Two-dimensional models of early-type fast rotating stars: new challenges in stellar physics

Two-dimensional models of rapidly rotating stars are already unavoidable for the interpretation of interferometric or asteroseismic data of this kind of stars. When combined with time evolution, they will allow the including of a more accurate physics for the computation of element transport and the determination of surface abundances. In addition, modeling the evolution of rotation will improve gyrochronology. Presently, two-dimensional ESTER models predict the structure and the large-scale flows (differential rotation and meridional circulation) of stars with mass larger than 1.7Msun at any rotation rate. Main sequence evolution can be mimicked by varying the hydrogen content of the convective core. Models have been successfully tested on half a dozen of nearby fast rotating stars observed with optical or infra-red interferometers. They are now the right tool to investigate the oscillation spectrum of early-type fast rotators.Comment: 10 pages, to appear in the proceedings of the conference "New advances in stellar physics: from microscopic to macroscopic processes", Roscoff, May 201

Gravity Darkening in Binary Stars

Context.Interpretation of light curves of many types of binary stars requires the inclusion of the (cor)relation between surface brightness and local effective gravity. Until recently, this correlation has always been modeled by a power law relating the flux or the effective temperature and the effective gravity, namely T_eff {\alpha} g_eff^{\beta}. Aims. We look for a simple model that can describe the variations of the flux at the surface of stars belonging to a binary system. Methods. This model assumes that the energy flux is a divergence-free vector anti-parallel to the effective gravity. The effective gravity is computed from the Roche model. Results. After explaining in a simple manner the old result of Lucy (1967), which says that {\beta}=0.08 for solar type stars, we first argue that one-dimensional models should no longer be used to evaluate gravity darkening laws. We compute the correlation between log T_eff and log g_eff using a new approach that is valid for synchronous, weakly magnetized, weakly irradiated binaries. We show that this correlation is approximately linear, validating the use of a power law relation between effective temperature and effective gravity as a first approximation. We further show that the exponent {\beta} of this power law is a slowly varying function, which we tabulate, of the mass ratio of the binary star and the Roche lobe filling factor of the stars of the system. The exponent {\beta} remains mostly in the interval (0.20, 0.25) if extreme mass ratios are eliminated. Conclusions. For binary stars that are synchronous, weakly magnetized and weakly irradiated, the gravity darkening exponent is well constrained and may be removed from the free parameters of the models

Modos de oscilación en estrellas con simetría axial

Las estrellas en rotación tienen gran importancia en Astrosismología. En la actualidad, existe una gran cantidad de observaciones de estrellas de tipo delta Scuti en las cuales se han detectado frecuencias de oscilación, aunque su estructura no está aún bien entendida. Desafortunadamente, hasta la fecha, los métodos disponibles para calcular las oscilaciones en este tipo de estrellas se basan en técnicas perturbativas, las cuales solamente son válidas para velocidades de rotación bajas. El objetivo de esta tesis es la elaboración de un algoritmo matemático y el correspondiente código numérico (OMASS2d) para calcular los modos acústicos de oscilación en una estrella cuya estructura está fuertemente deformada por la rotación. Usando este nuevo código se han encontrado varias propiedades acerca de la naturaleza de las oscilaciones de una estrella en rotación. En la estructura de los multipletes del espectro de oscilaciones encontramos varios efectos, entre los que se incluyen el apareamiento de las frecuencias de modos con igual n y l, pero distinto m. También observamos que los modos con igual l y m están igualmente espaciados en frecuencia. Asimismo se presentan resultados importantes sobre el acoplamiento de los modos de oscilación. Estas propiedades pueden servir de ayuda para la clasificación e identificación de los modos de oscilación de una estrella en rotació

The first two-dimensional stellar structure and evolution models of rotating stars

