Metallicity Dependence Research Articles

The Relationship between Age, Metallicity, and Abundances for Disk Stars in a Simulated Milky Way

Observations of the Milky Way’s low-α disk show that several element abundances correlate with age at fixed metallicity, with unique slopes and small scatters around the age–[X/Fe] relations. In this study, we turn to simulations to explore the age–[X/Fe] relations for the elements C, N, O, Mg, Si, S, and Ca that are traced in a FIRE-2 cosmological zoom-in simulation of a Milky Way–like galaxy, m12i, and understand what physical conditions give rise to the observed age–[X/Fe] trends. We first explore the distributions of mono-age populations in their birth and current locations, [Fe/H], and [X/Fe], and find evidence for inside-out radial growth for stars with ages <7 Gyr. We then examine the age–[X/Fe] relations across m12i’s disk and find that the direction of the trends agrees with observations, apart from C, O, and Ca, with remarkably small intrinsic scatters, σ int (0.01 − 0.04 dex). This σ int measured in the simulations is also metallicity dependent, with σ int ≈ 0.025 dex at [Fe/H] = −0.25 dex versus σ int ≈ 0.015 dex at [Fe/H] = 0 dex, and a similar metallicity dependence is seen in the GALAH survey for the elements in common. Additionally, we find that σ int is higher in the inner galaxy, where stars are older and formed in less chemically homogeneous environments. The age–[X/Fe] relations and the small scatter around them indicate that simulations capture similar chemical enrichment variance as observed in the Milky Way, arising from stars sharing similar element abundances at a given birth place and time.

The evolving structure of the global mining industry,

The green energy transition has been called a transition from a fossil fuel dependency to a metal and mineral dependency. Concerns about the security of future supplies are raised mainly in the EU and the USA with the Critical Raw Materials Act and the Inflation Reduction Act. The perspectives of these policies are centred on the demands created in the industrialised countries. The need for metals to lift billions of poor people out of poverty and to cater for the population growth is often, if not always, left out of the equation. While demand undoubtedly is increasing, the opposition to new mines and new renewable energy supply is strong and perhaps even increasing. It is necessary to find new ways to create a recognition that mining plays a key role for the green transition.

Salt-Toggled Capture Selection of Uric Acid Binding Aptamers.

Uric acid is the end-product of purine metabolism in humans and an important biomarker for many diseases. To achieve the detection of uric acid without using enzymes, we previously selected a DNA aptamer for uric acid with a Kd of 1 μM but the aptamer required multiple Na+ ions for binding. Saturated binding was achieved with around 700 mM Na+ and the binding at the physiological condition was much weaker. In this work, a new selection was performed by alternating Mg2+ -containing buffers with Na+ and Li+ . After 13 rounds of selection, a new aptamer sequence named UA-Mg-1 was obtained. Isothermal titration calorimetry confirmed aptamer binding in both selection buffers, and the Kd was around 8 μM. The binding of UA-Mg-1 to UA required only Mg2+ . This is an indicator of successful switching of metal dependency via the salt-toggled selection method. The UA-Mg-1 aptamer was engineered into a fluorescent biosensor based on the strand-displacement assay with a limit of detection of 0.5 μM uric acid in the selection buffer. Finally, comparison with the previously reported Na+ -dependent aptamer and a xanthine/uric acid riboswitch was also made.

Double-mode RR Lyrae star — robust distance and metallicity indicators

AbstractRR Lyrae (RR Lyr) stars are a well-known and useful distance indicator for old stellar populations such as globular clusters and dwarf galaxies. Fundamental-mode RR Lyr (RRab) stars are commonly used to measure distances, and the accuracy of the determined distance is strongly constrained by metallicity. Here, we investigate the metallicity dependence in the period–luminosity (PL) relation of double-mode RR Lyr (RRd) stars. We find and establish a linear relation between metallicity and period or period ratio for RRd stars. This relation can predict the metallicity as accurately as the low-resolution spectra. Based on this relation, we establish a metallicity-independent PL relation for RRd stars. Combining the distance of the Large Magellanic Cloud and Gaia parallaxes, we calibrate the zero point of the derived PL relation to an error of 0.022 mag. Using RRd stars, we measure the distances of globular clusters and dwarf galaxies with an accuracy of 2-3% and 1-2%, respectively. In the future, RRd stars could anchor galaxy distances to an accuracy of 1.0% and become an independent distance ladder in the Local Group.

