Showing papers by "Edward L. Wright published in 1993"

Dipole Anisotropy in the COBE Differential Microwave Radiometers First-Year Sky Maps

Abstract: We present a determination of the cosmic microwave background dipole amplitude and direction from the COBE Differential Microwave Radiometers (DMR) first year of data. Data from the six DMR channels are consistent with a Doppler-shifted Planck function of dipole amplitude ΔT=3.365±0.027 mK toward direction (l II , b II )=(264°.4±0°.3, 48°.4±0°.5). The implied velocity of the Local Group with respect to the CMB rest frame is v LG =627±22 km s −1 toward (l II , b II )=(276°±3°, 30°±3°). DMR has also mapped the dipole anisotropy resulting from the Earth's orbital motion about the Solar system barycenter, yielding a measurement of the monopole CMB temperature T 0 at 31.5, 53, and 90 GHz, T 0 =2.75±0.05 K

Statistics and Topology of the COBE DMR First Year Maps

Abstract: We use statistical and topological quantities to test the COBE-DMR first year sky maps against the hypothesis that the observed temperature fluctuations reflect Gaussian initial density perturbations with random phases Recent papers discuss specific quantities as discriminators between Gaussian and non-Gaussian behavior, but the treatment of instrumental noise on the data is largely ignored The presence of noise in the data biases many statistical quantities in a manner dependent on both the noise properties and the unknown CMB temperature field Appropriate weighting schemes can minimize this effect, but it cannot be completely eliminated Analytic expressions are presented for these biases, and Monte Carlo simulations used to assess the best strategy for determining cosmologically interesting information from noisy data The genus is a robust discriminator that can be used to estimate the power law quadrupole-normalized amplitude independently of the 2-point correlation function The genus of the DMR data are consistent with Gaussian initial fluctuations with Q_rms = 157 +/- 22 - (66 +/- 03)(n - 1) uK where n is the power law index Fitting the rms temperature variations at various smoothing angles gives Q_rms = 132 +/- 25 uK and n = 17 +03 -06 While consistent with Gaussian fluctuations, the first year data are only sufficient to rule out strongly non-Gaussian distributions of fluctuations

The interstellar Li-7/Li-6 isotope ratio toward Zeta Ophiuchi and Zeta Persei

Abstract: High S/N, high-resolution observations of the interstellar Li absorption lines toward the stars Zeta Ophiuchi and Zeta Persei are reported. Li I line profiles indicate the presence of both the Li-7 and Li-6 doublets in these two sightlines. Best-fit values for the interstellar Li-7/Li-6 isotope ratio are 6.8 (+1.4/-1.7) towards Zeta Ophiuchi and 5.5 (+ 1.3/-1.1) toward Zeta Persei. Measurement of 6.8 (+1.4/-1.7) for the interstellar Li-7/Li-6 isotope ratio towards Zeta Ophiuchi does not support the lower limit of 25 determined by Ferlet and Dennefeld (1984). The current value of the interstellar Li-7/Li-6 isotope ratio is the result of various lithium production and destruction processes involving stars, cosmic rays, and the big bang.

Noncosmological signal contributions to the COBE DMR anisotropy maps

Abstract: We examine the COBE Differential Microwave Radiometer (DMR) data for evidence of noncosmological source contributions. The DMR maps are cross-correlated with maps of rich clusters, extragalactic IRAS sources, HEAO 1 A-2 X-ray emission, and 5 GHz radio sources. We limit the rms contributions from these sources on a 7 deg angular scale to less than 10 micro-K (95 percent confidence level) in the DMR maps, although the LMC probably contributes about 50 micro-K to a limited region of the sky. Thus, our previous interpretation that the fluctuations in the COBE DMR data are most likely due to cosmic fluctuations at the surface of last scattering remains intact. The Comptonization parameter for hot electrons traced by rich clusters is limited to delta(y) less than 2 x 10 exp -6 (95 percent confidence level) averaged over the 7 deg DMR beam.

