Metallicity Dependence Research Articles

Measurement and Analysis of Normal-State Transport Properties of FeSe Superconductor

Transport properties such as thermal conductivity (κ), Seebeck coefficient (S) and electrical resistivity (ρ) of the FeSe superconductor were measured and analyzed theoretically. The samples were synthesized through a solid-state reaction route via vacuum encapsulation and characterized by X-ray diffraction and Rietveld refinement analysis. It is found that the Seebeck coefficient, S(T), exhibits an anomalous temperature dependence and shows a crossover of sign at around 190 K, which is an artifact of coexistence of electron and hole bands, wherein carrier diffusive Seebeck coefficient Sdiff(T) and phonon drag contribution Sdrag(T) can successfully explain the experimental results. The measured thermal conductivity κ(T) develops a phonon peak at around 80 K, presumably due to various phonon scattering mechanisms. Our thermal conductivity analysis indicates not only phonon thermal conductivity (κph), but also the carrier contribution to thermal conductivity (κc) is also important, particularly, around room temperatures. Electrical resistivity of FeSe shows superconducting transition (TC) around 10 K and shows a metallic temperature dependence above TC which is explained using the Bloch–Gruneisen function of the temperature-dependent resistivity.

The age and metallicity dependence of the near-infrared magnitudes of red clump stars

ABSTRACT Red clump (RC) stars are widely used as an excellent standard candle. To make them even better, it is important to know the dependence of their absolute magnitudes on age and metallicity. We observed star clusters in the Large Magellanic Cloud to fill age and metallicity parameter space, which previous work has not observationally studied. We obtained the empirical relations of the age and metallicity dependence of absolute magnitudes MJ, MH, and $M_{K_{S}}$, and colours J − H, J − KS, and H − KS of RC stars, although the coefficients have large errors. Mean near-infrared magnitudes of the RC stars in the clusters show relatively strong dependence on age for young RC stars. The J − KS and H − KS colours show the nearly constant values of 0.528 ± 0.015 and 0.047 ± 0.011, respectively, at least within the ages of 1.1–3.2 Gyr and [Fe/H] of −0.90 to −0.40 dex. We also confirmed that the population effects of observational data are in good agreement with the model prediction.

Rational Design of Metallic NiTex (x = 1 or 2) as Bifunctional Electrocatalysts for Efficient Urea Conversion

Electrocatalytic urea conversion (CO(NH2)2 + H2O → N2 + 3H2 + CO2) is a facile and scalable technique for urea-rich wastewater treatment, meanwhile with hydrogen evolution reaction (HER). However, it remains great challenge to develop a bifunctional catalyst for both HER and urea oxidation reaction (UOR) simultaneously due to the torpid kinetics of 6 e– transfer during UOR. Here, graphene oxide (GO) induced phase-controlled synthesis of nickel tellurides derived from Ni foam (NF) as freestanding electrocatalysts is reported. Results show that NF-assisted NiTe composited with reduced graphene oxide (rGO) exhibits superior activity for both HER and UOR. With the combined merits of HER and UOR, an efficient electrolyzer with integrated NiTe/rGO/NF was constructed as anode and cathode, representing overall urea decomposition at a low overpotential and even being driven by a commercial cell of 1.5 V. The metallic character and phase dependence of NiTe2 and NiTe toward UOR were simulated by density functional t...

