Asteroseismology and interferometry     

M. S. Cunha  C. Aerts  J. Christensen-Dalsgaard  A. Baglin  L. Bigot  T. M. Brown  C. Catala  O. L. Creevey  A. Domiciano de Souza  P. Eggenberger  P. J. V. Garcia  F. Grundahl  P. Kervella  D. W. Kurtz  P. Mathias  A. Miglio  M. J. P. F. G. Monteiro  G. Perrin  F. P. Pijpers  D. Pourbaix  A. Quirrenbach  K. Rousselet-Perraut  T. C. Teixeira  F. Thévenin  M. J. Thompson 《Astronomy and Astrophysics Review》2007,14(3-4):217-360

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.  相似文献   

The solar flares of February 1986 and the ensuing intense geomagnetic storm     

Howard A. Garcia  Murray Dryer 《Solar physics》1971,109(1):119-137

A very intense geomagnetic storm, the largest observed in 26 years, was observed in early February 1986 having just been preceded by a series of six solar flares during the period 3–7 February. The storm and its antecedent flares are currently a subject of great interest because of the unusually large magnitude of the various geomagnetic effects that obtained. The fact that the flares were moderate to large in soft X-ray intensity, but much smaller than the largest that the Sun is capable of producing, coupled with the fact that these events occurred near the minimum of the current solar activity cycle, adds to the uniqueness of the overall episode.This paper describes the special circumstances surrounding these events and offers an interpretation of the cause and effect relationships through a numerical simulation of the dynamical evolutionary processes that may have occurred in interplanetary space.  相似文献   

Proton Enhancements and Their Relation to the X-Ray Flares During the Three Last Solar Cycles   总被引：1，自引：0，他引：1  

A.?Belov  H.?Garcia  V.?Kurt  H.?MavromichalakiEmail author  M.?Gerontidou 《Solar physics》2005,229(1):135-159

Energetic proton measurements obtained from the GOES and IMP-8 satellites as well as from ground-based neutron monitors are compared with the GOES soft X-ray measurements of the associated solar flares for the period 1975–2003. The present study investigates a broad range of phenomenology relating proton events to flares (with some references to related interplanetary disturbances), including correlations of occurrence, intensities, durations and timing of both the particle event and the flare as well as the role of the heliographic location of the designated active region. 1144 proton events of > 10 MeV energy were selected from this 28-year period. Owing primarily to the low particle flux threshold employed more than half of this number was found to be reliably connected with an X-ray flare. The statistical analysis indicates that the probability and magnitude of the near-Earth proton enhancement depends critically on the flare's importance and its heliolongitude. In this study all flares of X-ray importance > X5 and located in the most propitious heliolongitude range, 15^∘W to 75^∘W, were succeeded by a detectable proton enhancement. It was also found that the heliolongitude frequently determines the character of the proton event time profile. In addition to intensity, duration and timing, proton events were found to be related to the other flare properties such as lower temperatures and longer loop lengths.  相似文献   

Triassic metasedimentary successions across the boundary between the southern Apennines and the Calabrian Arc (northern Calabria,Italy)     

