Abundance Dispersion Research Articles

Fluorine Abundances in Local Stellar Populations

We present the first fluorine measurements in 12 normal K giants belonging to the Galactic thin and thick disks using spectra obtained with the Phoenix infrared spectrometer on the 2.1 m telescope at Kitt Peak. Abundances are determined from the (1−0) R9 2.3358 μm feature of the molecule HF. Additionally, sodium abundances are derived in 25 giants in the thin disk, thick disk, and halo using the Na i line at 2.3379 μm. We report fluorine abundances for thin and thick disk stars in the metallicity range −0.7 < [Fe/H] < 0. We add two abundance measurements for stars with [Fe/H] < 0.5 dex, which are at a critical metallicity range to constrain models. We find a larger dispersion in fluorine abundances than sodium abundances despite both species having similar overall uncertainties due to atmospheric parameters, suggesting this dispersion is real and not observational. The dispersion is slightly larger in the thick disk than the thin. The thin and thick disk average [F/Fe] for our sample of stars combined with the literature differ by 0.03 dex. The observations are compared to available chemical evolution models.

The R-Process Alliance: detailed chemical composition of an r-process enhanced star with UV and optical spectroscopy

ABSTRACT We present a detailed chemical-abundance analysis of a highly r-process-enhanced (RPE) star, 2MASS J00512646-1053170, using high-resolution spectroscopic observations with Hubble Space Telescope/STIS in the UV and Magellan/MIKE in the optical. We determined abundances for 41 elements in total, including 23 r-process elements and rarely probed species such as Al ii, Ge i, Mo ii, Cd i, Os ii, Pt i, and Au i. We find that [Ge/Fe] = +0.10, which is an unusually high Ge enhancement for such a metal-poor star and indicates contribution from a production mechanism decoupled from that of Fe. We also find that this star has the highest Cd abundance observed for a metal-poor star to date. We find that the dispersion in the Cd abundances of metal-poor stars can be explained by the correlation of Cd i abundances with the stellar parameters of the stars, indicating the presence of NLTE effects. We also report that this star is now only the sixth star with Au abundance determined. This result, along with abundances of Pt and Os, uphold the case for the extension of the universal r-process pattern to the third r-process peak and to Au. This study adds to the sparse but growing number of RPE stars with extensive chemical-abundance inventories and highlights the need for not only more abundance determinations of these rarely probed species, but also advances in theoretical NLTE and astrophysical studies to reliably understand the origin of r-process elements.

R-process Abundance Patterns in the Globular Cluster M92

Whereas light-element abundance variations are a hallmark of globular clusters, there is little evidence for variations in neutron-capture elements. A significant exception is M15, which shows a star-to-star dispersion in neutron-capture abundances of at least one order of magnitude. The literature contains evidence both for and against a neutron-capture dispersion in M92. We conducted an analysis of archival Keck/HIRES spectra of 35 stars in M92, 29 of which are giants, which we use exclusively for our conclusions. M92 conforms to the abundance variations typical of massive clusters. Like other globular clusters, its neutron-capture abundances were generated by the r-process. We confirm a star-to-star dispersion in r-process abundances. Unlike M15, the dispersion is limited to “first-generation” (low-Na, high-Mg) stars, and the dispersion is smaller for Sr, Y, and Zr than for Ba and the lanthanides. This is the first detection of a relation between light-element and neutron-capture abundances in a globular cluster. We propose that a source of the main r-process polluted the cluster shortly before or concurrently with the first generation of star formation. The heavier r-process abundances were inhomogeneously distributed while the first-generation stars were forming. The second-generation stars formed after several crossing times (∼0.8 Myr); hence, the second generation shows no r-process dispersion. This scenario imposes a minimum temporal separation of 0.8 Myr between the first and second generations.

