The CoRoT Evolution and Seismic Tools Activity: Goals and Tasks

The forthcoming data expected from space missions such as CoRoT require the capacity of the available tools to provide accurate models whose numerical precision is well above the expected observational errors. In order to secure that these tools meet the specifications, a team has been established to test and, when necessary, to improve the codes available in the community. The CoRoT evolution and seismic tool activity (ESTA) has been set up with this mission. Several groups have been involved. The present paper describes the motivation and the organisation of this activity, providing the context and the basis for the presentation of the results that have been achieved so far. This is not a finished task as future even better data will continue to demand more precise and complete tools for asteroseismology.Comment: 11 pages, 3 figures, accepted for publication in Astrophysics and Space Science, 'CoRoT ESTA' special volum

Tight asteroseismic constraints on core overshooting and diffusive mixing in the slowly rotating pulsating B8.3V star KIC 10526294

KIC 10526294 is a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the mixing properties of the star. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra diffusive mixing. We find a tight mass, metallicity relation within the ranges $M$ ~ 3.13 to 3.25 Msun and $Z$ ~ 0.014 to 0.028. We deduce that an exponentially decaying diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of $f_{ov}$ between 0.017 and 0.018. Moreover, the inclusion of extra diffusive mixing with a value of $\log D_{\rm mix}$ between 1.75 and 2.00 dex (with $D_{\rm mix}$ in cm^2/sec) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra mixing is considered, irrespective of the $(M,Z)$ combination within the allowed seismic range. The inclusion of diffusive mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.Comment: 13 pages, 4 tables, 12 figures, accepted for publication in Astronomy & Astrophyic

On the shape of core overshooting in stellar model computations, and asteroseismic tests

Slowly pulsating B stars (SPB) and $\gamma$ Dor stars pulsate in high-order gravity (g-) modes. The frequencies of g-modes are sensitive to the detailed structure and evolution history of stars having convective cores. Receding convective cores in OB-type stars leave behind a chemically inhomogenous $\nabla_\mu>0$ radiative zone. Once a g-mode has radial nodes near the boundaries of these layers, the mode gets trapped and its period deviates from asymptotic period spacing. Careful study of such trapped modes allows constraining the extent of such layers by fitting individual pulsation frequencies. We employ 19 consecuitve dipole g-modes of a very rich Kepler SPB pulsator, KIC 10526294, to demonstrate the power of mode trapping in B-stars in studying the thermal and chemical stratification in the overshooting layer.Comment: 4 pages, 4 figures; to appear in the proceedings of "Physics of Evolved Stars 2015 - A conference dedicated to the memory of Olivier Chesneau

Grids of Stellar Models and Frequencies with CLES + LOSC

We present a grid of stellar models, obtained with the CLES evolution code, following the specification of ESTA-Task1, and the corresponfing seismic properties, computed with the LOSC code. We provide a complete description of the corresponding files that will be available on the ESTA web-pages.Comment: 8 pages, accepted for publication in Astrophys. Space Sci. (CoRoT/ESTA Volume

Risk premium shocks, monetary policy and exchange rate pass-through in the Czech Republic, Hungary and Poland

This paper investigates the role of monetary policy in a small open economy, where exchange rate shocks are important. VAR models are estimated for the Czech Republic, Hungary and Poland. Contemporaneous and sign restrictions are imposed in order to identify the effect of monetary policy and risk premium shocks. Estimates from the same model for Canada, Sweden and the UK are used as benchmark for developed economies with low inflation. The results suggest that the typical size a of risk premium shock renders it almost impossible for the interest rate policy to smooth the exchange rate with the aim of minimising inflationary consequences. On the other hand, low inflation may decrease the exchange rate pass-through, which helps the monetary policy ignore exchange rate shocks.monetary policy, risk premium shocks, exchange rate pass-through, structural VAR, sign restriction

The Dynamics of an Open Access: The case of the Baltic Sea Cod Fishery - A Strategic Approach -

The paper sets up a discrete-time, deterministic model of a single industry, in the light of the benchmark theory of Smith (1968). The model is used to de-scribe the dynamics of recovery from a replenishable resource such as the case of the eastern Baltic Cod fishery. The model advances from Smith’s (1968) theory since it includes a biological function dividing the change in the biomass into growth occurring during the year and recruits entering the spawning stock biomass and a dynamic entry/exit function applying a slightly more technical production function than the Schaefer production function. Theoretical possible types of steady state are discussed before the theory is applied to the eastern Baltic Sea cod fishery. The path the fishery has been following since 1982 is determined and it is discussed how it relates to the optimal path to steady state. The paper further throws light on questions as; Are we able to understand the dynamic behavior of fishermen in this fishery? Does a stable equilibrium exits and how is the path to this equilibrium described? When a fishery is regarded outside safe biological limits, could it be on the path to a positive steady state?

The Macroeconomics Shocks and the Brazilian Agricultural Price Evolution – A VAR Analysis Approach

The findings presented in this paper come from our study of the effects of Brazilian macroeconomic policy on the Brazilian Farm [product] Price Index using an adapted version of Frankel’s (1986 & 2006) theoretical model. The study examined the connection between Brazilian farm prices and external variables (worldwide importation of agribusiness products, international commodity prices, and foreign real interest rates) and between Brazilian farm prices and domestic variables (GDP, the real exchange rate, and local interest rates).