Non-linear motions of Australian geodetic stations induced by non-tidal ocean loading and the passage of tropical cyclones     

A. Mémin  C. Watson  I. D. Haigh  L. MacPherson  P. Tregoning 《Journal of Geodesy》2014,88(10):927-940

We investigate daily and sub-daily non-tidal oceanic and atmospheric loading (NTOAL) in the Australian region and put an upper bound on potential site motion examining the effects of tropical cyclone Yasi that crossed the Australian coast in January/February 2011. The dynamic nature of the ocean is important, particularly for northern Australia where the long-term scatter due to daily and sub-daily oceanic changes increases by 20–55 % compared to that estimated using the inverted barometer (IB) assumption. Correcting the daily Global Positioning System (GPS) time series for NTOAL employing either a dynamic ocean model or the IB assumption leads to a reduction of up to 52 % in the weighted scatter of daily coordinate estimates. Differences between the approaches are obscured by seasonal variations in the GPS precision along the northern coast. Two compensating signals during the cyclone require modelling at high spatial and temporal resolution: uplift induced by the atmospheric depression, and subsidence induced by storm surge. The latter dominates ( \(>\) 135 %) the combined net effect that reaches a maximum of 14 mm, and 10 mm near the closest GPS site TOW2. Here, 96 % of the displacement is reached within 15 h due to the rapid transit of cyclones and the quasi-linear nature of the coastline. Consequently, estimating sub-daily NTOAL is necessary to properly account for such a signal that can be 3.5 times larger than its daily-averaged value. We were unable to detect the deformation signal in 2-hourly GPS processing and show that seasonal noise in the Austral summer dominates and precludes GPS detection of the cyclone-related subsidence.  相似文献   

The effects of frequency-dependent quasar variability on the celestial reference frame     

Stanislav S. Shabala  Jonathan G. Rogers  Jamie N. McCallum  Oleg A. Titov  Jay Blanchard  James E. J. Lovell  Christopher S. Watson 《Journal of Geodesy》2014,88(6):575-586

We examine the relationship between source position stability and astrophysical properties of radio-loud quasars making up the International Celestial Reference Frame (ICRF2). Understanding this relationship is important for improving quasar selection and analysis strategies, and therefore reference frame stability. We construct flux density time series, known as light curves, for 95 of the most frequently observed ICRF2 quasars at both the 2.3 and 8.4 GHz geodetic very long baseline interferometry (VLBI) observing bands. Because the appearance of new quasar components corresponds to an increase in quasar flux density, these light curves alert us about potential changes in source structure before they appear in VLBI images. We test how source position stability depends on three astrophysical parameters: (1) flux density variability at X band; (2) time lag between flares in S and X bands; (3) spectral index root-mean-square (rms), defined as the variability in the ratio between S and X band flux densities. We find that the time lag between S and X band light curves provides a good indicator of position stability: sources with time lags $<$ 0.06 years are significantly more stable ( $>$ 20 % improvement in weighted rms) than sources with larger time lags. A similar improvement is obtained by observing sources with low $(<$ 0.12) spectral index variability. On the other hand, there is no strong dependence of source position stability on flux density variability in a single frequency band. These findings can be understood by interpreting the time lag between S and X band light curves as a measure of the size of the source structure. Monitoring of source flux density at multiple frequencies therefore appears to provide a useful probe of quasar structure on scales important to geodesy. The observed astrometric position of the brightest quasar component (the core) is known to depend on observing frequency. We show how multi-frequency flux density monitoring may allow the dependence on frequency of the relative core positions along the jet to be elucidated. Knowledge of the position–frequency relation has important implications for current and future geodetic VLBI programs, as well as the alignment between the radio and optical celestial reference frames.  相似文献   

HD 9770, a southern active-chromosphere system     

L.C. Watson  J.D. Pritchard  J.B. Hearnshaw  P.M. Kilmartin  A.C. Gilmore 《Monthly notices of the Royal Astronomical Society》2001,325(1):143-150