A. Iannace  F. J. Garcia‐Tortosa  S. Vitale 《Geological Journal》2005,40(2):155-171

The boundary area between the Apenninic fold‐and‐thrust belt and the crystalline Calabrian Arc, located around Sangineto in northern Calabria, has been investigated. New geological mapping in the Sant'Agata area has been performed on the Triassic successions traditionally attributed to the metasedimentary San Donato Unit. This, coupled with a reappraisal of the stratigraphy and tectonics of coeval successions present more to the south in the Cetraro Unit, results in a new reconstruction of the Triassic evolution of all the metasedimentary successions found in the region. Four informal stratigraphic units have been distinguished in the S. Agata area. The lowest one (Unit A) consists of well‐bedded metalimestones and bioturbated marly limestones that correlate with Ladinian–Carnian carbonates in nearby areas. A second unit (Unit B), never recognized before, contains a complex alternation of dolomites, phyllites and some meta‐arenites containing several beds of Cavernoso facies, attributed to the Carnian. They grade upward to platform and platform‐margin dolomites of Norian–Rhaetian age (Unit C) that in turn are replaced upward and laterally by a fourth unit (Unit D) consisting of well‐bedded, dark dolomites and metalimestones with marly interlayers locally found as resedimented large blocks in slope conglomerates. Unit D correlates with Rhaetian–Liassic beds in nearby areas. Several pieces of evidence of post‐metamorphic contractional tectonics, with 140°N and 30°N trends, are found together with evidence of SW‐directed extension. The siliciclastic Carnian beds of Unit B are correlated with the phyllites of Cetraro, formerly believed to be Middle Triassic; moreover, it is suggested that in the Cetraro area Unit C is almost totally replaced by Unit D. This demonstrates that the former distinction between the two tectonic units in the whole area has to be discarded. We have made a general palaeoenvironmental reconstruction which progresses laterally, during Ladinian–Carnian times, from (i) a coastal, mixed siliciclastic–carbonate–evaporitic area at Cetraro to (ii) a transitional carbonate shelf where siliciclastic input was only episodic, and finally to (iii) a bioconstructed margin which was later replaced by a steepened margin created by tectonic instability. Starting from the Norian, subsidence shifted toward the former coastal area where an intraplatform, restricted basin developed. The proposed stratigraphy corresponds closely to the Alpujarride units of the Betic Cordillera, Spain. Moreover, it is shown that strong affinities also exist, in terms of the structural framework, with the metamorphic units of Tuscany and Liguria. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The metahyaloclastitic matrix of a unique metavolcanic block reveals subduction in the Somozas Mélange (Cabo Ortegal Complex,NW Iberia): tectonic implications for the assembly of Pangea          下载免费PDF全文

I. Novo‐Fernández  A. Garcia‐Casco  R. Arenas  R. Díez Fernández 《Journal of Metamorphic Geology》2016,34(9):963-985

The allochthonous Cabo Ortegal Complex (NW Iberian Massif) contains a ~500 m thick serpentinite‐matrix mélange located in the lowest structural position, the Somozas Mélange. The mélange occurs at the leading edge of a thick nappe pile constituted by a variety of terranes transported to the East (present‐day coordinates; NW Iberian allochthonous complexes), with continental and oceanic affinities, and represents a Variscan suture. Among other types of metaigneous (calcalkaline suite dated at 527–499 Ma) and metasedimentary blocks, it contains close‐packed pillow‐lavas and broken pillow‐breccias with a metahyaloclastitic matrix formed by muscovite–paragonite–margarite–garnet–chlorite–kyanite–hematite–epidote–quartz–rutile. Pseudosection modelling in the MnCNTKFMASHO system indicates metamorphic peak conditions of ~17.5–18 kbar and ~550 °C followed by near‐isothermal decompression. This P–T evolution indicates subduction/accretion of an arc‐derived section of peri‐Gondwanan transitional crust. Subduction below the Variscan orogenic wedge evolved to continental collision with important dextral component. Closure of the remaining oceanic peri‐Gondwanan domain and associated release of fluid led to hydration of the overlying mantle wedge and the formation of a low‐viscosity subduction channel, where return flow formed the mélange. The submarine metavolcanic rocks were deformed and detached from the subducting transitional crust and eventually incorporated into the subduction channel, where they experienced fast exhumation. Due to the cryptic nature of the high‐P metamorphism preserved in its tectonic blocks, the significance of the Somozas Mélange had remained elusive, but it is made clear here for the first time as an important tectonic boundary within the Variscan Orogen formed during the late stages of the continental convergence leading to the assembly of Pangea.  相似文献   

