Limits on the primordial stellar multiplicity

Most stars - especially young stars - are observed to be in multiple systems. Dynamical evolution is unable to pair stars efficiently, which leads to the conclusion that star-forming cores must usually fragment into \geq 2 stars. However, the dynamical decay of systems with \geq 3 or 4 stars would result in a large single-star population that is not seen in the young stellar population. Additionally, ejections would produce a significant population of hard binaries that are not observed. This leads to a strong constraint on star formation theories that cores must typically produce only 2 or 3 stars. This conclusion is in sharp disagreement with the results of currently available numerical simulations that follow the fragmentation of molecular cores and typically predict the formation of 5--10 seeds per core. In addition, open cluster remnants may account for the majority of observed highly hierarchical higher-order multiple systems in the field.Comment: A&A in press, 5 pages (no figures

Dynamical Evolution of Young Embedded Clusters: A Parameter Space Survey

This paper investigates the dynamical evolution of embedded stellar clusters from the protocluster stage, through the embedded star-forming phase, and out to ages of 10 Myr -- after the gas has been removed from the cluster. The relevant dynamical properties of young stellar clusters are explored over a wide range of possible star formation environments using N-body simulations. Many realizations of equivalent initial conditions are used to produce robust statistical descriptions of cluster evolution including the cluster bound fraction, radial probability distributions, as well as the distributions of close encounter distances and velocities. These cluster properties are presented as a function of parameters describing the initial configuration of the cluster, including the initial cluster membership N, initial stellar velocities, cluster radii, star formation efficiency, embedding gas dispersal time, and the degree of primordial mass segregation. The results of this parameter space survey, which includes about 25,000 simulations, provide a statistical description of cluster evolution as a function of the initial conditions. We also present a compilation of the FUV radiation fields provided by these same cluster environments. The output distributions from this study can be combined with other calculations, such as disk photoevaporation models and planetary scattering cross sections, to ascertain the effects of the cluster environment on the processes involved in planet formation.Comment: 65 pages including 20 figures, accepted to ApJ Supplemen

Early Evolution of Stellar Groups and Clusters: Environmental Effects on Forming Planetary Systems

This paper studies the dynamical evolution of young stellar clusters with $N$ = 100 - 1000 members. We use N-body simulations to explore how evolution depends on system size $N$ and the initial conditions. Motivated by recent observations of extremely young systems, this study compares subvirial and virial starting states. Multiple realizations of equivalent cases (100 simulations per case) are used to build up a robust statistical description of these systems, e.g., distributions of closest approaches, mass profiles, and distributions of radial locations. These results provide a framework from which to assess the effects of these clusters on star and planet formation. The distributions of radial positions are used in conjunction with distributions of FUV luminosities (also calculated here) to determine the radiation exposure of circumstellar disks. The distributions of closest approaches are used in conjunction with scattering cross sections (calculated here from $10^5$ scattering experiments) to determine the probability of solar system disruption. We also use the nearby cluster NGC 1333 as a test case. Our main conclusion is that clusters in this size range have only a modest effect on forming planetary systems: Interaction rates are low so that the typical solar system experiences a single encounter within 1000 AU. Radiation exposure is low, with median FUV flux $G_0$ = 900, so that photoevaporation of disks is only important beyond 30 AU. Given the low interaction rates and modest radiation levels, we suggest that solar system disruption is a rare event in these clusters.Comment: 54 pages; accepted to Ap

Wolbachia and DNA barcoding insects: patterns, potential and problems

Wolbachia is a genus of bacterial endosymbionts that impacts the breeding systems of their hosts. Wolbachia can confuse the patterns of mitochondrial variation, including DNA barcodes, because it influences the pathways through which mitochondria are inherited. We examined the extent to which these endosymbionts are detected in routine DNA barcoding, assessed their impact upon the insect sequence divergence and identification accuracy, and considered the variation present in Wolbachia COI. Using both standard PCR assays (Wolbachia surface coding protein – wsp), and bacterial COI fragments we found evidence of Wolbachia in insect total genomic extracts created for DNA barcoding library construction. When >2 million insect COI trace files were examined on the Barcode of Life Datasystem (BOLD) Wolbachia COI was present in 0.16% of the cases. It is possible to generate Wolbachia COI using standard insect primers; however, that amplicon was never confused with the COI of the host. Wolbachia alleles recovered were predominantly Supergroup A and were broadly distributed geographically and phylogenetically. We conclude that the presence of the Wolbachia DNA in total genomic extracts made from insects is unlikely to compromise the accuracy of the DNA barcode library; in fact, the ability to query this DNA library (the database and the extracts) for endosymbionts is one of the ancillary benefits of such a large scale endeavor – for which we provide several examples. It is our conclusion that regular assays for Wolbachia presence and type can, and should, be adopted by large scale insect barcoding initiatives. While COI is one of the five multi-locus sequence typing (MLST) genes used for categorizing Wolbachia, there is limited overlap with the eukaryotic DNA barcode region

