共查询到20条相似文献，搜索用时 31 毫秒
1.
A. V. Devyatkin D. L. Gorshanov V. V. Kouprianov I. A. Verestchagina 《Solar System Research》2010,44(1):68-80
We describe in detail the Apex I and Apex II software packages created for astrometric and photometric reductions of astronomical
observations with CCD cameras. The Apex I software package has been created for the semiautomatic reduction of astronomical
observations and has a convenient user interface. The Apex II software package allows for the completely automatic reduction
of astrometric and photometric observations to be performed. 相似文献
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星系的形态与星系的形成和演化息息相关, 其形态学分类是星系天文学后续研究的重要一环. 当前海量天文观测数据的出现使得天文数据自动分析方法越来越得到重视, 针对此问题, 利用先进的深度学习骨干网络EfficientNetV2, 分析不同的注意力机制类型和使用节点对网络性能的影响, 构建了一种命名为EfficientNetV2-S-Triplet7 (即在EfficientNetV2-S stage7的$1\times1$卷积层后加入Triplet模块)的改进算法模型来实现星系形态学的自动分类. 使用第二期星系动物园(Galaxy Zoo 2, GZ2)中超过24万张的测光图像作为初始数据进行实验测试. 在对数据进行预处理时采取了尺寸抖动、翻转、色彩畸变等图像增强手段来解决图像数量的不平衡问题. 在同一系列经典和前沿的深度学习算法模型AlexNet、ResNet-34、MobileNetV2、RegNet进行对比实验后, 得出EfficientNetV2-S-Triplet7算法在分类准确率、查全率和F1分数等指标上具有最好的测试结果. 在9375张测试图像中的3项指标值分别可达到89.03%、90.21%、89.93%, 查准率达到89.69%, 在其他模型中排在第3位. 该结果表明将EfficientNetV2-S-Triplet7算法应用于大规模星系数据的形态学分类任务中有很好的效果. 相似文献
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Observations of present and future X‐ray telescopes include a large number of ipitous sources of unknown types. They are a rich source of knowledge about X‐ray dominated astronomical objects, their distribution, and their evolution. The large number of these sources does not permit their individual spectroscopical follow‐up and classification. Here we use Chandra Multi‐Wavelength public data to investigate a number of statistical algorithms for classification of X‐ray sources with optical imaging follow‐up. We show that up to statistical uncertainties, each class of X‐ray sources has specific photometric characteristics that can be used for its classification. We assess the relative and absolute performance of classification methods and measured features by comparing the behaviour of physical quantities for statistically classified objects with what is obtained from spectroscopy. We find that among methods we have studied, multi‐dimensional probability distribution is the best for both classifying source type and redshift, but it needs a sufficiently large input (learning) data set. In absence of such data, a mixture of various methods can give a better final result.We discuss some of potential applications of the statistical classification and the enhancement of information obtained in this way. We also assess the effect of classification methods and input data set on the astronomical conclusions such as distribution and properties of X‐ray selected sources. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Andrew Mennim Richard A. Battye Carsten van de Bruck 《Astrophysics and Space Science》2003,283(4):633-638
We discuss the problems faced in trying to deduce the evolution of cosmological perturbations in brane-world models. There
are two natural ways to formulate the problem: one which makes the equations of motion simple and the other which makes the
boundary condition simple. Unfortunately the problem is difficult to solve, even numerically, in either formalism. We present
a more phenomenological approach which, while it does not solve the problem for any given model, illustrates some generic
features one might expect to see in the tensor part of the cosmic microwave background power spectrum. We find that the observed
scale invariance of the cosmic microwave background provides bounds on brane world models.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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I. A. Dulova S. I. Skuratovsky N. V. Bondarenko Yu. V. Kornienko 《Solar System Research》2008,42(6):522-535
The possibility of reconstructing the surface topography from single images with the photometric method in the linear approximation is analyzed. The photometric method or surface topography Reconstruction employs a statistical approach to the problem formulation and is the most mathematically correct. This method allows determination of the most probable surface topography given specific observational data. When only one image is available, the photometric method is superior in comparison with the currently available photoclinometry. The processing of test surface topography with the photometric method shows that, under typical conditions, the error of surface relief reconstruction is of higher than 40% in terms of the standard deviation of the surface height. The surface relief of some Martian areas are reconstructed from HRSC images obtained by the Mars Express spacecraft. It is shown that the image-reconstructed surface topography is in good agreement with the topographic information for the same Martian areas obtained by the MOLA altimeter. 相似文献
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Maarten Baes † Herwig Dejonghe 《Monthly notices of the Royal Astronomical Society》2001,326(2):722-732
Accurate photometric and kinematic modelling of disc galaxies requires the inclusion of radiative transfer models. Because of the complexity of the radiative transfer equation (RTE), sophisticated techniques are required. Various techniques have been employed for the attenuation in disc galaxies, but a quantitative comparison of them is difficult, because of the differing assumptions, approximations and accuracy requirements that are adopted in the literature. In this paper, we present an unbiased comparison of four methods to solve the RTE, in terms of accuracy, efficiency and flexibility. We apply them all to one problem that can serve as a first approximation of large portions of disc galaxies: a one-dimensional plane-parallel geometry, with both absorption and multiple scattering taken into account, with arbitrary vertical distributions of stars and dust and an arbitrary angular redistribution of the scattering. We find that the spherical harmonics method is by far the most efficient way to solve the RTE, whereas both Monte Carlo simulations and the iteration method, which are straightforward to extend to more complex geometries, have a cost that is about 170 times larger. 相似文献
