Arthur H. Vaughan

THE ON-ORBIT PERFORMANCE OF THE GALAXY EVOLUTION EXPLORER

We report the first years on-orbit performance results for the Galaxy Evolution Explorer (GALEX), a NASA Small Explorer that is performing a survey of the sky in two ultraviolet bands. The instrument comprises a 50 cm diameter modified Ritchey-Chretien telescope with a 125 field of view, selectable imaging and objective-grism spectroscopic modes, and an innovative optical system with a thin-film multilayer dichroic beam splitter that enables simultaneous imaging by a pair of photon-counting, microchannel-plate, delay-line readout detectors. Initial measurements demonstrate that GALEX is performing well, meeting its requirements for resolution, efficiency, astrometry, bandpass definition, and survey sensitivity.

The galaxy evolution explorer

The Galaxy Evolution Explorer (GALEX), a NASA Small Explorer Mission planned for launch in Fall 2002, will perform the first Space Ultraviolet sky survey. Five imaging surveys in each of two bands (1350-1750Å and 1750-2800Å) will range from an all-sky survey (limit mAB~20-21) to an ultra-deep survey of 4 square degrees (limit mAB~26). Three spectroscopic grism surveys (R=100-300) will be performed with various depths (mAB~20-25) and sky coverage (100 to 2 square degrees) over the 1350-2800Å band. The instrument includes a 50 cm modified Ritchey-Chrétien telescope, a dichroic beam splitter and astigmatism corrector, two large sealed tube microchannel plate detectors to simultaneously cover the two bands and the 1.2 degree field of view. A rotating wheel provides either imaging or grism spectroscopy with transmitting optics. We will use the measured UV properties of local galaxies, along with corollary observations, to calibrate the UV-global star formation rate relationship in galaxies. We will apply this calibration to distant galaxies discovered in the deep imaging and spectroscopic surveys to map the history of star formation in the universe over the red shift range zero to two. The GALEX mission will include an Associate Investigator program for additional observations and supporting data analysis. This will support a wide variety of investigations made possible by the first UV sky survey.

The Optical Design of the 40-in. Telescope and of the Irenee DuPont Telescope at Las Campanas Observatory, Chile.

The optical specifications of two astronomical telescopes designed to permit wide-field photography with critical definition are presented and compared. The 40-in. (1.016-m) and DuPont 100-in. (2.54-m) telescopes use modifications of the Ritchey-Chretién design with Gascoigne correctors. By avoiding the need for field flatteners through choice of mirrors yielding zero Petzval sum (40-in. telescope) or bending of photographic plates to a moderate field curvature (100-in. telescope), it was possible to achieve monochromatic images of ? to (1/4) sec of arc over fields of 3 degrees and 2.1 degrees , respectively.

Pluto integrated camera spectrometer (PICS) instrument

Abstract We describe an integrated instrument that will perform the functions of three optical instruments required by a Pluto Fast Flyby mission: a near-IR spectrometer (256 spectral channels, 1300–2600 nm), a two-channel imaging camera (300–500 nm, 500–1000 nm), and a UV spectrometer (80 spectral channels, 70–150 nm). A separate port, aligned in a direction compatible with radio occultation experiments, is provided for measurement of a UV solar occultation and for spectral radiance calibration of the IR and visible subsystems. Our integrated approach minimizes mass and power use, and promotes the adoption of integrated observational sequences and power management to ensure compatible duty cycles for data acquisition, compression, and storage. From flight mission experience, we believe the integrated approach will yield substantial cost savings in design, integration, and sequence planning. The integrated payload inherently provides a cohesive mission data set, optimized for correlative analysis. A breadboard version of the instrument is currently being built and is expected to be fully functional by late summer.