The visual triple system HD 9770 (BB Scl) has been the subject of a four-year programme of UVB ( RI )_C photometry and H α échelle spectroscopy. Analysis of the data obtained over that period shows that star B, and probably also star A, of HD 9770 is a binary. The A system comprises a K1V star, which may be in a binary system with another K dwarf. The B system is an eclipsing binary of the BY Dra type in which both stars are chromospherically active. An orbital period of 0.476 525±0.000 013 d has been derived from the light curve in V . Physical parameters derived from analysis of the light curves in UBV ( RI )_C are presented.  相似文献   

Observations of the cosmic microwave background and galactic foregrounds at 12–17 GHz with the COSMOSOMAS experiment     

S. Fernández-Cerezo  C. M. Gutiérrez  R. Rebolo  R. A. Watson  R. J. Hoyland  S. R. Hildebrandt  J. A. Rubiño-Martín  J. F. Macías-Pérez  P. Sosa Molina 《Monthly notices of the Royal Astronomical Society》2006,370(1):15-24

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The 6dF Galaxy Survey: samples, observational techniques and the first data release     

D. Heath Jones  Will Saunders  Matthew Colless  Mike A. Read  Quentin A. Parker  Fred G. Watson  Lachlan A. Campbell  Daniel Burkey  Thomas Mauch  Lesa Moore  Malcolm Hartley  Paul Cass  Dionne James  Ken Russell  Kristin Fiegert  John Dawe  John Huchra  Tom Jarrett  Ofer Lahav  John Lucey  Gary A. Mamon  Dominique Proust  Elaine M. Sadler  Ken-ichi Wakamatsu 《Monthly notices of the Royal Astronomical Society》2004,355(3):747-763

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Analytic Magnetic Reconnection Solutions in Cylindrical Geometry     

Watson  P.G.  Craig  I.J.D. 《Solar physics》2002,207(2):337-354

In this paper we present a new class of exact reconnection solutions in cylindrical geometry. We point out that in the case of planar reconnection there is a natural cylindrical analog to the Cartesian Dawson function model for the magnetic field. Although the resistive energy release scalings of these solutions mimic the Cartesian models an important new feature is the presence of curvature in the current sheet. We go on to show that these solutions can be generalized to three dimensions.  相似文献   

Thermal and non-thermal radio variations in WR 147     

S. K. Watson  R. J. Davis  P. M. Williams  M. F. Bode 《Monthly notices of the Royal Astronomical Society》2002,334(3):631-636

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http://www.sciencedirect.com/science/article/pii/S1674987114000917     

Miyuki Tahata  Yusuke Sawaki  Yuichiro Ueno  Manabu Nishizawa  Naohiro Yoshida  Toshikazu Ebisuzaki  Tsuyoshi Komiya  Shigenori Maruyama 《地学前缘(英文版)》2015,6(1):121-136

Important ecological changes of the Earth(oxidization of the atmosphere and the ocean) increase in nutrient supply due to the break-up of the super continent(Rodinia) and the appearance of multi-cellular organisms(macroscopic algae and metazoan) took place in the Ediacaran period,priming the Cambrian explosion.The strong perturbations in carbon cycles in the ocean are recorded as excursions in carbonate and organic carbon isotope ratio(δ~(13)C_(carb) and δ~(13)C_(org)) from the Ediacaran through early Cambrian periods.The Ediacaran-early Cambrian sediment records of δ~(13)C_(carb) and δ~(13)C_(org),obtained from the drill-core samples in Three Gorges in South China,are compared with the results of numerical simulation of a simple one-zone model of the carbon cycle of the ocean,which has two reservoirs(i.e.,dissolved organic carbon(DOC) and dissolved inorganic carbon(DIC).The fluxes from the reservoirs are assumed to be proportional to the mass of the carbon reservoirs.We constructed a model,referred to here as the Best Fit Model(BFM),which reproduce δ~(13)C_(carb) and δ~(13)C_(org) records in the Ediacaran-early Cambrian period noted above.BFM reveals that the Shuram excursion is related to three major changes in the carbon cycle or the global ecological system of the Earth:(1) an increase in the coefficient of remineralization by a factor of ca.100,possibly corresponding to a change in the dominant metabolism from anaerobic respiration to aerobic respiration,(2) an increase of carbon fractionation index from 25‰ to 33‰,possibly corresponding to the change in the primary producer from rock-living cyanobacteria to free-living macro algae,and(3) an increase in the coefficient of the organic carbon burial by a factor of ca.100,possibly corresponding to the onset of a biological pump driven by the flourishing metazoan and zooplankton.The former two changes took place at the start of the Shuram excursion,while the third occurred at the end of the Shuram excursion.The other two excursions are explained by the tentative decrease in primary production due to cold periods,which correspond to the Gaskiers(ca.580 Ma) and Bikonor(ca.542 Ma) glaciations.  相似文献   