Inhomogeneous Galactic chemical evolution: modelling ultra-faint dwarf galaxies of the Large Magellanic Cloud

ABSTRACT Ultra-faint dwarf galaxies (UFDs) are among the oldest and most metal-poor galaxies in the cosmos, observed to contain no gas and a high dark matter mass fraction. Understanding the chemical abundance dispersion in such extreme environments could shed light on the very first generations of stars. We present a novel inhomogeneous chemical evolution model, i-getool, that we apply to two UFDs, Carina II and Reticulum II, both satellites of the Large Magellanic Cloud. Our model is based on the Monte Carlo sampling of the initial mass function as star formation proceeds in different gas cells of the galaxy volume. We account for the chemical enrichment of supernova (SN) bubbles as they spread in the interstellar medium, causing dispersion in the elemental abundances. We recreate the abundance patterns of α- and odd-Z elements, predicting two sequences in [C/Fe] and [N/Fe] at all metallicities. Our models underestimate [C/Fe] and [Ti/Fe] because of the large uncertainty in the adopted stellar nucleosynthesis yields. We discuss that the observed C and N abundances had likely been affected by internal mixing processes, which changed the initial surface abundances in the red giants. Our SN feedback scheme is responsible for driving galactic outflows, which quench the star formation activity at early times. We predict an average outflow mass-loading factor ≈103, which extrapolates towards very low galaxy stellar masses the trend observed at high masses. Finally, by combining our model with the MIST isochrone database, we compare our synthetic colour–magnitude diagrams to observations.

Untangling the Sources of Abundance Dispersion in Low-metallicity Stars

We measure abundances of 12 elements (Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni) in a sample of 86 metal-poor (−2 ≲ [Fe/H] ≲ −1) subgiant stars in the solar neighborhood. Abundances are derived from high-resolution spectra taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope, modeled using iSpec and MOOG. By carefully quantifying the impact of photon-noise (<0.05 dex for all elements), we robustly measure the intrinsic scatter of abundance ratios. At fixed [Fe/H], the rms intrinsic scatter in [X/Fe] ranges from 0.04 (Cr) to 0.16 dex (Na), with a median of 0.08 dex. Scatter in [X/Mg] is similar, and accounting for [α/Fe] only reduces the overall scatter moderately. We consider several possible origins of the intrinsic scatter with particular attention to fluctuations in the relative enrichment by core-collapse supernovae (CCSN) and Type Ia supernovae and stochastic sampling of the CCSN progenitor mass distribution. The stochastic sampling scenario provides a good quantitative explanation of our data if the effective number of CCSN contributing to the enrichment of a typical sample star is N ∼ 50. At the median metallicity of our sample, this interpretation implies that the CCSN ejecta are mixed over a gas mass ∼6 × 104 M ⊙ before forming stars. The scatter of elemental abundance ratios is a powerful diagnostic test for simulations of star formation, feedback, and gas mixing in the early phases of the Galaxy.

Multiple Populations in Low-mass Globular Clusters: Eridanus

Multiple populations (MPs), characterized by variations in light elemental abundances, have been found in stellar clusters in the Milky Way, Magellanic Clouds, as well as several other dwarf galaxies. Based on a large number of observations, mass has been suggested to be a key parameter affecting the presence and appearance of MPs in stellar clusters. To further investigate the existence of MPs in low-mass clusters and explore the mass threshold for the formation of MPs, we carried out a project studying the composition of the stellar population in several low-mass Galactic globular clusters. Here we present our study on the cluster Eridanus. With blue-UV low-resolution spectra obtained with the OSIRIS/Multi-object spectrograph on the Gran Telescopio Canarias, we computed the spectral indices of CH and CN for a sample of giant stars and derived their carbon and nitrogen abundances using model spectra. A significant dispersion in the initial surface abundance of nitrogen was found in the sample, indicating the existence of MPs in Eridanus. Inspecting the age–initial mass distribution of in situ clusters with MPs, we find a slight trend that initial mass increases with increasing age, and the lowest initial masses of ∼ 4.98 and 5.26 are found at the young and old end, respectively, which might provide a rough reference for the mass threshold for clusters to form MPs. However, more observations of clusters with low initial masses are still necessary before any firm conclusion can be drawn.

