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181.
Spectral Energy Distribution (SED) fitting is a well-developed astrophysical tool that has recently been applied to high-redshift Lyα-emitting galaxies. If rest-frame ultraviolet through near-infrared photometry is available, it allows the simultaneous determination of the star formation history and dust extinction of a galaxy. Lyα-emitter SED fitting results from the literature find star formation rates 3 M yr−1, stellar masses 109 M for the general population but 1010 M for the subset detected by IRAC, and very low dust extinction, AV 0.3, although a couple of outlying analyses prefer significantly more dust and higher intrinsic star formation rates. A checklist of 14 critical choices that must be made when performing SED fitting is discussed. 相似文献
182.
Organic matter in space: from star dust to the Solar System 总被引:1,自引:0,他引:1
Sun Kwok 《Astrophysics and Space Science》2009,319(1):5-21
Organic compounds of high degree of complexity are now known to be widespread in the Universe, ranging from objects in our
Solar System to distant galaxies. Through the techniques of millimeter-wave spectroscopy, over 140 molecules have been identified
through their rotational transitions. Space infrared spectroscopy has detected the stretching and bending modes of compounds
with aromatic and aliphatic structures. Analyses of samples of meteorites, comets, asteroids, and interplanetary dust also
revealed a rich content of organic substances, some of which could be of extra-solar origin. We review the current state of
understanding of the origin, evolution, nature, and distribution of organic matter in space. Also discussed are a number of
unexplained astronomical phenomena whose origins could be traced to organic carriers. 相似文献
183.
184.
Anthony F. J. Moffat 《Astrophysics and Space Science》1994,221(1-2):467-480
It seems more and more likely that one will have to abandon the paradigm of smooth outflows from (hot) stars in favour of a clumpy structure, possibly in a fractal-like hierarchy on all scales. Observationally, this is best established for Wolf-Rayet star winds (e.g. scaling laws, mass-spectrum, anisotropy,...), for which the consequences of clumping are discussed. These include four broad categories, which are outlined in this review: (a) an ideal laboratory for studying time-dependent astrophysical turbulence, (b) potential tracers of hot-wind global structure parameters, (c) reduced mass-loss rates, and (d) impact on massive binary studies. 相似文献
185.
M. Meixner J. R. Graham C. J. Skinner G. W. Hawkins E. Keto J. F. Arens J. G. Jernigan 《Experimental Astronomy》1994,3(1-4):53-56
We present 9.7 and 11.8 m narrow band (/=10%) images of three carbon (C-) rich proto-planetary nebulae with an unusual 21 m feature: IRAS 07134+ 1005, IRAS 22272+5435, and IRAS 04296+3429. The images were taken at UKIRT using the Berkeley/IGPP/LEA mid-IR camera. All three objects have a bipolar shape adding to the existing evidence that C-rich PPNe are by nature bipolar. Furthermore, we find the same bipolar morphology in a previous study of the C-rich, young planetary nebula, IRAS 21282+5050. We believe these four objects form an evolutionary sequence which links the C-rich asymptotic giant branch (AGB) stars with the C-rich planetary nebulae (PNe). From this evolutionary sequence, we conclude that bipolarity in C-rich PNe begins on the AGB and that the dynamical ages of these PPNe are in fair agreement with theoretical ages for a 0.6 M hydrogen burning core star. 相似文献
186.
本文利用势垒穿透模型计算重离子融合反应截面,我们发现理论计算结果同现有的实验数据符合得相当好。在此基础上,对~(12)C+~(12)C,~(12)C+~(14)N,~(12)C+~(16)O,~(14)N+~(14)N,~(14)N+~(16)O和~(16)O+~(16)O六种融合反应,在T_9=-0.1—5.0温度范内数值计算了这些热核反应率,并给出了它们随温度变化的近似解析表达式.对~(12)C+~(12)C,~(12)C+~(16)O和~(16)O+~(16)O这三种热核反应率,我们的新结果明显地低于Caughlan等人在1985年的列表值,特别是~(16)O+~(16)O的热核反应率比文[21中值低7—20倍,这将对整个大质量恒星的演化、超新星爆发以及核合成带来较大的影响,本文简略地讨论了这些影响. 相似文献
187.
《Chinese Astronomy and Astrophysics》2020,44(4):413-427
The new generation of large sky area spectroscopic survey project has produced nearly 10 million low-resolution stellar spectra. Based on these spectroscopic data, this paper introduces a machine learning algorithm named The Cannon. This algorithm is completely based on the known spectroscopic data of stellar atmospheric parameters (effective temperature, surface gravity, and metal abundance, etc.), this algorithm builds the characteristic vector by means of data driving, and establishes the functional relation between spectral flux characteristics and stellar parameters. Then it is applied to the observed spectral data to calculate the atmospheric parameters. The main advantage of The Cannon is that it is not directly based on any stellar physical models, it has an even higher applicability. Moreover, because of the use of full-spectrum information, even for the spectra with a low signal-to-noise ratio (SNR), it still can obtain the parameter solutions of high reliability. This algorithm has significant advantages in the data processing and parameter determination of large-scale stellar spectra. In addition, this paper presents two examples of using The Cannon to obtain the stellar parameters of K and M giants from the LAMOST spectral data. 相似文献
188.
189.
With the use of modern detectors stellar spectral classification libraries have been extended from the photographic regime to the near ℝ at 11000 Å. We have defined new spectral indices within this extended wavelength-range that can be used to determine the luminosity classification for G-K-M stars. An advantage of the new indices, which sample the stellar flux in and out of selected spectral features, is that they are insensitive to catalog differences. This facilitates the use of many catalogs, with varying resolution, different reddening corrections, and calibrations, hence extending the total number of stellar standards available. Furthermore, we demonstrate that the indices can be used to infer absolute magnitudes with good accuracy. The indices should prove useful for analysis of spectra from distant clusters, galaxies, and in particular for problems involving spectral synthesis of stellar populations of galaxies. 相似文献
190.