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Hurwitz, M.

Publications and source records attributed to Hurwitz, M..

10 records
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NASA NTRS1995

Medium-resolution far-ultraviolet spectroscopy of PKS 2155-304

Using the Berkeley spectrometer of the Orbiting Retrievable Far and Extreme Ultraviolet Spectrometer (ORFEUS) we observed the 87-117 nm UV spectrum of the BL Lac object PKS 2155-304 with about 0.5 A resolution. In addition to the expected interstellar lines we detected higher quantum number counterparts of the intergalactic Lyman alpha lines discovered earlier with IUE and the Hubble Space Telescope (HST) in the direction of PKS 2155-304. The Lyman discontinuities indicate for three of the redshifted clouds a combined H I column density of 2-5 x 10(exp 16)/sq cm, while the column density for another cloud appears to be well below 5 x 10(exp 15)/sq cm. No siginificant O VI absorption in the galactic halo toward PKS 2155-304 could be detected from our data. Assuming that saturation effects are negligible for these weak features, we obtain for the O VI column density toward PKS 2155-304 a 3 sigma upper limit of 2.7 x 10(exp 14)/sq cm.

Appenzeller, I.↗
NASA NTRS1995

Coronal gas in the Galactic halo: ORFEUS observations of NGC 346 #1

We present high resolution (lambda/delta lambda = 3000) observations of the Small Magellanic Cloud (SMC) star NGC 346 #1 near the O VI resonance doublet (1031.9, 1037.6 A). The data were collected with the Berkeley extreme/far ultraviolet (EUV/FUV) spectrometer in the ORFEUS telescope aboard the space platform Astro-SPAS during the missiom of space shuttle Discovery flown in September 1993. The O VI features shows broad absorption centered near nu(sub LSR) is approximately equal to +140 km/sec. This is almost certainly associated with the OB cluster NGC 346 itself, which also shows deep absorption at Si IV and C IV at comparable velocities. An absorption feature corresponding to O VI near nu(sub LSR) = -230 km/sec is present in our data, but this feature is caused by contamination from a second star, probably an early B-type main sequence star at lower standard of rest (LSR) velocity, which is also present in the 20 min circular aperture. Between these velocity extrema lies one broad feature (b is approximately equal 70 km/sec) or multiple narrower features, with a combined column density of about 1.4 x 10(exp 14)/sq cm. Assuming an exponential distribution of O VI with the in-plane density of Jenkins, we infer a scale height, H(sub 0), of no more than approximately equal 1.2 kpc toward NGC 346 #1. Our O VI column density is about a factor of 4 below the predictions of cooling fountain models, but our low scale height is consistent with more recent predictions.

Hurwitz, M.↗
NASA NTRS1994

Far-ultraviolet emission from the Taurus molecular cloud

Far-ultraviolet spectra of diffuse emission from a region in the Taurus molecular cloud are presented. These data were obtained with the Berkeley spectrometer on NASA's Ultraviolet Experiment (UVX) payload. The intensity of the continuum emission drops as the optical depth increases toward the denser part of the cloud, an effect which is the opposite of that observed for the diffuse flux at high galactic latitudes. At the center of the aperture, the optical depth is very large, and the continuum emission must be produced by backscattering. At the edges of the cloud, the continuum intensity rises by a factor of 2. The data are interpreted with a new radiative transfer model, which is significantly more sophisticated than its predecessors. If the grain scattering properties are constant across the cloud, a unique best-fit combination can be determined from the data. The best-fit albedo is 0.6 +/- 0.1 at 1600 A. The best-fit value for the phase factor g is 0.5 +/- 0.15. The intensity of the flourescence of H2, combined with an upper limit to the column density of atomic hydrogen associated with the cloud, sets a lower limit of about 130/cm to the density in the flourescence region. Our estimate of the flux incident on the cloud at 1000 A is a factor of 2 to 3 lower than the value required to produce the measured flourescence intensity. Most mechanisms which might reconcile the discrepancy reduce the derived albedo and phase factor.

Hurwitz, M.↗
NASA NTRS1991

The Berkeley EUV spectrometer for ORFEUS

A novel EUV spectrometer is presented for the ORFEUS-SPAS mission. It uses a set of four varied line-space spherical diffraction gratings to obtain high-resolution spectra of point sources at wavelengths between 390 and 1200 A. The spectra are recorded with two detector units, each containing curved-surface microchannel plates and a delay-line anode-readout system. An independent optical system detects the image of the source in the entrance aperture and tracks the source as it drifts during an observation, enabling a reconstruction of the spectra postflight. The overall system performance is discussed and illustrated by synthetic spectra.

Hurwitz, M.↗
NASA NTRS1986

FUSE/Lyman grant

A variety of options for a short wavelength spectrometer for the Lyman telescope has been studied, and the optimum configuration for this instrument identified. In this spectrometer option study it is assumed (consistent with performance goals outlined by the project) that the instrument, whose prime spectral domain is 900-12000A, will incorporate a grazing incidence telescope which will maintain good collecting efficiency down to 100A. In particular it is assumed that the telescope will have an effective focal length of 10 meters, an image quality of 1.5", and will provide a diverging f/10 beam. Designs compatible with this telescope are analyzed, and it is determined that a two-element grazing incidence spectrometer using as its first optic an ellipsoid to re-focus the beam and a varied line-space plane diffraction grating to disperse the light is the best overall design. This spectrometer could be fed by a small pick-off mirror located just behind the prime focus of the telescope and would clear the light path when not in use. A test of the diffraction efficiency of a low blaze angle grating is undertaken, which is the only technical uncertainty in the spectrometer design.

Hurwitz, M.↗
NASA NTRS1985

Prospects for determining the cosmological helium-3 to helium-4 ratio via absorption-line studies of the local interstellar medium

The prospects for determining the interstellar (He-3)/(He-4) ratio via absorption-line studies in the extreme ultraviolet are considered. A high-resolution extreme-ultraviolet spectrometer fed by a 1-meter-class telescope similar to that discussed in the Far Ultraviolet Spectroscopic Explorer Report (1983) is assumed, and it is found that detection of He-3 may be possible with less than three days of observing time. To measure the (He-3)/(He-4) ratio with sufficient precision to determine the number of light neutrino species will require over 50 days of integration time for each object studied.

Hurwitz, M.↗
NASA NTRS1969

Dielectrophoretic orientation.

Electric field influence on fluid oscillation modes for Korteweg-Helmholtz force density on incompressible dielectric liquid immersed in electric field

Guttman, D. S.↗