Automatic Determination of Stellar Atmospheric Parameters Using Neural Networks and Instance-Based Machine Learning     

Olac Fuentes 《Experimental Astronomy》2001,12(1):21-31

In this article we show how machine learning methods can beeffectively applied to the problem of automatically predictingstellar atmospheric parameters from spectral information, a veryimportant problem in stellar astronomy. We apply feedforwardneural networks, Kohonen's self-organizing maps andlocally-weighted regression to predict the stellar atmosphericparameters effective temperature, surface gravity and metallicityfrom spectral indices. Our experimental results show that thethree methods are capable of predicting the parameters with verygood accuracy. Locally weighted regression gives slightly betterresults than the other methods using the original dataset asinput, while self-organizing maps outperform the other methods when significant amounts of noise are added. We also implemented a heterogeneous ensemble of predictors, combining the results given by the three algorithms. This ensemble yields better results than any of the three algorithms alone, using both the original and the noisy data.  相似文献   

富氏谱分析法模拟地壳垂直运动的地学依据及其策应力模型     

张勤  范一中 《大地测量与地球动力学》2001,21(4):76-80

应用地壳波浪与镶嵌构造学说对富氏谱分析法提取地壳垂直形变信息的科学性做了地质学意义上的阐释 ,并提出了根据多期形变资料提取特定波段上构造策应力的数学模型  相似文献   

Accretion stream mapping of HU Aquarii     

Sonja Vrielmann  Axel D. Schwope 《Monthly notices of the Royal Astronomical Society》2001,322(2):269-279

We present a new mapping algorithm, the Accretion Stream Mapping (ASM), which uses the full phase-coverage of a light curve to derive spatially resolved intensity distributions along the accretion stream in magnetic cataclysmic variables of AM Herculis type (polars). The surface of the accretion stream is approximated as a 12-sided (duodecadon-shaped) tube. After successfully testing this method on artificial data we applied it to emission-line light curves of H β , H γ and He  ii λ 4686 of the bright eclipsing polar HU Aqr. We find hydrogen and helium line emission bright in the threading region of the stream where the stream couples on to magnetic field lines. It is particularly interesting that the stream is bright on the irradiated side facing the white dwarf, which highlights the interplay of collisional and radiative excitation/ionization.  相似文献   

An analytical expression for apsidal superhump precession and comparisons with numerical simulations and dwarf nova observations     

M.M. Montgomery 《Monthly notices of the Royal Astronomical Society》2001,325(2):761-766

We compare analytical expressions of precession rates from apsidal (positive) superhumps in close binary systems with numerical disc simulation results and observed values. In the analytical expressions, we include both the dynamical effects on the precession of the disc and effects caused by pressure forces that have been theorized to provide a retrograde effect (i.e. slowing) on the prograde disc precession. We establish new limits on density wave pitch angle to a normalized disc sound speed 60≥Ω_orb  d  tan  i / c >2.214 . Using average values for the density wave pitch angle i and speed of sound c , we find good correlation between numerical simulations and the analytical expression for the apsidal superhump period excess, which includes both the prograde and retrograde effects, for mass ratios of 0.025≤ q ≤0.33 . We also show good correlations with the four known eclipsing systems, OY Car, Z Cha, HT Cas, and WZ Sge. Our analytical expression for apsidal superhump period excess as a function of orbital period is consistent with the trend found in observed systems.  相似文献   

Erratum: Fluorescent H₂ in the reflection nebula NGC 2023 – I. Recent observations     

M. S. K. McCartney  P. W. J. L. Brand  M. G. Burton  A. Chrysostomou 《Monthly notices of the Royal Astronomical Society》2001,321(4):784-784

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Elastic solutions for stresses in a transversely isotropic half‐space subjected to three‐dimensional buried parabolic rectangular loads     