The catalytic mechanism, metal dependence, substrate specificity, and biodiversity of ribonuclease H.

Ribonucleoside monophosphates are inevitably misincorporated into the DNA genome inside cells, and they need to be excised to avoid chromosome instability. Ribonucleases H (RNases H) are enzymes that specifically hydrolyze the RNA strand of RNA/DNA hybrids or the RNA moiety from DNA containing a stretch of RNA, they therefore are required for DNA integrity. Extensive studies have drawn a mostly clear picture of the mechanisms of RNase H catalysis, but some questions are still lacking definitive answers. This review summarizes three alternative models of RNase H catalysis. The two-metal model is prevalent, but a three-metal model suggests the involvement of a third cation in catalysis. Apparently, the mechanisms underlying metal-dependent hydrolyzation are more complicated than initially thought. We also discuss the metal choices of RNases H and analyze how chemically similar cations function differently. Substrate and cleavage-site specificities vary among RNases H, and this is explicated in detail. An intriguing phenomenon is that organisms have diverse RNase H combinations, which may provide important hints to how rnh genes were transferred during evolution. Whether RNase H is essential for cellular growth, a key question in the study of in vivo functions, is also discussed. This article may aid in understanding the mechanisms underlying RNase H and in developing potentially promising applications of it.

The miniJPAS survey: stellar atmospheric parameters from 56 optical filters

ABSTRACT With a unique set of 54 overlapping narrow-band and two broader filters covering the entire optical range, the incoming Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) will provide a great opportunity for stellar physics and near-field cosmology. In this work, we use the miniJPAS data in 56 J-PAS filters and 4 complementary SDSS-like filters to explore and prove the potential of the J-PAS filter system in characterizing stars and deriving their atmospheric parameters. We obtain estimates for the effective temperature with a good precision (&amp;lt;150 K) from spectral energy distribution fitting. We have constructed the metallicity-dependent stellar loci in 59 colours for the miniJPAS FGK dwarf stars, after correcting certain systematic errors in flat-fielding. The very blue colours, including uJAVA − r, J0378 − r, J0390 − r, uJPAS − r, show the strongest metallicity dependence, around 0.25 mag dex−1. The sensitivities decrease to about 0.1 mag dex−1 for the J0400 − r, J0410 − r, and J0420 − r colours. The locus fitting residuals show peaks at the J0390, J0430, J0510, and J0520 filters, suggesting that individual elemental abundances such as [Ca/Fe], [C/Fe], and [Mg/Fe] can also be determined from the J-PAS photometry. Via stellar loci, we have achieved a typical metallicity precision of 0.1 dex. The miniJPAS filters also demonstrate strong potential in discriminating dwarfs and giants, particularly the J0520 and J0510 filters. Our results demonstrate the power of the J-PAS filter system in stellar parameter determinations and the huge potential of the coming J-PAS survey in stellar and Galactic studies.

An Improved Calibration of the Wavelength Dependence of Metallicity on the Cepheid Leavitt Law

The Cepheid period–luminosity (PL) relation (or Leavitt law) has served as the first rung of the most widely used extragalactic distance ladder and is central to the determination of the local value of the Hubble constant (H 0). We investigate the influence of metallicity on Cepheid brightness, a term that significantly improves the overall fit of the distance ladder, to better define its wavelength dependence. To this aim, we compare the PL relations obtained for three Cepheid samples having distinct chemical composition (in the Milky Way and Magellanic Clouds) and focusing on the use of improved and recent data while covering a metallicity range of about 1 dex. We estimate the metallicity effect (hereafter γ) in 15 filters from mid-IR to optical wavelengths, including five Wesenheit indices, and we derive a significant metallicity term in all filters, in agreement with recent empirical studies and models, in the sense of metal-rich Cepheids being brighter than metal-poor ones. We describe the contribution of various systematic effects in the determination of the γ term. We find no evidence of γ changing over the wavelength range 0.5–4.5 μm, indicating that the main influence of metallicity on Cepheids is in their luminosity rather than color. Finally, we identify factors that sharpen the empirical constraints on the metallicity term over past studies, including corrections for the depth of the Magellanic Clouds, better-calibrated Cepheid photometry, improved Milky Way extinction estimates, and revised and expanded metallicity measurements in the LMC.