Chemical Cartography with APOGEE: Multi-element Abundance Ratios

Abstract We map the trends of elemental abundance ratios across the Galactic disk, spanning R = 3 – 15 kpc and midplane distance ∣ Z ∣ = 0 – 2 kpc , for 15 elements in a sample of 20,485 stars measured by the SDSS/APOGEE survey (O, Na, Mg, Al, Si, P, S, K, Ca, V, Cr, Mn, Fe, Co, Ni). Adopting Mg rather than Fe as our reference element, and separating stars into two populations based on [Fe/Mg], we find that the median trends of [X/Mg] versus [Mg/H] in each population are nearly independent of location in the Galaxy. The full multi-element cartography can be summarized by combining these nearly universal median sequences with our measured metallicity distribution functions and the relative proportions of the low-[Fe/Mg] (high-α) and high-[Fe/Mg] (low-α) populations, which depend strongly on R and ∣ Z ∣ . We interpret the median sequences with a semi-empirical “two-process” model that describes both the ratio of core collapse and Type Ia supernova (SN Ia) contributions to each element and the metallicity dependence of the supernova yields. These observationally inferred trends can provide strong tests of supernova nucleosynthesis calculations. Our results lead to a relatively simple picture of abundance ratio variations in the Milky Way, in which the trends at any location can be described as the sum of two components with relative contributions that change systematically and smoothly across the Galaxy. Deviations from this picture and future extensions to other elements can provide further insights into the physics of stellar nucleosynthesis and unusual events in the Galaxy’s history.

Effect of Cu2+ and Zn2+ ions on human serum albumin interaction with plasma unsaturated fatty acids.

Human serum albumin (HSA) serves as a depot and carrier of multiple unrelated ligands including several participants of the pathogenesis of Alzheimer's disease (AD), such as amyloid β peptide (Aβ), Zn2+/Cu2+ ions, docosahexaenoic (DHA), linoleic (LA), and oleic (OA) acids. To explore the interplay between HSA interaction with Zn2+/Cu2+ and the plasma unsaturated fatty acids (DHA, LA, OA, and arachidonic acid (ArA)), we have studied the metal dependence of the fatty acid (FA) binding capacity of HSA (nmax) and structural consequences of the HSA-FA interactions. HSA loading with Zn2+ decreases nmax value by 0.3-1.5, while its saturation with Cu2+ causes the FA-dependent nmax changes by up to 0.9. The Cu2+-induced decline in nmax value for DHA is due to conformational rearrangements in HSA molecule. In other cases, the changes in nmax are attributed to steric hindarance/facilitation of the HSA-FA interaction because of the protein multimerization/monomerization, as confirmed by chemical crosslinking. The surface hydrophobicity of HSA is Cu2+-, Zn2+-, and FA-dependent and decreases upon the FA binding, according to bis-ANS fluorescence data. Overall, Zn2+ or Cu2+ binding selectively affect HSA interaction with the FAs studied, in part due to changes in quaternary structure of the protein.

Metal-Promoted Extraction Deprotonation of Bidentate Organophosphoric Reagents: Recovery of Uranium, Thorium, and Lanthanides

The extraction capacities to f elements are studied in a series of bidentate organophosphoric reagents that contain deprotonatable phenol moieties. The dependence of metal [thorium(IV), lanthanum(III), neodymium(III), and holmium(III)] recovery as a function of nitric acid concentration is represented by curves with a maximum, typical of extraction by monodentate organophosphoric reagents. The uranium recovery as a function of acid concentration is presented by curves with a minimum, indicating a change in extraction mechanism from ion exchange to solvation. The quantum-chemical modeling of reagent molecules and their complexes with uranyl ion is carried out. The reagents are structurally similar to reagent V, whose structure was determined by single-crystal X-ray diffraction. The results can be used in the hydrometallurgy of f elements.

