Core Populations Research Articles

On quasi-parallel whistler waves in the solar wind

Recent simulations showed that the whistler heat flux instability, which presumably produces the most of quasi-parallel coherent whistler waves in the solar wind, is not efficient in regulating the electron heat conduction. In addition, recent spacecraft measurements indicated that some fraction of coherent whistler waves in the solar wind may propagate anti-parallel to the electron heat flux, being produced due to a perpendicular temperature anisotropy of suprathermal electrons. We present the analysis of properties of parallel and anti-parallel whistler waves unstable at electron heat fluxes and temperature anisotropies of suprathermal electrons typical of the pristine solar wind. Assuming the electron population consisting of counterstreaming dense thermal core and tenuous suprathermal halo populations, we perform a linear stability analysis to demonstrate that anti-parallel whistler waves are expected to have smaller frequencies, wave numbers, and growth rates compared to parallel whistler waves. The stability analysis is performed over a wide range of parameters of core and halo electron populations. Using the quasi-linear scaling relation, we show that anti-parallel whistler waves saturate at amplitudes of one order of magnitude smaller than parallel whistler waves, which is about 10−3 B0 in the pristine solar wind. The analysis shows that the presence of anti-parallel whistler waves in the pristine solar wind is more likely to be obscured by turbulent magnetic field fluctuations because of lower frequencies and smaller amplitudes compared to parallel whistler waves. The presented results will also be valuable for numerical simulations of the electron heat flux regulation in the solar wind.

An Exploration of Tensor Virial Equilibrium in Magnetized Molecular Cloud Cores

Abstract PolCat is a software package designed to generate and constrain models of triaxial, magnetized molecular cloud cores using submillimeter polarization and continuum intensity data. Such models often compare well with observational data, but they are mathematically degenerate. As a result, many allowed models are either very elongated or flattened, and far from virial equilibrium. We present a tensor virial analysis of PolCat models with the aim of developing an optional new regularization constraint that can be used on the fly during the PolCat modeling process. This constraint is intended to guide PolCat toward models that are in or close to equilibrium on all three principal axes. While we have found the expected families of spheroidal solutions in tensor virial balance, we have also found a population of triaxial cores that are in three-axis tensor virial equilibrium. We find that models generated using the virial constraint have much more realistic shapes, with very elongated or flattened solutions now absent. Thus, these show that the tensor virial constraint may be useful for restricting PolCat’s solution space to more realistic models, thereby also reducing the degeneracy inherent in our approach. We also perform a Monte Carlo analysis to predict the range of projected axis ratios present in the population of equilibrium solutions to suggest how these cores may appear when observed.

Outer Radiation Belt Electron Lifetime Model Based on Combined Van Allen Probes and Cluster VLF Measurements

AbstractThe flux of energetic electrons in the outer radiation belt shows a high variability. The interactions of electrons with very low frequency (VLF) chorus waves play a significant role in controlling the flux variation of these particles. Quantifying the effects of these interactions is crucially important for accurately modeling the global dynamics of the outer radiation belt and to provide a comprehensive description of electron flux variations over a wide energy range (from the source population of 30 keV electrons up to the relativistic core population of the outer radiation belt). Here, we use a synthetic chorus wave model based on a combined database compiled from the Van Allen Probes and Cluster spacecraft VLF measurements to develop a comprehensive parametric model of electron lifetimes as a function of L‐shell, electron energy, and geomagnetic activity. The wave model takes into account the wave amplitude dependence on geomagnetic latitude, wave normal angle distribution, and variations of wave frequency with latitude. We provide general analytical formulas to estimate electron lifetimes as a function of L‐shell (for L = 3.0 to L = 6.5), electron energy (from 30 keV to 2 MeV), and geomagnetic activity parameterized by the AE index. The present model lifetimes are compared to previous studies and analytical results and also show a good agreement with measured lifetimes of 30 to 300 keV electrons at geosynchronous orbit.