Absolute Calibration of Cepheid Period–Luminosity Relations in NGC 4258

Owing to its accurate distance measured from water-maser motions, NGC 4258 is one of the most important anchors for calibrating the Cepheid period–luminosity relations (PLRs). We expand on previous efforts and carry out a new Cepheid search in this system using the Hubble Space Telescope. We discover and measure a sample of 669 Cepheids in four new and two archival NGC 4258 fields, doubling the number of known Cepheids in this galaxy and obtaining an absolute calibration of their optical PLRs. We determine a Wesenheit (W VI HST) PLR of , consistent with an independent Large Magellanic Cloud (LMC) calibration at the level of 0.032 ± 0.044 mag in its zero-point, after accounting for a metallicity dependence of −0.20 ± 0.05 mag dex−1. Our determination of the PLR slope also agrees with the LMC-based value within their uncertainties. We attempt to characterize the metallicity effect of Cepheid PLRs using only the NGC 4258 sample, but a relatively narrow span of abundances limits our sensitivity and yields a W VI HST zero-point dependence of −0.07 ± 0.21 mag dex−1. The Cepheid measurements presented in this study have been used as part of the data to derive the Hubble constant in a companion paper by the SH0ES team.

Fully Exposed Metal Clusters: Fabrication and Application in Alkane Dehydrogenation

Alkanes are the foremost basic energy sources and represent an important basic chemical material for industrial applications. Highly efficient activation of C–H bonds can convert abundant alkanes into value-added products, such as alkenes and their corresponding polymers. Therefore, C–H bond activation of alkanes has attracted widespread attention in heterogeneous catalysis. Fully exposed cluster catalysts (FECCs), as a bridge linking metal single atoms (SAs) and nanoparticles (NPs), have been widely studied for many catalytic reactions, especially for alkane dehydrogenation. On FECCs, the highly exposed active sites with multiple metal atoms can promote adsorption of alkanes and intermediates, thus enabling facile C–H activation. Moreover, the electron-rich surface can facilitate the desorption of products to suppress overdehydrogenation and coke formation. Therefore, FECCs have exhibited remarkable catalytic performance in alkane dehydrogenation, compared with SAs and NPs. In this Review, we highlight the developments on FECCs, including the structure design and their unique catalytic performance in dehydrogenation of alkanes. The synthetic methods to fabricate FECCs are discussed for alkane dehydrogenation. Subsequently, recent progresses on understanding the relationship between catalytic performance and geometric/electronic structure of FECCs are summarized, to provide the insights into the nature of structure dependence and metal dependence in alkane dehydrogenation. The strategies to stabilize FECCs for alkane dehydrogenation, including support confining and bimetallic system construction, are systematically reviewed to provide a useful guidance for the catalyst design. Lastly, major prospects in FECCs are illustrated from the viewpoint of alkane dehydrogenation.

A VINDICATION OF THE RR LYRAE FOURIER LIGHT CURVE DECOMPOSITION FOR THE CALCULATION OF METALLICITY AND DISTANCE IN GLOBULAR CLUSTERS

We report the mean metallicity and absolute magnitude of RR Lyrae stars in a sample of 37 globular clusters, calculated via the Fourier decomposition of their light curves and ad hoc semi-empirical calibrations, in an unprecedented homogeneous approach. This enabled a new discussion of the metallicity dependence of the horizontal branch (HB) luminosity, as a fundamental distance indicator. The calibration for the RRab and RRc stars should be treated separately. For the RRab the dispersion is larger and non-linear. For the RRc stars the correlation is less steep, very tight and linear. The relevance of the HB structural parameter L, is highlighted and we offer a non-linear calibration of the form MV ([Fe/H], L). Excellent agreement is found between values of [Fe/H] and MV from the light curve decomposition with spectroscopic values and distances obtained via Gaia-DR3 and HST. The variables census in 35 clusters includes 326 stars found by our program.

