In-Flight Performance of the ICON EUV Spectrograph.

We present in-flight performance measurements of the Ionospheric Connection Explorer EUV spectrometer, , a wide field ( ) extreme ultraviolet (EUV) imaging spectrograph designed to observe the lower ionosphere at tangent altitudes between 100 and 500 km. The primary targets of the spectrometer, which has a spectral range of 54-88 nm, are the Oii emission lines at 61.6 nmand 83.

Design and Performance of the ICON EUV Spectrograph.

We present the design, implementation, and on-ground performance measurements of the Ionospheric Connection Explorer EUV spectrometer, a wide field (17° x 12°) extreme ultraviolet (EUV) imaging spectrograph designed to observe the lower ionosphere at tangent altitudes between 100 and 500 km. The primary targets of the spectrometer, which has a spectral range of 54-88 nm, are the Oil emission lines at 61.6 nm and 83.

Microchannel Plate Imaging Photon Counters for Ultraviolet through NIR Detection with High Time Resolution.

Cross strip and cross delay line readout microchannel plate detectors in 18 mm, 25 mm and 40 mm active area formats including open face (UV/particle) and sealed tube (optical) configurations have been constructed. These have been tested with a field programmable gate array based electronics for single event encoding. Using small pore MCPs (6 μm) operated in a pair, we achieve gains of >1 × 10 which is sufficient to provide spatial resolution of ~17 μm FHWM with the 18 mm and 40 mm cross strip readouts.

Microchannel plate cross-strip detectors with high spatial and temporal resolution.

The cross-strip imaging readout employs charge division, and centroiding, of microchannel plate charge signals detected on two orthogonal layers of sense strips to encode event X-Y positions and times. We have developed cross-strip detectors and fully parallel channel position encoding electronics. The front-end amplifiers utilize two 32-channel pre-amplifier ASICs that send signals to a full 64-channel 60 MHz ADC circuit followed by a FPGA event-processing board.

Narcissistic Ghosts in Rowland-Mounted, Concave Gratings with nu = 0 degrees : a Cautionary Note.

Narcissistic ghost lines in a Rowland-grating spectrograph have been identified as arising from the reimaging of bright spectral features, which are incident on the face of a detector photocathode [Cesium iodide (CsI) on a microchannel plate], back onto the detector by the grating in zero order. The mean of the wavelength of the diffracted light and the apparent wavelength of the ghost allows the angle of the grating normal with respect to the input beam (alpha) to be determined. Measurements of ghost intensity as a function of wavelength are presented and are found to range between 7 x 10(-4) and 7 x 10(-3) of the parent line.

The activity and size of the nucleus of comet Hale-Bopp (C/1995 O1) [see comment].

Analysis of Hubble Space Telescope (HST) images of comet Hale-Bopp (C/1995 O1) suggests that the effective diameter of the nucleus is between 27 to 42 kilometers, which is at least three times larger than that of comet P/Halley. The International Ultraviolet Explorer and HST spectra showed emissions from OH (a tracer of H2O) and CS (a tracer of CS2) starting in April 1996, and from the CO Cameron system (which primarily traces CO2) starting in June 1996. The variation of the H2O production rate with heliocentric distance was consistent with sublimation of an icy body near its subsolar point.