Low-mass and sub-stellar eclipsing binaries in stellar clusters

We highlight the importance of eclipsing double-line binaries in our understanding on star formation and evolution. We review the recent discoveries of low-mass and sub-stellar eclipsing binaries belonging to star-forming regions, open clusters, and globular clusters identified by ground-based surveys and space missions with high-resolution spectroscopic follow-up. These discoveries provide benchmark systems with known distances, metallicities, and ages to calibrate masses and radii predicted by state-of-the-art evolutionary models to a few percent. We report their density and discuss current limitations on the accuracy of the physical parameters. We discuss future opportunities and highlight future guidelines to fill gaps in age and metallicity to improve further our knowledge of low-mass stars and brown dwarfs.Comment: 30 pages, 5 figures, no table. Review pape

A review on macrobenthic trophic relationships along subtropical sandy shores in southernmost Brazil

Main trophic relationships that occur along the exposed sandy shores in southernmost Brazil (,336 S) are established taking into account several biological compartments operating at morphodynamically distinct environments. Beaches are predominantly of the intermediate type but some stretches of coastline are truly dissipative (Cassino Beach) or tending-to-reflective (Concheiros Beach), presenting thus diverse biological compartments and inhabitant macrobenthic assemblages. Dense concentrations of the surf-zone diatom Asterionellopsis glacialis are responsible - at least for the intermediate shorelines - for the most year-round primary production, sustaining several consumers up to tertiary level. Among them, bivalves Amarilladesma mactroides, Donax hanleyanus and the hippid crab Emerita brasiliensis can account for more than 95% of all the surf-zone secondary production, in addition to the elevated biomass of the suspension-feeder polychaete Spio gaucha and the scavenger isopod Excirolana armata. Crabs, whelks, carnivorous polychaetes, seabirds and surf-zone fishes may also be present and occupy superior trophic levels depending on the beach morphodynamics. Based on the high species richness, abundance and the role of macrobenthic fauna in transferring matter and energy to seabirds and the surf-zone fish assemblages, we address this important issue on the Southwestern Atlantic ecology. Conservation efforts should be implemented for the southernmost Brazilian sandy shores, at least for those non urbanized areas.As principais relac¸o˜ es tro´ ficas observadas ao longo da costa arenosa exposta do extremo sul do Brasil (,336 S) sa˜o estabelecidas levando-se em considerac¸a˜o os va´ rios compartimentos biolo´ gicos que operam em ambientes morfodinamicamente distintos. Estas praias sa˜o predominantemente do tipo intermedia´ rio, embora alguns trechos sejam dissipativos (Praia do Cassino) ou apresentem tendeˆncias reflectivas (Praia dos Concheiros), possuindo compartimentos biolo´ gicos diversificados e associac¸o˜es macrobentoˆnicas residentes. Densas concentrac¸o˜ es da diatoma´cea Asterionellopsis glacialis sa˜o responsa´ veis - pelo menos para as praias intermedia´ rias - por grande parte da produtividade prima´ ria anual, sustentando va´ rios consumidores ate´ o nı´vel tercia´ rio. Entre estes, os bivalves Amarilladesma mactroides, Donax hanleyanus e o crusta´ceo Emerita brasiliensis sa˜o responsa´ veis por mais de 95% de toda a produc¸a˜o secunda´ ria da zona de surfe, em adic¸a˜o a` elevada biomassa do poliqueta suspensı´voro Spio gaucha e do iso´pode necro´fago Excirolana armata. Caranguejos, gastro´ podes, poliquetas carnı´voros, aves marinhas e peixes da zona de surfe tambe´m podem estar presentes, ocupando nı´veis tro´ ficos superiores dependendo da morfodinaˆmica praial. Baseado na alta riqueza de espe´cies, na abundaˆncia e no papel da macrofauna bentoˆ nica em transferir mate´ria e energia para as aves marinhas e as assemble´ias de peixes da zona de surfe, esta importante questa˜o ecolo´ gica do Atlaˆntico Sudoeste foi investigada. Esforc¸os de conservac¸a˜o devem ser implementados nas praias arenosas do extremo sul do Brasil, pelo menos naquelas a´ reas na˜o urbanizadas

The timing and effect of the earliest human arrivals in North America

The peopling of the Americas marks a major expansion of humans across the planet. However, questions regarding the timing and mechanisms of this dispersal remain, and the previously accepted model (termed ‘Clovis-first’)—suggesting that the first inhabitants of the Americas were linked with the Clovis tradition, a complex marked by distinctive fluted lithic points1—has been effectively refuted. Here we analyse chronometric data from 42 North American and Beringian archaeological sites using a Bayesian age modelling approach, and use the resulting chronological framework to elucidate spatiotemporal patterns of human dispersal. We then integrate these patterns with the available genetic and climatic evidence. The data obtained show that humans were probably present before, during and immediately after the Last Glacial Maximum (about 26.5–19 thousand years ago)2,3 but that more widespread occupation began during a period of abrupt warming, Greenland Interstadial 1 (about 14.7–12.9 thousand years before AD 2000)4. We also identify the near-synchronous commencement of Beringian, Clovis and Western Stemmed cultural traditions, and an overlap of each with the last dates for the appearance of 18 now-extinct faunal genera. Our analysis suggests that the widespread expansion of humans through North America was a key factor in the extinction of large terrestrial mammals