The discovery of new galaxy members in the NGC 5044 and 1052 groups     

N. P. F. MKay  C. G. Mundell †  S. Brough  Duncan A. Forbes  D. G. Barnes  P. A. James  P. Goudfrooij  V. Kozhurina-Platais  R. Whitaker 《Monthly notices of the Royal Astronomical Society》2004,352(4):1121-1134

  相似文献   

A reanalysis of the light curve of RT Persei with the W-D code     

M. T. Edalati  F. Zeinali 《Astrophysics and Space Science》1996,243(2):275-283

The UBV photometric observations of RT Per, from Sanwal and Chaubey (1981), were analyzed by the Wilson and Devinney code (1971). The light curves include reflection effects that for the first time has been suggested by Dugan (1911). RT Per has a semi-detached configuration where the lower-mass component is in contact with its respective Roche surface. The higher-mass component very nearly fills its Roche lobe. It has the characteristic of an Algol type system. The absolute dimensions for the primary and secondary of this system were calculated from its spectral types and by combining the photometric solution with inferred component radial velocities (Lu, 1990).  相似文献   

Revisiting Sustainable Development of Dry Valleys in Hengduan Mountains Region   总被引：5，自引：1，他引：4  

TANGYa XIEJiasui SUNHui 《山地科学学报》2004,1(1):38-45

Dry valleys are a striking geographic landscape in Hengduan Mountains Region and are characterized by low rainfall, desert type of vegetation and fragile environment. Past efforts and resources have been concentrated mainly on rehabilitation of degraded ecosystem and fragile environment, particularly reforestation, while socio-economic development has been largely overlooked. Despite successes in pocket areas, the overall trend of unsustainability and environmental deterioration are continuing. It is important to understand that uplift of the Tibetan Plateau is the root cause of development of dry valleys, and development and formation of dry valleys is a natural process. Human intervention has played a secondary role in development of dry valleys and degradation of dry valleys though human intervention in many cases has speeded up environmental degradation of the dry valleys. It is important to understand that dry valleys are climatic enclaves and an integrated approach that combines rehabilitation of degraded ecosystems and socio-economic development should be adopted if the overall goal of sustainable development of dry valleys is to be achieved. Promotion of niche-based cash crops, rural energy including hydropower, solar energy, biogas and fuelwood plantation is recommended as the priority activities.  相似文献   

Ca ii K interstellar observations towards early-type disc and halo stars – distances to intermediate- and high-velocity clouds     

J. V. Smoker  B. B. Lynn  W. R. J. Rolleston  H. R. M. Kay  E. Bajaja  W. G. L. Poppel  F. P. Keenan  P. M. W. Kalberla  C. J. Mooney  P. L. Dufton  R. S. I. Ryans 《Monthly notices of the Royal Astronomical Society》2004,352(4):1279-1290

  相似文献   

On the stability of particular solutions of the singly averaged Hill problem     

M. A. Vashkov’yak  N. M. Teslenko 《Astronomy Letters》2005,31(12):844-852

We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem.  相似文献   

Prospects for astrometry with the Hubble Space Telescope     

W. H. Jefferys  G. F. Benedict  P. D. Hemenway  P. J. Shelus  R. L. Duncombe 《Celestial Mechanics and Dynamical Astronomy》1985,37(3):299-305

The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by the National Aeronautics and Space Administration. This telescope will be placed into earth orbit by the space shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of ±0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package (ADRS). The variety of astrometric problems to be investigated with HST is discussed.  相似文献   

A comparison of theoretical Sv emission line strengths with extreme ultraviolet observations of a sunspot     

F. P. Keenan  J. G. Doyle 《Solar physics》1990,128(2):345-351

Electron impact excitation rates for transitions in the S v ion, calculated with theR-matrix code, are used to derive the electron temperature sensitive emission line ratiosR ₁ =I(854.8 Å)/I(786.9 Å),R ₂ =I(852.2 Å)/I(786.9 Å),R ₃ =I(849.2 Å)/I(786.9 Å), andR ₄ =I(1199.1 Å)/I(786.9 Å), which are found to be significantly different from previous estimates. A comparison of the present results with observational data for a sunspot obtained with the Harvard S-055 spectrometer on boardSkylab reveals generally good agreement between theory and experiment, except in the case ofR ₁, which is probably due to blending in the 854.8 Å feature. The possible effects of Lyman continuum absorption on the observed line ratios is briefly discussed.  相似文献   

The dust coma of periodic comet Churyumov-Gerasimenko (1982 VIII)     

M.S. Hanner  E. Tedesco  A.T. Tokunaga  G.J. Veeder  D.F. Lester  F.C. Witteborn  J.D. Bregman  J. Gradie  L. Lebofsky 《Icarus》1985,64(1):11-19

The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ～2 × 10⁵ g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ～0.04 at 1.25 μm and ～0.05 at 2.2 μm.  相似文献   

A study on the reference frame consistency in recent Earth gravitational models   总被引：1，自引：1，他引：0  

Christopher Kotsakis 《Journal of Geodesy》2009,83(1):31-50

All gravity field functionals obtained from an Earth gravitational model (EGM) depend on the underlying terrestrial reference frame (TRF), with respect to which the EGM’s spherical harmonic coefficients refer to. In order to maintain a coherent framework for the comparison of current and future EGMs, it is thus important to investigate the consistency of their inherent TRFs, especially when their use is intended for high precision studies. Following the methodology described in an earlier paper by Kleusberg (1980), the similarity transformation parameters between the associated reference frames for several EGMs (including the most recent CHAMP/GRACE models at the time of writing this paper) are estimated in the present study. Specifically, the differences between the spherical harmonic coefficients for various pairs of EGMs are parameterized through a 3D-similarity spatial transformation model that relates their underlying TRFs. From the least-squares adjustment of such a parametric model, the origin, orientation and scale stability between the EGMs’ reference frames can be identified by estimating their corresponding translation, rotation and scale factor parameters. Various aspects of the estimation procedure and its results are highlighted in the paper, including data weighting schemes, the sensitivity of the results with respect to the selected harmonic spectral band, the correlation structure and precision level of the estimated transformation parameters, the effect of the estimated differences of the EGMs’ reference frames on their height anomaly signal, and the overall feasibility of Kleusberg’s formulae for the assessment of TRF inconsistencies among global geopotential models.  相似文献   

Consideration of time-correlated errors in a Kalman filter applicable to GNSS   总被引：1，自引：0，他引：1  

M. G. Petovello  K. O’Keefe  G. Lachapelle  M. E. Cannon 《Journal of Geodesy》2009,83(1):51-56

An algorithm for considering time-correlated errors in a Kalman filter is presented. The algorithm differs from previous implementations in that it does not suffer from numerical problems; does not contain inherent time latency or require reinterpretation of Kalman filter parameters, and gives full consideration to additive white noise that is often still present but ignored in previous implementations. Simulation results indicate that the application of the new algorithm yields more realistic and therefore useful state and covariance information than the standard implementation. Results from a field test of the algorithm applied to the problem of kinematic differential GPS demonstrate that the algorithm provides slightly pessimistic covariance estimates whereas the standard Kalman filter provides optimistic covariance estimates.  相似文献