Engineering topics

Lindley, D.

Publications and source records attributed to Lindley, D..

5 records

NASA NTRS1985

Cosmological constraints on the lifetime of massive particles

Particles with masses more than a few MeV, decaying into photons or electrons, can cause destruction by photofission of cosmologically produced light elements. A previous calculation of this effect is corrected and extended, and used to derive maximum lifetimes for massive neutrinos; these range from a few thousand seconds upward, depending on the particle mass. Some approximate expressions are given that enable lifetime limits to be obtained for other particles, with different masses and abundances, such as gravitinos. These limits are generally stronger than previously determined constraints, such as distortion of the microwave background by energetic photons.

Lindley, D.↗

NASA NTRS1985

Big bang photosynthesis and pregalactic nucleosynthesis of light elements

Two nonstandard scenarios for pregalactic synthesis of the light elements (H-2, He-3, He-4, and Li-7) are developed. Big bang photosynthesis occurs if energetic photons, produced by the decay of massive neutrinos or gravitinos, partially photodisintegrate He-4 (formed in the standard hot big bang) to produce H-2 and He-3. In this case, primordial nucleosynthesis no longer constrains the baryon density of the universe, or the number of neutrino species. Alternatively, one may dispense partially or completely with the hot big bang and produce the light elements by bombardment of primordial gas, provided that He-4 is synthesized by a later generation of massive stars.

Audouze, J.↗

NASA NTRS1982

Medusa spectroscopy of A400, A576, A1767, and A2124

Galaxy velocity data taken with the Steward Observatory multiple aperture fiber optic spectrograph are presented for four Abell clusters. The root-mean-square external errors in these velocities are about 100 km/s; accuracy which compares favorably with that obtained from single-object observations. It is expected that the recent adoption of a CCD detector should decrease external errors to about 50 km/s. All four of the clusters observed are known X-ray sources and the present data agree well with empirically derived velocity dispersion-X-ray luminosity relations for clusters of galaxies. Abell 400 is interesting in this regard, since both its X-ray luminosity and its velocity dispersion are quite small. Such objects are particularly important in determining the slope of the velocity dispersion-X-ray luminosity relation. The large microwave decrement observed in A576 was initially interpreted as due to Compton scattering of the microwave background by the X-ray-emitting intracluster gas. White and Silk have presented Einstein X-ray data which indicate that A576 contains too little gas to produce the observed microwave decrement by Compton scattering. The velocity dispersion obtained here for 47 members of this cluster strengthens their conclusion.

Hintzen, P.↗

NASA NTRS1982

Multiple object fiber optic spectroscopy

The Steward Observatory of the University of Arizona employs short optical fiber lengths to bring light from galaxy images at the 2.3 m telescope's focus to a line along a spectrograph slit, thereby obtaining simultaneous spectra of many objects of the field of view. After describing this instrument, attention is given to the development of an improved version through which efficiency gains will be obtained by remotely positioning the fibers under computer control and by correctly matching fiber outputs to the spectrograph optics. A CCD will replace the presently employed image tube and photographic plate detector system, in order to permit sky subtraction, yield increased dynamic range, and provide more accurate wavelength calibration due to the detector's fixed format.

Hill, J. M.↗

NASA NTRS1980

Multiple object spectroscopy - The Medusa spectrograph

An instrument has been built to obtain simultaneous spectra of many objects in the field of view of the Steward 90 inch (2.29 m) telescope. Short lengths of fused silica fiber 300 microns in diameter are used to bring the light from galaxy images at the Cassegrain focus into a line along the spectrograph slit. From a single exposure of the cluster Abell 1904, which has a redshift of 20,000 km/s, the redshifts of 26 individual galaxies were determined, each with a precision of 100 km/s. The present device, while already giving a sixfold reduction in the mean telescope time per galaxy, has significant light losses because it is not ideally matched to the telescope. An instrument being designed for the prime focus will transmit light from each object as efficiently as a conventional spectrograph.

Hill, J. M.↗