Collisionless Heat Flux Regulation via the Electron Firehose Instability in the Presence of a Core and Suprathermal Population in the Expanding Solar Wind

Abstract The evolution of the electron heat flux in the solar wind is regulated by the interplay between several effects: solar wind expansion, which can potentially drive velocity–space instabilities, turbulence, wave–particle interactions, and, possibly, collisions. Here we address the respective role played by the solar wind expansion and the electron firehose instability (EFI), developing in the presence of multiple electron populations, in regulating the heat flux. We carry out fully kinetic, expanding box model simulations and separately analyze the enthalpy, bulk, and velocity distribution function skewness contributions for each of the electron species. We observe that the key factor determining electron energy flux evolution is the reduction of the drift velocity of the electron populations in the rest frame of the solar wind. In our simulations, redistribution of the electron thermal energy from the parallel to the perpendicular direction after the onset of the EFI is observed. However, this process seems to impact energy flux evolution only minimally. Hence, reduction of the electron species drift velocity in the solar wind frame appears to directly correlate with efficiency for heat flux instabilities.

Seedlings from marginal and core populations of European beech (Fagus sylvatica L.) respond differently to imposed drought and shade

Key messageLocal adaptation largely segregates between traits affecting light responses and water relations, but population-level differences in stomatal conductance when growth is unconstrained converge among populations under water stress.Warming temperatures and altered precipitation patterns threaten plant populations worldwide. European beech (Fagus sylvatica) is a species that expresses both high phenotypic plasticity and local adaptation among populations. Beech seedlings’ susceptibility to prolonged drought may be dictated by their immediate light environment. We tested whether seedlings of four beech provenances, from contrasting edaphoclimatic environments, expressed differences in trait responses to imposed water stress under sun and shade treatments. Populations from the southern range margin were expected to display greater water-stress tolerance and core populations’ faster growth rates in the absence of abiotic limitations. Both high light and water stress induced differences in trait responses among provenances, but traits that failed to respond to our experimental treatments likewise did not segregate at the provenance level. Hence, those traits responding to light, e.g., increasing leaf flavonol index and leaf mass area, also tended to differ among provenances. Similarly, there was evidence of local adaptation among provenances in traits, like midday leaf water potential, responding to water stress. Exceptionally, there was a three way interaction water- × -light- × -provenance for stomatal conductance which converged among provenances under water stress. Leaf chlorophyll content also varied both with light and water in a provenance-specific manner. We found core provenances’ growth traits to outperform others under favourable conditions, whereas southern and high-elevation populations displayed traits adapted to tolerate high irradiance. Only stomatal conductance produced a complementary interactive response between light- × -water across provenances, whereas other traits responded less to combined water stress and high irradiance than to either treatment alone.

Resequencing of a Core Rice Mutant Population Induced by Gamma-Ray Irradiation and Its Application in a Genome-Wide Association Study

A total of 2561 gamma ray-induced mutants (M7) were evaluated in six abiotic stress treatments, and then principal component analysis was performed to score their phenotypes. Resequencing was performed on 123 selected rice mutants and wild-type rice to assess the structural changes in the genomes of these mutants, such as single nucleotide polymorphisms (SNPs) and insertion/deletion (InDels). A total of 5160 (avg. 87.3 per plant) SNPs and 7195 (avg. 121.9) InDels were observed in the 200-Gy lines, whereas 5650 (avg. 88.3) SNPs and 7676 (avg. 119.9) InDels were found in the 300-Gy lines. We found that one candidate gene (Os02g0528900, which is similar to the gene for pleiotropic drug resistance (PDR)-like ATP-binding cassette (ABC) transporter) contained two SNPs that were included in principal component 4 via a genome-wide association study. The 300-42 line had the lowest phenotype score against heat, possibly suggesting the existence of a relationship between these SNPs and heat stress. Co-expression analysis of the candidate gene involved in responses to toxic substances and the chemical stimulation of significant biological processes. Therefore, the studied targeting induced local lesions in genome (TILLING) population could be a useful source of mutations in the breeding of new genetic resources for forward and reverse genetics.