Scientific results from the cosmic background explorer (COBE)

Abstract: The National Aeronautics and Space Administration (NASA) has flown the COBE satellite to observe the Big Bang and the subsequent formation of galaxies and large-scale structure. Data from the Far-Infrared Absolute Spectrophotometer (FIRAS) show that the spectrum of the cosmic microwave background is that of a black body of temperature T = 2.73 ± 0.06 K, with no deviation from a black-body spectrum greater than 0.25% of the peak brightness. The data from the Differential Microwave Radiometers (DMR) show statistically significant cosmic microwave background anisotropy, consistent with a scale-invariant primordial density fluctuation spectrum. Measurements from the Diffuse Infrared Background Experiment (DIRBE) provide new conservative upper limits to the cosmic infrared background. Extensive modeling of solar system and galactic infrared foregrounds is required for further improvement in the cosmic infrared background limits.

Recent Results from Cobe

Abstract: The Cosmic Background Explorer or COBE 1, NASA’s first space mission devoted primarily to cosmology, carries three scientific instruments to make precise measurements of the spectrum and anisotropy of the cosmic microwave background (CMB) radiation on angular scales greater than 7°and to conduct a search for a diffuse cosmic infrared background (CIB) radiation with 0.7° angular resolution. The observing strategy is designed to minimize and allow determination of systematic errors that could result from spacecraft operations, the local environment of the spacecraft, and emissions from foreground astrophysical sources such as the Galaxy and the solar system. Data from the Far-InfraRed Absolute Spectrophotometer (FIRAS) show that the spectrum of the CMB is that of a blackbody of temperature T= 2.73 ± 0.06 K, with no deviation from a blackbody spectrum greater than 0.25% of the peak brightness. Data from the first year of the Differential Microwave Radiometers (DMR) show statistically significant CMB anisotropy. The anisotropy is consistent with a scale invariant primordial density fluctuation spectrum and with the gravitational potential variations required to cause the observed present day structure. Infrared sky brightness measurements from the Diffuse InfraRed Background Experiment (DIRBE) provide new conservative upper limits to the CIB. Extensive modeling of solar system and galactic infrared foregrounds is required for further improvement in the CIB limits.

Morphology of the Interstellar Cooling Lines Detected by COBE

Abstract: The FIRAS instrument on the COBE satellite has conducted an unbiased survey of the far-infrared emission from our Galaxy. The first results of this survey were reported by Wright et al. (1991). We report the results of new analyses of this spectral survey, which includes emission lines from 158 um C+, 122 um and 205 um N+, 370 um and 609 um C, and CO J=2-1 through 5-4. We report the morphological distribution along the galactic plane (b=0) of the spectral line emission, and the high galactic latitude intensities of the C+ and 205 um N+ emission. The high galactic latitude intensity cosecant of the 158 um fine structure transition from C+ is presented, and C+ is seen to decrease more rapidly than the far infrared intensity with increasing galactic latitude. C+ and H I emission are closely correlated with a C+ cooling rate of (2.65 +/- 0.15)x10^{-26} erg/s/H-atom. We conclude that this emission arises almost entirely from the Cold Neutral Medium. The high galactic latitude intensity of the 205 um fine structure transition from N+ arises entirely from the Warm Ionized Medium, and its cosecant is presented. We estimate the total ionizing photon rate in the Galaxy to be 3.5x10^{53} ionizing photons per second, based on the 205 um N+ transition.

The interstellar 7Li/6Li isotope ratio toward ζ ophiuchi and ζ persei

Abstract: We report high S/N (>2000), high-resolution (≃1 km s −1 ) observations of the interstellar Li I absorption lines toward the stars ζ Oph and ζ Per. Our Li I line profiles indicate the presence of both the 7 Li (λ rest =6707.761, 6707.912 A) and 6 Li (6707.921, 6708.072 A) doublets in these two sightlines. The resultant best-fit values (using a single-component profile) for the interstellar 7 Li/ 6 Li isotope ratio are 6.8 (+1.4, −1.7) toward ζ Oph and 5.5 (+1.3, −1.1) toward ζ Per. It is clear from our data that the 7 li/ 6 Li ratio toward ζ Oph and ζ Per is less than the meteoritic value (12.6) representative of the early solar system