Newton Figueiredo

Degree-scale anisotropy in the cosmic microwave background: SP94 results

We present results from two observations of the cosmic microwave background (CMB) performed from the South Pole during the 1993-1994 austral summer. Each observation employed a 3 deg peak-to-peak sinusoidal, single-difference chop and consisted of a 20 deg x 1 deg strip on the sky. The first observation used a receiver which operates in three channels between 38 and 45 GHz (Q-band) with a full width half maximum (FWHM) beam which varies from 1 deg to 1.15 deg. The second observation overlapped the first observation and used a receiver which operates in four channels between 26 and 36 GHz (Ka-band) with a FWHM beam which varies from 1.5 deg to 1.7 deg. Significant correlated structure is observed in all channels for each observation. The spectrum of the structure is consistent with a CMB spectrum and is formally inconsistent with diffuse synchrotron and free-free emission at the 5 sigma level. The amplitude of the structure is inconsistent with 20 K interstellar dust; however, the data do not discriminate against flat or inverted spectrum point sources. The root mean square amplitude (+/- 1 sigma) of the combined (Ka + Q) data is Delta T(sub rms) = 41.2(sup +15.5, sub -6.7) micro-K for an average window function which has a peak value of 0.97 at l = 68 and drops to e(exp -0.5) of the peak value at l = 36 and l = 106. A band power estimate of the CMB power spectrum, C(sub l), gives average value of (C(sub l)l(l + 1)/(2 pi))(sub B) = 1.77(sup +1.58, sub -0.54) x 10(exp -10).

The second measurement of anisotropy in the cosmic microwave background radiation at 0.°5 scales near the star μ Pegasi

During the fifth flight of the Microwave Anisotropy Experiment (MAX5), we revisited a region with significant dust emission near the star mu Pegasi. A 3.5 cm(-1) low-frequency channel has been added since the previous measurement (Meinhold et al. 1993a). The data in each channel clearly show structure correlated with IRAS 100 mu m dust emission. The spectrum of the structure in the 6, 9, and 14 cm(-1)channels is described by I-v proportional to nu(beta)B(nu) (T-dust),where beta = 1.3 and T-dust = 19 K and B-v is the Planck function. However, this model predicts a smaller amplitude in the 3.5 cm(-1) band than is observed. Considering only linear combinations of the data independent of the best-fit foreground spectrum for the three lower channels, we find an upper limit to CMBR fluctuations of Delta T/T =(C(l)l(l + 1)/2 pi)(1/2) less than or equal to 1.3 x 10(-5) at the 95 percent confidence level. The result is for a flat-band power spectrum and does not include a 10 percent uncertainty in calibration. It is consistent with our previous observation in the region.

THE BACKGROUND EMISSION ANISOTROPY SCANNING TELESCOPE (BEAST) INSTRUMENT DESCRIPTION AND PERFORMANCES

The Background Emission Anisotropy Scanning Telescope (BEAST) is a millimeter wavelength experiment designed to generate maps offluctuations inthecosmicmicrowave background (CMB). The telescope is composed of an off-axis Gregorian optical systemwith a 2.2 mprimary thatfocuses the collected microwave radiation onto an array of cryogenically cooled high electron mobility transistor (HEMT) receivers. This array is composed of six corrugated scalar feed horns in the Q band (38 to 45 GHz) and two more in the Ka band (26 to 36 GHz) with one of the six Q-band horns connected to an ortho-mode transducer for extraction of both polarizations incident on the

Galactic foreground contribution to the BEAST cosmic microwave background anisotropy maps

