Jerry Edelstein

Far-Ultraviolet Performance of the Berkeley Spectrograph duringthe ORFEUS-SPAS II Mission*

The Berkeley spectrograph aboard the ORFEUS telescope made its second flight on the 14 day ORFEUS-SPAS II mission of the Space Shuttle Columbia in 1996 November/December. Approximately half of the available observing time was dedicated to the Berkeley spectrograph, which was used by both principal and guest investigators. The spectrographs full bandpass is 390-1218 A; here we discuss its in-flight performance at far-ultraviolet wavelengths, at which most of the observations were performed. The instruments effective area peaks at 8.9±0.5 cm2 near 1020 A, and the mean spectral resolution is 95 km s-1 FWHM for point sources. Over most of the spectral range, the typical nighttime background event rate in each spectral resolution element was ~0.003 s-1. Simultaneous background observations of an adjacent blank field were provided through a secondary, off-axis aperture. The Berkeley spectrographs unique combination of sensitivity and resolution provided valuable observations of approximately 105 distinct astronomical targets, which ranged in distance from the Earths own Moon to some of the brightest active galactic nuclei.

Observations of O VI Emission from the Diffuse Interstellar Medium

We report the —rst Far-Ultraviolet Spectroscopic Explorer measurements of diUuse O VI (jj1032, 1038) emission from the general diUuse interstellar medium outside of supernova remnants or superbubbles. We observed a 30@@ ] 30@@ region of the sky centered at and From the observed l \ 315i.0 b \[ 41i.3. intensities (2930 ^ 290 [random] ^ 410 [systematic] and 1790 ^ 260 [random] ^ 250 [systematic] photons cm~2 s~1 sr~1 in jj1032 and 1038, respectively), derived equations, and assumptions about the source location, we calculate the intrinsic intensity, electron density, thermal pressure, and emitting depth. The intensities are too large for the emission to originate solely in the Local Bubble. Thus, we conclude that the Galactic thick disk and lower halo also contribute. High-velocity clouds are ruled out because there are none near the pointing direction. The calculated emitting depth is small, indicating

OBSERVATION OF THE FAR-ULTRAVIOLET CONTINUUM BACKGROUND WITH SPEAR/FIMS

We present the general properties of the far-ultraviolet (FUV; 1370-1710 A) continuum background over most of the sky, obtained with the Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR) instrument (also known as FIMS), flown aboard the STSAT-1 satellite mission. We find that the diffuse FUV continuum intensity is well correlated with N H I , 100 μm, and Hα intensities but anti-correlated with soft X-ray intensity. The correlation of the diffuse background with the direct stellar flux is weaker than the correlation with other parameters. The continuum spectra are relatively flat. However, a weak softening of the FUV spectra toward some sight lines, mostly at high Galactic latitudes, is found not only in direct stellar but also in diffuse background spectra. The diffuse background is relatively softer than the direct stellar spectrum. We also find that the diffuse FUV background averaged over the sky has a bit softer spectrum compared to direct stellar radiation. A map of the ratio of 1370-1520 A to 1560-1710 A band intensity shows that the sky is divided into roughly two parts. However, this map shows a lot of patchy structures on small scales. The spatial variation of the hardness ratio seems to be largely determined by the longitudinal distribution of OB-type stars in the Galactic plane. A correlation of the hardness ratio with the FUV intensity is found at high intensities but an anti-correlation is found at low intensities. We also find evidence that the FUV intensity distribution is log-normal in nature.

High-Resolution Broadband Spectroscopy Using an Externally Dispersed Interferometer

An externally dispersed interferometer (EDI) is a series combination of a fixed delay interferometer and an external grating spectrograph. We describe how the EDI can boost the effective resolving power of an echelle or linear grating spectrograph by a factor of 2-3 or more over the spectrographs full bandwidth. The interferometer produces spectral fringes over the entire spectrographs bandwidth. The fringes heterodyne with spectral features to provide a low spatial frequency moire pattern. The heterodyning is numerically reversed to recover highly detailed spectral information unattainable by the spectrograph alone. We demonstrate resolution boosting for stellar and solar measurements of two-dimensional echelle and linear grating spectra. An effective spectral resolution of ~100,000 has been obtained from the ~50,000 resolution Lick Observatory two-dimensional echelle spectrograph, and that of ~50,000 from an ~20,000 resolution linear grating spectrograph.

Evidence against the Sciama Model of Radiative Decay of Massive Neutrinos

We report on spectral observations of the night sky in the band around 900 A where the emission line in the Sciama model of radiatively decaying massive neutrinos would be present. The data were obtained with a high-resolution, high-sensitivity spectrometer flown on the Spanish satellite MINISAT. The observed emission is far less intense than that expected in the Sciama model.

Reanalysis of Voyager Ultraviolet Spectrometer Limits to the Extreme-Ultraviolet and Far-Ultraviolet Diffuse Astronomical Flux

We reexamine Voyager Ultraviolet Spectrometer (UVS) data used to establish upper limits to the 500-900 A and 900-1100 A cosmic diffuse background. The measurement of diffuse flux with the Voyager UVS data requires complex corrections for noise sources which are far larger than the astronomical signal. In the analyses carried out to date, the upper limits obtained on the diffuse background show statistical anomalies which indicate that substantial systematic errors are present. We detail these anomalies and identify specific problems with the analyses. We derive statistically robust 2 σ upper limits for continuum flux of 570 photons s-1 cm-2 sr-1 A-1 and for the 1000 A diffuse line flux of 11,790 photons s-1 cm-2 sr-1. The true limits may be substantially higher because of unknown systematic uncertainties. The new statistical limits alone are insufficient to support previous conclusions based on the Voyager data, including work on the character of interstellar dust and estimates of the diffuse extragalactic far-UV background as absorbed by intergalactic dust.

Interferometric resolution boosting for spectrographs

Externally dispersed interferometry (EDI) is a technique for enhancing the performance of spectrographs for wide bandwidth high resolution spectroscopy and Doppler radial velocimetry. By placing a small angle-independent interferometer near the slit of a spectrograph, periodic fiducials are embedded on the recorded spectrum. The multiplication of the stellar spectrum times the sinusoidal fiducial net creates a moire pattern, which manifests high detailed spectral information heterodyned down to detectably low spatial frequencies. The latter can more accurately survive the blurring, distortions and CCD Nyquist limitations of the spectrograph. Hence lower resolution spectrographs can be used to perform high resolution spectroscopy and radial velocimetry. Previous demonstrations of ~2.5x resolution boost used an interferometer having a single fixed delay. We report new data indicating ~6x Gaussian resolution boost (140,000 from a spectrograph with 25,000 native resolving power), taken by using multiple exposures at widely different interferometer delays.

COMPARISON OF THE DIFFUSE Hα AND FUV CONTINUUM BACKGROUNDS: ON THE ORIGINS OF THE DIFFUSE Hα BACKGROUND

We compare the diffuse H

FAR-ULTRAVIOLET OBSERVATIONS OF THE OPHIUCHUS REGION WITH SPEAR

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Lunar reflectivity from Extreme Ultraviolet Explorer imaging and spectroscopy of the full moon

map of our Galaxy with the FUV (1370-1710\AA) continuum map. The H