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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
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NASA NTRS1976

Simultaneous X-ray and optical observations of X Persei

Photoelectric photometry of X Persei was obtained on five out of seven consective nights in January 1975, from the Lick and Leuschner Observatories. The observations yield B = 6.848 + or - 0.002, B-V = 0.139 + or - 0.001, with no strong evidence for variability during the observing run. These are the faintest and bluest photoelectric magnitudes and colors ever reported for X Per; this change apparently occured relatively uniformly during 1973-74 and is reminiscent of behavior last observed in approximately 1900. The suggested association of X Persei with the weak X-ray source 3U 0352+30 raises the possibility of detection of X-ray/optical covariability. On January 21, 1975, 7 hours of data were obtained from both observatories simulataneous with OAO Copernicus X-ray observations of 3U 0352+30. The X-ray data varied during this period by a factor of two, but there is no obviously correspondent optical activity, to a level of 0.02 mag. The optical data are also used to limit to 0.01 mag variations coincident with the X-ray periodicity.

Margon, B.↗
NASA NTRS1976

Line identifications in the ultraviolet spectra of Tau Herculis, B5 IV, and Zeta Draconis, B6 III

Tables of the lines found on two tracings each of the ultraviolet spectrum of Tau Her, B5 IV, and Zeta Dra, B6 III, made by the Copernicus satellite and possible identifications are given. The ranges 1025-1451A for Tau Her and 1035 to 1425A for Zeta Dra are covered by the U2 spectrometer at a resolution of 0.2A; the ranges 2028 to 2959A for Tau Her and 2000 to 3000A for Zeta Dra are covered by the V2 spectrometer at a resolution of 0.4A. The observed density of lines in the U2 region is 1.1 lines/A for Tau Her and 1.7 lines/A for Zeta Dra. In the V2 region it is 0.8 lines/A for Tau Her and 0.9 lines/A for Zeta Dra.

Underhill, A. B.↗
NASA NTRS1976

Ultraviolet observations of local gas

From satellite measurements of ultraviolet spectra of stars, an average density of approximately 1.1/cu cm for hydrogen atoms, in both atomic and molecular form, is estimated for regions of space along the galactic plane within about 1 kpc of the sun. About 20% of the atoms are bound in molecular form although this figure is uncertain since the ultraviolet measurements avoid the very dense interstellar clouds. Discrete values for this percentage are observed to vary markedly; regions with less than average density seem to have fractional abundances of H2 several orders of magnitude lower than average. A ratio of CO/H is observed for regions in front of stars observed by the Copernicus satellite.

Jenkins, E. B.↗
NASA NTRS1975

Ultraviolet studies of the interstellar gas

Sounding-rocket and satellite UV observations of interstellar gas clouds are reviewed with major attention given to Copernicus observations of interstellar absorption lines. Analysis of typical absorption-line data is outlined, and observations are reviewed for atomic hydrogen as well as interstellar H2, HD, and CO molecules. Investigations of atomic abundances in H I regions are summarized, measurements of atomic deuterium abundances in the interstellar gas are examined, and the properties of ionized interstellar gas are described. Theoretical analyses of the physical state of the interstellar gas are summarized with respect to ionization by energetic radiation, cool H I clouds, and the intercloud medium. The data obtained thus far are shown to indicate mean temperatures of about 80 K, particle densities between 10 and 1000 per cu cm, and a depletion of heavy elements that becomes greatly enhanced with increasing condensation temperature for those H I regions with strong H2 lines.

Spitzer, L., Jr.↗
NASA NTRS1975

UV stars and the interstellar medium - A statistical time-dependent model

A statistical time-dependent model for the effects on the interstellar gas of the ionizing radiation from UV stars is presented. The radiation from the stars is assumed to be emitted as monochromatic bursts at random times and locations. The thermal and ionization history of the gas is followed in a Monte Carlo simulation. Probability densities as well as mean values for the ionization fraction, temperature, and other observable quantities are derived. The fluctuations in observed quantities due to the stochastic nature of the model are estimated. Models of the interstellar medium perpendicular to the galactic plane are developed and compared with observations. The action of the UV stars can explain the bulk properties of the interstellar gas toward the galactic poles and is consistent with the Copernicus satellite observations toward lambda Scorpii.

Lyon, J.↗
NASA NTRS1975

Soft X-ray search of centre of Cygnus Loop

Equipment on the Copernicus satellite has been used to search for evidence of a compact object in the center of the Cygnus Loop supernova remnant. Rocket measurements reported by Rappaport et al. (1973) indicate that a central object exists. However, the study conducted with the aid of the satellite was negative. This negative result could indicate that the X-ray source was simply not in its high-intensity mode at the time of observation, or could arise because the source is at some other location in the Loop.

