Light elements in massive single and binary stars

We highlight the role of the light elements (Li, Be, B) in the evolution of massive single and binary stars, which is largely restricted to a diagnostic value, and foremost so for the element boron. However, we show that the boron surface abundance in massive early type stars contains key information about their foregoing evolution which is not obtainable otherwise. In particular, it allows to constrain internal mixing processes and potential previous mass transfer event for binary stars (even if the companion has disappeared). It may also help solving the mystery of the slowly rotating nitrogen-rich massive main sequence stars.Comment: 10 pages, 8 figures, to appear in proc. IAU-Symp. 268. C. Charbonnel et al., eds

An Investigation of the Large-scale Variability of the Apparently Single Wolf-Rayet Star WR 1

In recent years, much studies have focused on determining the origin of the large-scale line-profile and/or photometric patterns of variability displayed by some apparently single Wolf-Rayet stars, with the existence of an unseen (collapsed?) companion or of spatially extended wind structures as potential candidates. We present observations of WR 1 which highlight the unusual character of the variations in this object. Our narrowband photometric observations reveal a gradual increase of the stellar continuum flux amounting to Delta v = 0.09 mag followed by a decline on about the same timescale (3-4 days). Only marginal evidence for variability is found during the 11 following nights. Strong, daily line-profile variations are also observed but they cannot be easily linked to the photometric variations. Similarly to the continuum flux variations, coherent time-dependent changes are observed in 1996 in the centroid, equivalent width, and skewness of He II 4686. Despite the generally coherent nature of the variations, we do not find evidence in our data for the periods claimed in previous studies. While the issue of a cyclical pattern of variability in WR 1 is still controversial, it is clear that this object might constitute in the future a cornerstone for our understanding of the mechanisms leading to the formation of largely anisotropic outflows in Wolf-Rayet stars.Comment: 11 pages, 9 figures, accepted for publication in Astronomy & Astrophysic

Recherches écologiques sur une savane sahélienne du Ferlo septentrional, Sénégal : influence de la sécheresse de l’année 1972-1973 sur l’avifaune

Comparaison de l’avifaune dans une savane sahélienne (Fété Olé, Sénégal, 16° N, 15° W) en année « normalement » pluvieuse (303 mm de pluies, groupées entre juin et octobre) et en année anormalement sèche (33 mm de pluie). Inventaire des espèces recensées, analyses mensuelles de la structure de la population, de l’indice de diversité et de dominance pour les effectifs et les biomasses. L’avifaune s’est appauvrie en qualité et en quantité : moins d’espèces, chacune représentée par peu d’individus. L’effectif annuel moyen à l’hectare est passé de 6,3 à 2,9 et la biomasse moyenne annuelle, en grammes de poids frais à l’hectare, de 402 à 186 pour ces deux mêmes années. Alors qu’en 1969-70, les Tourte relles, oiseaux granivores buvant tous les jours, représentaient au moins le tiers des effectifs en saison sèche, celles-ci ont complète ment disparu en 1972-73, laissant la place à des oiseaux ne buvant pas (insectivores et frugivores), ou à des granivores capables de faire de longs vols pour boire (Gangas). La diminution de la population s’explique par les conditions trophiques du milieu : absence de renouvellement du tapis gra- minéen et de mares temporaires après les pluies. Ceci a contraint beaucoup d’espèces à migrer. D’autre part, les populations ont été soumises au seul facteur de la mortalité, puisque aucune espèce n’a été capable de se reproduire.A comparison was made of the bird populations of a dry thornbush savanna at Fété Olé, Senegal (16°N, 15°W) over two years ; one with normal rainfall (303 mm from June to October) and an exceptionnally dry one (33 mm). A check-list, a monthly analysis of the population structure, the diversity and dominance indices of the birds numbers and biomass, are given. A decrease of the number of different species, as well as total bird population, was observed on the IBP quadrat. The annual average number of birds per ha dropped from 6.3 to 2.9, and the annual average biomass from 402 g to 186 g. Seed eaters (doves), which need to drink daily, contributed at least one third of the dry season population in 1969-70, whereas they completely disappeared in 1972-73. Species that do not need to drink regularly (insectivores and fruit-eaters), or species which can fly long dis tances to water holes (sandgrouse) were able to stay. In 1972-73 the decrease in population numbers can obviously be related to the shortage of food : the very low rainfall did not allow the germination of seeds and no water was able to accumu late in the hollows after the rains. Many species were thus compelled to move away. No breeding took place in 1972-73 and the bird population was unable to compensate for the losses due to mortality

Power calculation for gravitational radiation: oversimplification and the importance of time scale

A simplified formula for gravitational-radiation power is examined. It is shown to give completely erroneous answers in three situations, making it useless even for rough estimates. It is emphasized that short timescales, as well as fast speeds, make classical approximations to relativistic calculations untenable.Comment: Three pages, no figures, accepted for publication in Astronomische Nachrichte

