R. E. Vogt

LIGO: The Laser Interferometer Gravitational-Wave Observatory

The goal of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Project is to detect and study astrophysical gravitational waves and use data from them for research in physics and astronomy. LIGO will support studies concerning the nature and nonlinear dynamics of gravity, the structures of black holes, and the equation of state of nuclear matter. It will also measure the masses, birth rates, collisions, and distributions of black holes and neutron stars in the universe and probe the cores of supernovae and the very early universe. The technology for LIGO has been developed during the past 20 years. Construction will begin in 1992, and under the present schedule, LIGOs gravitational-wave searches will begin in 1998.

Cosmic ray investigation for the Voyager missions; energetic particle studies in the outer heliosphere — and beyond

A cosmic-ray detector system (CRS) has been developed for the Voyager mission which will measure the energy spectrum of electrons from ≈3–110 MeV and the energy spectra and elemental composition of all cosmic-ray nuclei from hydrogen through iron over an energy range from ≈ 1–500 MeV/nuc. Isotopes of hydrogen through sulfur will be resolved from ≈ 2–75 MeV/nuc. Studies with CRS data will provide information on the energy content, origin and acceleration process, life history, and dynamics of cosmic rays in the galaxy, and contribute to an understanding of the nucleosynthesis of elements in the cosmic-ray sources. Particular emphasis will be placed on low-energy phenomena that are expected to exist in interstellar space and are known to be present in the outer Solar System. This investigation will also add to our understanding of the transport of cosmic rays, Jovian electrons, and low-energy interplanetary particles over an extended region of interplanetary space. A major contribution to these areas of study will be the measurement of three-dimensional streaming patterns of nuclei from H through Fe and electrons over an extended energy range, with a precision that will allow determination of anisotropies down to 1%. The required combination of charge resolution, reliability and redundance has been achieved with systems consisting entirely of solid-state charged-particle detectors.

IMPROVED SENSITIVITY IN A GRAVITATIONAL WAVE INTERFEROMETER AND IMPLICATIONS FOR LIGO

Sensitivity enhancements in the laser interferometer gravitational wave observatory (LIGO) projects 40 m interferometer have been achieved through two major instrumental improvements. Improved vibration isolation has reduced the noise due to ground motion. New test masses with less mechanical dissipation were installed to lower the thermal noise associated with mirror vibrations. The minimum interferometer noise (square root of the spectral density of apparent differential displacement) reached 3 x 10^(-19) m/Hz^(1/2) near 450 Hz.

Voyager 1 - Energetic ions and electrons in the Jovian magnetosphere

The observations of the cosmic-ray subsystem have added significantly to our knowledge of Jupiters magnetosphere. The most surprising result is the existence of energetic sulfur, sodium, and oxygen nuclei with energies above 7 megaelectron volts per nucleon which were found inside of Ios orbit. Also, significant fluxes of similarly energetic ions reflecting solar cosmic-ray composition were observed throughout the magnetosphere beyond 11 times the radius of Jupiter. It was also found that energetic protons are enhanced by 30 to 70 percent in the active hemisphere. Finally, the first observations were made of the magnetospheric tail in the dawn direction out to 160 Jupiter radii.

Energetic charged particles in Saturn's magnetosphere: Voyager 2 results

Results from the cosmic-ray system on Voyager 2 in Saturns magnetosphere are presented. During the inbound pass through the outer magnetosphere, the ≥ 0.43-million-electron-volt proton flux was more intense, and both the proton and electron fluxes were more variable, than previously observed. These changes are attributed to the influence on the magnetosphere of variations in the solar wind conditions. Outbound, beyond 18 Saturn radii, impulsive bursts of 0.14- to > 1.0- million-electron-volt electrons were observed. In the inner magnetosphere, the charged particle absorption signatures of Mimas, Enceladus, and Tethys are used to constrain the possible tilt and offset of Saturns internal magnetic dipole. At ∼ 3 Saturn radii, a transient decrease was observed in the electron flux which was not due to Mimas. Characteristics of this decrease suggest the existence of additional material, perhaps another satellite, in the orbit of Mimas.