Snyder, W. A.↗
NASA NTRS1975

The depletion of interstellar elements and the interaction between gas and dust in space

Observational data obtained by the Copernicus satellite and ground-based facilities are discussed which show that the depletion of interstellar elements apparently varies with cloud density in the way to be expected if the depletions were due to accretion of gas atoms or ions onto grains. It is shown that the depletion-by-accretion mechanism is supported by a good correlation between depletions and first ionization potentials of the elements (except for lithium, sodium, and potassium) and that this mechanism offers an alternative to the grain-condensation hypothesis in which most of the interstellar medium is required to have been processed through stellar nebulae. It is noted that if the grains do not normally carry positive charges, ion-grain encounters are the most important interactions between gas and dust and may be significant in determining ionization equilibrium, especially if there is a large population of very small grains.

Snow, T. P., Jr.↗
NASA NTRS1975

Interstellar absorption lines toward gamma Arae

The available data on interstellar absorption lines in the spectrum of gamma Ara observed from the ground and with the Copernicus telescope have been analyzed to give column densities of various ion stages of H, C, N, O, Na, Mg, Si, P, S, Ar, Ca, Mn, and Fe. The element abundances with respect to H nuclei in H I regions are similar to the values for zeta Oph, with depletions relative to the sun tending to increase with increasing condensation temperature. For example, toward gamma Ara, Fe is depleted by a factor of 50; Mg, Si, and Mn by about 10; and S, P, and N little or none. Interstellar Si IV and probably S IV appear stronger than in most other stars, but still their low ratios to Si III and S III suggest that soft X-rays and low-energy cosmic rays are not important sources of ionization. The width of the O VI lines and the absence of N V have been interpreted as evidence for a collisionally ionized region with a temperature between 300,000 and 700,000 K containing at least 0.0004 of the total interstellar column density.

Morton, D. C.↗
NASA NTRS1975

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.↗
NASA NTRS1976

The abundance of deuterium relative to hydrogen in interstellar space

Copernicus satellite observations of the deuterium and hydrogen Lyman lines in the lines of sight to mu COl, gamma-2 Vel, alpha Cru AB, and alpha Vir AB are reported. Together with previously published data for beta Cen A, the results yield a value N(D)/N(H) of approximately 0.000018 (m.e.) or a total deuterium mass portion of approximately 0.000025. Values for all stars with their error bars are contained within a band ranging from 0.25 to 2.0 times the quoted mean ratio. These limits are probably representative of the region within 200 pc of the sun. The results for these stars are essentially independent of assumptions about the Doppler parameter describing the formation of the lines, although this value can be derived from the observations. The results are consistent with a maximum temperature of 6000 K for the lines of sight studied.

York, D. G.↗
NASA NTRS1976

P Cygni profiles in zeta Ophiuchi and zeta Puppis

Detailed P Cygni profiles are plotted using data from selected regions of the far-UV spectra of zeta OPh and zeta Pup obtained by the Copernicus satellite. Equivalent widths and velocity shifts of both emission and absorption features are also presented. For zeta Oph, it is found that only the C IV and N V resonance lines exhibit the P Cygni phenomenon; for zeta Pup, the resonance lines of C III, N III, Si IV, C IV, P V, S VI, N V, and O VI all show strong P Cygni lines, although the emission component seems to be absent in N III. For both stars, it is shown that parts of most absorption profiles exceed the escape velocity, indicating mass ejection. The short-wavelength edges of the resonance lines are found to average about -1590 km/s in zeta Oph and about -2660 km/s in zeta Pup, with no significant dependence on ionization potential. It is noted that the equivalent width of the emission component is always considerably less than that of the absorption component, suggesting that absorption occurs close to the stellar surface.

Morton, D. C.↗
NASA NTRS1976

Evidence for mass loss at moderate to high velocity in Be stars

Ultraviolet spectra of intermediate resolution have been obtained with Copernicus for 12 objects classified as Be or shell stars and for 19 additional early B dwarfs. Some of these spectra show marked asymmetries in certain resonance lines, especially the Si IV doublet at 1400 A, indicating the presence in some cases of outflowing material with maximum velocities of nearly 1000 km/s. Direct evidence for mass loss at these velocities is seen for the first time in dwarf stars as late as B1.5; the only objects later than B0.5 which show this effect are Be or shell stars. Among the stars considered, there is a correlation between the presence of mass-loss effects and projected rotational velocity, suggesting that the ultraviolet flux from B1-B2 dwarfs is sufficient to drive high-velocity stellar winds only if rotational effects reduce the effective gravity near the equator. The mass-loss rate for one of the most active Be stars, 59 Cyg, is crudely estimated to be one billionth or one ten-billionth of a solar mass per year. The data suggest that the extended atmospheres associated with Be-star phenomena may be formed by mass ejection.

