Engineering topics

Clapp, A. C.

Publications and source records attributed to Clapp, A. C..

8 records

NASA NTRS1994

Measurements of anisotropy in the cosmic microwave background radiation at degree angular scales near the stars Sigma Herculis and Iota Draconis

We present results from two four-frequency observations centered near the stars Sigma Herculis and Iota Draconis during the fourth flight of the Millimeter-wave Anisotropy eXperiment (MAX). The observations were made of 6 deg x 0.6 deg strips of the sky with a 1.4 deg peak to peak sinusoidal chop in all bands. The full width at half maximum (FWHM) beam sizes were calculated 0.55 deg +/- 0.05 deg at 3.5/cm and a 0.75 deg +/- 0.05 deg at 6, 9, and 14/cm. Significant correlated structures were observed at 3.5, 6, and 9/cm. The spectra of these signals are inconsistent with thermal emission from known interstellar dust populations. The extrapolated amplitudes of synchrotron and free-free emission are too small to account for the amplitude of the observed structures. If the observed structures are attributed to cosmic microwave background (CMB) anisotropy with a Gaussian autocorrelation function and a coherence angle of 25 min, then the most probable values at Delta T/T(sub CMB) = 3.1 (sup +1.7 sub -1.3) x 10(exp -5) for the Sigma Herculis scan, and Delta T/T(sub CMB) = 3.3(sup +1.1 sub -1.1) x 10(exp -5) for the Iota Draconis scan (95% confidence upper, lower limits).

Clapp, A. C.↗

NASA NTRS1994

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/T(sub CMB) in the 3.5, 6 and 9 per cm bads are (4.3 +2.7/-1.6) x 10(exp -5), 2.8 (+4.3/-1/1) x 10(exp -5), and 3.5 (+3.0/-1.6) x 10(exp -5) (95% confidence upper and lower limits), respectively.

Devlin, M. J.↗

NASA NTRS1993

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.

Gundersen, J. O.↗

NASA NTRS1992

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.

Fischer, M. L.↗

NASA NTRS1992

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.

Alsop, D. C.↗

NASA NTRS1992

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

The performance of a bolometric system designed to measure the anisotropy of the cosmic microwave background (CMB) radiation on angular scales from 0.3 to 3 deg is presented. 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, 6, 9, and 12/cm (90, 180, 270, and 360 GHz). The telescope has been flown three times with the bolometric receiver and has demonstrated detector noise limited performance capable of reaching sensitivity levels of about 0.00001 with detectors operated at 0.3 K.

Fischer, M. L.↗

NASA NTRS1992

A broadband THz receiver for low background space applications

We have developed a sensitive bolometric receiver for low background space applications. In a 10 percent bandwidth at 1 THz, this receiver is approximately 100 times more sensitive than a quantum limited heterodyne receiver with a 1 GHz IF bandwidth. This receiver is designed to be used for the long wavelength band (200-700 microns) in the MIPS instrument on NASA's SIRTF satellite. The bolometers are cooled to 100 mK by an adiabatic demagnetization refrigerator. Roughly 60 g of cesium chrome alum salt is partially demagnetized to 100 mK, followed by a slow regulated downramp to compensate for the heat leak. The hold time of the ADR system is about 18 hours with a temperature stability of delta T(sub rms) approx. equals 10 micro-K. The composite bolometers have electrical responsivities of 10(exp 9)V/W and electrical NEP's of about 3x10(exp -17) W/square root of Hz. The bolometer signals are read out by JFET preamplifiers located on the helium plate and operated at 120 K. We have addressed a number of space qualification issues, such as the development of an analog magnet controller, construction of a cryogenic shake-table for bolometers and selection of the paramagnetic salt CCA which can survive a bakeout at 50 C. The receiver is scheduled to be flown in the spring of 1992 on a balloon telescope. This flight has a dual purpose. One is to provide realistic test of the capabilities of the new receiver. The other is to search for anisotropies in the cosmic microwave background on scales of a few degrees.

Hagmann, C.↗

NASA NTRS1991

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, He-3-cooled bolometric photometer with passbands centered at 3, 6, 9, and 12/cm. The second flight, in July 1990, employed improved bolometric detectors. The 3/cm band was removed in order to increase the efficiency of the remaining bands. Preliminary analysis of the data gives a factor of 3 improvement in sensitivity over the first flight in the 6/cm band. Future plans include a new receiver to provide an additional factor of 5 improvement in sensitivity and a new balloon-borne telescope which is optimized for low-background bolometric detectors at millimeter wavelengths.

Fischer, M. L.↗