An image-stabilized telescope - Ten channel ultraviolet spectrometer for sounding rocket observations
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Giles, J. W.↗
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Rocket and spacecraft studies of ultraviolet emissions from astrophysical targets
Rocket and spacecraft far-UV spectral measurements of several astrophysical targets are reviewed. These include observations of Ly-alpha emissions from Arcturus, Apollo-17 far-UV spectrometry of eta UMa and five other stars, Apollo-17 observations of the lunar atmosphere and the diffuse UV background, and far-UV spectral studies of Venus, Jupiter, and Comet Kohoutek. The Arcturus observations indicated a chromosphere with neutral atomic-hydrogen and atomic-oxygen emissions as well as a very weak atomic-carbon line. The planetary studies revealed O I and C I emissions in the Venusian spectrum as well as large Ly-alpha emissions and possible molecular-hydrogen emissions in that of Jupiter. The lunar observations demonstrated that solar protons do not produce an atomic-hydrogen atmosphere on the moon.
Fastie, W. G.↗
Low-resolution ultraviolet spectroscopy of several hot stars observed from Apollo 17
Low-resolution ultraviolet spectra were obtained for six early-type stars in 1972 December, using an Ebert spectrometer mounted in the service module of the Apollo 17 spacecraft. The spectrometer scanned from 1180 A to 1680 A, with a speed that varied with wavelength according to a program chosen for lunar studies. Spectral resolution was 11 A. The ultraviolet absolute calibration of the instrument was determined by comparison with National Bureau of Standards calibrated photodiodes, and is believed known to plus or minus 10 percent. The absolute intensities are in good general agreement with the observations of other stars and with the predictions of stellar model-atmosphere calculations.
Henry, R. C.↗
Ultraviolet observations of cool stars. III - Chromospheric and coronal lines in alpha Tauri, beta Geminorum, and alpha Bootis
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Mcclintock, W.↗
Ultraviolet observations of cool stars. IV - Intensities of Lyman-alpha and Mg II in epsilon Pegasi and epsilon Eridani, and line width-luminosity correlations
A spectrometer on the Copernicus satellite has been used to confirm the existence of a line width-luminosity relation for the Ly-alpha and Mg II 2800-A chromospheric emission lines in K-type stars by observation of a K2 dwarf (epsilon Eri) and a K2 supergiant (epsilon Peg). Combined with previously reported observations of lines in three K giants (alpha Boo, alpha Tau, and beta Gem), the data are consistent with an identical dependence of line width on absolute visual magnitude for the Ca II K, Ly-alpha, and Mg II 2795-A lines. Surface fluxes of Ly-alpha, Mg II 2800-A, and O V 1218-A (upper limit) for epsilon Eri, and of Mg II 2800-A for epsilon Peg are also compared with values reported previously for the three giant stars.
Mcclintock, W.↗
Ultraviolet observations of cool stars. V - The local density of interstellar matter
A high-resolution Copernicus observation of the chromospheric Ly-alpha emission line of the nearby (3.3 pc) K dwarf epsilon Eri sets limits on the velocity, the velocity dispersion, and the density of atomic hydrogen in the local interstellar medium. Analysis shows that the interstellar Ly-alpha absorption is on the flat portion of the curve of growth. An upper limit of 0.12 per cu cm is derived for the atomic-hydrogen density. The value of this density is 0.08 (plus or minus 0.04 per cu cm if the velocity-dispersion parameter is 9 km/s, corresponding to a temperature of 5000 K. Also, the interstellar deuterium Ly-alpha line may be present in the spectrum.
Mcclintock, W.↗
Spectroscopic survey of the far-ultraviolet /1160-1700 A/ emissions of Capella
A far-ultraviolet spectral survey of Capella (Alpha Aur, G5 III + G0 III) has been obtained using a highly sensitive rocketborne spectrograph with a microchannel plate detector. The spectral distribution is very similar to that of the sun; however, if the line surface fluxes are due to the primary (G5 III), then, except for Ly-alpha, they are about an order of magnitude greater than those of the quiet sun
Vitz, R. C.↗
The far-ultraviolet /1180-1950 A/ emission spectrum of Arcturus
The far-ultraviolet (1180-1950 A) emission spectrum of the K2 IIIp star, Arcturus, has been obtained with a rocket-borne multichannel spectrometer. The use of multiple detectors gave an increase in effective observing time and permitted an improvement in spectral resolution over two previous rocket measurements. H I at 1216-A and O I at 1304 A are the only identified emissions, and the observed H I 1216-A flux is low compared with previous observations. A third unidentified feature was observed at 1511 A. The absence of many lines found in emission from the sun is striking. The absence of certain features implies that the coronal temperature must be either below 50,000 K or above 350,000 K.