Rotation is a key ingredient in the theory of stellar structure and evolution. Until now, stellar evolution codes operate in a 1-D framework for which the validity domain in regards to the rotation rate is not well understood. This letter aims at presenting the first results of self-consistent stellar models in two spatial dimensions that compute the time evolution of a star and its rotation rate along the main sequence together with a comparison to observations. We make use of an extended version of the ESTER code that solves the stellar structure of a rotating star in two dimensions with time evolution, including chemical evolution, and an implementation of rotational mixing. We have computed evolution tracks for a 12Msun model, once for an initial rotation rate equal to 15% of the critical frequency, and once for 50%. We first show that our model initially rotating at 15% of the critical frequency is able to reproduce all the observations of the $\beta$ Cephei star HD 192575 recently studied by Burssens et al. with asteroseismology. Beyond the classical surface parameters like effective temperature or luminosity, our model also reproduces the core mass along with the rotation rate of the core and envelope at the estimated age of the star. This particular model also shows that the meridional circulation has a negligible influence on the transport of chemical elements, like nitrogen, for which the abundance may be increased at the stellar surface. Furthermore, it shows that in the late main sequence, nuclear evolution is faster than the relaxation time needed to reach a steady state of the star angular momentum distribution. We have demonstrated that we have successfully taken the new step towards 2-D evolutionary modelling of rotating stars. It opens new perspectives on the understanding of the dynamics of fast rotating stars and on the way rotation impacts stellar evolution.Comment: Accepted for publication in Astronomy & Astrophysics Letters, 9 page

The key points for communication by material means during the Late Holocene in central-west Santa Cruz (Southern Patagonia, Argentina)

Se estudian puntos claves en el espacio para la comunicación por medios materiales durante los últimos 2500 años en Patagonia meridional. Se caracterizan los sitios con mayor cantidad de motivos rupestres en la meseta del Strobel (Argentina) considerando cuatro ejes: emplazamientos seleccionados, intensidad de producción rupestre, variedad de información comunicada y lapsos temporales representados. Se busca comprender los criterios de selección de estos espacios y de las estrategias de circulación de información en este período. Se evalúa la importancia de estos sitios en una escala espacial amplia y se resalta su relevancia para comprender los circuitos de comunicación entre poblaciones humanas durante el Holoceno Tardío.Key points in space for communication by material means during the last 2500 years in southern Patagonia are studied. The sites with the greatest number of rock art motifs on the Strobel plateau (Argentina) are characterized in terms of four axes: the selected locations, the intensity of rock art production, the variety of information communicated, and the time periods represented. We seek to understand the criteria for the selection of these spaces and the strategies related to the circulation of information during this period of time. The importance of these sites in a wide spatial scale is evaluated, and their relevance for the understanding of the communication circuits among human populations during the Late Holocene is highlighted.Fil: Re, Anahi. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentina. Universidad de Buenos Aires; ArgentinaFil: Guichon, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Actividades Espaciales. Conae Sede Buenos Aires; Argentina. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; ArgentinaFil: Espinosa, Mariana. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; ArgentinaFil: Martínez, Lara. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentin

The Energetic Particle Detector: Energetic particle instrument suite for the Solar Orbiter mission

After decades of observations of solar energetic particles from space-based observatories, relevant questions on particle injection, transport, and acceleration remain open. To address these scientific topics, accurate measurements of the particle properties in the inner heliosphere are needed. In this paper we describe the Energetic Particle Detector (EPD), an instrument suite that is part of the scientific payload aboard the Solar Orbiter mission. Solar Orbiter will approach the Sun as close as 0.28 au and will provide extra-ecliptic measurements beyond ∼30° heliographic latitude during the later stages of the mission. The EPD will measure electrons, protons, and heavy ions with high temporal resolution over a wide energy range, from suprathermal energies up to several hundreds of megaelectronvolts/nucleons. For this purpose, EPD is composed of four units: the SupraThermal Electrons and Protons (STEP), the Electron Proton Telescope (EPT), the Suprathermal Ion Spectrograph (SIS), and the High-Energy Telescope (HET) plus the Instrument Control Unit that serves as power and data interface with the spacecraft. The low-energy population of electrons and ions will be covered by STEP and EPT, while the high-energy range will be measured by HET. Elemental and isotopic ion composition measurements will be performed by SIS and HET, allowing full particle identification from a few kiloelectronvolts up to several hundreds of megaelectronvolts/nucleons. Angular information will be provided by the separate look directions from different sensor heads, on the ecliptic plane along the Parker spiral magnetic field both forward and backwards, and out of the ecliptic plane observing both northern and southern hemispheres. The unparalleled observations of EPD will provide key insights into long-open and crucial questions about the processes that govern energetic particles in the inner heliosphere.Ministerio de Economía y CompetitividadAgencia Estatal de Investigació