Extremely metal‐poor stars in SDSS fields     

P. Bonifacio  E. Caffau  P. Franois  L. Sbordone  H.‐G. Ludwig  M. Spite  P. Molaro  F. Spite  R. Cayrel  F. Hammer  V. Hill  M. Nonino  S. Randich  B. Stelzer  S. Zaggia 《Astronomische Nachrichten》2011,332(3):251-257

Some insight on the first generation of stars can be obtained from the chemical composition of their direct descendants, extremely metal‐poor stars (EMP), with metallicity less than or equal to 1/1000 of the solar metallicity. Such stars are exceedingly rare, the most successful surveys, for this purpose, have so far provided only about 100 stars with 1/1000 the solar metallicity and 4 stars with about 1/10000 of the solar metallicity. The Sloan Digital Sky Survey has the potential to provide a large number of candidates of extremely low metallicity. X‐shooter has the unique capability of performing the necessary follow‐up spectroscopy providing accurate metallicities and abundance ratios for several elements (Mg, Al, Ca, Ti, Cr, Sr,...) for EMP candidates. We here report on the results for the first two stars observed in the course of our Franco‐Italian X‐shooter GTO. The two stars were targeted to be of metallicity around –3.0, the analysis of the X‐shooter spectra showed them to be of metallicity around –2.0, but with a low α to iron ratio, which explains the underestimate of the metallicity from the SDSS spectra. The efficiency of X‐shooter allows an in situ study of the outer halo, for the two stars studied here we estimate distances of 3.9 and 9.1 kpc, these are likely the most distant dwarf stars studied in detail to date (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Boron isotopes in tourmaline as a tracer of metasomatic processes in the Bamble sector of Southern Norway     

R.?BastEmail author  E.?E.?Scherer  K.?Mezger  H.?Austrheim  T.?Ludwig  H.?R.?Marschall  A.?Putnis  K.?L?wen 《Contributions to Mineralogy and Petrology》2014,168(4):1069

The Bamble sector of southern Norway comprises metagabbros and metasediments that were metasomatically altered to various extents during a late stage of the Sveconorwegian orogeny (~1.06 Ga). The infiltration of highly saline brines along veins led to penetrative scapolitization and albitization on a regional scale and the local deposition of Fe–Ti oxides. Typical secondary mineral assemblages include either scapolite + apatite + amphibole + phlogopite + tourmaline, or albite + epidote + calcite + chlorite + white mica, indicating that the fluids introduced large amounts of Na, Cl, Mg, Ca, K, P, and B to the system. Metasomatic tourmalines associated with different alteration stages as identified by variations in major-element composition and initial ⁸⁷Sr/⁸⁶Sr were analyzed for B isotopic compositions to constrain possible sources and the evolution of the hydrothermal fluid(s). Measured δ¹¹B values range from ?5 to +27 ‰ relative to SRM-951, suggesting marine evaporites interlayered with various amounts of continental detritus and pelagic clay as a possible B source reservoir. The influence of a seawater-derived component is clearly indicated by the heavy B isotope signature of tourmaline related to Al–Mg-rich metapelites. In contrast, negative δ¹¹B values can be explained by the influence of pneumatolytic fluids associated with granitic pegmatites. On a regional scale (i.e., several km), δ¹¹B values in tourmaline vary widely, whereas variations within a single outcrop (tens of m) are typically small and can be ascribed to different generations of tourmaline related to several fluid pulses.  相似文献   

Climatic and environmental changes recorded in loess     

Ian J. Smalley  Slobodan B. Markovic  Ludwig Zöller  János Kovács 《Central European Journal of Geosciences》2010,2(1):1-2

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Global streamflow and thermal habitats of freshwater fishes under climate change     

Michelle T. H. van Vliet  Fulco Ludwig  Pavel Kabat 《Climatic change》2013,121(4):739-754

Climate change will affect future flow and thermal regimes of rivers. This will directly affect freshwater habitats and ecosystem health. In particular fish species, which are strongly adapted to a certain level of flow variability will be sensitive to future changes in flow regime. In addition, all freshwater fish species are exotherms, and increasing water temperatures will therefore directly affect fishes’ biochemical reaction rates and physiology. To assess climate change impacts on large-scale freshwater fish habitats we used a physically-based hydrological and water temperature modelling framework forced with an ensemble of climate model output. Future projections on global river flow and water temperature were used in combination with current spatial distributions of several fish species and their maximum thermal tolerances to explore impacts on fish habitats in different regions around the world. Results indicate that climate change will affect seasonal flow amplitudes, magnitude and timing of high and low flow events for large fractions of the global land surface area. Also, significant increases in both the frequency and magnitude of exceeding maximum temperature tolerances for selected fish species are found. Although the adaptive capacity of fish species to changing hydrologic regimes and rising water temperatures could be variable, our global results show that fish habitats are likely to change in the near future, and this is expected to affect species distributions.  相似文献   