Statistics of solar wind electron breakpoint energies using machine learning techniques

Solar wind electron velocity distributions at 1 au consist of a thermal “core” population and two suprathermal populations: “halo” and “strahl”. The core and halo are quasi-isotropic, whereas the strahl typically travels radially outwards along the parallel or anti-parallel direction with respect to the interplanetary magnetic field. Using Cluster-PEACE data, we analyse energy and pitch angle distributions and use machine learning techniques to provide robust classifications of these solar wind populations. Initially, we used unsupervised algorithms to classify halo and strahl differential energy flux distributions to allow us to calculate relative number densities, which are of the same order as previous results. Subsequently, we applied unsupervised algorithms to phase space density distributions over ten years to study the variation of halo and strahl breakpoint energies with solar wind parameters. In our statistical study, we find both halo and strahl suprathermal breakpoint energies display a significant increase with core temperature, with the halo exhibiting a more positive correlation than the strahl. We conclude low energy strahl electrons are scattering into the core at perpendicular pitch angles. This increases the number of Coulomb collisions and extends the perpendicular core population to higher energies, resulting in a larger difference between halo and strahl breakpoint energies at higher core temperatures. Statistically, the locations of both suprathermal breakpoint energies decrease with increasing solar wind speed. In the case of halo breakpoint energy, we observe two distinct profiles above and below 500 km s−1. We relate this to the difference in origin of fast and slow solar wind.

Plant morphological variability at the distribution edges: the case of Dryas octopetala (Rosaceae) in northern Greece

Plant populations at their distribution limits may often deviate morphologically from those at the centre of their range (core populations). A similar pattern was observed in Dryas octopetala (Rosaceae), a circumpolar, arctic-alpine species distributed in northern and central Europe, reaching south to northern Greece. The three southernmost populations of Europe, located in Greece, were sampled and specific leaf morphometric traits were measured and analysed using canonical variates analysis (CVA) and hierarchical cluster analysis. CVA revealed that the three samples of D. octopetala did not form one group but were significantly discriminated. Despite the rather similar climatic conditions of Mts Falakron and Orvilos, the sample of Mt Falakron was grouped with that of Mt Tzena, based on leaf morphology. These findings contradict findings from other studies on the ways with which plants react and adapt on areas of harsh climatic conditions. Micro-site conditions or a potentially different post-glacial origin could possibly explain the pattern observed in this study.Citation: Varsamis G., Karapatzak E., Tseniklidou K., Merou Th. & Tsiftsis S. 2020: Plant morphological variability at the distribution edges: the case of Dryas octopetala (Rosaceae) in northern Greece. – Willdenowia 50: 267–277. doi: https://doi.org/10.3372/wi.50.50212Version of record first published online on 25 June 2020 ahead of inclusion in August 2020 issue.

Stress and immunity: Field comparisons among populations of invasive cane toads in Florida.

Cane toads (Rhinella marina) were introduced worldwide and have become invasive in multiple locations, representing a major driver of biodiversity loss through competition (food, shelter, territory), predation, and the poisoning of native species. These toads have been used in Australia as a model for studies concerning invasion biology and ecoimmunology, as longer-established (core) and invasion front (edge) populations show altered stress and immune response profiles. Although cane toads were also introduced into the United States in the 1950s, these patterns have yet to be evaluated for the populations spanning Florida. Toads introduced into Florida have dispersed primarily northward along a latitudinal gradient, where they encounter cooler temperatures that may further impact stress and immune differences between core and edge populations. In this study, we sampled cane toads from nine different locations spanning their invasion in Florida. Cane toads from southern populations showed higher plasma bacterial killing ability and natural antibody titers than the toads from the northern populations, indicating they have a better immune surveillance system. Also, southern toads were more responsive to a novel stressor (1 hr restraint), showing a higher increase in corticosterone levels. These results indicate that possible trade-offs have occurred between immune and stress responses as these toads have become established in northern cooler areas in Florida.

