Measuring the primordial power spectrum: principal component analysis of the cosmic microwave background     

Samuel Leach 《Monthly notices of the Royal Astronomical Society》2006,372(2):646-654

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Absolute Parameters of Early-Type Close Binaries in the LMC     

S. Nesslinger  H. Drechsel 《Astrophysics and Space Science》2006,304(1-4):211-214

A project is presented which aims at high-precision determination of absolute parameters of close early-type eclipsing binaries in the LMC. We will use multi-object spectrographs (MOS) to measure RV curves of a large number of program stars selected from the MACHO archive. Spectroscopic mass ratios will be used as input for our light curve analysis code MORO. Application of the Simplex-based algorithm FITSB2 will achieve spectrum disentangling and fitting of NLTE model (TLUSTY) atmospheres, yielding orbital and atmospheric parameters. The method was extensively tested by application to time series of synthetic binary spectra for the expected range of S/N and MOS instrumental resolution. log g and T _eff were reestablished with a precision of better than 5%, radial velocity amplitudes with errors of <3%. An important by-product of our project will be the improvement of the distance modulus of the LMC, a topic which is still being intensely discussed.  相似文献   

1.4-GHz polarimetric observations of the two fields imaged by the DASI experiment     

G. Bernardi  E. Carretti †  R. J. Sault  S. Cortiglioni  S. Poppi 《Monthly notices of the Royal Astronomical Society》2006,370(4):2064-2070

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Lines in the cosmic microwave background spectrum from the epoch of cosmological hydrogen recombination     

J. A. Rubiño-Martín  J. Chluba  R. A. Sunyaev 《Monthly notices of the Royal Astronomical Society》2006,371(4):1939-1952

We compute the spectral distortions of the cosmic microwave background (CMB) arising during the epoch of cosmological hydrogen recombination within the standard cosmological (concordance) model for frequencies in the range 1–3500 GHz. We follow the evolution of the populations of the hydrogen levels including states up to principle quantum number   n = 30  in the redshift range  500 ≤ z ≤ 3500  . All angular momentum substates are treated individually, resulting in a total number of 465 hydrogen levels. The evolution of the matter temperature and the fraction of electrons coming from He  ii are also included. We present a detailed discussion of the distortions arising from the main dipolar transitions, for example Lyman and Balmer series, as well as the emission due to the two-photon decay of the hydrogen 2s level. Furthermore, we investigate the robusteness of the results against changes in the number of shells considered. The resulting spectral distortions have a characteristic oscillatory behaviour, which might allow experimentalists to separate them from other backgrounds. The relative distortion of the spectrum exceeds a value of 10⁻⁷ at wavelengths longer than 21 cm. Our results also show the importance of detailed follow-up of the angular momentum substates, and their effect on the amplitude of the lines. The effect on the residual electron fraction is only moderate, and mainly occurs at low redshifts. The CMB angular power spectrum is changed by less than 1 per cent. Finally, our computations show that if the primordial radiation field is described by a pure blackbody, then there is no significant emission from any hydrogen transition at redshifts greater than   z ∼ 2000  . This is in contrast to some earlier works, where the existence of a 'pre-recombination' peak was claimed.  相似文献   

Detecting Sunyaev–Zel'dovich clusters with Planck– III. Properties of the expected SZ cluster sample     

Björn Malte Schäfer  Matthias Bartelmann 《Monthly notices of the Royal Astronomical Society》2007,377(1):253-268

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Evaluating the potential of a blended passive microwave‐interactive multi‐sensor product for improved mapping of snow cover and estimations of snow water equivalent     

Cezar Kongoli  Charles A. Dean  Sean R. Helfrich  Ralph R. Ferraro 《水文研究》2007,21(12):1597-1607