CHAOS. VII. A Large-scale Direct Abundance Study in M33

The dispersion in chemical abundances provides a very strong constraint on the processes that drive the chemical enrichment of galaxies. Due to its proximity, the spiral galaxy M33 has been the focus of numerous chemical abundance surveys to study the chemical enrichment and dispersion in abundances over large spatial scales. The CHemical Abundances Of Spirals project has observed ∼100 H ii regions in M33 with the Large Binocular Telescope (LBT), producing the largest homogeneous sample of electron temperatures (T e ) and direct abundances in this galaxy. Our LBT observations produce a robust oxygen abundance gradient of −0.037 ± 0.007 dex kpc−1 and indicate a relatively small (0.043 ± 0.015 dex) intrinsic dispersion in oxygen abundance relative to this gradient. The dispersions in N/H and N/O are similarly small, and the abundances of Ne, S, Cl, and Ar relative to O are consistent with the solar ratio as expected for α-process or α-process-dependent elements. Taken together, the ISM in M33 is chemically well-mixed and homogeneously enriched from inside out, with no evidence of significant abundance variations at a given radius in the galaxy. Our results are compared to those of the numerous studies in the literature, and we discuss possible contaminating sources that can inflate abundance dispersion measurements. Importantly, if abundances are derived from a single T e measurement and T e –T e relationships are relied on for inferring the temperature in the unmeasured ionization zone, this can lead to systematic biases that increase the measured dispersion up to 0.11 dex.

The Pristine survey – XVII. The C-19 stream is dynamically hot and more extended than previously thought

ABSTRACT The C-19 stream is the most metal-poor stellar system ever discovered, with a mean metallicity [Fe/H] = −3.38 ± 0.06. Its low metallicity dispersion (σ[Fe/H] &amp;lt; 0.18 at the 95 per cent confidence level) and variations in sodium abundances strongly suggest a globular cluster origin. In this work, we use Very Large Telescope (VLT)/UV–Visual Echelle Spectrograph (UVES) spectra of seven C-19 stars to derive more precise velocity measurements for member stars, and to identify two new members with radial velocities and metallicities consistent with the stream’s properties. One of these new member stars is located 30° away from the previously identified body of C-19, implying that the stream is significantly more extended than previously known and that more members likely await discovery. In the main part of C-19, we measure a radial velocity dispersion σv = 6.2$^{+2.0}_{-1.4}{\rm \, km\, s^{-1}}$ from nine members, and a stream width of 0.56° ± 0.08°, equivalent to ∼158 pc at a heliocentric distance of 18 kpc. These confirm that C-19 is comparatively hotter, dynamically, than other known globular cluster streams and shares the properties of faint dwarf galaxy streams. On the other hand, the variations in the Na abundances of the three newly observed bright member stars, the variations in Mg and Al for two of them, and the normal Ba abundance of the one star where it can be measured provide further evidence for a globular cluster origin. The tension between the dynamical and chemical properties of C-19 suggests that its progenitor experienced a complex birth environment or disruption history.

A GALAH view of the chemical homogeneity and ages of stellar strings identified in Gaia

ABSTRACT The advent of Gaia has led to the discovery of nearly 300 elongated stellar associations (called ‘strings’) spanning hundreds of parsecs in length and mere tens of parsecs in width. These newfound populations present an excellent laboratory for studying the assembly process of the Milky Way thin disc. In this work, we use data from GALAH DR3 to investigate the chemical distributions and ages of 18 newfound stellar populations, 10 of which are strings and 8 of which are compact in morphology. We estimate the intrinsic abundance dispersions in [X/H] of each population and compare them with those of both their local fields and the open cluster (OC) M 67. We find that all but one of these groups are more chemically homogeneous than their local fields. Furthermore, half of the strings, namely Theias 139, 169, 216, 303, and 309, have intrinsic [X/H] dispersions that range between 0.01 and 0.07 dex in most elements, equivalent to those of many OCs. These results provide important new observational constraints on star formation and the chemical homogeneity of the local interstellar medium (ISM). We investigate each population’s Li and chemical clock abundances (e.g. [Sc/Ba], [Ca/Ba], [Ti/Ba], and [Mg/Y]) and find that the ages suggested by chemistry generally support the isochronal ages in all but six structures. This work highlights the unique advantages that chemistry holds in the study of kinematically related stellar groups.