2146-PUB: Features of Acute Myocardial Infarction in Patients with Diabetes Mellitus of the Buryat Population

The inflammatory processes that develop in patients with type 2 diabetes mellitus (T2DM) vary in different ethnic groups. The level of cytokines in the peripheral blood characterizes the severity of the disease and the dynamics of the pathological process in the acute period of myocardial infarction. The study included 34 individuals of the Buryat population. The Buryats are the main northern group of Mongolians, they are a core population of Siberia with a compact residence close to Lake Baikal. The first group included 14 patients with T2DM and ST-elevation acute myocardial infarction (STEMI) (5 men and 9 women), with a median age was of 62.5 years. The second group consisted of 20 individuals of the control group without diabetes and STEMI (11 men and 9 women), a median age was of 62 years. We studied levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10 (IL-10), tumor necrosis factor alpha (TNF-α), high sensitivity C-reactive protein (hs-CRP) admitted within 24 h after the symptoms onset (Table 1). In Buryat patients with T2DM and STEMI, production of pro-inflammatory cytokines IL-1β and IL-6 relative to the control group without diabetes and STEMI (p <0.05) is reduced. In addition, in Buryat patients with T2DM and STEMI, a significant increase in the level of hs-CRP was registered relatively to the control group (p<0.05). Disclosure T. Bardymova: None. T. Belokhvostikova: None. S. Tsyretorova: None.

An environmental DNA tool for monitoring the status of the Critically Endangered Smalltooth Sawfish, Pristis pectinata, in the western Atlantic

The Critically Endangered Smalltooth Sawfish, Pristis pectinata, was once widespread in the tropical and subtropical waters of the Atlantic Ocean, but following substantial declines over the past century, the remaining population(s) are currently confined to Florida in the U.S., and the Bahamas. Recent research and verified public encounter reports suggest that the core population in south and southwest Florida may be stabilizing and potentially expanding into formerly occupied areas of their historic range in the western Atlantic; however, the status of this species outside of core waters is not well understood. Environmental DNA (eDNA) methods provide a relatively cost effective and rapid assessment tool for monitoring species occurrence in aquatic habitats. Here, we have developed an eDNA tool: a species-specific Droplet Digital™ PCR assay targeting a 100-base pair portion of the mitochondrial NADH dehydrogenase subunit 2 gene in P. pectinata, with the ability to reliably detect as little as 0.25 pg of target DNA. The assay was validated by analyzing a water sample from an occupied nursery in southwest Florida, which was found to contain an average of 11.54 copies of target DNA/µL (SE = 0.72) in the reaction. The assay was then further tested by placing a juvenile sawfish in an ex situ tank and analyzing water samples collected at time intervals. The implementation of this eDNA tool into field surveys will provide additional, reliable data to assess species recovery and aid in prioritizing localities in which to focus new research, conservation, and education initiatives.

Innate immunity of Florida cane toads: how dispersal has affected physiological responses to LPS.

Physiological tradeoffs occur in organisms coping with their environments, which are likely to increase as populations reach peripheries of established ranges. Invasive species offer opportunities to study tradeoffs that occur, with many hypotheses focusing on how immune responses vary during dispersal. The cane toad (Rhinella marina) is a well-known invasive species. Populations near the expanding edge of the Australian invasion have altered immune responses compared to toads from longer-established core populations, although this has not been well-documented for Florida populations. In this study, cane toads from a northern edge [New Port Richey (NPR)] and southern core (Miami) population in Florida were collected and injected with lipopolysaccharide (LPS) to compare immune responses. Core population individuals injected with LPS showed greater metabolic increases compared to their baseline rates that were higher compared to those from the edge population. In addition, LPS-injected core individuals had different circulating leukocyte profiles compared to saline-injected cane toads while edge individuals did not. There was a significant interaction between plasma bacteria-killing capability (BKA) and treatment, such that BKA decreased with time in saline compared to LPS-injected individuals, and saline-injected toads from the edge population had lower BKA compared to LPS-injected edge toads at 20h post-injection. There was also a significant interaction between location and time on circulating corticosterone (CORT) levels following injections with saline or LPS, with CORT decreasing more with time in core population toads. The differential CORT response indicates that differential stress responses contribute to the tradeoffs observed with immunity and dispersal.