Characterizing web pornography consumption from passive measurements

Web pornography represents a large fraction of the Internet traffic, with thousands of websites and millions of users. Studying web pornography consumption allows understanding human behaviors and it is crucial for medical and psychological research. However, given the lack of public data, these works typically build on surveys, limited by different factors, e.g. unreliable answers that volunteers may (involuntarily) provide. In this work, we collect anonymized accesses to pornography websites using HTTP-level passive traces. Our dataset includes about $15\,000$ broadband subscribers over a period of 3 years. We use it to provide quantitative information about the interactions of users with pornographic websites, focusing on time and frequency of use, habits, and trends. We distribute our anonymized dataset to the community to ease reproducibility and allow further studies.Comment: Passive and Active Measurements Conference 2019 (PAM 2019). 14 pages, 7 figure

A Classification of Countable Lower 1-transitive Linear Orders

This paper contains a classification of countable lower 1-transitive linear orders. This is the first step in the classification of countable 1-transitive trees given in Chicot and Truss (2009): the notion of lower 1-transitivity generalises that of 1-transitivity for linear orders, and it is essential for the structure theory of 1-transitive trees. The classification is given in terms of coding trees, which describe how a linear order is fabricated from simpler pieces using concatenations, lexicographic products and other kinds of construction. We define coding trees and show that a coding tree can be constructed from a lower 1-transitive linear order (X,≤) by examining all the invariant partitions on X. Then we show that a lower 1-transitive linear order can be recovered from a coding tree up to isomorphism

GeneRax: A Tool for Species-Tree-Aware Maximum Likelihood-Based Gene Family Tree Inference under Gene Duplication, Transfer, and Loss

Inferring phylogenetic trees for individual homologous gene families is difficult because alignments are often too short, and thus contain insufficient signal, while substitution models inevitably fail to capture the complexity of the evolutionary processes. To overcome these challenges, species-tree-aware methods also leverage information from a putative species tree. However, only few methods are available that implement a full likelihood framework or account for horizontal gene transfers. Furthermore, these methods often require expensive data preprocessing (e.g., computing bootstrap trees) and rely on approximations and heuristics that limit the degree of tree space exploration. Here, we present GeneRax, the first maximum likelihood species-tree-aware phylogenetic inference software. It simultaneously accounts for substitutions at the sequence level as well as gene level events, such as duplication, transfer, and loss relying on established maximum likelihood optimization algorithms. GeneRax can infer rooted phylogenetic trees for multiple gene families, directly from the per-gene sequence alignments and a rooted, yet undated, species tree. We show that compared with competing tools, on simulated data GeneRax infers trees that are the closest to the true tree in 90% of the simulations in terms of relative Robinson–Foulds distance. On empirical data sets, GeneRax is the fastest among all tested methods when starting from aligned sequences, and it infers trees with the highest likelihood score, based on our model. GeneRax completed tree inferences and reconciliations for 1,099 Cyanobacteria families in 8 min on 512 CPU cores. Thus, its parallelization scheme enables large-scale analyses. GeneRax is available under GNU GPL at https://github.com/BenoitMorel/GeneRax (last accessed June 17, 2020)

Lie Superalgebras and the Multiplet Structure of the Genetic Code II: Branching Schemes

Continuing our attempt to explain the degeneracy of the genetic code using basic classical Lie superalgebras, we present the branching schemes for the typical codon representations (typical 64-dimensional irreducible representations) of basic classical Lie superalgebras and find three schemes that do reproduce the degeneracies of the standard code, based on the orthosymplectic algebra osp(5|2) and differing only in details of the symmetry breaking pattern during the last step.Comment: 34 pages, 9 tables, LaTe

First orbital solution for the non-thermal emitter Cyg OB2 #9

After the first detection of its binary nature, the spectroscopic monitoring of the non-thermal radio emitter Cyg OB2 #9 (P=2.4yrs) has continued, doubling the number of available spectra of the star. Since the discovery paper of 2008, a second periastron passage has occurred in February 2009. Using a variety of techniques, the radial velocities could be estimated and a first, preliminary orbital solution was derived from the HeI5876 line. The mass ratio appears close to unity and the eccentricity is large, 0.7--0.75. X-ray data from 2004 and 2007 are also analyzed in quest of peculiarities linked to binarity. The observations reveal no large overluminosity nor strong hardness, but it must be noted that the high-energy data were taken after the periastron passage, at a time where colliding wind emission may be low. Some unusual X-ray variability is however detected, with a 10% flux decrease between 2004 and 2007. To clarify their origin and find a more obvious signature of the wind-wind collision, additional data, taken at periastron and close to it, are needed.Comment: 15 pages, 4 figures, accepted by Ap