The impact of turbulent mixing on the galactic r-process enrichment by binary neutron star mergers

ABSTRACT We study the enrichment of the interstellar medium (ISM) with rapid neutron capture (r-process) elements produced in binary neutron star (BNS) mergers. We use a semi-analytic model to describe galactic evolution, with merger rates and time delay distributions of BNS mergers consistent with the latest population synthesis models. In order to study the dispersion of the relative abundances of r-process elements and iron, we applied a turbulent mixing scheme, where the freshly synthesized elements are gradually dispersed in the ISM. We show that within our model the abundances observed in Milky Way stars, in particular the scatter at low metallicities, can be entirely explained by BNS mergers. Our results suggest that BNS mergers could be the dominant source of r-process elements in the Galaxy.

Matter accretion in metal-poor stars down to extremely metal-poor stars and the lithium problem

Context. The formation and evolution of light elements in the Universe act as important cosmological constraints. It has long been assumed that the oldest stars of the Galaxy display the primordial lithium abundance in their outer layers, although studies of stellar physics have proven that this abundance must have decreased with time. The primordial Li abundance deduced from the observations of the cosmic background is, indeed, larger than the maximum observed in these stars. Recent observations have given evidence of a large Li abundance dispersion in very metal-poor stars. Many of these stars are carbon-rich, that is, the so-called carbon-enhanced metal-poor (CEMP) stars. A large number of them also present overabundances of s process elements (CEMP-s). Aims. We address the general question of the observed abundances in metal-poor stars and we focus our study on the case of CEMP-s stars. We study how the accretion of the wind of stellar companions, especially asymptotic giant branch stars, modifies the element abundances of metal-poor stars and, in particular, lithium, taking into account the stellar structure and the hydrodynamic processes that take place after accretion. We compare the results with the observations of lithium and heavier elements in these old stars on the main sequence. Methods. We use the Montréal/Montpellier stellar evolution code, which includes atomic diffusion and thermohaline convection, to compute the internal structure of the proto-CEMP-s stars and their evolution, from [Fe/H] = −2.31 down to [Fe/H] = −5.45. We study a number of cases that vary according to the masses of the stars, their ages, metallicities, and the distances to their respective companions. Results. We show that the observations of lithium dispersion that is associated (or not) with carbon enrichment are well accounted for in terms of accretion on to the metal-poor stars of the winds of stellar companions, with accreted masses smaller than those considered in previous studies. The derived primordial value is in accordance with the cosmological results.

Floodplain land cover affects biomass distribution of fish functional diversity in the Amazon River

Land-cover change often shifts the distribution of biomass in animal communities. However, the effects of land-cover changes on functional diversity remain poorly understood for many organisms and ecosystems, particularly, for floodplains. We hypothesize that the biomass distribution of fish functional diversity in floodplains is associated with land cover, which would imply that fish traits affect behavioral and/or demographic responses to gradients of land cover. Using data from surveys of 462 habitats covering a range of land-cover conditions in the Amazon River floodplain, we fitted statistical models to explain landscape-scale variation in functional diversity and biomass of all fish species as well as subsets of species possessing different functional traits. Forest cover was positively associated with fish biomass and the strength of this relationship varied according to functional groups defined by life history, trophic, migration, and swimming-performance/microhabitat-use traits. Forty-two percent of the functional groups, including those inferred to have enhanced feeding opportunities, growth, and/or reproductive success within forested habitats, had greater biomass where forest cover was greater. Conversely, the biomass of other functional groups, including habitat generalists and those that directly exploit autochthonous food resources, did not vary significantly in relation to forest cover. The niche space occupied by local assemblages (functional richness) and dispersion in trait abundances (functional dispersion) tended to increase with forest cover. Our study supports the expectation that deforestation in the Amazon River floodplain affects not only fish biomass but also functional diversity, with some functional groups being particularly vulnerable.