Stellar science from a blue wavelength range     

C. J. Hansen  H.‐G. Ludwig  W. Seifert  A. Koch  W. Xu  E. Caffau  N. Christlieb  A. J. Korn  K. Lind  L. Sbordone  G. Ruchti  S. Feltzing  R. S. de Jong  S. Barden  O. Schnurr 《Astronomische Nachrichten》2015,336(7):665-676

From stellar spectra, a variety of physical properties of stars can be derived. In particular, the chemical composition of stellar atmospheres can be inferred from absorption line analyses. These provide key information on large scales, such as the formation of our Galaxy, down to the small‐scale nucleosynthesis processes that take place in stars and supernovae. By extending the observed wavelength range toward bluer wavelengths, we optimize such studies to also include critical absorption lines in metal‐poor stars, and allow for studies of heavy elements (Z ≥ 38) whose formation processes remain poorly constrained. In this context, spectrographs optimized for observing blue wavelength ranges are essential, since many absorption lines at redder wavelengths are too weak to be detected in metal‐poor stars. This means that some elements cannot be studied in the visual‐redder regions, and important scientific tracers and science cases are lost. The present era of large public surveys will target millions of stars. It is therefore important that the next generation of spectrographs are designed such that they cover a wide wavelength range and can observe a large number of stars simultaneously. Only then, we can gain the full information from stellar spectra, from both metal‐poor to metal‐rich ones, that will allow us to understand the aforementioned formation scenarios in greater detail. Here we describe the requirements driving the design of the forthcoming survey instrument 4MOST, a multi‐object spectrograph commissioned for the ESO VISTA 4 m‐telescope. While 4MOST is also intended for studies of active galactic nuclei, baryonic acoustic oscillations, weak lensing, cosmological constants, supernovae and other transients, we focus here on high‐density, wide‐area survey of stars and the science that can be achieved with high‐resolution stellar spectroscopy. Scientific and technical requirements that governed the design are described along with a thorough line blending analysis. For the high‐resolution spectrograph, we find that a sampling of ≥2.5 (pixels per resolving element), spectral resolution of 18000 or higher, and a wavelength range covering 393–436 nm, is the most well‐balanced solution for the instrument. A spectrograph with these characteristics will enable accurate abundance analysis (±0.1 dex) in the blue and allow us to confront the outlined scientific questions. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

U-Th systematics and Th ages of carbonate chimneys at the Lost City Hydrothermal Field     

Kristin A. Ludwig  Chuan-Chou Shen  Deborah S. Kelley  R. Lawrence Edwards 《Geochimica et cosmochimica acta》2011,75(7):1869-6329

The Lost City Hydrothermal Field (LCHF) is a serpentinite-hosted vent field located 15 km west of the spreading axis of the Mid-Atlantic Ridge. In this study, uranium-thorium (U-Th) geochronological techniques have been used to examine the U-Th systematics of hydrothermal fluids and the ²³⁰Th ages of hydrothermally-precipitated carbonate chimneys at the LCHF. Fluid sample analyses indicate that endmember fluids likely contain only 0.0073 ng/g U or less compared to 3.28 ± 0.03 ng/g of U in ambient seawater. For fluid samples containing only 2-21% ambient seawater (1.1-11 mmol/kg Mg), Th concentration is 0.11-0.13 pg/g and surrounding seawater concentrations average 0.133 ± 0.016 pg/g. The ²³⁰Th/²³²Th atomic ratios of the vent fluids range from 1 (±10) × 10⁻⁶ to 11 (±5) × 10⁻⁶, are less than those of seawater, and indicate that the vent fluids may contribute a minor amount of non-radiogenic ²³⁰Th to the LCHF carbonate chimney deposits. Chimney ²³⁸U concentrations range from 1 to 10 μg/g and the average chimney corrected initial δ²³⁴U is 147.2 ± 0.8, which is not significantly different from the ambient seawater value of 146.5 ± 0.6. Carbonate ²³²Th concentrations range broadly from 0.0038 ± 0.0003 to 125 ± 16 ng/g and ²³⁰Th/²³²Th atomic ratios vary from near seawater values of 43 (±8) × 10⁻⁶ up to 530 (±25) × 10⁻³. Chimney ages, corrected for initial ²³⁰Th, range from 17 ± 6 yrs to 120 ± 13 kyrs. The youngest chimneys are at the intersection of two active, steeply-dipping normal faults that cut the Atlantis Massif; the oldest chimneys are located in the southwest portion of the field. Vent deposits on a steep, fault-bounded wall on the east side of the field are all <4 kyrs old, indicating that mass wasting in this region is relatively recent. Comparison of results to prior age-dating investigations of submarine hydrothermal systems shows that the LCHF is the most long-lived hydrothermal system known to date. It is likely that seismic activity and active faulting within the Atlantis Massif and the Atlantis Fracture Zone, coupled with volumetric expansion of the underlying serpentinized host rocks play major roles in sustaining hydrothermal activity at this site. The longevity of venting at the LCHF may have implications for ecological succession of microorganisms within serpentinite-hosted vent environments.  相似文献   