Delineating coastal groundwater discharge processes in a wetland area by means of electrical resistivity imaging, 224Ra and 222Rn          下载免费PDF全文

Mario Zarroca  Rogelio Linares  Valentí Rodellas  Jordi Garcia‐Orellana  Carles Roqué  Joan Bach  Pere Masqué 《水文研究》2014,28(4):2382-2395

Coastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peníscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra‐enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra‐rich groundwater have induced high activities of Ra isotopes and ²²²Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modelling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers (²²⁴Ra, ²²²Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater‐fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Structure and recent evolution of the Hazar Basin: a strike‐slip basin on the East Anatolian Fault,Eastern Turkey     

D. Garcia Moreno  A. Hubert‐Ferrari  J. Moernaut  J. G. Fraser  X. Boes  M. Van Daele  U. Avsar  N. Çağatay  M. De Batist 《Basin Research》2011,23(2):191-207

The Hazar Basin is a 25 km‐long, 7 km‐wide and 216 m‐deep depression located on the central section of the East Anatolian Fault zone (eastern Turkey) and predominantly overlain by Lake Hazar. This basin has been described previously as a pull‐apart basin because of its rhombic shape and an apparent fault step‐over between the main fault traces situated at the southwestern and northeastern ends of the lake. However, detailed structural investigation beneath Lake Hazar has not been undertaken previously to verify this interpretation. Geophysical and sedimentological data from Lake Hazar were collected during field campaigns in 2006 and 2007. The analysis of this data reveals that the main strand of the East Anatolian Fault (the Master Fault) is continuous across the Hazar Basin, connecting the two segments previously assumed to be the sidewall faults of a pull‐apart structure. In the northeastern part of the lake, an asymmetrical subsiding sub‐basin, bounded by two major faults, is cross‐cut by the Master Fault, which forms a releasing bend within the lake. Comparison of the structure revealed by this study with analogue models produced for transtensional step‐overs suggests that the Hazar Basin structure represents a highly evolved pull‐apart basin, to the extent that the previous asperity has been bypassed by a linking fault. The absence of a step‐over structure at the Hazar Basin means that no significant segmentation boundary is recognised on the East Anatolian Fault between Palu and Sincik. Therefore, this fault segment is capable of causing larger earthquakes than recognised previously.  相似文献   

The United Nations system responds to Agenda 21.17: Oceans     

Heiner Naeve  Serge M. Garcia 《Ocean & Coastal Management》1995,29(1-3)

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On spin-driven inflation from inflation fields in General Relativity and COBE data     

L. C. Garcia de Andrade 《Astrophysics and Space Science》2004,294(3-4):213-217

Obukhov spin-driven inflation in general relativity is extended to include inflation fields. A de Sitter phase solution is obtained and new slow-rolling conditions for the spin potential are obtained. The spin potential reduces to Obukhov result at the present epoch of the Universe where the spin density is low with comparison to the Early Universe spin densities. A relation between the spin density energy and the temperature fluctuation can be obtained which allow us to determine the spin density energy in terms of the COBE data for temperature fluctuations.  相似文献   

The solar flares of February 1986 and the ensuing intense geomagnetic storm     

Howard A. Garcia  Murray Dryer 《Solar physics》1987,109(1):119-137

A very intense geomagnetic storm, the largest observed in 26 years, was observed in early February 1986 having just been preceded by a series of six solar flares during the period 3–7 February. The storm and its antecedent flares are currently a subject of great interest because of the unusually large magnitude of the various geomagnetic effects that obtained. The fact that the flares were moderate to large in soft X-ray intensity, but much smaller than the largest that the Sun is capable of producing, coupled with the fact that these events occurred near the minimum of the current solar activity cycle, adds to the uniqueness of the overall episode. This paper describes the special circumstances surrounding these events and offers an interpretation of the cause and effect relationships through a numerical simulation of the dynamical evolutionary processes that may have occurred in interplanetary space.  相似文献