The stellar and sub-stellar IMF of simple and composite populations

The current knowledge on the stellar IMF is documented. It appears to become top-heavy when the star-formation rate density surpasses about 0.1Msun/(yr pc^3) on a pc scale and it may become increasingly bottom-heavy with increasing metallicity and in increasingly massive early-type galaxies. It declines quite steeply below about 0.07Msun with brown dwarfs (BDs) and very low mass stars having their own IMF. The most massive star of mass mmax formed in an embedded cluster with stellar mass Mecl correlates strongly with Mecl being a result of gravitation-driven but resource-limited growth and fragmentation induced starvation. There is no convincing evidence whatsoever that massive stars do form in isolation. Various methods of discretising a stellar population are introduced: optimal sampling leads to a mass distribution that perfectly represents the exact form of the desired IMF and the mmax-to-Mecl relation, while random sampling results in statistical variations of the shape of the IMF. The observed mmax-to-Mecl correlation and the small spread of IMF power-law indices together suggest that optimally sampling the IMF may be the more realistic description of star formation than random sampling from a universal IMF with a constant upper mass limit. Composite populations on galaxy scales, which are formed from many pc scale star formation events, need to be described by the integrated galactic IMF. This IGIMF varies systematically from top-light to top-heavy in dependence of galaxy type and star formation rate, with dramatic implications for theories of galaxy formation and evolution.Comment: 167 pages, 37 figures, 3 tables, published in Stellar Systems and Galactic Structure, Vol.5, Springer. This revised version is consistent with the published version and includes additional references and minor additions to the text as well as a recomputed Table 1. ISBN 978-90-481-8817-

Different distribution of cardiovascular risk factors according to ethnicity: A study in a high risk population

This study compares the distribution of cardiovascular risk factors in different ethnic groups at high risk of developing cardiovascular diseases within general practices. A total of 430 patients (179 Dutch, 126 Turks, 50 Surinamese, 23 Moroccans, 23 Antilleans and 29 from other ethnic groups) were included in the study. Data collection consisted of questionnaires and physical and clinical examinations. 54% was female. The mean age was 53.1 (sd 9.9) years. There were important ethnic differences in the distribution of cardiovascular risk factors. Compared to the Dutch, ethnic minorities had significantly greater odds of being diabetic (OR = 3.2-19.4); but were less likely to smoke (OR = 0.10-0.53). Turkish individuals had a lower prevalence of hypercholesterolemia but were 2.4 times more likely to be obese than the Dutch. Hypertension was very common in all ethnic groups and no significant ethnic differences were found. These findings provide additional evidence of the need for tailored interventions for different ethnic groups in general practices

Phylogenetic relationships and systematics of the Amazonian poison frog genus Ameerega using ultraconserved genomic elements

The Amazonian poison frog genus Ameerega is one of the largest yet most understudied of the brightly colored genera in the anuran family Dendrobatidae, with 30 described species ranging throughout tropical South America. Phylogenetic analyses of Ameerega are highly discordant, lacking consistency due to variation in data types and methods, and often with limited coverage of species diversity in the genus. Here, we present a comprehensive phylogenomic reconstruction of Ameerega, utilizing state-of-the-art sequence capture techniques and phylogenetic methods. We sequenced thousands of ultraconserved elements from over 100 tissue samples, representing almost every described Ameerega species, as well as undescribed cryptic diversity. We generated topologies using maximum likelihood and coalescent methods and compared the use of maximum likelihood and Bayesian methods for estimating divergence times. Our phylogenetic inference diverged strongly from those of previous studies, and we recommend steps to bring Ameerega taxonomy in line with the new phylogeny. We place several species in a phylogeny for the first time, as well as provide evidence for six potential candidate species. We estimate that Ameerega experienced a rapid radiation approximately 7–11 million years ago and that the ancestor of all Ameerega was likely an aposematic, montane species. This study underscores the utility of phylogenomic data in improving our understanding of the phylogeny of understudied clades and making novel inferences about their evolution

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio

Interaction of Rickettsia felis with histone H2B facilitates the infection of a tick cell line

Haematophagous arthropods are the primary vectors in the transmission of Rickettsia, yet the molecular mechanisms mediating the rickettsial infection of arthropods remain elusive. This study utilized a biotinylated protein pull-down assay together with LC-MS/MS to identify interaction between Ixodes scapularis histone H2B and Rickettsia felis. Co-immunoprecipitation of histone with rickettsial cell lysate demonstrated the association of H2B with R. felis proteins, including outer-membrane protein B (OmpB), a major rickettsial adhesin molecule. The rickettsial infection of tick ISE6 cells was reduced by approximately 25 % via RNA-mediated H2B-depletion or enzymic treatment of histones. The interaction of H2B with the rickettsial adhesin OmpB suggests a role for H2B in mediating R. felis internalization into ISE6 cells