Constraining non-gaussianities in WMAP1 and WMAP2     

Istvn Szapudi  Gang Chen 《New Astronomy Reviews》2006,50(11-12):896

We measure the 2-1 cumulant correlator power spectrum, a degenerate three-point statistic or integrated bispectrum, from the WMAP first and three year data releases (WMAP1 and WMAP2, respectively). We present a method of estimating these statistics using the pseudo-C_l-based SpICE estimator. We interpret the measurements in a maximum likelihood framework using theoretical predictions based on the simplest f_NL model. All calculations are repeated on Monte Carlo simulations to obtain covariance matrices of our measurements. Application of the theory of random matrices revealed that the experimental covariances are consistent with a random matrix approximation. Finally, our χ² analysis yields f_NL = 22 ± 52(1σ) from WMAP2.  相似文献   

No Higher Criticism of the Bianchi-corrected Wilkinson Microwave Anisotropy Probe data     

L. Cayón  A. J. Banday  T. Jaffe  H. K. Eriksen  F. K. Hansen  K. M. Gorski  J. Jin 《Monthly notices of the Royal Astronomical Society》2006,369(2):598-602

Higher Criticism (HC) has been proposed by Donoho & Jin as an effective statistic to detect deviations from Gaussianity. Motivated by the success of the Bianchi VII_h model in addressing many of the anomalies observed in the Wilkinson Microwave Anisotropy Probe ( WMAP ) data (Jaffe et al.), we present calculations in real and in wavelet space of the HC statistic of the Bianchi-corrected WMAP first-year data. At the wavelet scale of 5°, the HC of the WMAP map drops from a value above the 99 per cent confidence level (c.l.) to a value below the 68 per cent CL when corrected by the Bianchi template. An important property of the HC statistic is its ability to locate the pixels that account for the deviation from Gaussianity. The analysis of the uncorrected WMAP data pointed to a cold spot in the Southern hemisphere, centred at   l ∼ 209°, b ∼−57°  . The HC of the Bianchi-corrected map indicates that this spot remains prominent, albeit at a level completely consistent with Gaussian statistics. Consequently, it is debatable how much emphasis should be placed on this residual feature, but we consider the effect of modestly increasing the scaling of the template. A factor of only 1.2 renders the spot indistinguishable from the background level, with no noticeable impact on the results published in Jaffe et al. for the low- l anomalies, large-scale power asymmetry or wavelet kurtosis. A trivial interpretation would be that the Bianchi template may require a small enhancement of power on scales corresponding to the wavelet scale of 5°.  相似文献   

Pulsating subsidence during a rift episode: stratigraphic and tectonic consequences (Aptian–Albian, northern Spain)     

Joaquín García-Mondéjar  Mikel A. López-Horgue  Arantxa Aranburu  Pedro A. Fernández-Mendiola 《地学学报》2005,17(6):517-525

Backstripping analysis has been carried out on nine outcrop sections of the Basque-Cantabrian Aptian and Albian of northern Spain which consist of shallow-water marine deposits up to 7000 m thick. It reveals four main pulses of common accelerated subsidence: I (Early Aptian), II (Early Albian), III (lower Late Albian), and IV (uppermost Late Albian) separated by tectonic quiescent intervals. Tectonic subsidence rates of 70 m Myr^–1 for the Aptian and 101 m Myr^–1 for the Albian were recorded (Sopuerta section). The calculated stretching factor referred to a pre-rift continental crust of 35 km is (β_s=1.32) and represents approximately 8.5 km of crustal thinning. Points of change towards lesser subsidence rate in the curves are correlated with major unconformities in the sections, in the Basque-Cantabrian Basin and in Boreal Europe, suggesting geodynamic changes related with the opening of Bay of Biscay. Minor variations of spreading direction and intensity are proposed to explain the subsidence pulses.  相似文献   

Classical T Tauri Stars and Substellar Analogs     

D. Barrado Y Navascués  E.L. Martín  R. Jayawardhana  S. Mohanty 《Astrophysics and Space Science》2004,292(1-4):665-672

We propose a spectroscopic criterion based on Hα equivalent width and spectral type to classify classical T Tauri stars and substellar analogs. We argue that accreting objects can be identified from low-resolution optical spectroscopy, when their Hα flux is stronger than the saturation limit at Log {Lum(Hα)/Lum(bol)} = ?3.3. Additional criteria, such as the relation between HeI5876 or HeI6678 and Hα, or the ratios between the components of the CaII infrared triplet, are also discussed. We have tested the reliability of these criteria by applying them to several objects with masses in the range 0.11–0.025 M_⊙, which belong to nearby star forming regions and the TW Hya association.  相似文献   