Li, Be, B concentrations and δ7Li values in plagioclase phenocrysts of dacites from Nea Kameni (Santorini, Greece)     

Joan Cabato  Rainer Altherr  Thomas Ludwig  Hans-Peter Meyer 《Contributions to Mineralogy and Petrology》2013,165(6):1135-1154

Li, Be, B and δ⁷Li SIMS analyses of plagioclase phenocrysts from the 1040–1941 Niki dacite lava (Nea Kameni, Santorini, Greece) exhibit varied processes. From their anorthite contents alone, the crystals may be segregated into four main types: type-N shows the normal decline in An during crystallisation (An_62–40); type-O has only oscillatory zoning accompanied by resorption surfaces (An_58–39); type-C is complex with high-An cores (subtype C1: An_64–58, subtype C2: An_88–73) and normal rims (An_55–42). Type-A plagioclase with high An content (An_92–82) is found within mafic enclaves. On the basis of their Li concentrations, type-O crystals may be subdivided into subtype O1 with flat Li concentration profiles and subtype O2 with decreasing Li concentration from core to rim. The concentrations of Be and B of all four types show a negative correlation with anorthite content (An), but Li concentration profiles differ amongst the different plagioclase types. Types N and O1, and the cores of type-C, are equilibrated in Li concentration. Types O2 and A, and the mantles of type-C display an initial enrichment in Li, probably from volatile influx into the melt. Consistent with the propensity towards equilibrium with the melt, these crystals display dramatic rim-ward declines in Li concentration. All analysed plagioclase crystals, except for the xenocrystic type-A, have nearly the same Li, Be and B concentrations at their rims. These coincide with the composition of plagioclase microlites in the groundmass, thereby affording estimates of plagioclase-melt partitioning for the light elements: K _Li = 0.19–0.28, K _Be = 0.24–0.38 and K _B = 0.007–0.009. δ⁷Li profiles in type-O2 and type-A phenocrysts manifest an unmistakable inverse relation to Li concentration, with variations of up to ~39 ‰, revealing preferential kinetic diffusion. This may have been driven by Li loss from the melt, most likely through degassing during decompression, perhaps in the course of magma ascent to subsequent eruption. Considering the rapid diffusion of Li in plagioclase, in situ phenocryst analyses may yield useful information about processes leading up to, or even causing, eruptions.  相似文献   

Sulphur abundances in halo stars from multiplet 3 at 1045 nm     

E. Caffau  L. Sbordone  H.‐G. Ludwig  P. Bonifacio  M. Spite 《Astronomische Nachrichten》2010,331(7):725-730

Sulphur is a volatile α ‐element which is not locked into dust grains in the interstellar medium (ISM). Hence, its abundance does not need to be corrected for dust depletion when comparing the ISM to the stellar atmospheres. The abundance of sulphur in the photosphere of metal‐poor stars is a matter of debate: according to some authors, [S/Fe] versus [Fe/H] forms a plateau at low metallicity, while, according to other studies, there is a large scatter or perhaps a bimodal distribution. In metal‐poor stars sulphur is detectable by its lines of multiplet 1 at 920 nm, but this range is heavily contaminated by telluric absorptions, and one line of the multiplet is blended by the hydrogen Paschen ζ line. We study the possibility of using multiplet 3 (at 1045 nm) for deriving the sulphur abundance because this range, now observable at the VLT with the infra‐red spectrograph CRIRES, is little contaminated by telluric absorption and not affected by blends at least in metal‐poor stars. We compare the abundances derived from multiplets 1 and 3, taking into account NLTE corrections and 3D effects. Here we present the results for a sample of four stars, although the scatter is less pronounced than in previous analysis, we cannot find a plateau in [S/Fe], and confirm the scatter of the sulphur abundance at low metallicity (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The periodicity of storm surges in the Bering Sea from 1898 to 1993, based on newspaper accounts     

Owen K. Mason  David K. Salmon  Stefanie L. Ludwig 《Climatic change》1996,34(1):109-123