The retrieval of Snow Water Equivalent (SWE) from remote sensing satellites continues to be a very challenging problem. In this paper, we evaluate the accuracy of a new SWE product derived from the blending of a passive microwave SWE product based on the Advanced Microwave Sounding Unit (AMSU) with a multi‐sensor snow cover extent product based on the Interactive Multi‐sensor Snow and Ice Mapping System (IMS). The microwave measurements have the ability to penetrate the snow pack, and thus, the retrieval of SWE is best accomplished using the AMSU. On the other hand, the IMS maps snow cover more reliably due to the use of multiple satellite and ground observations. The evolution of global snow cover from the blended, the AMSU and the IMS products was examined during the 2006 snow season. Despite the overall good inter‐product agreement, it was shown that the retrievals of snow cover extent in the blended product are improved when using IMS, with implications for improved microwave retrievals of SWE. In a separate investigation, the skill of the microwave SWE product was also examined for its ability to correctly estimate SWE globally and regionally. Qualitative evaluation of global SWE retrievals suggested dependence on land surface temperature: the lower the temperature, the higher the SWE retrieved. This temperature bias was attributed in part to temperature effects on those snow properties that impact microwave response. Therefore, algorithm modifications are needed with more dynamical adjustments to account for changing snow cover. Quantitative evaluation over Slovakia in central Europe, for a limited period in 2006, showed reasonably good performance for SWE less than 100 mm. Sensitivity to deeper snow decreased significantly. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Parameterized first-guess spectrum method for retrieving directional spectrum of swell-dominated waves and huge waves from SAR images   总被引：3，自引：0，他引：3  

孙建  管长龙 《中国海洋湖沼学报》2006,24(1):12-20

A method to retrieve ocean wave spectra from SAR images, named Parameterized First-guess Spectrum Method (PFSM), was proposed after interpretation of the theory to ocean wave imaging and analysis of the drawbacks of the retrieving model generally used. In this method, with additional information and satellite parameters, the separating wave-number is first calculated to determine the maximum wave-number beyond which the linear relation can be used. The separating wave-number can be calculated using the additional information on wind velocity and parameters of SAR satellite. And then the SAR spectrum can be divided into SAR spectrum of wind wave and of swell according to the result of separating wave-number. The portion of SAR spectrum generated by wind wave, is used to search for the most suitable parameters of ocean wind wave spectrum, including propagation direction of ocean wave, phase speed of dominating wave and the angle spreading coefficient. The swell spectrum is acquired by directly inversing the linear relation of ocean wave spectrum to SAR spectrum given the portion of SAR spectrum generated by swell. We used the proposed method to retrieve the ocean wave spectrum from ERS-SAR data from the South China Sea and compared the result with altimeter data. The agreement indicates that the PFSM is reliable.  相似文献   

High Galactic latitude polarized emission at 1.4 GHz and implications for cosmic microwave background observations     

E. Carretti  G. Bernardi  R. J. Sault  S. Cortiglioni  S. Poppi 《Monthly notices of the Royal Astronomical Society》2005,358(1):1-12

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Non-random phases in non-trivial topologies     

Patrick Dineen  Graca Rocha  Peter Coles 《Monthly notices of the Royal Astronomical Society》2005,358(4):1285-1289

We present a new technique for constraining the topology of the Universe. The method exploits the existence of correlations in the phases of the spherical harmonic coefficients of the cosmic microwave background (CMB) temperature pattern associated with matched pairs of circles seen in the sky in universes with non-trivial topology. The method is computationally faster than all other statistics developed to hunt for these matched circles. We applied the method to a range of simulations with topologies of various forms and on different scales. A characteristic form of phase correlation is found in the simulations. We also applied the method to preliminary CMB maps derived from WMAP , but the separation of topological effects from e.g. foregrounds is not straightforward.  相似文献   

Detection of the integrated Sachs–Wolfe effect and corresponding dark energy constraints made with directional spherical wavelets     

J. D. McEwen  P. Vielva  M. P. Hobson  E. Martínez-González  A. N. Lasenby 《Monthly notices of the Royal Astronomical Society》2007,376(3):1211-1226

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