) stars from the Tycho-2 Catalogue. The following Oort
constants have been found: A = 15.9+-0.2 km/s/kpc and B = -12.0+-0.2 km/s/kpc.
Using 3632 RGC stars with known proper motions, radial velocities, and
photometric distances, we show that, apart from the star centroid velocity
components relative to the Sun, only the model parameters that describe the
stellar motions in the XY plane differ significantly from zero. We have studied
the contraction (a negative K-effect) of the system of RGC stars as a function
of their heliocentric distance and elevation above the Galactic plane. For a
sample of distant (500--1000 pc) RGC stars located near the Galactic plane
(|Z|<200 pc) with an average distance of d=0.7 kpc, the contraction velocity is
shown to be Kd= -3.5+-0.9 km/s; a noticeable vertex deviation, lxy = 9.1+-0.5
degrees, is also observed for them. For stars located well above the Galactic
plane (|Z|>=200 pc), these effects are less pronounced, Kd = -1.7+-0.5 km/s and
lxy = 4.9+-0.6 degrees. Using RGC stars, we have found a rotation around the
Galactic X axis directed toward the Galactic center with an angular velocity of
-2.5+-0.3 km/s/kpc, which we associate with the warp of the Galactic
stellar-gaseous disk.Comment: 23 pages, 7 figures, 4 table
Kinematic groups beyond the Solar neighbourhood with RAVE
We analyse the kinematics of disc stars observed by the RAVE survey in and
beyond the Solar neighbourhood.We detect significant overdensities in the
velocity distributions using a technique based on the wavelet transform.We find
that the main local kinematic groups are large scale features, surviving at
least up to ~1 kpc from the Sun in the direction of anti-rotation, and also at
~700 pc below the Galactic plane.We also find that for regions located at
different radii than the Sun, the known groups appear shifted in the velocity
plane. For example, the Hercules group has a larger azimuthal velocity for
regions inside the Solar circle and a lower value outside. We have also
discovered a new group at (U, V) = (92,-22) km/s in the Solar neighbourhood and
confirmed the significance of other previously found groups. Some of these
trends detected for the first time are consistent with dynamical models of the
effects of the bar and the spiral arms. More modelling is required to
definitively characterise the non-axisymmetric components of our Galaxy using
these groups.Comment: Minor changes to match the accepted version in MNRAS Letter
The Seventh Data Release of the Sloan Digital Sky Survey
This paper describes the Seventh Data Release of the Sloan Digital Sky Survey
(SDSS), marking the completion of the original goals of the SDSS and the end of
the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most
of the roughly 2000 deg^2 increment over the previous data release lying in
regions of low Galactic latitude. The catalog contains five-band photometry for
357 million distinct objects. The survey also includes repeat photometry over
250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A
coaddition of these data goes roughly two magnitudes fainter than the main
survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2
in the Northern Galactic Cap, closing the gap that was present in previous data
releases. There are over 1.6 million spectra in total, including 930,000
galaxies, 120,000 quasars, and 460,000 stars. The data release includes
improved stellar photometry at low Galactic latitude. The astrometry has all
been recalibrated with the second version of the USNO CCD Astrograph Catalog
(UCAC-2), reducing the rms statistical errors at the bright end to 45
milli-arcseconds per coordinate. A systematic error in bright galaxy photometr
is less severe than previously reported for the majority of galaxies. Finally,
we describe a series of improvements to the spectroscopic reductions, including
better flat-fielding and improved wavelength calibration at the blue end,
better processing of objects with extremely strong narrow emission lines, and
an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor
correction
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