We report limits on the Galactic foreground emission contribution to the Background Emission Anisotropy Scanning Telescope (BEAST) Ka- and Q-band CMB anisotropy maps. We estimate the contribution from the cross-correlations between these maps and the foreground emission templates of an H? map, a destriped version of the Haslam et al. 408 MHz map, and a combined 100 ?m IRAS DIRBE map. Our analysis samples the BEAST ~10? declination band into 24 one-hour (R.A.) wide sectors with ~7900 pixels each, where we calculate (1) the linear correlation coefficient between the anisotropy maps and the templates; (2) the coupling constants between the specific intensity units of the templates and the antenna temperature at the BEAST frequencies; and (3) the individual foreground contributions to the BEAST anisotropy maps. The peak sector contributions of the contaminants in the Ka-band are of 56.5% free-free with a coupling constant of 8.3 ? 0.4 ?K R-1, and 67.4% dust with 45.0 ? 2.0 ?K MJy-1 sr-1. In the Q band the corresponding values are of 64.4% free-free with 4.1 ? 0.2 ?K R-1 and 67.5% dust with 24.0 ? 1.0 ?K MJy-1 sr-1. Using a lower limit of 10% in the relative uncertainty of the coupling constants, we can constrain the sector contributions of each contaminant in both maps to <20% in 21 (free-free), 19 (dust), and 22 (synchrotron) sectors. At this level, all these sectors are found outside of the b = 146 region. By performing the same correlation analysis as a function of Galactic scale height, we conclude that the region within b = ?175 should be removed from the BEAST maps for CMB studies in order to keep individual Galactic contributions below ~1% of the maps rms.

The Cosmic Microwave Background Anisotropy Power Spectrum from the BEAST Experiment

The Background Emission Anisotropy Scanning Telescope (BEAST) is a 2.2 m off-axis telescope with an eightelement mixed Q-band (38–45 GHz) and Ka-band (26–36 GHz) focal plane, designed for balloon-borne and ground-basedstudiesofthe cosmicmicrowavebackground(CMB).Herewepresentthe CMB angularpowerspectrumcalculatedfrom682hrofdataobservedwiththeBEASTinstrument.Weuseabinnedpseudo-Cl estimator(the MASTER method). We find results that are consistent with other determinations of the CMB anisotropy for angular wavenumbers l between 100 and 600. We also perform cosmological parameter estimation. The BEAST data alone produce a good constraint on k � 1 � tot ¼� 0:074 � 0:070, consistent with a flat universe. A joint parameter estimation analysis with a number of previous CMB experiments produces results consistent with previous determinations. Subject heading gs: cosmicmicrowavebackground — cosmology:observations — large-scalestructureofuniverse

The Optical Design of the Background Emission Anisotropy Scanning Telescope (BEAST)

We present the optical design of the Background Emission Anisotropy Scanning Telescope (BEAST), an offaxis Gregorian telescope designed to measure the angular distribution of the cosmic microwave background radiation (CMBR)at30and 41.5 GHzonangularscalesrangingfrom 20 0 to10 � .Theapertureof thetelescope is1.9m, and our design meets the strict requirements imposed by the scientific goals of the mission: the beam size is 20 0 at 41.5 GHz and 26 0 at 30 GHz, while the illumination at the edge of the mirrors is lower than � 30 dB for the central horn.Theprimarymirror isanoff-axissectionofaparaboloid,andthesecondaryanoff-axissectionofanellipsoid.A spinning flat mirror located between the sky and the primary provides a two-dimensional chop by rotating the beams around an ellipse on the sky. BEAST uses a receiver array of cryogenic low noise InP High Electron Mobility Transistor (HEMT) amplifiers. The baseline array has seven horns matched to one amplifier each and one horn matchedtotwoamplifiers(twopolarizations)foratotalofnineamplifiers.Twohornsoperatearound30GHz,andsix operate around 41.5 GHz. Subsequent campaigns will include 90 GHz and higher frequency channels. Subject heading gs: cosmic microwave background — cosmology: observations — telescopes

Spillover and diffraction sidelobe contamination in a double-shielded experiment for mapping Galactic synchrotron emission

