Search for exoplanets with the radial-velocity technique: quantitative diagnostics of stellar activity

Aims: Stellar activity may complicate the analysis of high-precision radial-velocity spectroscopic data when looking for exoplanets signatures. We aim at quantifying the impact of stellar spots on stars with various spectral types and rotational velocities and comparing the simulations with data obtained with the HARPS spectrograph. Methods: We have developed detailed simulations of stellar spots and estimated their effects on a number of observables commonly used in the analysis of radial-velocity data when looking for extrasolar planets, such as radial-velocity curves, cross-correlation functions, bisector spans and photometric curves. The computed stellar spectra are then analyzed in the same way as when searching for exoplanets. Results: 1) A first grid of simulation results is built for F-K type stars, with different stellar and spot properties. 2) It is shown quantitatively that star spots with typical sizes of 1% can mimic both radial-velocity curves and the bisector behavior of short-period giant planets around G-K type stars with a vsini lower than the spectrograph resolution. For stars with intermediate vsini, smaller spots may produce similar features. In these cases, additional observables (e.g., photometry, spectroscopic diagnostics) are mandatory to confirm the presence of short-period planets. We show that, in some cases, photometric variations may not be enough to clearly rule out spots as explanations of the observed radial-velocity variations. This is particularly important when searching for super-Earth planets. 3) It is also stressed that quantitative values obtained for radial-velocity and bisector span amplitudes depend strongly on the detailed star properties, on the spectrograph used, on the set of lines used, and on the way they are measured.Comment: 12 pages, 16 figures, accepted for publication in A&

Financial Risks of Investments in Coal

Analyzes the regulatory, commodity, and construction risks of investing in coal mining and coal-fired power plants. Examines industry analysts' consensus on viable alternatives to coal, including natural gas, solar, wind, and energy efficiency

Analogy electromagnetism-acoustics: Validation and application to local impedance active control for sound absorption

An analogy between electromagnetism and acoustics is presented in 2D. The propagation of sound in presence of absorbing material is modeled using an open boundary microwave package. Validation is performed through analytical and experimental results. Application to local impedance active control for free field sound absorption is finally described

Fluctuating thermal environments of shallow-water rocky reefs in the Gulf of California, Mexico.

As part of a broad-scale study of the biogeography of rocky reefs in the Gulf of California, Mexico (GOC), we collected a continuous 1-yr temperature time series at ~5 m water depth at 16 sites spanning 5° of latitude and ~700 km along the western boundary of the basin. Throughout the region, thermal conditions were most variable in summer with fluctuations concentrated at diurnal and semi-diurnal frequencies, likely associated with solar and wind forcing and vertical water column oscillations forced by internal waves. Temperatures in winter were less variable than in summer, and minimum temperatures also differed among sites. Thermal variability integrated across the diurnal and semi-diurnal frequency bands was greatest near the Midriff Islands in the northern GOC and decreased toward the southern sites. Diurnal variability was greater than semi-diurnal variability at 13 of the 16 sites. A statistic-of-extremes analysis indicated shortest return times for cooling events in summer, and reef organisms at many of the sites may experience anomalous 2 to 5 °C cooling events multiple times per month. The significant extent of local temperature variability may play important roles in limiting species occurrences among sites across this biogeographic region

The Conversion of Spatial Planning in Denmark: Changes in National and Regional Planning Policies and Governance Structures

ntaciones estructurales, funcionales y conceptuales durante las últimas dos décadas. El marco jerárquico de administración en el que las políticas y las prácticas del ordenamiento territorial solían llevarse a cabo fue ampliamente modificado después de una reforma del gobierno local implementada en 2007. Dicha reforma propició la revocación del nivel regional, lo que indujo el reescalamiento de las políticas, las funciones y las responsabilidades del ordenamiento territorial a los niveles municipal y nacional. A través del análisis de estos cambios estructurales, este artículo se sumerge en la reorientación de las políticas de ordenamiento territorial a diferentes escalas, en la evolución del rol de la ordenación del territorio en la gestión del crecimiento y del desarrollo, y en los cambios de las estructuras de gobernanza asociados a la ordenación del territorio en Dinamarca.Danish spatial planning has been increasingly subjected to significant structural, functional and conceptual reorientations over the past two decades. The comprehensive hierarchical framework wherein planning policies and practices used to operate became considerably modified after the implementation of a local government reform back in 2007. The reform abolished the county level, which implied the re-scaling of planning policies, functions and responsibilities to municipal and national levels. This situation brought about radical shifts concerning the implementation of land-use tasks and the performance of institutional arrangements within and beyond the planning system. Based on an analysis concerned with these structural changes, the paper delves into the reorientation of spatial planning in Denmark in terms of the evolving conception of planning policies at different territorial scales, the changing role of planning in catering to growth and development matters, and the shifting institutional arrangements associated with the planning domain.L’ordenació del territori a Dinamarca ha estat significativament sotmesa a reorientacions estructurals, funcionals i conceptuals durant les darreres dues dècades. El marc jeràrquic d’administració en què les polítiques i les pràctiques de l’ordenament territorial solien dur-se a terme fou àmpliament modificat després d’una reforma del govern local implantada el 2007. Aquesta reforma propicià la revocació del nivell regional, induint el reescalament de les polítiques, les funcions i les responsabilitats de l’ordenament territorial als nivells municipal i nacional. A través de l’anàlisi d’aquests canvis estructurals, aquest article s’immergeix en la reorientació de les polítiques d’ordenament territorial a diferents escales, en l’evolució del paper de l’ordenació del territori en la gestió del creixement i del desenvolupament, i en els canvis de les estructures de governança associats a l’ordenació del territori a Dinamarca

Extrasolar planets and brown dwarfs around A-F type stars VI. High precision RV survey of early type dwarfs with HARPS

(Abridged) Aims: Systematic surveys to search for exoplanets have been mostly dedicated to solar-type stars sofar. We developed in 2004 a method to extend such searches to earlier A-F type dwarfs and started spectroscopic surveys to search for planets and quantify the detection limit achievable when taking into account the stars properties and their actual levels of intrinsic variations. We give here the first results of our southern survey with HARPS. Results: 1) 64% of the 170 stars with enough data points are found to be variable. 20 are found to be binaries or candidate binaries (with stars or brown dwarfs). More than 80% or the latest type stars (once binaries are removed) are intrinsically variable at a 2 m/s precision level. Stars with earlier spectral type (B-V <= 0.2) are either variable or associated to levels of uncertainties comparable to the RV rms observed on variable stars of same B-V. 2) We have detected one long-period planetary system around an F6IV-V star. 3) We have quantified the jitter due to stellar activity and we show that taking into account this jitter in addition to the stellar parameters, it is still possible to detect planets with HARPS with periods of 3 days (resp. 10 days and 100 days) on 91% (resp. 83%, 61%) of them. We show that even the earliest spectral type stars are accessible to this type of search, provided they have a low vsini and low levels of activity. 4) Taking into account the present data, we compute the actually achieved detection limits for 107 targets and discuss the limits as a function of B-V. Given the data at hand, our survey is sensitive to short-period (few days) planets and to longer ones (100 days) at a lower extent (latest type stars). We derive first constrains on the presence of planets around A-F stars for these ranges of periods.Comment: 18 pages, 12 figures, 5 tables, A&A accepte