Contrasting types of micaceous kimberlite-lamproite magmatism from the Man Craton (West Africa): New insights from petrography and mineral chemistry

Diamondiferous rock types worldwide are broadly divided into kimberlite and lamproite, the latter of which have unique characteristics in different regions and include carbonate-rich varieties (formerly orangeites/Group II kimberlites). Diamondiferous rocks in West Africa are typically micaceous and share petrographic, mineralogical, and geochemical characteristics with both kimberlites and lamproites. To further constrain the classification and petrogenesis of diamondiferous rocks worldwide and their variability between different cratonic regions, in this study we combine detailed petrographic observations with olivine, phlogopite, and spinel chemistry for hypabyssal samples from the Jurassic Tongo dike (Sierra Leone) and the Neoproterozoic Weasua cluster (Liberia).The Tongo dike contains macrocrysts of olivine and phlogopite in a groundmass of olivine, abundant phlogopite, spinel, perovskite, and apatite with a base of calcite, dolomite, and lesser serpentine. The phlogopite is characterised by concurrent FeO and Al2O3 enrichment, which is typical of kimberlites and unlike lamproites. These features and the kimberlite-like spinel compositions allow us to classify the Tongo samples as micaceous kimberlites. The Weasua rocks comprise macrocrysts of olivine in a groundmass of olivine, phlogopite, diopside (zoned towards aegirine-rich rims), spinel, perovskite, and apatite with a base of serpentine and less common calcite. The composition of Weasua phlogopite trends to significant FeO enrichment and Al2O3 depletion, i.e. towards tetraferriphlogopite. The enrichment in mica, phlogopite chemistry and presence of magmatic diopside indicates that these rocks are olivine lamproites.The populations of olivine macrocrysts and microcrysts at Tongo and Weasua are similar and characterised by distinct core and rim zones. Two distinct olivine core populations are observed. 1) forsterite-rich (Fo > 90) olivine interpreted to reflect xenocrysts from typical mantle peridotites. Al-in-olivine thermometry suggests that these cores have P-T equilibration within diamond stability at Weasua and Tongo. 2) Al-, Ca- and Na- rich cores with P-T formation conditions extending beyond the mantle adiabat. These cores are interpreted to reflect metasomatic and thermal perturbation linked with the infiltration of kimberlite/lamproite melts in the deep lithosphere shortly before entrainment in the ascending magma. The olivine rims at Tongo and Weasua show limited variations in Fo contents at similar values of 88.9 ± 0.8 for Tongo and 89.6 ± 1.2 for Weasua, as well as similar minor and trace element concentrations. Thus, whereas the Tongo and Weasua rock types are classified as kimberlite and olivine lamproite, respectively, the olivine chemistry suggests a similar petrogenetic evolution.

Differential effects of habitat loss on occupancy patterns of the eastern green lizard Lacerta viridis at the core and periphery of its distribution range.