Non-LTE chemical abundances in Galactic open and globular clusters

Aims. We study the effects of non-local thermodynamic equilibrium (NLTE) on the determination of stellar parameters and abundances of Fe, Mg, and Ti from the medium-resolution spectra of FGK stars. Methods. We extended the Payne fitting approach to draw on NLTE and LTE spectral models. These were used to analyse the spectra of the Gaia-ESO benchmark stars and the spectra of 742 stars in 13 open and globular clusters in the Milky Way: NGC 3532, NGC 5927, NGC 2243, NGC 104, NGC 1851, NGC 2808, NGC 362, M 2, NGC 6752, NGC 1904, NGC 4833, NGC 4372, and M15. Results. Our approach accurately recovers effective temperatures, surface gravities, and abundances of the benchmark stars and clusters members. The differences between NLTE and LTE are significant in the metal-poor regime, [Fe/H] ≲ −1. The NLTE [Fe/H] values are systematically higher, whereas the average NLTE [Mg/Fe] abundance ratios are ∼0.15 dex lower, compared to LTE. Our LTE measurements of metallicities and abundances of stars in Galactic clusters are in a good agreement with the literature. Though, for most clusters, our study yields the first estimates of NLTE abundances of Fe, Mg, and Ti. Conclusion. All clusters investigated in this work are homogeneous in Fe and Ti, with the intra-cluster abundance variations of less then 0.04 dex. NGC 2808, NGC 4833, M 2, and M 15 show significant dispersions in [Mg/Fe]. Contrary to common assumptions, the NLTE analysis changes the mean abundance ratios in the clusters, but it does not influence the intra-cluster abundance dispersions.

Catalog of Chromium, Cobalt, and Nickel Abundances in Globular Clusters and Dwarf Galaxies*

Abstract We present measurements of the abundances of chromium, cobalt, and nickel in 4113 red giants, including 2277 stars in globular clusters (GCs), 1820 stars in the Milky Way’s dwarf satellite galaxies, and 16 field stars. We measured the abundances from mostly archival Keck/DEIMOS medium-resolution spectroscopy with a resolving power of R ∼ 6500 and a wavelength range of approximately 6500–9000 Å. The abundances were determined by fitting spectral regions that contain absorption lines of the elements under consideration. We used estimates of temperature, surface gravity, and metallicity that we previously determined from the same spectra. We estimated systematic error by examining the dispersion of abundances within mono-metallic GCs. The median uncertainties for [Cr/Fe], [Co/Fe], and [Ni/Fe] are 0.20, 0.20, and 0.13, respectively. Finally, we validated our estimations of uncertainty through duplicate measurements, and we evaluated the accuracy and precision of our measurements through comparison to high-resolution spectroscopic measurements of the same stars.

Cosmological evolution of the nitrogen abundance

The abundance of nitrogen in the interstellar medium is a powerful probe of star for- mation processes over cosmological timescales. Since nitrogen can be produced both in massive and intermediate-mass stars with metallicity-dependent yields, its evolution is challenging to model, as evidenced by the differences between theoretical predictions and observations. In this work we attempt to identify the sources of these discrepancies using a cosmic evolution model. To further complicate matters, there is considerable dispersion in the abundances from observations of DLAs at redshift 2 - 3. We study the evolution of nitrogen with a detailed chemical evolution model and find good agreement with observations, including the relative abundances of N/O and N/Si ratios. We find that the principal contribution of nitrogen comes from intermediate mass stars, with the exception of systems with the lowest N/H, where nitrogen production might possibly be dominated by massive stars. This last result could be strengthened if stellar rotation which is important at low metallicity can produce significant amounts of nitrogen. Moreover, these systems likely reside in host galaxies with stellar masses below 10**8.5 solar mass. We also study the origin of the observed dispersion in nitrogen abundances using the cosmological hydrodynamical simulations Horizon-AGN. We conclude that this dispersion can originate from two effects: differ- ence in the masses of the DLA host galaxies, and difference in the their position inside the galaxy.