Mixing-length calibration from field stars

Aims. We critically analysed the theoretical foundation and statistical reliability of the mixing-length calibration by means of standard (Teff, [Fe/H]) and global asteroseismic observables (Δν,νmax) of field stars. We also discussed the soundness of inferring a possible metallicity dependence of the mixing-length parameter from field stars.Methods. We followed a theoretical approach based on mock datasets of artificial stars sampled from a grid of stellar models with a fixed mixing-length parameterαml. We then recovered the mixing-length parameter of the mock stars by means of SCEPtER maximum-likelihood algorithm. We finally analysed the differences between the true and recovered mixing-length values quantifying the random errors due to the observational uncertainties and the biases due to possible discrepancies in the chemical composition and input physics between artificial stars and the models adopted in the recovery.Results. We verified that theαmlestimates are affected by a huge spread, even in the ideal configuration of perfect agreement between the mock data and the recovery grid of models. While the artificial stars were computed at fixed solar-calibratedαml = 2.10, the recovered values had a mean of 2.20 and a standard deviation of 0.52. Then we explored the case in which the solar heavy-element mixture used to compute the models is different from that adopted in the artificial stars. We found an estimated mixing-length mean of 2.24 ± 0.48 and, more interestingly, a metallicity relationship in whichαmlincreases by 0.4 for an increase of 1 dex in [Fe/H]. Thus, a simple heavy-element mixture mismatch induced a spurious, but statistically robust, dependence of the estimated mixing-length on metallicity. The origin of this trend was further investigated considering the differences in the initial helium abundanceY– [Fe/H] – initial metallicityZrelation assumed in the models and data. We found that a discrepancy between the adopted helium-to-metal enrichment ratio ΔY/ΔZcaused the appearance of spurious trends in the estimated mixing-length values. An underestimation of its value from ΔY/ΔZ = 2.0 in the mock data to ΔY/ΔZ = 1.0 in the recovery grid resulted in an increasing trend, while the opposite behaviour occurred for an equivalent overestimation. A similar effect was caused by an offset in the [Fe/H] to global metallicityZconversion. A systematic overestimation of [Fe/H] by 0.1 dex in the recovery grid of models forced an increasing trend ofαmlversus [Fe/H] of about 0.2 per dex. We also explored the impact of some possible discrepancies between the adopted input physics in the recovery grid of models and mock data. We observed an induced trend with metallicity of about Δαml = 0.3 per dex when the effect of the microscopic diffusion is neglected in the recovery grid, while no trends originated from a wrong assumption on the effective temperature scale by ±100 K. Finally, we proved that the impact of different assumptions on the outer boundary conditions was apparent only in the RGB phase.Conclusions. We showed that the mixing-length estimates of field stars are affected by a huge spread even in an ideal case in which the stellar models used to estimateαmlare exactly the same models as used to build the mock dataset. Moreover, we proved that there are many assumptions adopted in the stellar models used in the calibration that can induce spurious trend of the estimatedαmlwith [Fe/H]. Therefore, any attempt to calibrate the mixing-length parameter by means ofTeff, [Fe/H], Δν, andνmaxof field stars seems to be statistically poorly reliable. As such, any claim about the possible dependence of the mixing-length on the metallicity for field stars should be considered cautiously and critically.

Quantum phase transition in ultrahigh mobility SiGe/Si/SiGe two-dimensional electron system

The metal-insulator transition (MIT) is an exceptional test bed for studying strong electron correlations in two dimensions in the presence of disorder. In the present study, it is found that in contrast to previous experiments on lower-mobility samples, in ultra-high mobility SiGe/Si/SiGe quantum wells the critical electron density, $n_{\text{c}}$, of the MIT becomes smaller than the density, $n_{\text{m}}$, where the effective mass at the Fermi level tends to diverge. Near the topological phase transition expected at $n_{\text{m}}$, the metallic temperature dependence of the resistance should be strengthened, which is consistent with the experimental observation of more than an order of magnitude resistance drop with decreasing temperature below $\sim1$ K.

The AMBRE Project: [Y/Mg] stellar dating calibration with Gaia

Chemical abundance dating methods open new paths for temporal evolution studies of the Milky Way stellar populations. In this paper, we use a high spectral resolution database of turn-off stars in the solar neighbourhood to study the age dependence of the [Y/Mg] chemical abundance ratio. Our analysis reveals a clear correlation between [Y/Mg] and age for thin disc stars of different metallicities, in synergy with previous studies of solar-type stars. In addition, no metallicity dependence with stellar age is detected, allowing us to use the [Y/Mg] ratio as a reliable age proxy. Finally, the [Y/Mg]–age relation presents a discontinuity between thin and thick disc stars around 9–10 Gyr. For thick disc stars, the correlation has a different zero point and probably a steeper trend with age, reflecting the different chemical evolution histories of the two disc components.