Spectral analysis of 96 yr of Bering Sea storm records reported in the Nome News (1899–1903) and Nome Nugget (1901–1993) newspapers indicate regularities in the 11-, 5–7- and 3-yr periods. Statistical tests on the 11-yr period found no statistically significant correlation with sunspot cyclicity despite a tendency toward maximum storminess during low sunspot periods. The 3- and 5–7-yr cycles may correlate with variability in the El Niño Southern Oscillation and easterly shifts in the mean position of North Pacific low pressure anomalies. Storm surges were infrequent from 1916 to 1928 and 1947 to 1959, while the most frequent and intense storms hit during 1900–1913, 1936–1946, 1974–1976 and in 1992.  相似文献   

Ein Beitrag zur Petrographie Melilith-führender Olivinnephelinite aus dem Gebiet Fritzlar—Naumburg (Nordhessen)     

Dr. Ludwig Lohmann 《Contributions to Mineralogy and Petrology》1964,9(6):533-584

Zusammenfassung Tertiäre Olivinnephelinite aus dem Gebiet zwischen Naumburg und Fritzlar südwestlich des Habichtswaldes bei Kassel wurden optisch, röntgenographisch und chemisch untersucht. Die Basalte gehören dem Stamm der Alkali-Olivin-Basalte an und zeigen bis auf Vorkommen im Nordteil des Untersuchungsgebietes ein in den Hauptgemengteilen petrographisch einheitliches Bild.Im Norden des Gebietes treten Limburgite sowie Basalte mit der Paragenese Analcim + Alkalifeldspat + Nephelin auf.Tuffe Bind nur im mittleren Teil des Untersuchungsgebietes aufgeschlossen, welches infolge seiner Morphologie als ein Haupteruptionszentrum anzusehen ist.In einem Teil der Basalte trio (örtlich im Bereich weniger m) Melilith stellen-Weise mit sanduhrförmig eingelagertem Pyroxen auf. Häufig ist der Melilith pseudomorphosiert zu Karbonat und Zeolith oder einer nicht näher bestimmbaren Tonmineralkomponente.Aus dem einheitlichen Bild dieser Basalte wird geschlossen, daß in sämtlichen Vorkommen außer im nördlichen Teil des Gebietes Melilith hätte gebildet werden können. Eine solche Möglichkeit lassen die in der Literatur angegebenen experimentellen Untersuchungen der jeweiligen Systeme zu. Gegen die Bildung von SiO₂-untersättigten Schmelzen durch Assimilation von Sedimenten werden petrographische und geochemische Beobachtungen angeführt. Die Frage nach der Bildung solcher Schmelzen kann jedoch an Hand des Untersuchungsmaterials nicht beantwortet werden. Es werden Reaktionen von Olivin, Pyroxen und Magnetit mit der Sehmelze beobachtet, die denen in experimentell untersuchten Systemen entsprechen.Für das sporadische Auftreten des Melilithes bzw. seiner Pseudomorphosen werden Reaktionen mit Restschmelzen angenommen. Ein Abquetschen dieser Restschmelzen vom Ort ihrer Entstehung kann für die Bildung von Analeim-Basalten im Norden des Untersuchungsgebietes verantwortlich sein.

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Tertiary olivine-nephelinites from the region between Naumburg and Fritzlar, southwest of the Habichtswald near Kassel were investigated by optical, x-ray, and chemical methods. The basalts belong to the alkali-olivine-type. They are petrographically uniform in terms of major constituents, except a few occurrences of limburgites and analcite-basalts in the northern part of the area. The latter contain the paragenesis analcite + alkali feldspar + nepheline. Pyroclastics are only exposed in the central part of the area. Because of its morphology this part may be considered as the main eruption center. Several of the basalt-masses contain melilite, locally in patches of a few meters in extent. Hour glass-shaped inclusions of pyroxene are observed in some of them. In many rocks melilite is replaced by carbonates and zeolites or a clay mineral which could not be precisely identified. It is concluded from the uniform character of these basalts that in all occurrences except the northern part of the area melilite could have been formed. This assumption is in accordance with the experimental results of the systems related to our problem (literature data). Petrological and geochemical observations in this area do not favour the formation of undersaturated liquids from the assimilation of sediments (hypothesis ofDaly andShand). Reactions are observed between the liquid and the minerals olivine, pyroxene and magnetite corresponding to those in experimentally investigated systems. The sporadic occurrence of melilite and its alteration products is derived from reactions with residual liquids. The analcite-basalts in the northern part of the area may originate from a separated residual liquid squeezed off its place of origin.

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Mit 18 Textabbildungen  相似文献