Sodium abundances of AGB and RGB stars in Galactic globular clusters

Aims. We investigate the Na abundance distribution of asymptotic giant branch (AGB) stars in Galactic globular clusters (GCs) and its possible dependence on GC global properties, especially age and metallicity. Methods. We analyze high-resolution spectra of a large sample of AGB and red giant branch (RGB) stars in the Galactic GCs NGC 104, NGC 6121, and NGC 6809 obtained with FLAMES/GIRAFFE at ESO/VLT, and determine their Na abundances. This is the first time that the AGB stars in NGC 6809 are targeted. Moreover, to investigate the dependence of AGB Na abundance dispersion on GC parameters, we compare the AGB [Na/H] distributions of a total of nine GCs, with five determined by ourselves with homogeneous method and four from literature, covering a wide range of GC parameters. Results. NGC 104 and NGC 6809 have comparable AGB and RGB Na abundance distributions revealed by the K−S test, while NGC 6121 shows a lack of very Na-rich AGB stars. By analyzing all nine GCs, we find that the Na abundances and multiple populations of AGB stars form complex picture. In some GCs, AGB stars have similar Na abundances and/or second-population fractions as their RGB counterparts, while some GCs do not have Na-rich second-population AGB stars, and various cases exist between the two extremes. In addition, the fitted relations between fractions of the AGB second population and GC global parameters show that the AGB second-population fraction slightly anticorrelates with GC central concentration, while no robust dependency can be confirmed with other GC parameters. Conclusions. Current data roughly support the prediction of the fast-rotating massive star (FRMS) scenario. However, considering the weak observational and theoretical trends where scatter and exceptions exist, the fraction of second-population AGB stars can be affected by more than one or two factors, and may even be a result of stochasticity.

Identification of Cupressaceae species from airborne pollen grains using chloroplastic markers: implications for reproductive interference evaluation in a remnant natural population of Chamaecyparis pisifera (Sieb. et Zucc.) Endl

ABSTRACTMany wild populations of Chamaecyparis pisifera (Cupressaceae) are recently fragmented and surrounded by coniferous plantations. To distinguish the species composition of pollens that are dispersed to female flowers of C. pisifera, genetic markers (Chaps-trnL01 and Chaps-trnL02) were developed based on the differences in trnL (UAA) intron region of chloroplast DNA. This region in C. pisifera contains the site of the Cla I restriction enzyme and allows the distinction of C. pisifera from other Cupressaceae species after digestion of the products with the enzyme resulting in the development of cleaved amplified polymorphic sequence (CAPS) markers. The availability of markers was determined by single-pollen genotyping. Amplification success rates of 75.0, 58.3, and 100% were obtained for the pollens of C. pisifera, Chamaecyparis obtusa, and Cryptomeria japonica, respectively. Then, the markers and genotyping methods were applied to airborne pollen grains sampled from a remnant natural stand of C. pisifera. Over 90% of the pollen grains were identified as belonging to C. obtusa. Thus, we concluded that abundant heterospecific pollen dispersal was present during the flowering periods of C. pisifera. These results suggest that the remnant C. pisifera population might suffer reproductive interference due to the lower chances to be pollinated with conspecific pollens.

Rotational mixing in Be stars: nitrogen abundances for a sample of Be stars from the MiMeS survey

Photospheric nitrogen abundances for a sample of 26 Be stars and 16 normal B stars were found using high-resolution spectra from the Magnetism in Massive Stars (MiMeS) spectroscopic survey. Nitrogen abundances were obtained using non-LTE equivalent widths and line profiles, and Monte Carlo simulation was used to determine the error bounds of the measured nitrogen abundances due to uncertainties in the adopted stellar parameters, continuum normalization, and atomic data. In addition, the effects of the gravitational darkening and disk contamination on the measured Be star nitrogen abundances were investigated. About one third of the sample Be stars and half of the normal B-type stars have nitrogen enrichments that may be due to rotational mixing in these rapidly rotating objects. Corrections for gravitational darkening and disk contamination do not significantly change the overall results for the Be star sample. The average nitrogen abundance of the B and Be star samples coincide with the solar abundance, although the dispersion in the nitrogen abundances is much larger in the Be star sample. The Be star sample also has a significant fraction of sub-solar nitrogen abundance objects which are not present in significant numbers in the B star sample. This may point to yet unresolved systematic errors in the analysis of the Be stars