Metallicity dependence of the Hercules stream in Gaia/RAVE data – explanation by non-closed orbits

The origin of the Hercules stream, the most prominent velocity substructure in the Solar neighbour disc stars, is still under debate. Recent accurate measurements of position, velocity, and metallicity provided by Tycho Gaia Astrometric Solution (TGAS) and RAdial Velocity Experiments (RAVE) have revealed that the Hercules stream is most clearly seen in the metal-rich region ([Fe/H] > 0), while it is not clearly seen in lower metallicity region ([Fe/H] < -0.25). By using a large number of chemo-dynamical 2D test-particle simulations with a rotating bar and/or spiral arms, we find that the observed [Fe/H] dependence of the Hercules stream is a natural consequence of the inside-out formation of the stellar disc and the existence of highly non-closed orbits in the rotating frame of the bar or spiral arms. Our successful models that reproduce the observed properties of the Hercules stream include not only fast-bar-only and fast-bar+spiral models, but also slow-bar+spiral models. This indicates that it is very difficult to estimate the pattern speed of the bar or spiral arms based only on the observations of the Hercules stream in the Solar neighbourhood. As a by-product of our simulations, we make some predictions about the locations across the Galactic plane where we can observe velocity bimodality that is not associated with the Hercules stream. These predictions can be tested by the Gaia Data Release 2, and such a test will improve our understanding of the evolution of the Milky Way stellar disc.

On a New Method to Estimate the Distance, Reddening, and Metallicity of RR Lyrae Stars Using Optical/Near-infrared (B, V, I, J, H, K) Mean Magnitudes: ω Centauri as a First Test Case

Abstract We developed a new approach to provide accurate estimates of the metal content, reddening, and true distance modulus of RR Lyrae stars (RRLs). The method is based on homogeneous optical (BVI) and near-infrared (JHK) mean magnitudes and on predicted period–luminosity–metallicity relations (IJHK) and absolute mean magnitude–metallicity relations (BV). We obtained solutions for three different RRL samples in ω Cen: first overtone (RRc, 90), fundamental (RRab, 80), and global (RRc+RRab) in which the period of first overtones were fundamentalized. The metallicity distribution shows a well defined peak at [Fe/H]∼−1.98 and a standard deviation of σ = 0.54 dex. The spread is, as expected, metal-poor ([Fe/H] ≤ −2.3) objects. The current metallicity distribution is ∼0.3 dex more metal-poor than similar estimates for RRLs available in the literature. The difference vanishes if the true distance modulus we estimated is offset by −0.06/−0.07 mag in true distance modulus. We also found a cluster true distance modulus of μ = 13.720 ± 0.002 ± 0.030 mag, where the former error is the error on the mean and the latter is the standard deviation. Moreover, we found a cluster reddening of E(B − V) = 0.132 ± 0.002 ± 0.028 mag and spatial variations of the order of a few arcmin across the body of the cluster. Both the true distance modulus and the reddening are slightly larger than similar estimates available in the literature, but the difference is within 1σ. The metallicity dependence of distance diagnostics agrees with theory and observations, but firm constraints require accurate and homogeneous spectroscopic measurements.

APOGEE DR14/DR15 Abundances in the Inner Milky Way

Abstract We present an overview of the distributions of 11 elemental abundances in the Milky Way’s (MW) inner regions, as traced by APOGEE stars released as part of the Sloan Digital Sky Survey Data Release 14/15 (DR14/DR15), including O, Mg, Si, Ca, Cr, Mn, Co, Ni, Na, Al, and K. This sample spans ∼4000 stars with R GC ≤ 4.0 kpc, enabling the most comprehensive study to date of these abundances and their variations within the innermost few kiloparsecs of the MW. We describe the observed abundance patterns ([X/Fe]–[Fe/H]), compare to previous literature results and to patterns in stars at the solar Galactocentric radius (R GC), and discuss possible trends with DR14/DR15 effective temperatures. We find that the position of the [Mg/Fe]–[Fe/H] “knee” is nearly constant with R GC, indicating a well-mixed star-forming medium or high levels of radial migration in the early inner Galaxy. We quantify the linear correlation between pairs of elements in different subsamples of stars and find that these relationships vary; some abundance correlations are very similar between the α-rich and α-poor stars, but others differ significantly, suggesting variations in the metallicity dependencies of certain supernova yields. These empirical trends will form the basis for more detailed future explorations and for the refinement of model comparison metrics. That the inner MW abundances appear dominated by a single chemical evolutionary track and that they extend to such high metallicities underscore the unique importance of this part of the Galaxy for constraining the ingredients of chemical evolution modeling and for improving our understanding of the evolution of the Galaxy as a whole.