An Updated Metal-dependent Theoretical Scenario for Classical Cepheids

To properly quantify the possible residual systematic errors affecting the classical Cepheid distance scale, a detailed theoretical scenario is recommended. By extending the set of nonlinear, convective pulsation models published for Z = 0.02 to Z = 0.004, Z = 0.008, and Z = 0.03, we provide a detailed homogeneous, nonlinear model grid taking into account simultaneous variations of the mass–luminosity relation, the efficiency of superadiabatic convection, and the chemical composition. The dependence of the inferred period–radius, period–mass–radius, and period–mass–luminosity–temperature relations on the input parameters is discussed for both the fundamental and first overtone modes. The trend of the instability strip getting redder as the metallicity increases is confirmed for the additional mass–luminosity assumptions and mixing length values. From the obtained multifilter light curves, we derive the mean magnitudes and colors, and in turn the period–luminosity–color and period–Wesenheit relations, for each assumed chemical composition, mass–luminosity relation, and efficiency of superadiabatic convection. Application to a well-studied sample of Cepheids in the Large Magellanic Cloud allows us to constrain the dependence of the inferred distance modulus on the assumed mass–luminosity relation, and the inclusion of the metallicity term in the derivation of the period–Wesenheit relations allows us, for each assumed mass–luminosity relation, to predict the metallicity dependence of the Cepheid distance scale. The obtained metal-dependent, period–Wesenheit relations are compared with recent results in the literature and applied to a sample of Gaia Early Data Release 3 Galactic Cepheids with known metal abundances to derive individual parallaxes. The comparison of these predictions with Gaia results is finally discussed.

Thickness dependence of metal–insulator transition in SrMoO3 thin films

We have investigated the thickness-dependent transport properties of SrMoO3 thin films deposited on LaAlO3 substrates. Metal–insulator transitions (MITs) were observed in SrMoO3 thin films with thickness below 10 nm. The low-temperature resistivity of these films can be explained by quantum corrections of the conductivity. An insulating behavior is observed when the thickness becomes 3.5 nm, and the resistivity can be described by the variable range hopping model with 2D fitting. The magneto-transport measurement of an SrMoO3 thin film with small positive magnetoresistance confirms that the driving force behind MIT is the renormalized electron–electron interaction.

H2O2 activation by two-dimensional metal-organic frameworks with different metal nodes for micropollutants degradation: Metal dependence of boosting reactive oxygen species generation

The existence of organic micropollutants (OPMs) in water poses a considerable threat to the environment. A centralized approach towards pollutants abatement has dominated over the recent decades wherein heterogeneous Fenton-like based advanced oxidation processes can be a promising technology. The application of engineered nanomaterials offers more opportunities to enhance their catalyst properties. This study synthesizes a series of ultrathin two-dimensional (2D) Metal-organic frameworks (MOFs) nanosheets with tunable metal clusters. The formation of reactive oxygen species (•OH and 1O2) can be significantly boosted via transferring the adsorbed H2O2 onto the solid-liquid interface by systematically tuning the metal species. The Co-MOF nanosheets exhibited an ultrafast degradation kinetic for BPA with a rate of 2.23 min−1 (4.98 times higher than that of the bulk MOF) and TOF (turnover frequency) value of 9.99 min−1, which are observably greater than that of the existing materials reported to date. Density functional theory simulation and experimental results unravel the mechanism for ROS formation, which is strongly metal-depend. We further loaded the powder onto a flow-through poly (vinylidene fluoride) (PVDF) microfiltration membrane and observed that the representative OPMs could be rapidly degraded, indicating promising properties for practical application.

Protostellar-disc fragmentation across all metallicities

ABSTRACT Cosmic metallicity evolution possibly creates the diversity of star formation modes at different epochs. Gravitational fragmentation of circumstellar discs provides an important formation channel of multiple star systems, including close binaries. We here study the nature of disc fragmentation, systematically performing a suite of 2D radiation-hydrodynamic simulations, in a broad range of metallicities, from the primordial to the solar values. In particular, we follow relatively long-term disc evolution over 15 kyr after the disc formation, incorporating the effect of heating by the protostellar irradiation. Our results show that the disc fragmentation occurs at all metallicities 1–$0 \, \rm {Z}_{\odot }$, yielding self-gravitating clumps. Physical properties of the clumps, such as their number and mass distributions, change with the metallicity due to different gas thermal evolution. For instance, the number of clumps is the largest for the intermediate metallicity range of 10−2–$10^{-5} \, \rm {Z}_{\odot }$, where the dust cooling is effective exclusively in a dense part of the disc and causes the fragmentation of spiral arms, although the disc might fragment at a similar rate, also at lower metallicities 10−6–$0 \, \rm {Z}_{\odot }$ with higher spatial resolution. The disc fragmentation is more modest for 1–$0.1 \, \rm {Z}_{\odot }$, thanks to the disc stabilization by the stellar irradiation. Such metallicity dependence agrees with the observed trend that the close binary fraction increases with decreasing metallicity in the range of 1–$10^{-3} \, \rm {Z}_{\odot }$.

