Forbidden lines of Ca II in the photospheric spectrum     

D. L. Lambert  E. A. Mallia  B. Warner 《Solar physics》1969,7(1):11-16

On scans obtained with the Oxford photoelectric spectrometer, the [Ca ii] transition 4s ²S_1/2-3d ²D_3/2; is identified with a weak Fraunhofer line. It is argued that the strength of the line is consistent with the abundance of calcium which is derived from the permitted lines of Ca i and Ca ii.  相似文献   

On the general properties of the secondaries of cataclysmic variable stars     

Brian Warner 《Astrophysics and Space Science》1995,232(1):89-97

The mass-radius, mass-orbital period, spectral type-orbital period and absolute magnitude-orbital period relationships for the secondary star components of cataclysmic variable (CV) binary stars are discussed. By comparing these with those expected for systems containing Roche lobe-filling main sequence stars, using empirical data for low-mass main sequence stars, it is shown thatas a group the CV secondaries do not differ significantly from main sequence stars.  相似文献   

57-second oscillations in Nova Centauri 1986 (V842 Cen)     

Patrick A. Woudt  Brian Warner  Julian Osborne  Kim Page 《Monthly notices of the Royal Astronomical Society》2009,395(4):2177-2182

High-speed photometry in 2008 shows that the light curve of V842 Cen possesses a coherent modulation at 56.825 s, with sidebands at 56.598 and 57.054 s. These have appeared since this nova remnant was observed in 2000 and 2002. We deduce that the dominant signal is the rotation period of the white dwarf primary and the sidebands are caused by reprocessing from a surface moving with an orbital period of 3.94 h. Thus, V842 Cen is an intermediate polar (IP) of the DQ Herculis subclass, is the fastest rotating white dwarf among the IPs and is the third fastest known in a cataclysmic variable. As in other IPs, we see no dwarf nova oscillations, but there are often quasi-periodic oscillations in the range 350–1500 s. There is a strong brightness modulation with a period of 3.78 h, which we attribute to negative superhumps, and there is an even stronger signal at 2.886 h which is of unknown origin but is probably a further example of that seen in GW Lib and some other systems. We used the Swift satellite to observe V842 Cen in the ultraviolet and in X-rays, although no periodic modulation was detected in the short observations. The X-ray luminosity of this object appears to be much lower than that of other IPs in which the accretion region is directly visible.  相似文献   

Spin rate distribution of small asteroids     

P. Pravec  A.W. Harris  B.D. Warner  K. Hornoch  D. Higgins  A. Galád  Š. Gajdoš  J. Világi  Yu.N. Krugly  V. Chiorny  W.R. Cooney Jr.  D. Terrell  R.D. Stephens  V. Reddy  F. Colas  R. Durkee  R.A. Koff 《Icarus》2008,197(2):497-504

The spin rate distribution of main belt/Mars crossing (MB/MC) asteroids with diameters 3-15 km is uniform in the range from f=1 to 9.5 d⁻¹, and there is an excess of slow rotators with f<1 d⁻¹. The observed distribution appears to be controlled by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. The magnitude of the excess of slow rotators is related to the residence time of slowed down asteroids in the excess and the rate of spin rate change outside the excess. We estimated a median YORP spin rate change of ≈0.022 d⁻¹/Myr for asteroids in our sample (i.e., a median time in which the spin rate changes by 1 d⁻¹ is ≈45 Myr), thus the residence time of slowed down asteroids in the excess is ≈110 Myr. The spin rate distribution of near-Earth asteroids (NEAs) with sizes in the range 0.2-3 km (∼5 times smaller in median diameter than the MB/MC asteroids sample) shows a similar excess of slow rotators, but there is also a concentration of NEAs at fast spin rates with f=9-10 d⁻¹. The concentration at fast spin rates is correlated with a narrower distribution of spin rates of primaries of binary systems among NEAs; the difference may be due to the apparently more evolved population of binaries among MB/MC asteroids.  相似文献   

Instrumentation Development for In Situ 40Ar/39Ar Planetary Geochronology          下载免费PDF全文

Leah E. Morgan  Madicken Munk  Brett Davidheiser‐Kroll  Nicholas H. Warner  Sanjeev Gupta  Rachel Slaybaugh  Patrick Harkness  Darren F. Mark 《Geostandards and Geoanalytical Research》2017,41(3):381-396

The chronology of the Solar System, particularly the timing of formation of extra‐terrestrial bodies and their features, is an outstanding problem in planetary science. Although various chronological methods for in situ geochronology have been proposed (e.g., Rb‐Sr, K‐Ar), and even applied (K‐Ar), the reliability, accuracy, and applicability of the ⁴⁰Ar/³⁹Ar method makes it by far the most desirable chronometer for dating extra‐terrestrial bodies. The method however relies on the neutron irradiation of samples, and thus a neutron source. Herein, we discuss the challenges and feasibility of deploying a passive neutron source to planetary surfaces for the in situ application of the ⁴⁰Ar/³⁹Ar chronometer. Requirements in generating and shielding neutrons, as well as analysing samples are described, along with an exploration of limitations such as mass, power and cost. Two potential solutions for the in situ extra‐terrestrial deployment of the ⁴⁰Ar/³⁹Ar method are presented. Although this represents a challenging task, developing the technology to apply the ⁴⁰Ar/³⁹Ar method on planetary surfaces would represent a major advance towards constraining the timescale of solar system formation and evolution.  相似文献   

Combining long- and short-term probabilistic volcanic hazard assessment with cost-benefit analysis to support decision making in a volcanic crisis from the Auckland Volcanic Field,New Zealand   总被引：2，自引：2，他引：0  