Bright Type IIP Supernovae in Low-metallicity Galaxies

Abstract We present measurements of the pseudo-equivalent width of the Fe ii λ5018 absorption feature in the spectra of 12 Type IIP supernovae (SNe II) in low-luminosity (M &gt; −17) dwarf host galaxies. The Fe ii λ5018 line has been called a useful diagnostic of the metallicity of the supernova (SN) progenitor stars. The events in our sample were discovered photometrically by the PanSTARRS Survey for Transients, and classified spectroscopically by us. Comparing our sample to 24 literature SNe II, we find that those in low-luminosity hosts have significantly weaker Fe ii features, with a probability of 10−4 that the two samples are drawn from the same distribution. Because low-mass galaxies are expected to contain a lower fraction of metals, our findings are consistent with a metallicity dependence for Fe ii λ5018, and therefore support the use of this line as a metallicity probe, in agreement with a number of recent works. In addition, we find that the SNe in faint (low-metallicity) hosts may be more luminous on average than those in the literature sample, suggesting possible physical differences between Type IIP SNe at low and high metallicity. However, accurate determinations of host galaxy extinction will be needed to quantify such an effect.

Fabrication of high quality and large area graphite thin films by pyrolysis and graphitization of polyimides

We have developed large-area, high-quality graphite thin films that are 0.5–3 μm thick. To prepare the graphite films, we used pyrolysis and graphitization of polyimide up to temperatures in the range 2900 °C-3300 °C, which is applicable to industrial-production processing. Given that the graphite layers of the films are highly oriented in the surface plane, they have good physical properties. The resulting electrical conductivity of graphite film of thickness 1.4 μm and area 10 × 10 cm2 that was treated at 3200 °C is 24,800 S/cm, and the electrical conductivity showed metallic temperature dependence. The carrier mobility of the film is 11,700 V/cm2, and the carrier concentrations of electrons (Ne) and holes (Nh) are 6.98 × 1018 cm−3 and 5.90 × 1018 cm−3, respectively. We consider the high electrical conductivity and mobility to have been derived from the homogeneous, highly oriented graphite layers. We found that graphitization of films less than 3 μm thick progresses uniformly throughout the film, and the resulting graphite films have structures with uniform, highly oriented layers. The produced graphite thin films have excellent physical properties and can be easily handled, so we believe that many industrial applications are possible.

EoS Dependence of the Relic Supernova Neutrino Spectrum

Understanding the mechanism of core-collapse supernova explosions requires knowledge of the nuclear equation of state (EoS). Recent multi-dimensional numerical simulations indicate that explosions are possible. Nevertheless, it is not yet fully understood which equation of state is realized in the proto-neutron star formed during SN explosions. We examine the EoS sensitivity of the relic supernova neutrino spectrum as a probe of the nuclear EoS. This sensitivity arises largely from the contribution to neutrino emission from failed supernovae. We consider a variety of astrophysical scenarios, which include different progenitor masses for a successful explosion, the cosmological star formation rate, starbursts, quiescent star formation, and the metallicity dependence of the initial mass function. We find that the EoS signature remains robust under a variety of conditions. We demonstrate the viability of future neutrino detectors to distinguish the nuclear EoS via the relic supernova neutrino spectrum.

