排序方式: 共有25条查询结果,搜索用时 15 毫秒
1.
2.
M. P. Hobson A. W. Jones A. N. Lasenby & F. R. Bouchet 《Monthly notices of the Royal Astronomical Society》1998,300(1):1-29
A maximum entropy method (MEM) is presented for separating the emission resulting from different foreground components from simulated satellite observations of the cosmic microwave background radiation (CMBR). In particular, the method is applied to simulated observations by the proposed Planck Surveyor satellite. The simulations, performed by Bouchet &38; Gispert, include emission from the CMBR and the kinetic and thermal Sunyaev–Zel'dovich (SZ) effects from galaxy clusters, as well as Galactic dust, free–free and synchrotron emission. We find that the MEM technique performs well and produces faithful reconstructions of the main input components. The method is also compared with traditional Wiener filtering and is shown to produce consistently better results, particularly in the recovery of the thermal SZ effect. 相似文献
3.
François R. Bouchet 《Astrophysics and Space Science》2004,290(1-2):69-85
After recalling the current understanding of the formation of the large scale structures of the Universe which the distribution of galaxies revealed, I review what the imprint on the Cosmic Microwave Background (CMB) of the seeds of these structures can tell us, has already told us, and what it should tell us within the next five years. 相似文献
4.
5.
A stellar occultation by Uranus and its rings was observed on August 15, 1980, from the European Southern Observatory (Chile), at the 3.6-m telescope equipped with an infrared (2.2 μm) photometer. The recording presents the best signal-to-noise ratio obtained since the discovery of the Uranian rings in March 1977. The nine rings were observed, and the profiles of rings α, β, and ? were resolved, the ring α exhibiting a double structure. Strong diffraction peaks are visible in the γ ring profile suggesting an opaque ring with very sharp edges. A broad and faint structure extends outward from the η ring, on a radial scale of about 55 km. Apart from the ring occultations, unexplained sharp and deep events were recorded, and no interpretation is possible until future observations are made. Furthermore, the stellar light curve during the immersion of the star behind the planet provides (via an inversion computation) the temperature profile of the upper atmosphere of Uranus. The temperature is close to 145 ± 10°K at the 3 × 10?2-mbar pressure level and is nearly constant (155 ± 15°K) in the pressure interval from 10?2 to 10?3 mbar. The thermal inversion is as strong as the inversion on Neptune but is located at higher altitudes. This high stratospheric temperature is consistent with the upper limit of the brightness temperature at 8 μm only if CH4 follows its saturation law. 相似文献
6.
S. Prunet Shiv K. Sethi F. R. Bouchet 《Monthly notices of the Royal Astronomical Society》2000,314(2):348-353
We estimate the accuracy with which various cosmological parameters can be determined from the cosmic microwave background (CMB) temperature and polarization data when various galactic unpolarized and polarized foregrounds are included and marginalized using the multi-frequency Wiener filtering technique. We use the specifications of the future CMB missions MAP and Planck for our study. Our results are in qualitative agreement with earlier results obtained without foregrounds, though the errors in most parameters are higher because of degradation of the extraction of polarization signal in the presence of foregrounds. 相似文献
7.
8.
B. Sicardy M. Combes J. Lecacheux P. Bouchet A. Brahic P. Laques C. Perrier L. Vapillon Y. Zeau 《Icarus》1985,64(1):88-106
Stratospheric temperature profiles of Uranus were derived from the stellar occultation of 22 April 1982 in the pressure range 5–30 μbar. The observations were made at the European Southern Observatory, Chile, and at the Observatoire du Pic du Midi et de Toulouse, France with two telescopes in both sites. The study of these profiles confirms that Uranus' stratosphere is warmer than had been expected from radiative models (J. F. Appleby, 1980, Atmospheric Structures of the Giant Planets from Radiative-Convective Equilibrium Models. PhD. Thesis, State University of New York at Stony Brook) and that there has been a general increase of temperature since 1977 (R. G. French, J. L. Elliot, E. W. Dunham, D. A. Allen, J. H. Elias, J. A. Frogel, and W. Liller, 1983, Icarus53, 399–414). Furthermore, the profiles exhibit a nonisothermal feature with a maximum temperature around the 8-μbar pressure level. The amplitude of this feature increases linearly with the diurnally averaged insolation 〈D〉 up to the observed value 〈D〉 ~ 0.15. Moreover, the temperature at 8 μbar, as well as the mean stratospheric temperature, reaches a plateau around the equator of the planet which is far from maximum insolation. For a nominal abundance of methane ηCH4 ~ 3 × 10?5 and normal incidence, the UV absorption could compete with the IR methane absorption bands at the pressure level 8 μbar. However, the high temperatures observed even at grazing incidence imply important circulation phenomena to isothermalize distant regions of the planet. Alternatively, the observed profiles may suggest that an optically thin aerosol layer distributed over one scale height is responsible for the temperature maximum at 8 μbar. The total mass of dust necessary to heat this region up significantly would be a small fraction (6 × 1010 g vs 5 × 1018 g) of the Uranian ring system, which appears then as a possible reservoir of dust. However, a falling rate of ~1 msec?1 would deplete the rings in a short time (≈2 × 105 years) so that a dynamical process is needed to sustain the aerosol layer. 相似文献
9.
10.
J. M. Lamarre J. L. Puget F. Bouchet P. A. R. Ade A. Benoit J. P. Bernard J. Bock P. De Bernardis J. Charra F. Couchot J. Delabrouille G. Efstathiou M. Giard G. Guyot A. Lange B. Maffei A. Murphy F. Pajot M. Piat I. Ristorcelli D. Santos R. Sudiwala J. F. Sygnet J. P. Torre V. Yurchenko D. Yvon 《New Astronomy Reviews》2003,47(11-12):1017
The High Frequency Instrument (HFI) of Planck is the most sensitive CMB experiment ever planned. Statistical fluctuations (photon noise) of the CMB itself will be the major limitation to the sensitivity of the CMB channels. Higher frequency channels will measure galactic foregrounds. Together with the Low Frequency Instrument, this will make a unique tool to measure the full sky and to separate the various components of its spectrum. Measurement of the polarization of these various components will give a new picture of the CMB. In addition, HFI will provide the scientific community with new full sky maps of intensity and polarization at six frequencies, with unprecedented angular resolution and sensitivity. This paper describes the logics that prevailed to define the HFI and the performances expected from this instrument. It details several features of the HFI design that has not been published up to now. 相似文献