Hilda asteroids among Jupiter family comets     

Romina P. Di Sisto  Adrián Brunini  Lorena D. Dirani  Rosa B. Orellana 《Icarus》2005,174(1):81-89

Hilda asteroids and comets are similar from the compositional point of view. The D-taxonomic class prevailing among Hildas has all the characteristics found in cometary spectra. Jupiter Family Comets (JFCs) coming from the trans-neptunian region are under the gravitational control of Jupiter, making them a dynamically unstable population with a mean dynamical lifetime of 10⁴ to ¹⁰⁵ years. In contrast, Hilda asteroids residing in the 3:2 mean motion resonance with Jupiter are a very stable population. But once they escape from the resonance, they are dynamically controlled by Jupiter, and in this sense their behavior resembles that of JFC. We performed a numerical simulation to analyze the dynamical evolution that Hildas follow after escaping from the resonance, and their contribution to the JFC population. We found that 8% of the particles leaving the resonance end up impacting Jupiter. 98.7% of the escaped Hildas live at least 1000 years as a JFC, with a mean lifetime of 1.4×¹⁰⁶ years. In particular, escaped Hildas stay mainly in the region of perihelion distances greater than 2.5 AU. On the other hand, the number of escaped Hildas reaching the inner Solar System (q<2.5 AU) is negligible. So, there are almost no Hilda asteroids among the NEO population. We also analyzed the possibility that the Shoemaker-Levy 9 were an escaped Hilda asteroid. In this case, it would be possible to give stronger constraints to its pre-capture orbital elements.  相似文献   

Behaviour of the SMF method for the numerical integration of satellite orbits     

Pablo Martín  José M. Ferrándiz 《Celestial Mechanics and Dynamical Astronomy》1995,63(1):29-40

The SMF algorithms were recently developed by the authors as a multistep generalization of the ScheifeleG-functions one-step method. Like the last, the proposed codes integrate harmonic oscillations without truncation error and the perturbing parameter appears as a factor of that error when integrating perturbed oscillations. Therefore they seemed to be convenient for the accurate integration of orbital problems after the application of linearizing transformations, such as KS or BF. In this paper we present several numerical experiments concerning the propagation of Earth satellite orbits, that illustrate the performance of the the SMF method. In general, it provides greater accuracy than the usual standard algorithms for similar computational cost.  相似文献   

Fast estimation of polarization power spectra using correlation functions     

Gayoung Chon  Anthony Challinor  Simon Prunet  Eric Hivon  István Szapudi 《Monthly notices of the Royal Astronomical Society》2004,350(3):914-926

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Long-Term Photometry of RT Lacertae: 1. Light and Colour Variation     

C. Íbanoğlu  E.R. Pekünlü  V. KESKÍn  Z. Tunca  S. Evren  M.C. Akan 《Astrophysics and Space Science》1997,257(1):11-21

The peculiar chromospherically active binary system RT Lac was observed in B and V bands between 1989 and 1992. The four-year photoelectric B and V light curves are presented. The light and colour variations in the four special regions of the light curve between 1978 and 1992 are discussed. The available photometry obtained by the present authors defines at least three consecutive maxima in the variation of the brightness of the system at second maximum and in mid-primary eclipse. The behaviour of the light and colour changes in mid-primary and at second maximum harmonizes with the common property of the RS CVn-type binaries. However, the light changes at first maximum do not resemble either at second maximum or in mid-primary minimum. Therefore, we conclude that the observed features cannot be attributed to the spottedness of the more massive component alone. The signs of the starspots are masked by the matter in front of the more massive component at the first maximum. The present data indicate that the magnetic cycle in RT Lac is about 12 years, which is analogous to the Sun's 11-year sunspot cycle.  相似文献   

Comments on the Magnetic Alternative to Missing Mass     

F. J. Sánchez-Salcedo 《Astrophysics and Space Science》1997,249(2):223-226

The arguments against the magnetic alternative given by Katz (1994) are discussed. Our conclusion is that the major problem regarding this alternative to dark matter is the flaring of the disk as suggested by Cuddeford and Binney (1993). We propose that the study of the equilibrium in the vertical direction should be carried out in dwarf spirals. Magnetic tension could alter the rotation curve of spiral galaxies but is not able to eliminate the necessity of dark matter. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The ionized gas in the Galactic Center Radio Arc     

N.J. RodrÍguez-Fernández  J. MartÍn-Pintado  P. de Vicente 《Astrophysics and Space Science》2002,281(1-2):333-334

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