We have analyzed observations from a radioas- tronomical experiment to survey the sky at decimetric wavelengths along with feed pattern measurements in or- der to account for the level of ground contamination enter- ing the sidelobes. A major asset of the experiment is the use of a wire mesh fence around the rim-halo shielded an- tenna with the purpose of levelling out and reducing this source of stray radiation for zenith-centered 1-rpm circu- lar scans. We investigate the shielding performance of the experiment by means of a geometric diraction model in order to predict the level of the spillover and diraction sidelobes in the direction of the ground. Using 408 MHz and 1465 MHz feed measurements, the model shows how a weakly-diracting and unshielded antenna conguration becomes strongly-diracting and double-shielded as far- eld diraction eects give way to near-eld ones. Due to the asymmetric response of the feeds, the orientation of their radiation elds with respect to the secondary must be known a priori before comparing model predictions with observational data. By adjusting the attenuation coe- cient of the wire mesh the model is able to reproduce the amount of dierential ground pick-up observed during test measurements at 1465 MHz.

A Spin-Modulated Telescope to Make Two-Dimensional Cosmic Microwave Background Maps

We describe the HEMT Advanced Cosmic Microwave Explorer (HACME), a balloon-borne experiment designed to measure subdegree-scale cosmic microwave background anisotropy over hundreds of deg2, using a unique two-dimensional scanning strategy. A spinning flat mirror that is canted relative to its spin axis modulates the direction of beam response in a nearly elliptical path on the sky. The experiment was successfully flown in 1996 February, achieving near laboratory performance for several hours at float altitude. A map free of instrumental systematic effects is produced for a 3.5 hr observation of 630 deg2, resulting in a flat-band power upper limit of l(l + 1)Cl/(2π)0.5 < 77 μK at l = 38 (95% confidence). The experiment design, flight operations, and data, including atmospheric effects and noise performance, are discussed.

COSMIC MICROWAVE BACKGROUND MAPS FROM THE HACME EXPERIMENT

We present cosmic microwave background (CMB) maps from the Santa Barbara HACME balloon experiment (Staren et al.), covering about 1150 square degrees split between two regions in the northern sky, near the stars c Ursae Minoris and a Leonis, respectively. The FWHM of the beam is in D0i.77 three frequency bands centered on 39, 41, and 43 GHz. The results demonstrate that the thoroughly interconnected scan strategy employed allows efficient removal of 1/f-noise and slightly variable scan- synchronous oUsets. The maps display no striping, and the noise correlations are found to be virtually isotropic, decaying on an angular scale D1i. The noise performance of the experiment resulted in an upper limit on CMB anisotropy. However, our results demonstrate that atmospheric contamination and other systematics resulting from the circular scanning strategy can be accurately controlled and bode well for the planned follow-up experiments BEAST and ACE, since they show that even with the overly cautious assumption that 1/f-noise and oUsets will be as dominant as for HACME, the problems they pose can be readily overcome with the mapmaking algorithm discussed. Our prewhitened notch-—lter algorithm for destriping and oUset removal is proving useful also for other balloon- and ground-based experiments whose scan strategies involve substantial interleaving, e.g., Boomerang. Subject headings: balloonscosmic microwave backgroundcosmology: observations On-line material: color —gures

As complexidades inerentes ao tema "mudanças climáticas": desafios e perspectivas para o ensino de física

RESUMO: A articulacao entre a fisica e a tematica ambiental apresenta oportunidades para a construcao de praticas educativas que privilegiam o tratamento das controversias e das complexidades associadas aos temas ambientais, como ocorre com o fenomeno das mudancas climaticas. Neste ensaio teorico destaca-se que a natureza complexa desse fenomeno climatico favorece o surgimento das controversias, o que proporciona aos professores da Educacao Basica possibilidades para o tratamento educativo diferenciado desse tema. De modo especial, apresentam-se e discutem-se alguns aspectos, do ponto de vista da fisica, relativos a complexidade inerente ao tema “mudancas climaticas”, a fim de contribuir para uma reflexao voltada para a natureza dessas complexidades e para suas potencialidades educativas. Palavras-chave: Ensino de fisica. Complexidade. Mudancas climaticas.