A. C. Clapp

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.

A bolometric millimeter-wave system for observations of anisotropy in the cosmic microwave background radiation on medium angular scales

We report the performance of a bolometric system designed to measure the anisotropy of the cosmic microwave background (CMB) radiation on angular scales from 0 deg 3 min to 3 deg. The system represents a collaborative effort combining a low-background 1 m diameter balloon-borne telescope with new multimode feed optics, a beam modulation mechanism with high stability, and a four-channel bolometric receiver with passbands centered near frequencies of 3 (90), 6 (180), 9 (270), and 12 (360) cm(exp -1) (GHz). The telescope was flown three times with the bolometric receiver and has demonstrated detector noise limited performance capable of reaching sensitivity levels of Delta(T)/T(sub CMB) is approximately equal to 10(exp -5) with detectors operated at T = 0.3 K.

A degree scale anisotropy measurement of the cosmic microwave background near the star Gamma Ursae Minoris

Results from a search for anisotropy in the cosmic microwave background (CMB) are presented from the third flight of the Millimeter-wave Anisotropy experiment. The CMB observation occurred over 1.37 hours and covered a 6.24 sq deg area of the sky where very little foreground emission is expected. Significant correlated structure is observed at 6 and 9/cm. At 12/cm we place an upper limit on the structure. The relative amplitudes at 6, 9, and 12/cm are consistent with a CMB spectrum. The spectrum of the structure is inconsistent with thermal emission from known forms of interstellar dust. Synchrotron and free-free emission would both require unusually flat spectral indices at cm wavelengths in order to account for the amplitude of the observed structure. Although known systematic errors are not expected to contribute significantly to any of the three optical channels, excess sidelobe contamination cannot be definitively ruled out. If all the structure is attributed to CMB anisotropy, a value of the weighted rms of the 6 and 9/cm channels of Delta T/T(CMB) = 4.7 +/- 0.8 x 10 exp -5 (+/- 1 sigma) was measured. If the CMB anisotropy is assumed to have a Gaussian autocorrelation function with a coherence angle of 25 arcmin, then the most probable value is Delta T/T(CMB) = 4.2 +1.7 or -1.1 x 10 exp -5, where the +/- refers to the 95 percent confidence limits.

A search for anisotrophy in the cosmic microwave background on intermediate angular scales

The results of a search for anisotropy in the cosmic microwave background on angular scales near 1 deg are presented. Observations were simultaneously performed in bands centered at frequencies of 6, 9, and 12 per cm with a multifrequency bolometric receiver mounted on a balloon-borne telescope. The statistical sensitivity of the data is the highest reported to date at this angular scale, which is of critical importance for understanding the formation of structure in the universe. Signals in excess of random were observed in the data. The experiment, data analysis, and interpretation are described.

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.

100-mK magnetic refrigerators for low background bolometric receivers

This paper provides a brief description of the development of adiabatic demagnetization refrigerators (ADRs) at Berkeley for cooling bolometric infrared detectors. This development was stimulated by the needs of the Multi-Band Imaging Photometer (MIPS) for the NASA Space Infrared Telescope Facility (SIRTF). A description will be given of the ways in which classical ADR technology has been developed to provide a compact refrigerator to meet the requirements of this space experiment. Similar refrigerators will be useful in a number of forthcoming space missions for cooling both infrared and X-ray bolometers.

A millimeter‐wave anisotropy experiment (MAX) to search for anisotropy in the cosmic background radiation on medium angular scales

We report preliminary results from two balloon flights of a millimeter‐wave telescope designed to measure anisotropy in the cosmic microwave background (CMB) on angular scales from 0.3 to 3 degrees. The receiver used in the first flight, in November 1989, was a dichroic, 3He‐cooled bolometric photometer with passbands centered at 3, 6, 9, and 12 cm−1. During this flight we measured the spectrum of the brightness of the galactic plane at a galactic longitude of lII=24 degrees and searched for CMB anisotropy at nine points centered near the north celestial pole (NCP). The noise in the 6 cm−1 band integrated down to one sigma errors of 140 μK per point over the 40 minute observation near th NCP. After further analysis these data will set an upper limit on CMB anisotropy of ΔT/T<1–2×10−4 (95% CL) for Gaussian correlation functions with a correlation length of 0.5 degree. The second flight, in July 1990, employed improved bolometric detectors. The 3 cm−1 band was removed in order to increase the efficiency of ...

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.