Showing papers by "Edward L. Wright published in 1992"
TL;DR: In this paper, the first year of data from the differential microwave radiometers on the Cosmic Background Explorer was presented, and the angular autocorrelation of the signal in each radiometer channel and cross-correlation between channels were consistent and gave a primordial fluctuation power-law spectrum with index of 1.1 +/- 0.5, and an rms-quadrupole-normalized amplitude of 16 +/- 4 micro-K.
Abstract: Results of the first year of data from the differential microwave radiometers on the Cosmic Background Explorer are presented. Statistically significant structure that is well described as scale-invariant fluctuations with a Gaussian distribution is shown. The rms sky variation, smoothed to a total 10-deg FWHM Gaussian, is 30 +/-5 micro-K for Galactic latitude greater than 20-deg data with the dipole anisotropy removed. The rms cosmic quadrupole amplitude is 13 +/-4 micro-K. The angular autocorrelation of the signal in each radiometer channel and cross-correlation between channels are consistent and give a primordial fluctuation power-law spectrum with index of 1.1 +/-0.5, and an rms-quadrupole-normalized amplitude of 16 +/-4 micro-K. These features are in accord with the Harrison-Zel'dovich spectrum predicted by models of inflationary cosmology.
2,195 citations
TL;DR: The COBE mission as mentioned in this paper is the first space mission devoted to cosmology and is described and the spacecraft concepts central to enabling the mission to achieve its scientific objectives are examined, including the major components of the COBE instrument and spacecraft modules.
Abstract: The COBE mission, NASA's first space mission devoted primarily to cosmology, is described and the spacecraft concepts central to enabling the mission to achieve its scientific objectives are examined. The major components of the COBE instrument and spacecraft modules are shown and their characteristics are given. Early scientific results are summarized and plans for continuing satellite operations and data analysis are addressed.
354 citations
TL;DR: The large-scale cosmic background anisotropy detected by the COBE Differential Microwave Radiometer (DMR) instrument is compared to the sensitive previous measurements on various angular scales, and to the predictions of a wide variety of models of structure formation driven by gravitational instability as discussed by the authors.
Abstract: The large-scale cosmic background anisotropy detected by the COBE Differential Microwave Radiometer (DMR) instrument is compared to the sensitive previous measurements on various angular scales, and to the predictions of a wide variety of models of structure formation driven by gravitational instability. The observed anisotropy is consistent with all previously measured upper limits and with a number of dynamical models of structure formation. For example, the data agree with an unbiased cold dark matter (CDM) model with H0 = 50 km/s Mpc and Delta-M/M = 1 in a 16 Mpc radius sphere. Other models, such as CDM plus massive neutrinos (hot dark matter (HDM)), or CDM with a nonzero cosmological constant are also consistent with the COBE detection and can provide the extra power seen on 5-10,000 km/s scales.
249 citations
TL;DR: In this article, preliminary models of microwave emission from the Milky Way Galaxy based on COBE and other data are constructed for the purpose of distinguishing cosmic and Galactic signals, with the modeled Galactic emission removed, with a quadrupole distribution.
Abstract: Preliminary models of microwave emission from the Milky Way Galaxy based on COBE and other data are constructed for the purpose of distinguishing cosmic and Galactic signals. Differential Microwave Radiometer (DMR) maps, with the modeled Galactic emission removed, are fitted for a quadrupole distribution. Autocorrelation functions for individual Galactic components are presented. When Galactic emission is removed from the DMR data, the residual fluctuations are virtually unaffected, and therefore they are not dominated by any known Galactic emission component.
194 citations
TL;DR: The techniques available for the identification and subtraction of sources of dynamic uncertainty from data of the Differential Microwave Radiometer (DMR) instrument aboard COBE are discussed in this article.
Abstract: The techniques available for the identification and subtraction of sources of dynamic uncertainty from data of the Differential Microwave Radiometer (DMR) instrument aboard COBE are discussed. Preliminary limits on the magnitude in the DMR 1 yr maps are presented. Residual uncertainties in the best DMR sky maps, after correcting the raw data for systematic effects, are less than 6 micro-K for the pixel rms variation, less than 3 micro-K for the rms quadruple amplitude of a spherical harmonic expansion, and less than 30 micro-(K-squared) for the correlation function.
61 citations
TL;DR: In this paper, the authors used the Doppler effect due to the earth's motion around the barycenter of the solar system as an external calibration source to calibrate the DMR.
Abstract: The COBE spacecraft was launched November 18, 1989 UT carrying three scientific instruments into earth orbit for studies of cosmology. One of these instruments, the Differential Microwave Radiometer (DMR), is designed to measure the large-angular-scale temperature anisotropy of the cosmic microwave background radiation at three frequencies (31.5, 53, and 90 GHz). This paper presents three methods used to calibrate the DMR. First, the signal difference between beam-filling hot and cold targets observed on the ground provides a primary calibration that is transferred to space by noise sources internal to the instrument. Second, the moon is used in flight as an external calibration source. Third, the signal arising from the Doppler effect due to the earth's motion around the barycenter of the solar system is used as an external calibration source. Preliminary analysis of the external source calibration techniques confirms the accuracy of the currently more precise ground-based calibration. Assuming the noise source behavior did not change from the ground-based calibration to flight, a 0.1-0.4 percent relative and 0.7-2.5 percent absolute calibration uncertainty is derived, depending on radiometer channel.
47 citations
TL;DR: In this paper, the 1989 diffuse UV background data of Fix et al. were used to estimate an extragalactic UV background of 4 +/- 80 units at 0.15 micron, compared to the absorption cross section in the visible.
Abstract: The 1989 diffuse UV background data of Fix et al. (1989), when modeled as an optically thin, geometrically thin Galactic disk, implies an extragalactic UV background of 4 +/- 80 units at 0.15 micron, rather than the 530 +/- 80 units given by Fix et al. A more conservative fit allowing for forward scattering by dust and a finite optical depth to the Galactic pole gives a best-fit value of 45 units for the extragalactic flux, with a conservative limit of less than 500 units, similar to the lowest observed flux. Comparing the gradient of the UV flux versus csc absolute value of b with the IRAS 100 micron gradient implies an unexpectedly low scattering cross section for dust at 0.15 micron, compared to the absorption cross section in the visible.
20 citations
01 Jan 1992
TL;DR: The FIRAS instrument on COBE has mapped almost the entire sky with a 7° beam and a spectral resolution of about 1 em-1 over the 1-100 em 1 range.
Abstract: The FIRAS instrument on COBE has mapped almost the entire sky with a 7° beam and a spectral resolution of about 1 em-1 over the 1-100 em-1 range. Maps showing the strengths of the three main components: dust continuum, [C II] and [N II] are presented. A mean spectrum of the galactic emission is found. These results are used to compare the Milky Way to other galaxies.