The X-ray and extreme-ultraviolet flux evolution of SS Cygni throughout outburst     

Peter J. Wheatley  Christopher W. Mauche  Janet A. Mattei 《Monthly notices of the Royal Astronomical Society》2003,345(1):49-61

We present the most complete multiwavelength coverage of any dwarf nova outburst: simultaneous optical, Extreme Ultraviolet Explorer and Rossi X-ray Timing Explorer observations of SS Cygni throughout a narrow asymmetric outburst. Our data show that the high-energy outburst begins in the X-ray waveband 0.9–1.4 d after the beginning of the optical rise and 0.6 d before the extreme-ultraviolet rise. The X-ray flux drops suddenly, immediately before the extreme-ultraviolet flux rise, supporting the view that both components arise in the boundary layer between the accretion disc and white dwarf surface. The early rise of the X-ray flux shows that the propagation time of the outburst heating wave may have been previously overestimated.
The transitions between X-ray and extreme-ultraviolet dominated emission are accompanied by intense variability in the X-ray flux, with time-scales of minutes. As detailed by Mauche & Robinson, dwarf nova oscillations are detected throughout the extreme-ultraviolet outburst, but we find they are absent from the X-ray light curve.
X-ray and extreme-ultraviolet luminosities imply accretion rates of  3 × 10¹⁵ g s⁻¹  in quiescence,  1 × 10¹⁶ g s⁻¹  when the boundary layer becomes optically thick, and  ∼10¹⁸ g s⁻¹  at the peak of the outburst. The quiescent accretion rate is two and a half orders of magnitude higher than predicted by the standard disc instability model, and we suggest this may be because the inner accretion disc in SS Cyg is in a permanent outburst state.  相似文献   

Richtmyer-Meshkov Experiments on the Omega Laser     

R. M. Hueckstaedt  S. H. Batha  M. M. Balkey  N. D. Delamater  J. R. Fincke  R. L. Holmes  N. E. Lanier  G. R. Magelssen  J. M. Scott  J. M. Taccetti  C. J. Horsfield  K. W. Parker  S. D. Rothman 《Astrophysics and Space Science》2005,298(1-2):255-259

Observations of the interstellar medium reveal a dynamic realm permeated by shocks. These shocks are generated on a large range of scales by galactic rotation, supernovae, stellar winds, and other processes. Whenever a shock encounters a density interface, Richtmyer-Meshkov instabilities may develop. Perturbations along the interface grow, leading to structure formation and material mixing. An understanding of the evolution of Richtmyer-Meshkov instabilities is essential for understanding galactic structure, molecular cloud morphology, and the early stages of star formation. An ongoing experimental campaign studies Richtmyer-Meshkov mixing in a convergent, compressible, miscible plasma at the Omega laser facility. Cylindrical targets, consisting of a low density foam core and an aluminum shell covered by an epoxy ablator, are directly driven by fifty laser beams. The aluminum shell is machined to produce different perturbation spectra. Surface types include unperturbed (smooth), single-mode sinusoids, multi-mode (rough), and multi-mode with particular modes accentuated (specified-rough). Experimental results are compared to theory and numerical simulations.  相似文献   

The correlation of solar flare production with magnetic energy in active regions     

E. B. Mayfield  John K. Lawrence 《Solar physics》1985,96(2):293-305

An investigation of 531 active regions was made to determine the correlation between energy released by flares and the available energy in magnetic fields of the regions. Regions with magnetic flux greater than 10²¹ maxwell during the years 1967–1969, which included sunspot maximum, were selected for the investigation. A linear regression analysis of flare production on magnetic flux showed that the flare energy is correlated with magnetic energy with a coeificient of correlation of 0.78. Magnetic classification and field configuration also significantly affect the production of flares.This work was supported by the Aerospace Sponsored Research Program.  相似文献   

Biological and granulometric controls on sedimentary organic matter of an intertidal mudflat     

Lawrence M. Mayer  Peter T. Rahaim  William Guerin  Stephen A. Macko  Les Watling  Franz E. Anderson 《Estuarine, Coastal and Shelf Science》1985,20(4):491-503

A variety of measures of organic matter concentration and quality were made on samples collected from the top few mm of intertidal mudflat sediment over the course of a year, in order to assess the relative importance of biological and sedimentological influences on sedimentary organic matter. Winter and summer were times of relatively fine-grained sediment accumulation, caused by biological deposition or stabilization processes and resulting in higher organic matter concentrations. Stable carbon isotope and Br:C ratios indicated a planktonic source of bulk organic matter. Ratios of organic carbon to specific surface area of the sediments were consistent with an organic monolayer coverage of sediment grains. Correction for changing grain size during the year showed no change in the organic concentration per unit surface area, in spite of organic matter inputs by in situ primary production, buildup of heterotroph biomass and mucus coatings, and biodeposition of organic-rich seston. There were also no indications of changes in bulk organic quality, measured as hydrolyzable carbohydrates and amino acids, in response to these biological processes. It is concluded that biological processes on a seasonal time scale affect the bulk organic matter of these sediments via a modulation of grain size rather than creation or decay of organic matter.  相似文献   