Cheng‐Der Wang  Jyh‐Jong Liao 《国际地质力学数值与分析法杂志》2002,26(14):1449-1476

In many areas of engineering practice, applied loads are not uniformly distributed but often concentrated towards the centre of a foundation. Thus, loads are more realistically depicted as distributed as linearly varying or as parabola of revolution. Solutions for stresses in a transversely isotropic half‐space caused by concave and convex parabolic loads that act on a rectangle have not been derived. This work proposes analytical solutions for stresses in a transversely isotropic half‐space, induced by three‐dimensional, buried, linearly varying/uniform/parabolic rectangular loads. Load types include an upwardly and a downwardly linearly varying load, a uniform load, a concave and a convex parabolic load, all distributed over a rectangular area. These solutions are obtained by integrating the point load solutions in a Cartesian co‐ordinate system for a transversely isotropic half‐space. The buried depth, the dimensions of the loaded area, the type and degree of material anisotropy and the loading type for transversely isotropic half‐spaces influence the proposed solutions. An illustrative example is presented to elucidate the effect of the dimensions of the loaded area, the type and degree of rock anisotropy, and the type of loading on the vertical stress in the isotropic/transversely isotropic rocks subjected to a linearly varying/uniform/parabolic rectangular load. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

The age of the Geminids: a constraint from the spin-up time-scale     

Martin Beech 《Monthly notices of the Royal Astronomical Society》2002,336(2):559-563

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A Chandra detection of the radio hotspot of 3C 123     

M. J. Hardcastle  M. Birkinshaw  D. M. Worrall 《Monthly notices of the Royal Astronomical Society》2001,323(2):L17-L22

Chandra X-ray Observatory observations of the powerful, peculiar radio galaxy 3C 123 have resulted in an X-ray detection of the bright eastern hotspot, with a 1-keV flux density of ∼5 nJy. The X-ray flux and spectrum of the hotspot are consistent with the X-rays being inverse-Compton scattering of radio synchrotron photons by the population of electrons responsible for the radio emission ('synchrotron self-Compton emission') if the magnetic fields in the hotspot are close to their equipartition values. 3C 123 is thus the third radio galaxy to show X-ray emission from a hotspot which is consistent with being in equipartition. Chandra also detects emission from a moderately rich cluster surrounding 3C 123, with L _X(2–10 keV)=2×10⁴⁴ erg s⁻¹ and kT ∼5 keV, and absorbed emission from the active nucleus, with an inferred intrinsic column density of 1.7×10²² cm⁻² and an intrinsic 2–10 keV luminosity of 10⁴⁴ erg s⁻¹.  相似文献   

Evolution of the luminosity function and colours of galaxies in a Λ cold dark matter universe     

K. Nagamine †  M. Fukugita  R. Cen  J.P. Ostriker 《Monthly notices of the Royal Astronomical Society》2001,327(1):L10-L14

The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Λ cold dark matter universe with the aid of a stellar population synthesis model. At     , the resulting B -band luminosity function has a flat faint-end slope of     with the characteristic luminosity and the normalization in fair agreement with observations, while the dark matter halo mass function is steep with a slope of     . The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from     to 5. A large evolution of the characteristic mass in the stellar mass function as a result of number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from     to 2, and then declines towards higher redshift, while the B -band luminosity density continues to increase from     to 5 (but only slowly at     .  相似文献   

The re-analysis of the ROSAT data of Nova Mus 1983 using white dwarf atmosphere emission models     

&#;. Balman  J. Krautter 《Monthly notices of the Royal Astronomical Society》2001,326(4):1441-1447

The analyses of X-ray emission from classical novae during the outburst stage have shown that the soft X-ray emission below 1 keV, which is thought to originate from the photosphere of the white dwarf, is inconsistent with the simple blackbody model of emission. Thus, ROSAT Position Sensitive Proportional Counter (PSPC) archival data of the classical Nova Mus 1983 (GQ Mus) have been re-analysed in order to understand the spectral development in the X-ray wavelengths during the outburst stage. The X-ray spectra are fitted with the hot white dwarf (WD) atmosphere emission models developed for the remnants of classical novae near the Eddington luminosity. The post-outburst X-ray spectra of the remnant white dwarf are examined in the context of evolution on the Hertzsprung–Russell diagram using C–O enhanced atmosphere models. The data obtained in 1991 August (during the ROSAT All Sky Survey) indicate that the effective temperature is         . The 1992 February data show that the white dwarf had reached an effective temperature in the range         with an unabsorbed X-ray flux (i.e. ∼ bolometric flux) between     and     . We show that the H burning at the surface of the WD had most likely ceased at the time of the X-ray observations. Only the 1991 August data show evidence for ongoing H burning.  相似文献