Unravelling UBC 274: A morphological, kinematical, and chemical analysis of a disrupting open cluster

Context.Open clusters in the process of disruption help to understand the formation and evolution of the Galactic disk. The wealth and homogeneity ofGaiadata have led to the discovery of several open clusters with signs of disruption. Detailed chemical information for these clusters is essential in order to study the timescales and interplay between the star formation process and cluster disruption.Aims.We perform a morphological, kinematic, and chemical analysis of the disrupting cluster UBC 274 (2.5 Gyr,d = 1778 pc), to study its global properties.Methods.We use HDBSCAN to obtain a new membership list up to 50 pc from its centre and up to magnitudeG = 19 usingGaiaEDR3 data. We use high-resolution and high signal-to-noise spectra to obtain atmospheric parameters of six giants and sub-giants, and individual abundances of 18 chemical species.Results.The cluster has a highly eccentric (0.93) component, tilted ∼10 deg with respect to the plane of the Galaxy, which is morphologically compatible with the results of a test-particle simulation of a disrupting cluster. Our abundance analysis shows that the cluster has a sub-solar metallicity of [Fe/H] = −0.08 ± 0.02. Its chemical pattern is compatible with that of Ruprecht 147, of similar age but located closer to the Sun, with the remarkable exception of neutron-capture elements, which present an overabundance of [n/Fe] ∼ 0.1.Conclusions.The cluster’s elongated morphology is associated with the internal part of its tidal tail, following the expected dynamical process of disruption. We find a significant sign of mass segregation, where the most massive stars appear 1.5 times more concentrated than other stars. The cluster’s overabundance of neutron-capture elements can be related to the metallicity dependence of the neutron-capture yields due to the secondary nature of these elements, predicted by some models. UBC 274 presents a high chemical homogeneity at the level of 0.03 dex in the sampled region of its tidal tails.

The redshift dependence of black hole mass distribution: is it reliable for standard sirens cosmology?

ABSTRACT An upper limit on the mass of a black hole set by the pair-instability supernovae (PISN) process can be useful in inferring the redshift of the gravitational wave (GW) sources by lifting the degeneracy between mass and redshift. However, for this technique to work, it is essential that the PISN mass scale is redshift independent or at least has a predictable redshift dependence. We show that the observed PISN mass scale can get smeared and the position of the PISN mass scale is likely to exhibit a strong redshift dependence due to a combined effect from the non-zero value of the delay time between the formation of a star and the merging of two black holes and the metallicity dependence of PISN mass scale. Due to the unknown form of the delay-time distribution, the redshift dependence of the PISN mass cutoff of the binary black holes (BBHs) cannot be well characterized and will exhibit a large variation with the change in redshift. As a result, the use of a fixed PISN mass scale to infer the redshift of the BBHs from the observed masses will be systematically biased. Though this uncertainty is not severe for the third observation run conducted by the LIGO–Virgo–KAGRA collaboration, in the future this uncertainty will cause a systematic error in the redshift inferred from the PISN mass scale. The corresponding systematic error will be a bottleneck in achieving a few per cent precision measurements of the cosmological parameters using this method in the future.

Two step synthesis of ultrathin transition metal tellurides

Transition metal tellurides (TMTs) are an exciting group of two-dimensional materials with a wide variety of polytypes and properties. Here, we demonstrate a simple and versatile two-step method for producing MoTe2, WTe2, and PtTe2 films via tellurization of thin metals at temperatures between 400 and 700 °C. Across this temperature range, monoclinic 1T′ phase of MoTe2, orthorhombic Td phase of WTe2, and hexagonal 2H phase of PtTe2 were formed. Based on x-ray diffraction and Raman analysis, temperatures greater than 600 °C were found to produce the best quality MoTe2 and WTe2. In contrast, lower temperatures (400 °C) were preferred for PtTe2, which becomes discontinuous and eventually decomposes above 650 °C. The presence of H2 in the tellurization process was critical to facilitate the formation of H2Te, which is known to be more reactive than Te vapor. In the absence of H2, neither MoTe2 nor WTe2 formed, and although PtTe2 was formed under pure N2, the crystal quality was significantly reduced. Temperature-dependent resistivity (ρ) measurements were performed on the best quality TMT films revealing all films to be highly conductive. MoTe2 showed metallic behavior up to 205 K where it underwent a phase transition from the semimetallic Td to semiconducting 1T′ phase. WTe2 exhibited a consistent semiconducting behavior with a small positive increase in ρ with decreasing temperature, and PtTe2 showed a metallic dependence from 10 K up to room temperature. Spectroscopic ellipsometry for TMT films provides complex optical constants n and k from ultraviolet to infrared.