Mckinney, W. R.↗
Sensitive far UV spectrograph with a multispectral element microchannel plate detector for rocket-borne astronomy
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Weiser, H.↗
The far ultraviolet /1200-1900 A/ spectrum of Jupiter obtained with a rocket-borne multichannel spectrometer
Far-ultraviolet spectra of Jupiter with a significant improvement in sensitivity and spectral resolution have been obtained from a sounding rocket by using a 10-channel spectrometer behind a pointing telescope. The major results obtained from these spectra are: (1) measurement of the Jovian H I 1216-A brightness (a comparison with other measurements indicates that the Ly-alpha emission is likely to be variable); (2) measurement of the wavelength-dependent albedo for Rayleigh-scattered solar radiation from about 1550 to 1875 A with approximately 25-A resolution, making it possible to set revised upper limits on the abundances of some of the minor constituents in the upper Jovian atmosphere; and (3) a demonstration that weak emissions between approximately 1250 and 1500 A and near 1600 A are probably the Lyman bands of H2 excited by low-energy electrons.
Giles, J. W.↗
Copernicus observations of Nova Cygni 1975
Near-ultraviolet radiation from Nova Cygni 1975 was detected by the Copernicus satellite on five occasions from 1975 September 1 to 1975 September 9. The nova was not seen in the UV after this date. The principal result was the observation of a broad emission feature from the Mg II doublet at 2800 A. The absence of strong UV radiation at shorter wavelengths suggests that these lines are produced by collisional excitation in the outer layers of an expanding shell with electron temperature of approximately 4000 K. The absence of observed emission lines from highly ionized species indicates that the amount of material with log T between 4.4 and 5.7 is less than 0.001 times that which produces the Mg II emission. The continuum flux in the near-UV decreased as the nova evolved, showing that the total luminosity decreased as the nova faded in the visible.
Jenkins, E. B.↗
Photoabsorption cross sections of methane from 1400 to 1850 A
Photoabsorption cross sections of methane in the 1400-1850-A spectral region have been measured. Cross sections at wavelengths greater than 1475 A are approximately 200 times smaller than those currently accepted. This has a significant effect on the interpretation of spectral measurements of the Jovian planets in this wavelength region.
Mount, G. H.↗
Detection of Lyman-alpha emission from the Saturnian disk and from the ring system
A rocket-borne spectrograph detected H I Lyman-alpha emission from the disk of Saturn and from the vicinity of the planet. The signal is consistent with an emission brightness of 700 rayleighs for the disk and 200 rayleighs for the vicinity of Saturn. The emission from the vicinity of the planet may be due to a hydrogen atmosphere associated with the Saturnian ring system.
Weiser, H.↗
A general study of techniques for ultraviolet astrophysical studies on space vehicles
Recent accomplishments in three areas of UV instrumentation for space astronomy are discussed. These areas include reliable UV photometry, sensitive photon-detection techniques, and precise telescope pointing. Calibration facilities for spectrometers designed to operate in the spectral regions above 1200 A and down to 400 A are described which employ a series of diodes calibrated against electron synchrotron radiation as well as other radiometric standards. Improvements in photon-detection sensitivity achieved with the aid of pulse-counting electronics and multispectral detectors are reported, and the technique of precise subarcsecond telescope pointing is briefly noted. Some observational results are presented which demonstrate the advantages and precision of the instruments and techniques considered.
Moos, H. W.↗
A sensitive observation of the far-ultraviolet /1160-1700 A/ spectrum of Arcturus and implications for its outer atmosphere
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Weinstein, A.↗
Ultraviolet spectrometer experiment for the Voyager mission
An objective grating spectrometer covering the wavelength range of 500 to 1700 A with a 10-A resolution is employed for the Voyager ultraviolet spectrometer experiment. In determining the composition and structure of the atmospheres of Saturn, Jupiter and several satellites, the ultraviolet spectrometer will rely on airglow mode observations to measure radiation from the atmospheres due to resonant scattering of solar flux, and the occultation mode for assessments of the atmospheric extinction of solar or stellar radiation as the spacecraft enters shadow zones. Since it is capable of prolonged stellar observations in the 500 to 1000 A wavelength range, the spectrometer is expected to make important contributions to exploratory studies of UV sources.
Broadfoot, A. L.↗
A rocket observation of the far-ultraviolet spectrum of Saturn
Far-ultraviolet (1160-1750 A) spectra of the Saturnian disk and the ring system have been obtained by using a very sensitive rocket-borne spectrograph with a microchannel plate detector. The use of two apertures of different diameter in the telescope focal plane permitted the separation of the contribution of the planetary disk from that of the rings. H I lambda 1216 was the only atomic spectral line emission detected in the planet and the rings. A weak signal from the disk between 1300 A and 1500 A was observed. Geometric disk albedos, averaged over 50 A, were determined from 1500 A to 1700 A. Measurements of the ring reflectivity longward of 1650 A are compatible with H2O frost but not NH3 frost.
Weiser, H.↗
Ultraviolet observations of cool stars. VI - L alpha and Mg II emission line profiles /and a search for flux variability/ in Arcturus
High-precision, high-resolution profiles of the L alpha and Mg II k chromospheric emission lines from Arcturus (alpha Boo) obtained with the Princeton Experimental Package aboard the Copernicus satellite are presented. Asymmetries seen in the profiles of these lines are probably intrinsic to the star, rather than the result of interstellar absorption. In contrast to previous observations of the Ca II K emission line, no evidence is found during a three-year period for variability in the profiles or in the total fluxes from these lines on time scales ranging from hours to months. Also presented is a flux profile of the O I 1302 line and flux upper limits for L beta, O VI 1032, Si III 1206, and O V 1218.
Mcclintock, W.↗