The effects of habitat loss on the distribution of populations are often linked with species specialization degree. Specialist species can be more affected by changes in landscape structure and local patch characteristics compared to generalist species. Moreover, the spatial scale at which different land covers (eg. habitat, cropland, urban areas) affect specialist species can be smaller. Specialization is usually assumed as a constant trait along the distribution range of species. However, for several taxa, there is evidence of higher specialization degree in peripheral populations compared with populations in the core. Hence, peripheral populations should have a higher sensitivity to habitat loss, and strongest effects should be found at a smaller spatial scale. To test these expectations, we implemented a patch-landscape approach at different spatial scales, and compared effects of landscape structure and patch characteristics on occupancy probability among northern peripheral, more specialized populations (Czech Republic) and core populations (Bulgaria) of the eastern green lizard Lacerta viridis. We found that landscape structure and patch characteristics affect differently the occupancy probability of Lacerta viridis in each region. Strongest effects of habitat loss were found at a spatial scale of 150m around patches in the periphery, but at a scale of 500m in the core. In the periphery occupancy probability of populations was principally affected by landscape composition, and the effect of habitat quality was stronger compared to core populations. In the core, persistence of populations was mainly explained by characteristics of the spatial configuration of habitat patches. We discuss possible ecological mechanisms behind the relationship between sensitivity to habitat loss, populations' specialization degree and position in the distribution range, and suggest conservation measures for L. viridis.

The impact of limb deficiency impairment on Para swimming performance

ABSTRACTSwimmers with limb deficiency are a core population within Para Swimming, accordingly this study examined the contribution of limb segments to race performance in these swimmers. Data were obtained for 174 male Para swimmers with limb deficiency. Ensemble partial least squares regression showed accurate predictions when using relative limb segment lengths to estimate Para swimmers’ personal best race performances. The contribution of limb segments to performance in swim events was estimated using these regression models. The analysis found swim stroke and event distance to influence the contributions of limb segments to performance. For freestyle swim events, these changes were primarily due to the increased importance of the hand, and decreased importance of the foot and shank, as the distance of the event increased. When comparing swim strokes, higher importance of the thigh and shank in the 100 m breaststroke compared with other swim strokes confirms the separate SB class. Varied contributions of the hand, upper arm and foot suggest that freestyle could also be separated from backstroke and butterfly events to promote fairer classification. This study shows that swim stroke and event distance influence the activity limitation of Para swimmers with limb deficiency suggesting classification should account for these factors.

Will Lynx Lose Their Edge? Canada Lynx Occupancy in Washington

ABSTRACTPopulations of species located at southern range edges may be particularly vulnerable to the effects of climate change as warming temperatures and subsequent changes to ecosystems exceed species‐specific tolerances. One such species is Canada lynx (Lynx canadensis), a cold‐adapted mesocarnivore that maintains a large core population in Alaska, USA, and Canada but exists within several peripheral populations in the contiguous United States. Increases in temperature, declines in snow pack, and climate‐influenced increases in fire frequency and intensity, could negatively affect lynx populations, threatening their long‐term persistence in the continental United States. Despite these threats, our understanding of broad‐scale effects on lynx occupancy and the extent of current lynx distribution in many of these peripheral populations is minimal. We conducted an occupancy survey of lynx in Washington, USA, using a spatially extensive camera‐trapping array covering 7,000 km2 of potential lynx habitat. We used the resulting database of detection data to develop single‐season occupancy models to examine the abiotic and biotic effects on current lynx occupancy and predict future lynx distribution based on climate change forecasts. Our results show lynx occupancy across the Washington landscape is restricted and dictated largely by abiotic factors, disturbance regimes, and distance from source populations in Canada. Predictions of future distribution suggest lynx will be increasingly challenged by climatic changes, particularly at the southern and lower elevation portions of their range in Washington. Our results paint an alarming picture for lynx persistence in Washington that is relevant to current deliberations regarding lynx delisting from the Endangered Species Act. Our simple camera design was a highly effective method for surveying lynx across broad spatial scales, and could be a key monitoring tool for lynx that is easy to implement by researchers and government agencies. © 2020 The Wildlife Society.