The non-uniformity of galaxy cluster metallicity profiles

We study a sample of 207 nearby galaxy groups and clusters observed with XMM-Newton. Key aspects of this sample include the large size, the high data quality, and the large diversity of cluster dynamical states. We determine the overall metallicity within 0.3R$_{500}$ and the radial distribution of the metals. On average, we find a mild dependence of the core metallicity with the average temperature of the system in agreement with previous results. However, we identify the cause of this mild dependence to be due to relaxed systems only; disturbed systems do not show this trend, on average. The large scatter observed in this relation is strongly associated with the dynamical state of the systems: relaxed systems have on average a higher metallicity in the core than disturbed objects. The radial profiles of relaxed systems are centrally peaked and show a steep decrease with radius, flattening beyond 0.3-0.4R$_{500}$. The metallicity of disturbed systems is also higher in the center but at much lower values than what is observed for relaxed objects. This finding is consistent with the picture that cluster mergers mix the abundance distribution by inducing large scale motions. The scatter of the radial profiles is quite large, but while for relaxed systems it decreases almost monotonically as function of the radius, for disturbed systems it shows a significant boost at large radii. Systems with a central radio source have a flatter profile indicating that central AGNs are an efficient mechanism to uplift and redistribute the metals in the ICM.

Towards the enzymatic formation of artificial metal base pairs with a carboxy-imidazole-modified nucleotide

The identification of synthetic nucleotides that sustain the formation of orthogonal, unnatural base pairs is an important goal in synthetic biology. Such artificial synthons have been used for the generation of semi-synthetic organisms as well as functional nucleic acids with enhanced binding properties. The enzymatic formation of artificial metal-base pairs is a vastly underexplored and alluring alternative to existing systems. Here, we report the synthesis and biochemical characterization of 1‑(2-deoxy‑β‑d‑ribofuranosyl) imidazole‑4‑carboxylate nucleoside triphosphate (dImCTP) which is equipped with a carboxylic acid moiety on the imidazole moiety in order to increase the coordination environment to [2 + 2] and [2 + 1]. A clear metal dependence was observed for the single incorporation of the modified nucleotide into DNA by the DNA polymerase from Thermus aquaticus (Taq). The presence of AgI in primer extension reactions conducted with combinations of 1‑(2‑deoxy‑β‑d‑ribofuranosyl) imidazole nucleoside triphosphate (dImTP) and dImCTP supported the unusual [2 + 1] coordination pattern. The efficiency of the tailing reactions mediated by the terminal deoxynucleotidyl transferase (TdT) was markedly improved when using dImCTP instead of dImTP. Even though products with multiple modified nucleotides were not observed, the appendage of additional metal binding ligands on the imidazole nucleobase appears to be a valid approach to improve the biochemical properties of modified triphosphates in the context of an expansion of the genetic alphabet with metal base pairs.

Isolation, Purification and Characterisation of a D-galactose and N-acetyl-D-galactosamine Specific Lectin from Marine Sponge Fasciospongia cavernosa.

Marine sponges, belonging to the phylum Porifera, are gaining more attention by researchers and industrial sectors from all over the world due to their ability to produce a variety of bioactive secondary metabolites that have many applications including drug discovery. Marine sponges are a promising source of bioactive lectins, which are structurally diverse, many of them in the form of glycoproteins. To purify and characterize lectin from a marine sponge Fasciospongia cavernosa and to study its antibacterial activity. Lectin from a marine sponge Fasciospongia cavernosa was purified by guar gum affinity chromatography and checked for its biophysical and antibacterial properties. The lectin was subjected to evaluation for inhibition of microbial growth against bacteria by aggregation test. The activity of FCL against the biofilms formed by P. aeruginosa was also carried out. Biofilm is defined as the undesirable accumulation of microorganisms on artificial surfaces immersed in a common matrix. The effect of FCL on biofilm-forming gram negative bacteria P. aeruginosa was tested by crystal violet assay. This lectin, named FCL, has a molecular weight of 80 KDa approximately, was found to agglutinate human ABO, rat, rabbit and chicken erythrocytes. The hemagglutinating activity of FCL was reduced by demetallisation with E.D.T.A and regained by the addition of Ca2+, Mg2+, Mn2+, Ba2+ and Fe2+, which shows the metal dependency of the lectin. The hemagglutinating activity by the lectin was inhibited by D-galactose and N-acetyl-D-galactosamine. The lectin was stable over a range of pH from 2 to 10.5, and up to a temperature 70°C for 20 min. FCL agglutinated B. subtilis, S. aureus and P. aeruginosa and was able to reduce biofilm mass formed by P. aeruginosa. Thus, the marine sponge F. cavernosa lectin, FCL could be used as an antibacterial agent. FCL significantly reduced the biomass of bacterial biofilm tested. Biofilm mass of P. aeruginosa, K. pneumoniae and E. coli were decreased in a dose dependent manner. A novel lectin was isolated and purified from marine sponge F. cavernosa. FCL, a galactose-binding lectin displayed considerable antimicrobial activity in vitro, particularly against gram-positive bacteria and also exhibited a strong antibiofilm activity.