Discovery of the 'missing' mode in HR 1217 by the Whole Earth Telescope     

D. W.Kurtz  S. D.Kawaler  R. L.Riddle  M. D.Reed †  M. S.Cunha  M.Wood  N.Silvestri  T. K.Watson  N.Dolez  P.Moskalik  S.Zola  E.Pallier  J. A.Guzik  T. S.Metcalfe  A. S.Mukadam  R. E.Nather  D. E.Winget  D. J.Sullivan  T.Sullivan  K.Sekiguchi  X.Jiang  R.Shobbrook  B. N.Ashoka  S.Seetha  S.Joshi  D.O'Donoghue  G.Handler  M.Mueller  J. M.Gonzalez Perez  J.-E.Solheim  F.Johannessen  A.Ulla  S. O.Kepler  A.Kanaan  A.da Costa  L.Fraga  O.Giovannini  J. M.Matthews 《Monthly notices of the Royal Astronomical Society》2002,330(3):57-61

HR 1217 is a prototypical rapidly oscillating Ap star that has presented a test to the theory of non-radial stellar pulsation. Prior observations showed a clear pattern of five modes with alternating frequency spacings of 33.3 and 34.6 μHz, with a sixth mode at a problematic spacing of 50.0 μHz (which equals  1.5×33.3 μHz)  to the high-frequency side. Asymptotic pulsation theory allowed for a frequency spacing of 34 μHz, but Hipparcos observations rule out such a spacing. Theoretical calculations of magnetoacoustic modes in Ap stars by Cunha predicted that there should be a previously undetected mode 34 μHz higher than the main group, with a smaller spacing between it and the highest one. In this Letter, we present preliminary results from a multisite photometric campaign on the rapidly oscillating Ap star HR 1217 using the 'Whole Earth Telescope'. While a complete analysis of the data will appear in a later paper, one outstanding result from this run is the discovery of a newly detected frequency in the pulsation spectrum of this star, at the frequency predicted by Cunha.  相似文献   

The component masses of the cataclysmic variable V347 Puppis     

T. D. Thoroughgood  V. S. Dhillon  D. Steeghs  C. A. Watson  D. A. H. Buckley  S. P. Littlefair  D. A. Smith  M. Still †  K. J. van der Heyden  B. Warner 《Monthly notices of the Royal Astronomical Society》2005,357(3):881-894

We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variable V347 Pup (=LB 1800). There is evidence of irradiation on the inner hemisphere of the secondary star, which we correct for using a model to give a secondary-star radial velocity of   K _R= 198 ± 5 km s⁻¹  . The rotational velocity of the secondary star in V347 Pup is found to be   v sin  i = 131 ± 5 km s⁻¹  and the system inclination is   i = 840 ± 23  . From these parameters we obtain masses of   M ₁= 0.63 ± 0.04 M_⊙  for the white dwarf primary and   M ₂= 0.52 ± 0.06 M_⊙  for the M0.5V secondary star, giving a mass ratio of   q = 0.83 ± 0.05  . On the basis of the component masses, and the spectral type and radius of the secondary star in V347 Pup, we find tentative evidence for an evolved companion. V347 Pup shows many of the characteristics of the SW Sex stars, exhibiting single-peaked emission lines, high-velocity S-wave components and phase-offsets in the radial velocity curve. We find spiral arms in the accretion disc of V347 Pup and measure the disc radius to be close to the maximum allowed in a pressureless disc.  相似文献