Laura Sandri  Gill Jolly  Jan Lindsay  Tracy Howe  Warner Marzocchi 《Bulletin of Volcanology》2012,74(3):705-723

By using BET_VH, we propose a quantitative probabilistic hazard assessment for base surge impact in Auckland, New Zealand. Base surges resulting from phreatomagmatic eruptions are among the most dangerous phenomena likely to be associated with the initial phase of a future eruption in the Auckland Volcanic Field. The assessment is done both in the long-term and in a specific short-term case study, i.e. the simulated pre-eruptive unrest episode during Exercise Ruaumoko, a national civil defence exercise. The most important factors to account for are the uncertainties in the vent location (expected for a volcanic field) and in the run-out distance of base surges. Here, we propose a statistical model of base surge run-out distance based on deposits from past eruptions in Auckland and in analogous volcanoes. We then combine our hazard assessment with an analysis of the costs and benefits of evacuating people (on a 1 × 1-km cell grid). In addition to stressing the practical importance of a cost-benefit analysis in creating a bridge between volcanologists and decision makers, our study highlights some important points. First, in the Exercise Ruaumoko application, the evacuation call seems to be required as soon as the unrest phase is clear; additionally, the evacuation area is much larger than what is recommended in the current contingency plan. Secondly, the evacuation area changes in size with time, due to a reduction in the uncertainty in the vent location and increase in the probability of eruption. It is the tradeoff between these two factors that dictates which cells must be evacuated, and when, thus determining the ultimate size and shape of the area to be evacuated.  相似文献   

BET_VH: exploring the influence of natural uncertainties on long-term hazard from tephra fallout at Campi Flegrei (Italy)   总被引：2，自引：0，他引：2  

Jacopo Selva  Antonio Costa  Warner Marzocchi  Laura Sandri 《Bulletin of Volcanology》2010,72(6):717-733

In this paper, we explore the effects of the intrinsic uncertainties upon long-term volcanic hazard by analyzing tephra fall hazard at Campi Flegrei, Italy, using the BET_VH model described in Marzocchi et al. (Bull Volcanol, 2010). The results obtained show that volcanic hazard based on the weighted average of all possible eruptive settings (i.e. size classes and vent locations) is significantly different from an analysis based on a single reference setting, as commonly used in volcanic hazard practice. The long-term hazard map for tephra fall at Campi Flegrei obtained here accounts for a wide spectrum of uncertainties which are usually neglected, largely reducing the bias intrinsically introduced by the choice of a specific reference setting. We formally develop and apply a general method to recursively integrate simulations from different models which have different characteristics in terms of spatial coverage, resolution and physical details. This outcome of simulations will be eventually merged with field data through the use of the BET_VH model.  相似文献   

Two-dimensional dam break flooding simulation: a GIS-embedded approach   总被引：2，自引：2，他引：0  

Massimiliano?CannataEmail author  Roberto?Marzocchi 《Natural Hazards》2012,61(3):1143-1159

In the twenty-first century, around 200 notable dam and reservoir failures happened worldwide causing massive fatalities and economic costs. In order to reduce the losses, managers usually define mitigation strategies identifying flooding area due to dam break by using standalone hydrodynamic models and then importing the results within a GIS to perform risk analysis. This two-step procedure is time expensive, error prone due to export/import requirements and not user friendly. For this reason with this work, a new numerical model for the solution of the two-dimensional dam break problem has been implemented in the GRASS GIS with a GIS-embedded approach. The model solves the conservative form of the 2D shallow water equations using a finite volume method; the intercell flux is computed by one-side upwind conservative scheme extended to a two-dimensional problem. The newly developed GIS module, among others outputs, allows to derive maximum intensity maps that can be directly used for risk assessment. Finally, the model has been (1) tested against two standard synthetic problems referenced in literature showing differences in estimated water depth of 2, 3 and 15% and (2) verified against official flooding map of an existing dam (Verzasca) detecting 75% of similarity. The problem formulation, the new GRASS module and its validation is presented.  相似文献   

New views of Betelgeuse: multi-wavelength surface imaging and implications for models of hotspot generation     

J. S. Young  J. E. Baldwin  R. C. Boysen  C. A. Haniff  P. R. Lawson  †  C. D. Mackay  D. Pearson  J. Rogers  D. St.-Jacques  ‡  P. J. Warner  D. M. A. Wilson  R. W. Wilson § 《Monthly notices of the Royal Astronomical Society》2000,315(3):635-645

We report contemporaneous multi-wavelength interferometric imaging of the red supergiant star Betelgeuse ( α Orionis), using the Cambridge Optical Aperture Synthesis Telescope (COAST) and the William Herschel Telescope (WHT), at wavelengths of 700, 905 and 1290 nm. We find a strong variation in the apparent symmetry of the stellar brightness distribution as a function of wavelength. At 700 nm the star is highly asymmetric, and can be modelled as the superposition of three bright spots on a strongly limb-darkened disc. However, at 905 nm only a single low-contrast feature is visible and at 1290 nm the star presents a featureless symmetric disc. The change in spot contrast with wavelength is consistent with a model in which the bright spots represent unobscured areas of elevated temperature, owing perhaps to convection, on a stellar disc that itself has a different appearance, i.e. geometrical extent and limb-darkening profile, at different wavelengths. The featureless centre-to-limb brightness profile seen at 1290 nm is consistent with this model and suggests that future interferometric monitoring of the star to quantify the size changes associated with radial velocity variations should be performed at similar wavelengths in the near-infrared.  相似文献   

The international transport workers' federation and flag of convenience shipping: Herbert R. Northrup and Richard I. Rowan The Wharton School,University of Pennsylvania,PA, 1983, 251 pp     

David W. Warner 《Marine Policy》1985,9(1):80-81

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