Snow, T. P., Jr.↗
NASA NTRS1976

Interstellar molecular hydrogen toward zeta Puppis

This paper reports the measurement of some 136 interstellar H2 absorption lines found in a continuous scan of the far-ultraviolet spectrum of zeta Pup at 0.05-A resolution with the Copernicus telescope. Absorptions from only the rotational levels 0 to 5 of the lowest vibrational state of the ground electronic state were observed. The total H2 column density is 2.8 by 10 to the 14th power molecules/sq cm; the ratio of H nuclei in H2 to the number in H I plus molecules is 6 by 10 to the -6th power; the population of the rotational levels can be represented by a single excitation temperature of 1120 (plus or minus 80) K. The radial velocities of all rotational levels were the same within 7 km/s and differed from most atoms and first ions by no more than 4.5 km/s on the average. The tables also list the best available data on wavelengths, oscillator strengths, and radiative damping constants for all the H2 lines with zero vibrational level likely to be observed in the interstellar gas.

Morton, D. C.↗
NASA NTRS1976

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.↗
NASA NTRS1976

Components in interstellar molecular hydrogen

Results are reported for precise spectrophotometric measurements of the profiles of selected Lyman absorption lines produced by hydrogen molecules in various rotational levels along the line of sight to 13 stars which have shown some evidence for an increase in line width with increasing rotational quantum number (J). The line profiles were measured by multiple scans with the Copernicus satellite telescope. Based on analysis of the radial velocities, derivations of the column densities, and line-profile fitting, the following conclusions are made: (1) the increase in interstellar H2 line width with increasing J results from the presence of the most shortward component, which is relatively weak at low J but becomes more important at higher J; (2) the relative column densities found for the different J levels in each component may be fitted by a theoretical model in which rotational excitation is due to absorption of UV photons followed by radiative quadrupole spontaneous transitions or collisionally induced downward transitions between different J levels; (3) the atomic hydrogen density is between 300 and 1000 per cu cm in the most shortward component for each of three stars; (4) the approaching gas which produces each shortward component must be in the form of thin sheets; and (5) the sheets are the compressed gas behind a shock front moving through the interstellar medium.

Spitzer, L., Jr.↗
NASA NTRS1976

An analysis of the interstellar material in the line of sight toward Omicron Persei

Chemical abundances and physical conditions in the interstellar gas toward Omicron Per are analyzed using Copernicus UV spectrophotometric data on 69 lines due to ions and atoms as well as 19 lines of H2 and HD. The UV extinction toward the star is determined along with the column densities of atomic and molecular hydrogen, the atomic column densities and temperature in the H I region, and the nature of the ionized regions along the line of sight. It is concluded that: (1) Omicron Per is apparently embedded in the near edge of an extended dense molecular cloud, the outer parts of which give rise to the observed absorption lines; (2) the H I region may consist of more than one cloud; (3) the far-UV extinction rise is unusually steep, indicating a high proportion of small grains; (4) the element depletions are somewhat greater than in Zeta Oph, particularly for sulfur and argon; and (5) the molecular abundances are generally consistent with gas-phase formation models rather than with molecular formation on grain surfaces, unless a substantial amount of small grains is present to increase the available surface area.

Snow, T. P., Jr.↗
NASA NTRS1976

Hydrogen molecules in interstellar space

The most important results obtained from Copernicus satellite observations of ultraviolet H2 absorption features are summarized. The properties of the hydrogen molecule are described along with the radiative processes in which it can be involved. Techniques and equipment used in observing H2 absorption features from space are reviewed. The results are discussed in terms of the fraction of hydrogen in molecular form, rotational excitation of H2, physical conditions within interstellar gas clouds, and approaching clouds characterized by high excitation and negative radial velocity. It is shown that: (1) an appreciable fraction of the hydrogen in denser and thicker clouds is molecular, (2) at least some of the interstellar clouds are far from pressure equilibrium, (3) the approaching clouds are apparently dense thick sheets moving toward the sun as viewed in the local standard of rest, (4) these clouds are probably shock waves produced in the interstellar gas by old supernova remnants or expanding H II regions, and (5) the abundances relative to H of such elements as O, Mg, Si, and Cl in these clouds are nearly equal to the solar values, which is in contrast to the depletions observed in many other interstellar clouds.

Spitzer, L.↗
NASA NTRS1976

Simultaneous photometry of X Persei and 3U 0352+30

The suggested association of X Persei with the weak X-ray source 3U 0352+30 raises the possibility of detection of X-ray/optical covariability. The paper reports a successfully conducted simultaneous optical/X-ray observation utilizing ground-based photometry and a satellite-borne proportional counter. Photoelectric photometry of X Persei was obtained on five out of seven consecutive nights in January 1975. The observations yield the faintest and bluest photoelectric magnitudes and colors ever reported for X Per; this change apparently occurred relatively uniformly during 1973-74 and is reminiscent of behavior last observed in about 1900. On January 21, 7 hr of data were obtained simultaneously with OAO Copernicus X-ray observations of 3U 0352+30. The X-ray flux varied during this period by a factor of 2, but there is no obviously correspondent optical activity, to a level of 0.02 mag. The optical data are also used to limit the 0.01-mag variations coincident with the X-ray periodicity reported by White et al. (1976).

Margon, B.↗