S. T. Tanaka

Measurements of Anisotropy in the Cosmic Microwave Background Radiation at 0.′5 Scales near the Stars HR 5127 and φ Herculis

We present measurements of cosmic microwave background (CMB) anisotropy near the stars HR 5127 and Herculis from the fifth flight of the Millimeter-wave Anisotropy eXperiment (MAX). We scanned 8° strips of the sky with an approximately Gaussian 05 FWHM beam and a 14 peak to peak sinusoidal chop. The instrument has four frequency bands centered at 3.5, 6, 9, and 14 cm-1. The IRAS 100 μm map predicts that these two regions have low interstellar dust contrast. The HR 5127 data are consistent with CMB anisotropy. The Herculis data, which were measured at lower flight altitudes, show time variability at 9 and 14 cm-1, which we believe to be due to atmospheric emission. However, the Herculis data at 3.5 and 6 cm-1 are essentially independent of this atmospheric contribution and are consistent with CMB anisotropy. Confusion from Galactic foregrounds is unlikely based on the spectrum and amplitude of the structure at these frequencies. If the observed HR 5127 structure and the atmosphere-independent Herculis structure are attributed to CMB anisotropy, then we find ΔT/T = l(l + 1)Cl/2π1/2 = 1.2+ 0.4−0.3 × 10-5 for HR 5127 and 1.9+ 0.7−0.4 × 10-5 for Herculis in the flat band approximation. The upper and lower limits represent a 68% confidence interval added in quadrature with a 10% calibration uncertainty.

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.

MAX 4 and MAX 5 Cosmic Microwave Background Anisotropy Measurement Constraints on Open and Flat-Λ Cold Dark Matter Cosmogonies

We account for experimental and observational uncertainties in likelihood analyses of cosmic microwave background (CMB) anisotropy data from the MAX 4 and MAX 5 experiments. These analyses use CMB anisotropy spectra predicted in open and spatially flat Λ cold dark matter cosmogonies. Among the models considered, the combined MAX data set is most consistent with the CMB anisotropy shape in Ω0 ~ 0.1-0.2 open models and less so with that in old (t0 15-16 Gyr, i.e., low-h), high baryon density (ΩB 0.0175 h-2), low-density (Ω0 ~ 0.2-0.4), flat-Λ models. The MAX data alone do not rule out any of the models we consider at the 2 σ level. Model normalizations deduced from the combined MAX data are consistent with those drawn from the UCSB South Pole 1994 data, except for the flat bandpower model for which MAX favors a higher normalization. The combined MAX data normalization for open models with Ω0 ~ 0.1-0.2 is higher than the upper 2 σ value of the DMR normalization. The combined MAX data normalization for old (low-h), high baryon density, low-density flat-Λ models is below the lower 2 σ value of the DMR normalization. Open models with Ω0 ~ 0.4-0.5 are not far from the shape most favored by the MAX data, and for these models, the MAX and DMR normalizations overlap. The MAX and DMR normalizations also overlap for Ω0 = 1 and some higher h, lower ΩB, low-density flat-Λ models.

Measurements of anisotropy in the cosmic microwave background radiation at 0.5 deg angular scales near the star gamma ursae minoris

We present results from a four-frequency observation of a 6 deg x 0.6 deg strip of the sky centered near the star Gamma Ursae Minoris (GUM) during the fourth flight of the Millimeter-wave Anistropy experiment(MAX). The observation was made with a 1.4 deg peak-to-peak sinusoidal chop in all bands. The FWHM beam sizes were 0.55 deg +/- 0.05 deg at 3.5 per cm and 0.75 deg +/- 0.05 deg at 6, 9, and 14 per cm. During this observation significant correlated structure was observed at 3.5, 6 and 9 per cm with amplitudes similar to those observed in the GUM region during the second and third fligts of MAX. The frequency spectrum is consistent with cosmic microwave background (CMB) and inconsistent with thermal emission from interstellar dust. The extrapolated amplitudes of synchrotron and free-free emission are too small to account for the amplitude of the observed structure, If all of the structure is attributed to CMB anisotropy with a Gaussian autocorrelation function and a coherence angle of 25 min, then the most probable values of delta T/TCMB in the 3.5, 6 and 9 per cm bads are (4.3 +2.7/-1.6) x 10-5, 2.8 (+4.3/-1/1) x 10-5, and 3.5 (+3.0/-1.6) x 10-5 (95% confidence upper and lower limits), respectively.

Construction technique and performance of a 2 GHz rectangular corrugated horn

A large rectangular horn antenna with a center frequency of 2.0 GHz, corrugated on the E-plane walls, made out of aluminium sheet, has been designed, constructed, and tested. A technique has been developed to solder thin aluminium strips onto the back plane to form the corrugations. The radiation beam pattern shows half-power beamwidths of 12 degrees and 14 degrees in the H- and E-planes, respectively, and sidelobe response below -40 dB at angles greater than 50 degrees from the horn axis. The measured return loss is greater than 20 dB (VSWR >

100-mK bolometric receiver for low-background astronomy

The design and construction of 100 mK composite bolometers for low background submillimeter and millimeter-wave astronomy are discussed. The bolometers are cooled to 100 mK using an adiabatic demagnetization refrigerator. The bolometers consist of a silicon substrate suspended by nylon fibers, a bismuth film absorber, a neutron transmutation doped germanium thermometer with graphite fiber electrical leads, and a brass wire thermal strap. Heated JFET amplifiers located on the 1.5 K cold plate are used to read out the bolometer signals. Electrically measured noise equivalent powers as low as 2 X 10-17 W/(root)Hz have been achieved.