The Faint Sky Variability Survey – I. Goals and data reduction process     

P. J. Groot  P. M. Vreeswijk  M. E. Huber  M. E. Everett  S. B. Howell  G. Nelemans  J. van Paradijs  E. P. J. van den Heuvel  T. Augusteijn  E. Kuulkers  R. G. M. Rutten  J. Storm 《Monthly notices of the Royal Astronomical Society》2003,339(2):427-434

  相似文献   

A multi-phase chemo-dynamical SPH code for galaxy evolution. Testing the code     

Peter Berczik  Gerhard Hensler  Christian Theis  Rainer Spurzem 《Astrophysics and Space Science》2003,284(2):865-868

  相似文献   

The NAIAD experiment for WIMP searches at Boulby mine and recent results     

B. Ahmed  G. J. Alner  H. Araujo  J. C. Barton  A. Bewick  M. J. Carson  D. Davidge  J. V. Dawson  T. Gamble  S. P. Hart  R. Hollingworth  A. S. Howard  W. G. Jones  M. K. Joshi  V. A. Kudryavtsev  T. B. Lawson  V. Lebedenko  M. J. Lehner  J. D. Lewin  P. K. Lightfoot  I. Liubarsky  R. Lüscher  J. E. McMillan  B. Morgan  G. Nicklin  S. M. Paling  R. M. Preece  J. J. Quenby  J. W. Roberts  M. Robinson  N. J. T. Smith  P. F. Smith  N. J. C. Spooner  T. J. Sumner  D. R. Tovey 《Astroparticle Physics》2003,19(6):691-702

The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented.  相似文献   

Theoretical and experimental lifetime and oscillator strength determination in singly ionized neodymium (Nd ii)     

H. L. Xu  S. Svanberg  R. D. Cowan  P.-H. Lefèbvre  P. Quinet  E. Biémont 《Monthly notices of the Royal Astronomical Society》2003,346(2):433-440

Radiative lifetime measurements were performed with time-resolved laser-induced fluorescence techniques for 24 levels of Nd  ii in the energy range 20 500–32 500 cm⁻¹. For 17 levels, no previous experimental data exist. These results have allowed the testing of new theoretical calculations with the relativistic Hartree–Fock method taking configuration interactions and core-polarization effects into account, and a satisfying agreement has been found for this complex ion. A new set of calculated oscillator strengths, accurate within a few per cent for the strongest transitions, is presented for 107 lines of astrophysical interest appearing in the wavelength range 358.0–1100.0 nm. These results will be useful to evaluate abundance values of neodymium in chemically peculiar stars in relation with cosmochronology.  相似文献   

Circular Polarisation Observations of SS433     

D.G. McCormick  R.E. Spencer  R.P. Fender 《Astrophysics and Space Science》2003,288(1-2):97-103

We present four epochs of observations of the Galactic X-ray binarySS433 using the Australian Telescope Compact Array (ATCA). These observations, taken on 4 February, 29 February, 23 March and 27 June 2000, at four frequencies ranging from 1–9 Ghz, are used to monitor the circular polarised emission from the source. We obtain circular polarisation spectra for the first three epochs with spectralindices α, (m _c ∝ν ^α), equal to 0.07±0.10, –1.07±0.09 and –0.18±0.05 and also observe a sign change in Stokes V. This change of handedness may indicate along-term restructuring of the magnetic field.  相似文献   

Tidal dwarfs in the M81 group: the second generation?     

L. Makarova  E. Grebel  I. Karachentsev  A. Dolphin  V. Karachentseva  M. Sharina  D. Geisler  P. Guhathakurta  P. Hodge  A. Sarajedini  P. Seitzer 《Astrophysics and Space Science》2003,285(1):107-111

We present a quantitative star formation history derivation of the four suspected tidal dwarf galaxies in the M 81 group: Holmberg IX, BK3N,Arp-loop (A0952+69) and Garland using HST/WFPC2 images of these galaxies. We construct a library of synthetic Colour-Magnitude Diagrams(CMDs) based on theoretical isochrones and data-derived determinations of photometric errors. These synthetic CMDs were combined linearly andχ²-compared to observed photometry. All the galaxies show continuous star formation between about 20 and 200 Myr ago with star formation rates between 7.5⋅10^-3 M_⊙/yr and 7.67⋅10^-4 M_⊙/yr. The metallicity of the detected stars is spanning rather a wide range, being lower than solar abundance. We suppose, that all the galaxies were formed out of material from metal-poor outer part of the giant spiral galaxy M81after tidal interaction about 200 Myr ago. However, this suggestion requires significantly more deep color-magnitude diagrams to be sure with the scenario of the galaxy evolution. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献