Chemical Complexity in the Eu-enhanced Monometallic Globular NGC 5986∗

Abstract NGC 5986 is a poorly studied but relatively massive Galactic globular cluster that shares several physical and morphological characteristics with “iron-complex” clusters known to exhibit significant metallicity and heavy-element dispersions. In order to determine whether NGC 5986 joins the iron-complex cluster class, we investigated the chemical composition of 25 red giant branch and asymptotic giant branch cluster stars using high-resolution spectra obtained with the Magellan-M2FS instrument. Cluster membership was verified using a combination of radial velocity and [Fe/H] measurements, and we found the cluster to have a mean heliocentric radial velocity of +99.76 km s−1 (σ = 7.44 km s−1). We derived a mean metallicity of [Fe/H] = −1.54 dex (σ = 0.08 dex), but the cluster’s small dispersion in [Fe/H] and low [La/Eu] abundance preclude it from being an iron-complex cluster. NGC 5986 has 〈 [ Eu / Fe ] 〉 = + 0.76 dex (σ = 0.08 dex), which is among the highest ratios detected in a Galactic cluster, but the small [Eu/Fe] dispersion is puzzling because such high values near [Fe/H] ∼ −1.5 are typically only found in dwarf galaxies exhibiting large [Eu/Fe] variations. NGC 5986 exhibits classical globular cluster characteristics, such as uniformly enhanced [α/Fe] ratios, a small dispersion in Fe-peak abundances, and (anti)correlated light-element variations. Similar to NGC 2808, we find evidence that NGC 5986 may host at least four to five populations with distinct light-element compositions, and the presence of a clear Mg–Al anticorrelation along with an Al–Si correlation suggests that the cluster gas experienced processing at temperatures ≳65–70 MK. However, the current data do not support burning temperatures exceeding ∼100 MK. We find some evidence that the first- and second-generation stars in NGC 5986 may be fully spatially mixed, which could indicate that the cluster has lost a significant fraction of its original mass.

Context-dependent functional dispersion across similar ranges of trait space covered by intertidal rocky shore communities.

Functional diversity is intimately linked with community assembly processes, but its large‐scale patterns of variation are often not well understood. Here, we investigated the spatiotemporal changes in multiple trait dimensions (“trait space”) along vertical intertidal environmental stress gradients and across a landscape scale. We predicted that the range of the trait space covered by local assemblages (i.e., functional richness) and the dispersion in trait abundances (i.e., functional dispersion) should increase from high‐ to low‐intertidal elevations, due to the decreasing influence of environmental filtering. The abundance of macrobenthic algae and invertebrates was estimated at four rocky shores spanning ca. 200 km of the coast over a 36‐month period. Functional richness and dispersion were contrasted against matrix‐swap models to remove any confounding effect of species richness on functional diversity. Random‐slope models showed that functional richness and dispersion significantly increased from high‐ to low‐intertidal heights, demonstrating that under harsh environmental conditions, the assemblages comprised similar abundances of functionally similar species (i.e., trait convergence), while that under milder conditions, the assemblages encompassed differing abundances of functionally dissimilar species (i.e., trait divergence). According to the Akaike information criteria, the relationship between local environmental stress and functional richness was persistent across sites and sampling times, while functional dispersion varied significantly. Environmental filtering therefore has persistent effects on the range of trait space covered by these assemblages, but context‐dependent effects on the abundances of trait combinations within such range. Our results further suggest that natural and/or anthropogenic factors might have significant effects on the relative abundance of functional traits, despite that no trait addition or extinction is detected.