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Luigi R. Bedin † Santi Cassisi Fiorella Castelli Giampaolo Piotto Jay Anderson Maurizio Salaris Yazan Momany Adriano Pietrinferni 《Monthly notices of the Royal Astronomical Society》2005,357(3):1038-1048
We propose a zero-point photometric calibration of the data from the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) on board the Hubble Space Telescope , based on a spectrum of Vega and the most up-to-date in-flight transmission curves of the camera. This calibration is accurate at the level of a few hundredths of a magnitude. The main purpose of this effort is to transform the entire set of evolutionary models into a simple observational photometric system for ACS/WFC data, and to make them available to the astronomical community. We provide the zero-points for the most used ACS/WFC bands, and give basic recipes for calibrating both the observed data and the models. We also present the colour–magnitude diagram from ACS data of five Galactic globular clusters, spanning the metallicity range −2.2 <[Fe/H] < −0.04 , and we provide fiducial points representing their sequences from several magnitudes below the turn-off to the red giant branch tip. The observed sequences are compared with the models in the newly defined photometric system. 相似文献
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Guy J. Monnet 《Experimental Astronomy》2009,25(1-3):91-106
Spectroscopic astronomical instrumentation has much evolved in the last 40 years. Long-slit grating spectrographs with a photographic plate as the detector working in the 0.3–1 μm range were prevalent up to the early 1970s. The replacement of photographic plates by two-dimensional digital detectors provided gains in sensitivity of two orders of magnitude and much better photometric and radial velocity precision, and opened the 1 to 25 μm infrared domain. Another gain in speed by up to two orders of magnitude was then obtained through the development of various spectroscopic systems, each optimized for a subset of astronomical objects. This development was underpinned by a number of technological advances, in particular the development of automatic data reduction pipelines using sophisticated algorithms. With ever larger and more complex instrument systems for the present 8–10 m diameter telescopes—and soon even more for the next generation of Extremely Large Telescopes, the development of an instrument is now a big enterprise, ranging all the way from long-term enabling technology efforts to management of large teams for construction and deployment over typically 7–8 years. 相似文献
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R. D'Abrusco G. Longo N. A. Walton 《Monthly notices of the Royal Astronomical Society》2009,396(1):223-262
We present a method for the photometric selection of candidate quasars in multiband surveys. The method makes use of a priori knowledge derived from a subsample of spectroscopic confirmed quasi-stellar objects (QSOs) to map the parameter space. The disentanglement of QSOs candidates and stars is performed in the colour space through the combined use of two algorithms, the probabilistic principal surfaces and the negative entropy clustering, which are for the first time used in an astronomical context. Both methods have been implemented in the voneural package on the Astrogrid Virtual Observatory platform. Even though they belong to the class of the unsupervised clustering tools, the performances of the method are optimized by using the available sample of confirmed quasars and it is therefore possible to learn from any improvement in the available 'base of knowledge'. The method has been applied and tested on both optical and optical plus near-infrared data extracted from the visible Sloan Digital Sky Survey (SDSS) and infrared United Kingdom Infrared Deep Sky Survey-Large Area Survey public data bases. In all cases, the experiments lead to high values of both efficiency and completeness, comparable if not better than the methods already known in the literature. A catalogue of optical candidate QSOs extracted from the SDSS Data Release 7 Legacy photometric data set has been produced and is publicly available at the URL http://voneural.na.infn.it/qso.html . 相似文献
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Zdeněk Kopal 《Astrophysics and Space Science》1982,88(2):313-329
In continuation of our preceding investigation (Kopal, 1982c) of photometric consequences of free oscillations — radial or nonradial — of the eclipsing component on the light changes of close binary systems, the aim of the present paper will be to extend the scope of our inquiry to include the effects of similar oscillations of the component which undergoes eclipse, with arbitrary period and phase.In Sections 2 and 3 which follow a brief introduction to the particular aspect of the problem treated in this paper, a theory will be given of photometric effects caused by arbitrary harmonic oscillations of the components of eclipsing binary systems distorted by equilibrium tides, or by axial rotation with constant angular velocity. A translation of these effects into the frequency domain constitutes a problem which is solvable in a closed form only if the eclipse in question ends in totality. In any other case, the desired effects can be mathematically described only in terms of infinite series (of satisfactory asymptotic properties); and a construction of their explicit forms will be given in the Appendix. 相似文献
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M. D. CAMPBELL P. G. BROWN A. G. LEBLANC R. L. HAWKES J. JONES S. P. WORDEN R. R. CORRELL 《Meteoritics & planetary science》2000,35(6):1259-1267