Elemental composition of solar energetic particles

The Low Energy Telescopes on the Voyager spacecraft are used to measure the elemental composition (2 ≤ Z ≤ 28) and energy spectra (5 to 15 MeV /nucleon) of solar energetic particles (SEPs) in seven large flare events. Four flare events are selected which have SEP abundance ratios approximately independent of energy/nucleon. The abundances for these events are compared from flare to flare and are compared to solar abundances from other sources: spectroscopy of the photosphere and corona, and solar wind measurements. The selected SEP composition results may be described by an average composition plus a systematic flare-to-flare deviation about the average. For each of the four events, the ratios of the SEP abundances to the four-flare average SEP abundances are approximately monotonic functions of nuclear charge Z in the range 6 ≤ Z ≤ 28. An exception to this Z-dependent trend occurs for He, whose abundance relative to Si is nearly the same in all four events. The four-flare average SEP composition is significantly different from the solar composition determined by photospheric spectroscopy: The elements C, N and O are depleted in SEPs by a factor of about five relative to the elements Na, Mg, Al, Si, Ca, Cr, Fe and Ni. For some elemental abundance ratios (e.g. Mg/O), the difference between SEP and photospheric results is persistent from flare to flare and is apparently not due to a systematic difference in SEP energy/nucleon spectra between the elements, nor to propagation effects which would result in a time-dependent abundance ratio in individual flare events. The four-flare average SEP composition is in agreement with solar wind abundance results and with a number of recent coronal abundance measurements. The evidence for a common depletion of oxygen in SEPs, the corona and the solar wind relative to the photosphere suggests that the SEPs originate in the corona and that both the SEPs and solar wind sample a coronal composition which is significantly and persistently different from that of the photosphere.

Enrichment of heavy nuclei in ^3He-rich flares

Five ^3He-rich solar-flare particle events were observed in 1973-1974 with ^3He/^4He ranging from 0.2 to ~8 at 2.9-12.7 MeV per nucleon. In all five events the (Z ≥ 6)/^1H ratio at ~3 MeV per nucleon was enriched by ~10 to ~100 times and the (Z ~ 6)/^4He ratio was enriched by ~3 to ~30 times, when compared with average solar-particle abundances measured over this 2-year period. It is suggested that the simultaneous enhancement of Z ≥ 6 and ^3He nuclei and the absence of ^2H and ^3H may be partly due to a preferential acceleration process which depends on the Z^2/A of the nuclei.

The isotopic composition of solar flare accelerated neon

The individual isotopes of neon in energetic solar flare particles have been clearly resolved with arms mass resolution of 0.20 amu. We find ^(20)Ne/^(22)Ne = 7.6 (+2.0, -1.8) and ^(21)Ne/^(22)Ne ≾ 0.11 in the 11-26 MeV per nucleon interval. This isotopic composition is essentially the same as that of meteoritic planetary neon-A and is significantly different from that of the solar wind.

High-Resolution Measurements of Galactic Cosmic-Ray Neon, Magnesium and Silicon Isotopes

The individual isotopes of galactic cosmic-ray Ne, Mg, and Si at ~0.20 amu. Our results suggest that the cosmic ray source is enriched in ^(22)Ne, ^(25)Mg, and ^(26)Mg when compared to the solar system. In particular, we find (^(25)Mg + ^(26)Mg)/^(24)Mg = 0.49(+0.23, -0.14) compared with the solar system value of 0.27, suggesting that the cosmic-ray source and solar system material were synthesized under different conditions.

A Cosmic Ray Isotope Spectrometer

We describe a new instrument to be flown on ISEE-C which is optimized to measure the isotopic composition of solar and galactic cosmic rays with ~5 to ~250 MeV/nucleon. A mass resolution of <0.3 AMU should be achieved for all elements with charge Z < 30.