The wide binary fraction of solar-type stars: emergence of metallicity dependence at a &amp;lt; 200 au

ABSTRACT We combine a catalogue of wide binaries constructed from Gaia DR2 with [Fe/H] abundances from wide-field spectroscopic surveys to quantify how the binary fraction varies with metallicity over separations 50 ≲ s/au ≲ 50 000. At a given distance, the completeness of the catalogue is independent of metallicity, making it straightforward to constrain intrinsic variation with [Fe/H]. The wide binary fraction is basically constant with [Fe/H] at large separations (s ≳ 250 au) but becomes quite rapidly anticorrelated with [Fe/H] at smaller separations: for 50 &amp;lt; s/au &amp;lt; 100, the binary fraction at $\rm [Fe/H] = -1$ exceeds that at $\rm [Fe/H] = 0.5$ by a factor of 3, an anticorrelation almost as strong as that found for close binaries with a &amp;lt; 10 au. Interpreted in terms of models where disc fragmentation is more efficient at low [Fe/H], our results suggest that 100 &amp;lt; a/au &amp;lt; 200 is the separation below which a significant fraction of binaries formed via fragmentation of individual gravitationally unstable discs rather than through turbulent core fragmentation. We provide a public catalogue of 8407 binaries within 200 pc with spectroscopically determined [Fe/H] for at least one component.

The Cepheid period–luminosity–metallicity relation based on Gaia DR2 data

Aims. We use parallax data from the Gaia second data release (GDR2), combined with parallax data based on HIPPARCOS and HST data, to derive the period–luminosity–metallicity (PLZ) relation for Galactic classical cepheids (CCs) in the V, K, and Wesenheit WVK bands. Methods. An initial sample of 452 CCs are extracted from the literature with spectroscopically derived iron abundances. Reddening values, classifications, pulsation periods, and mean V- and K-band magnitudes are taken from the literature. Based on nine CCs with a goodness-of-fit (GOF) statistic smaller than 8 and with an accurate non-Gaia parallax (σπ comparable to that in GDR2), a parallax zero-point offset of −0.049 ± 0.018 mas is derived. Selecting a GOF statistic smaller than 8 removes about 40% of the sample most likely related due to binarity. Excluding first overtone and multi-mode cepheids and applying some other criteria reduces the sample to about 200 stars. Results. The derived PL(Z) relations depend strongly on the parallax zero-point offset. The slope of the PL relation is found to be different from the relations in the LMC at the 3σ level. Fixing the slope to the value found in the LMC leads to a distance modulus (DM) to the LMC of order 18.7 mag, larger than the canonical distance. The canonical DM of around 18.5 mag would require a parallax zero-point offset of order −0.1 mas. Given the strong correlation between zero point, period and metallicity dependence of the PL relation, and the parallax zero-point offset there is no evidence for a metallicity term in the PLZ relation. Conclusions. The GDR2 release does not allow us to improve on the current distance scale based on CCs. The value of and the uncertainty on the parallax zero-point offset leads to uncertainties of order 0.15 mag on the distance scale. The parallax zero-point offset will need to be known at a level of 3 μas or better to have a 0.01 mag or smaller effect on the zero point of the PL relation and the DM to the LMC.