Imaging Michelson Spectrometer For Hubble Space Telescope

Hubble Imaging Michelson Spectrometer (HIMS), a proposed instrument currently completing its definition phase, is designed to provide background-limited imaging capability and to exploit the diffraction-limited imaging capability of the Hubble Space Telescope (HST) in the wavelength range extending from 1000 to 2500 nanometers. The HIMS instrument also provides spectral resolution with resolving power [λ/Δλ] from 1 to 104. The basic opto-mechanical characteristics and design considerations for the instrument are described.

Simplified solution of diffraction from a Lyot system.

This paper presents a derivation of a simplified analytical solution of diffraction from a Lyot (1939) system designed for observation of the solar corona outside of eclipses. Applying the theorem of Papoulis (1986) to simplify the calculations, a simplified solution is derived which is found to be in reasonable agreement with the exact solution. The simplified solution suffices for the preliminary evaluation of the amount of diffraction reduction needed to meet certain system requirements and also serves as a guideline for further apodization.

Telescope simulators for Hubble - An overview of optical designs

Various optical configurations for Hubble Space Telescope simulators have been proposed, and some are being built for use as verification tools to characterize the performance of second-generation instruments during ground testing. We describe the Hubble Space Telescope, present an overview of three optical designs for simulators, and discuss the relative advantages and disadvantages of each configuration.

Lens design using group indices of refraction

Abstract An approach to lens design is described in which the ratio of the group velocity to the speed of light (the group index) in glass is used, in conjunction with the more familiar phase index of refraction, to control certain chromatic properties of a system of thin lenses in contact. It is shown that, at the wavelength of a maximum or minimum (where the phase power of a lens is locally independent of wavelength), the group power is equal to the phase power. It is further shown that, in a lens consisting of three or more elements, the phase and group powers can be constrained to be both equal and independent of wavelength (achromatic) at one or more wavelengths. In the neighbourhood of such wavelengths, both the first and the second derivatives of phase power with respect to wavelength are zero, giving this type of lens (in principle) an exceptionally high degree of achromatism not previously described, herein called group achromatism. The first-order design of thin-lens systems is illustrated by ex...

The Helium λ 10830 Line in Planetary Nebulae and the Orion Nebula

Interferometric observations of profiles of Hei λ 10830 emission lines in 11 planetary nebulae, and in selected regions of the Orion Nebula, are presented. In common with the Orion Nebula, the planetaries are shown to emit a P Cygni-like λ 10830 line, with the absorption component shifted toward the violet with respect to the laboratory wavelength in a frame of reference at rest in the centre of expansion of the gas. The emission components are shifted toward the red. In planetaries, the negative displacements of the absorption edges are, in general, approximately equal to the widths, β, of the emission components which, in turn, range from about 12 km/sec in IC 418 to about 28 km/sec in NGC 6210. The emission red-shift is about 0.7β on the average, but individual shifts vary from 0.5β in IC 2149 to 1.05β in NGC 6826. The line widths and shifts tend to increase in nebulae with larger expansion velocities. In Orion, the absorption edges in the λ 10830 line coincide in velocity with those in the line Hei λ 3888 observed against the spectra of the Trapezium stars. In planetaries, the absorption edges in the λ 10830 line appear qualitatively similar to those in the line Hei λ 3888, but a coincidence in velocity could not be demonstrated.

Application of group indices of refraction to achromatic lens design

An approach to color correction is described in which the ratio of the group velocity to the speed of light in vacuum (the group index of refraction) in glass is used, in conjunction with the more familiar phase index of refraction, to control longitudinal color in a system of thin lenses in contract. It is shown that at the wavelength of a turning point where the phase power of a lens is locally independent of wavelength, the phase power is equal to the group power. It is further shown that in a lens consisting of three or more elements, if the phase and group powers are equal and the group power has a turning point at the same wavelength, the second derivative of phase power with respect to wavelength is zero at that wavelength (the lens is confocal and achromatic in both phase and group power and the secondary spectrum is locally zero). The group index of refraction and the concept of group aberrations can equally by applied to exact raytracing for thick lens systems. In using easily calculated derivatives of the phase index of refraction the approach affords a computational simplicity that is well suited to computer-aided lens design.