Properties of the dense core population in Orion B as seen by the Herschel Gould Belt survey

We present a detailed study of the Orion B molecular cloud complex (d ~ 400 pc), which was imaged with the PACS and SPIRE photometric cameras at wavelengths from 70 to 500 μm as part of the Herschel Gould Belt survey (HGBS). We release new high-resolution maps of column density and dust temperature for the whole complex, derived in the same consistent manner as for other HGBS regions. In the filamentary subregions NGC 2023 and 2024, NGC 2068 and 2071, and L1622, a total of 1768 starless dense cores were identified based on Herschel data, 490–804 (~28−45%) of which are self-gravitating prestellar cores that will likely form stars in the future. A total of 76 protostellar dense cores were also found. The typical lifetime of the prestellar cores was estimated to be tpreOrionB = 1.7−0.6+0.8Myr. The prestellar core mass function (CMF) derived for the whole sample of prestellar cores peaks at ~0.5 M⊙ (in dN/dlogM format) and is consistent with a power-law with logarithmic slope −1.27 ± 0.24 at the high-mass end, compared to the Salpeter slope of − 1.35. In the Orion B region, we confirm the existence of a transition in prestellar core formation efficiency (CFE) around a fiducial value AVbg ~ 7 mag in background visual extinction, which is similar to the trend observed with Herschel in other regions, such as the Aquila cloud. This is not a sharp threshold, however, but a smooth transition between a regime with very low prestellar CFE at AVbg < 5 and a regime with higher, roughly constant CFE at AVbg ≳ 10. The total mass in the form of prestellar cores represents only a modest fraction (~20%) of the dense molecular cloud gas above AVbg ≳ 7 mag. About 60–80% of the prestellar cores are closely associated with filaments, and this fraction increases up to >90% when a more complete sample of filamentary structures is considered. Interestingly, the median separation observed between nearest core neighbors corresponds to the typical inner filament width of ~0.1 pc, which is commonly observed in nearby molecular clouds, including Orion B. Analysis of the CMF observed as a function of background cloud column density shows that the most massive prestellar cores are spatially segregated in the highest column density areas, and suggests that both higher- and lower-mass prestellar cores may form in denser filaments.

Physical properties of the star-forming clusters in NGC 6334

Aims. We aim to characterise certain physical properties of high-mass star-forming sites in the NGC 6334 molecular cloud, such as the core mass function (CMF), spatial distribution of cores, and mass segregation. Methods. We used the Atacama Large Millimeter/sub-millimeter Array (ALMA) to image the embedded clusters NGC 6334-I and NGC 6334-I(N) in the continuum emission at 87.6 GHz. We achieved a spatial resolution of 1300 au, enough to resolve different compact cores and fragments, and to study the properties of the clusters. Results. We detected 142 compact sources distributed over the whole surveyed area. The ALMA compact sources are clustered in different regions. We used different machine-learning algorithms to identify four main clusters: NGC 6334-I, NGC 6334-I(N), NGC 6334-I(NW), and NGC 6334-E. The typical separations between cluster members range from 4000 au to 12 000 au. These separations, together with the core masses (0.1–100 M⊙), are in agreement with the fragmentation being controlled by turbulence at scales of 0.1 pc. We find that the CMFs show an apparent excess of high-mass cores compared to the stellar initial mass function. We evaluated the effects of temperature and unresolved multiplicity on the derived slope of the CMF. Based on this, we conclude that the excess of high-mass cores might be spurious and due to inaccurate temperature determinations and/or resolution limitations. We searched for evidence of mass segregation in the clusters and we find that clusters NGC 6334-I and NGC 6334-I(N) show hints of segregation with the most massive cores located in the centre of the clusters. Conclusions. We searched for correlations between the physical properties of the four embedded clusters and their evolutionary stage (based on the presence of H II regions and infrared sources). NGC 6334-E appears as the most evolved cluster, already harbouring a well-developed H II region. NGC 6334-I is the second-most evolved cluster with an ultra-compact H II region. NGC 6334-I(N) contains the largest population of dust cores distributed in two filamentary structures and no dominant H II region. Finally, NGC 6334-I(NW) is a cluster of mainly low-mass dust cores with no clear signs of massive cores or H II regions. We find a larger separation between cluster members in the more evolved clusters favouring the role of gas expulsion and stellar ejection with evolution. The mass segregation, seen in the NGC 6334-I and NGC 6334-I(N) clusters, suggests a primordial origin for NGC 6334-I(N). In contrast, the segregation in NGC 6334-I might be due to dynamical effects. Finally, the lack of massive cores in the most evolved cluster suggests that the gas reservoir is already exhausted, while the less evolved clusters still have a large gas reservoir along with the presence of massive cores. In general, the fragmentation process of NGC 6334 at large scales (from filament to clump, i.e. at about 1 pc) is likely governed by turbulent pressure, while at smaller scales (scale of cores and sub-fragments, i.e. a few hundred au) thermal pressure starts to be more significant.