Structural Phase Transition and Possible Valence Instability of Ce-4f Electron Induced by Pressure in CeCoSi

X-ray powder diffraction and electrical resistivity measurements were performed on the tetragonal compound CeCoSi under pressure to elucidate the phase boundary of the pressure-induced structural transition and the change in the 4$f$ electronic state. The temperature-pressure phase diagram has been determined from the shift of the Bragg peaks and from the anomaly in the resistivity. The critical pressure, $P_{\rm s}$ $\sim$ 4.9 GPa at 300 K, decreases to $P_{\rm s}$ $\sim$ 3.6 GPa at 10 K. The decrease of $P_{\rm s}$ is due not only to the decrease in volume of the unit cell but also to an anisotropic shrinkage by cooling. When crossing the boundary to the high-pressure phase, the resistivity shows a significant drop to exhibit a metallic temperature dependence. The results of this study strongly suggest that the structural phase transition can be ascribed to valence instability of Ce-$4f$ electron.

Not That Simple: The Metallicity Dependence of the Wide Binary Fraction Changes with Separation and Stellar Mass

The metallicity dependence of the wide binary fraction (WBF) is critical for studying the formation of wide binaries. While controversial results have been found in recent years, here we combine the wide binary catalog recognized from Gaia EDR3 and stellar parameters from LAMOST to investigate this topic. Taking the bias of the stellar temperature at given separations into account, we find that the relationship between the WBF and metallicity depends on the temperature for the thin disk at s > 200 au. It changes from negative to positive as the temperature increases from 4000 to 7500 K. This temperature/mass dependence is not seen for the thick disk. Besides, the general tendency between the WBF and metallicity varies with the separation, consistent with previous results. It shows anticorrelation at small separations, s < 200 au for the thin disk and s < 600 au for the thick disk. Then it becomes an “arcuate” shape at larger separations (hundreds to thousands of astronomical units), peaking at [Fe/H] ≈0.1 for the thin disk and [Fe/H] ≈−0.5 for the thick disk. Finally it becomes roughly flat for the thin disk at 1000 < s < 10,000 au. Our work provides new observational evidence for theoretical studies on binary formation and evolution.

The iron and oxygen content of LMC Classical Cepheids and its implications for the extragalactic distance scale and Hubble constant

Classical Cepheids are primary distance indicators and a crucial stepping stone to determining the present-day Hubble constant Ho to the precision and accuracy required to constrain apparent deviations from the LCDM Concordance Cosmological Model. We have measured the iron and oxygen abundances of of 89 Cepheids in the LMC, one of the anchors of the local Distance Scale, quadrupling the prior sample and including 68 of the 70 Cepheids used to constrain Ho by the SH0ES program. The goal is to constrain the extent to which the Cepheid luminosity is influenced by their chemical composition, an important contributor to the uncertainty on the determination of the Ho itself and a critical factor in the internal consistency of the distance ladder. We have derived stellar parameters and abundances from a self-consistent spectroscopic analysis based on Equivalent Width of absorption lines. The [Fe/H] distribution of LMC Cepheids is a single Gaussian with a mean of -0.4079+-0.003 dex (0.1 dex systematic uncertainty) and sigma 0.076+-0.003 dex. The latter is fully compatible with the measurement error and supports the low dispersion of 0.069 mag seen in the NIR HST LMC period-luminosity relation. The uniformity of the abundance has the important consequence that the LMC Cepheids alone cannot provide any meaningful constraint on the dependence of the Cepheid Period-Luminosity relation on chemical composition at any wavelength. This revises a prior claim based on a small sample of 22 LMC Cepheids that there was little dependence (or uncertainty) between composition and NIR luminosity, a conclusion which would produce a conflict between anchors of the distance ladder with different mean abundance. The chemical homogeneity of the LMC Cepheid population makes it an ideal environment to calibrate the metallicity dependence between the more metal poor SMC and metal rich Milky Way and NGC4258.