Abstract— Two‐station electro‐optical observations of the 1998 Leonid shower are presented. Precise heights and light curves were obtained for 79 Leonid meteors that ranged in brightness (at maximum luminosity) from +0.3 to +6.1 astronomical magnitude. The mean photometric mass of the data sample was 1.4 × 10?6 kg. The dependence of astronomical magnitude at peak luminosity on photometric mass and zenith angle was consistent with earlier studies of faint sporadic meteors. For example, a Leonid meteoroid with a photometric mass of ～1.0 × 10‐7 kg corresponds to a peak meteor luminosity of about +4.5 astronomical magnitudes. The mean beginning height of the Leonid meteors in this sample was 112.6 km and the mean ending height was 95.3 km. The highest beginning height observed was 144.3 km. There is relatively little dependence of either the first or last heights on mass, which is indicative of meteoroids that have clustered into constituent grains prior to the onset of intensive grain ablation. The height distribution, combined with numerical modelling of the ablation of the meteoroids, suggests that silicate‐like materials are not the principal component of Leonid meteoroids and hints at the presence of a more volatile component. Light curves of many Leonid meteors were examined for evidence of the physical structure of the associated meteoroids: similar to the 1997 Leonid meteors, the narrow, nearly symmetric curves imply that the meteoroids are not solid objects. The light curves are consistent with a dustball structure. 相似文献
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Interpretation of photometric and polarimetric observations of atmosphereless celestial bodies faces the problems connected with both the insufficient accuracy and level of details in groundbased observations and the current state of the theory of the multiple scattering of light. In application to sparse media, where the electromagnetic waves, propagating between the scatterers, can be considered as spherical (the socalled far-field approximation), this theory is rather well developed for both the diffuse and coherent components of the scattered radiation. In this paper, we show that this theory can be also successfully applied to the measurements of polarization of light scattered by densely packed, though nonabsorbing or weakly absorbing, media. For this purpose, we calculated the models for a semi-infinite layer of the medium composed of randomly oriented clusters of spherical particles and compared them with the data of laboratory and astronomical measurements. The potential of the present approach is illustrated by an example of the interpretation of the polarization measurements of the ice satellites of Saturn—Rhea and Enceladus—which allowed some properties of the surface of these celestial bodies to be estimated. In particular, the ratio of the surface area that makes no contribution to the negative polarization of light reflected at small phase angles to the area producing the negative polarization branch was found. Under the assumption of the same albedo of these areas, this ratio turned out to be 3.31–3.66 and 1.7–3.8 for Rhea and Enceladus, respectively. For Enceladus, it is difficult to obtain a sufficiently narrow range of the estimated parameters, since the number of measurement points in the phase dependence of polarization of this satellite is small. For the surface of Rhea, the estimated packing density of particles, participating in the opposition effects, is approximately 15%, while their smallest size is of the order of the wavelength of visible light. 相似文献
16.
K.D. Borne 《Astronomische Nachrichten》2008,329(3):255-258
We describe the largest data‐producing astronomy project in the coming decade – the LSST (Large Synoptic Survey Telescope). The enormous data output, database contents, knowledge discovery, and community science expected from this project will impose massive data challenges on the astronomical research community. One of these challenge areas is the rapid machine learning, data mining, and classification of all novel astronomical events from each 3‐gigapixel (6‐GB) image obtained every 20 seconds throughout every night for the project duration of 10 years.We describe these challenges and a particular implementation of a classification broker for this data fire hose. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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The artificial night sky brightness mapped from DMSP satellite Operational Linescan System measurements 总被引：2，自引：0，他引：2
P. Cinzano F. Falchi C. D. Elvidge K. E. Baugh 《Monthly notices of the Royal Astronomical Society》2000,318(3):641-657
We present a method to map the artificial sky brightness across large territories in astronomical photometric bands with a resolution of approximately 1 km. This is of use in quantifying the situation regarding night sky pollution, recognizing potential astronomical sites and allowing future monitoring of trends. The artificial sky brightness present in the chosen direction at a given position on the surface of the Earth is obtained by the integration of the contributions produced by every surface area in the surroundings . Each contribution is computed via detailed models for the propagation in the atmosphere of the upward light flux emitted by the area. The light flux is measured with top-of-atmosphere radiometric observations made by the Defense Meteorological Satellite Program (DMSP) Operational Linescan System.
We have applied the described method to Europe, obtaining maps of artificial sky brightness in the V and B bands. 相似文献
We have applied the described method to Europe, obtaining maps of artificial sky brightness in the V and B bands. 相似文献
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We have used the extensive set of photometric data in the VBLUW system (Pel, 1976) to perform a thorough statistical analysis of the physical properties of Cepheid variables, which can be inferred directly from these data. We have dealt with the problem of determining colour excesses and mean colours and temperatures; theoretical masses, radii and luminosities have been recalculated. 相似文献