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251.
Near infrared measurements in the J, H and K bands have been carried out for a number of symbiotic stars with the 1.5 m telescope
at the Rothney Astrophysical Observatory (RAO). A comparison with the earlier observations shows that the S-type symbiotic
stars do not have any significant variation in the infrared flux over the past five years. However a small variation ∼ 0.3
magnitude in the infrared flux has been detected for CH Cygni. The observations of HM Sagittae show large decreases in the
infrared flux compared to the previous measurements. The variability in the infrared fluxes of both these objects could be
attributed to a variation in the temperature due to the cooling of the dust shell. The variability observed for V1016 Cygni
is found consistent with the previous measurements. 相似文献
252.
C. Simon Jeffery 《Journal of Astrophysics and Astronomy》2005,26(2-3):261-271
Subdwarf B stars play a significant role in close binary evolution and in the hot star content of old stellar populations,
in particular in giant elliptical galaxies. While the question of their origin poses several problems for stellar evolution
theory, one of their most fascinating properties is the presence of multi-periodic 2–3 minute oscillations. Interpreting these
oscillations optimally requires the correct identification of the modes. Partial identifications can be obtained using high-speed
observations of radial velocity and colour variations. We review some of the several attempts to make such observations, most
recently with the Multi-Site Spectroscopic Telescope campaign and withULTRACAM. 相似文献
253.
Alessandro Morbmelli Jacques Henrard 《Celestial Mechanics and Dynamical Astronomy》1991,51(2):131-167
In this paper a theoretical perturbation approach to the problem of the dynamics in secular resonance is exposed. This approach avoids any expansion of the main term of the Hamiltonian (linear term in the masses) with respect to the eccentricity or the inclination of the asteroid, in order to achieve results valid for any value of these variables. Moreover suitable action-angle variables are introduced to take properly into account the dynamics related to the motion of the argument of perihelion of the asteroid, which is relevant at high inclination. A class of secular resonances wider than that usually considered is found. An explicit computation of the location of the main secular resonances, estimating also the contribution of the quadratic term in the masses by means of classical series expansion, is reported in the last sections. The accuracy of computations obtained by series expansion is discussed in the paper. 相似文献
254.
We briefly discuss the current status of our radiation-hydrodynamical models of pulsation in various stellar objects and of dust-driven mass loss in LPVs. We emphasize the importance of a future combined modelling of pulsation and mass loss in AGB stars which has to be based on reliable physical and numerical methods. 相似文献
255.
Chun-Hua Zhu Chao-Zheng Zha Department of Physics Xinjiang University Urumqi 《中国天文和天体物理学报》2005,5(4):419-425
By means of a population synthesis code, we investigate the Mira variables. Their birth rate (over 0.65 yr-1) and their number (-130000) in the Galaxy are estimated. For all possible Mira variables, ranges of their initial masses, pulsating periods, mass losses and lifetimes are given. We check our model with the observed Mira variables near the Sun and our results prove to be valid. 相似文献
256.
Martin Šolc 《Astrophysics and Space Science》2005,296(1-4):43-54
Several important turning points appeared in the personal life and scientific career of Zdeněk Kopal, every time, when he
entered a new field of research. Four particular periods of his life will be commented in the present paper: the studies in
Prague and early observations in the variable star programme of the Czech Astronomical Society; the first lectures on close
binaries at Harvard; the intermezzo of lunar research; and the last period after 1989, when Zdeněk Kopal returned several
times to Prague University. 相似文献
257.
Zhao-Xia Han Li Zhang Department of Physics Yunnan University Kunming National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 《中国天文和天体物理学报》2005,5(3):256-264
The variability of γ-ray sources listed in the third EGRET catalog is studied using three variability indices. These indices are found to be statistically equivalent if the observed data are sufficiently accurate. Using the three indices,30 EGRET point sources which are positionally coincident with pulsars and 40 persistent unidentified sources at low latitudes are analyzed for their variability status. It is found that 14 of the 30 point sources may have genuine or plausible associations with pulsars, and 16 of the 40 persistent unidentified sources are possible pulsar candidates. 相似文献
258.
259.
260.
Roshanak Darvishzadeh Andrew Skidmore Clement Atzberger Sip van Wieren 《International Journal of Applied Earth Observation and Geoinformation》2008
The retrieval of canopy biophysical variables is known to be affected by confounding factors such as plant type and background reflectance. The effects of soil type and plant architecture on the retrieval of vegetation leaf area index (LAI) from hyperspectral data were assessed in this study. In situ measurements of LAI were related to reflectances in the red and near-infrared and also to five widely used spectral vegetation indices (VIs). The study confirmed that the spectral contrast between leaves and soil background determines the strength of the LAI–reflectance relationship. It was shown that within a given vegetation species, the optimum spectral regions for LAI estimation were similar across the investigated VIs, indicating that the various VIs are basically summarizing the same spectral information for a given vegetation species. Cross-validated results revealed that, narrow-band PVI was less influenced by soil background effects (0.15 ≤ RMSEcv ≤ 0.56). The results suggest that, when using remote sensing VIs for LAI estimation, not only is the choice of VI of importance but also prior knowledge of plant architecture and soil background. Hence, some kind of landscape stratification is required before using hyperspectral imagery for large-scale mapping of vegetation biophysical variables. 相似文献