The young massive SMC cluster NGC 330 seen by MUSE

Context.A majority of massive stars are part of binary systems, a large fraction of which will inevitably interact during their lives. Binary-interaction products (BiPs), that is, stars affected by such interaction, are expected to be commonly present in stellar populations. BiPs are thus a crucial ingredient in the understanding of stellar evolution.Aims.We aim to identify and characterize a statistically significant sample of BiPs by studying clusters of 10 − 40 Myr, an age at which binary population models predict the abundance of BiPs to be highest. One example of such a cluster is NGC 330 in the Small Magellanic Cloud.Methods.Using MUSE WFM-AO observations of NGC 330, we resolved the dense cluster core for the first time and were able to extract spectra of its entire massive star population. We developed an automated spectral classification scheme based on the equivalent widths of spectral lines in the red part of the spectrum.Results.We characterize the massive star content of the core of NGC 330, which contains more than 200 B stars, 2 O stars, 6 A-type supergiants, and 11 red supergiants. We find a lower limit on the Be star fraction of 32 ± 3% in the whole sample. It increases to at least 46 ± 10% when we only consider stars brighter thanV = 17 mag. We estimate an age of the cluster core between 35 and 40 Myr and a total cluster mass of 88−18+17× 103M⊙.Conclusions.We find that the population in the cluster core is different than the population in the outskirts: while the stellar content in the core appears to be older than the stars in the outskirts, the Be star fraction and the observed binary fraction are significantly higher. Furthermore, we detect several BiP candidates that will be subject of future studies.

Stabilization of the stochastic point reactor kinetic equation through power feedback

Most basic models for the power (or equivalently, the neutron population) in a nuclear core consider the power as a function of time (with an energetic and spatial distribution) and lead to deterministic description of the reactor kinetics. While these models are of common use and are undoubtedly the main analytic tool in understanding the reactor kinetics, the true nature of the power in a reactor core is stochastic and should be considered as a stochastic process in time. The stochastic fluctuations of the power around the mean field (which is given by the deterministic models) are referred to as “reactor noise”, and understanding them is a basic topic in nuclear science and engineering. Traditionally, most models for reactor noise consider a sub-critical core, reaching steady state after exposure to an external source. The focus on a sub-critical setting is driven by two main factors. First, from a practical point of view, measuring the power fluctuations in a sub-critical core (known as “noise experiments”) has proven to be a very efficient tool for estimating the static and kinetic parameters of the core. Second, once we assume a critical setting, the current models become statistically unstable, while the mean field solution has a stationary solution, the variance tends to $$\infty $$ linearly in time. The instability of the stochastic models is a known problem, and it has been conjectured in the past that this (some what strange) increase in the variance—that is not observed in physical systems—can be restrained by power feedback. However, this conjecture was never proven. The outline of the present study is to present a stochastic analysis to the point reactor kinetics model, proving that once the reactivity has a negative feedback, it not only forces a specific steady-state solution (in terms of the mean field equation), but also prevents the variance to “explode”, and the variance is bounded in time.