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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

A survey of interstellar H I from L-alpha absorption measurements. II

This paper presents interstellar H I column densities, mean H I space densities, total neutral hydrogen column densities, and total mean hydrogen space densities toward 100 stars surveyed in the L-alpha region with the U2 detector of the Copernicus satellite. The data for 47 stars are compared with OAO 2 results, and ratios of gas to E(B-V) color excess are computed for 30 'intercloud' stars, 45 'cloud' stars, and the combined sample of 75 stars. A definitive value of 5.8 x 10 to the 21st power atoms/sq cm per mag is obtained for the mean ratio of total neutral hydrogen to color excess, indicating that this ratio seems to be a constant, independent of location in the sky, except possibly toward stars with anomalous extinction. The anomalous ratio determined for Rho Oph is examined, and the galactic distribution of neutral hydrogen is evaluated. The following values are estimated for matter in the galactic plane within 500 pc of the sun: a total mean hydrogen space density of 1.15 atoms/cu cm, a mean H2 space density of 0.143 molecule/cu cm (possibly a lower limit), and a mean H I space density of 0.86 atom/cu cm (a possible overestimate).

Bohlin, R. C.↗
NASA NTRS1978

Spectrophotometric variability in the Be star Gamma Cassiopeiae - Simultaneous ultraviolet and H-alpha observations

Simultaneous scans of the ultraviolet Si IV and Mg II resonance doublets in the spectrum of Gamma Cas with the Copernicus satellite during 64 continuous hours of observation, and H-alpha scans from a ground station, are described. No evidence is found for a rotation period of Gamma Cas, but narrow emission components in both ultraviolet doublets are reported along with a sudden emission increase on January 29.1, 1977 UT which appeared to be present in both H-alpha and the ultraviolet lines.

Slettebak, A.↗
NASA NTRS1978

Five years in the life of an inertial system operating in orbit

The paper describes the in-orbit performance of the gyroscopes and strapdown attitude reference system for the OAO-C (Copernicus) satellite, launched on Aug. 21, 1972. In order to fulfill NASA requirements, the inertial system had to: (1) operate for at least one year in orbit without failure, (2) maintain an inertial reference with an uncertainty of 50 microradians or less for at least one hour, and (3) control attitude changes with an accuracy of at least 30 parts per million. During the orbit period, the inertial system has demonstrated a capability for maintaining an inertial reference that is significantly better than these performance goals.

Harris, R. A.↗
NASA NTRS1978

Ultraviolet observations of cool stars. VIII - Interstellar matter toward Procyon

The profile of the chromospheric L-alpha emission line of the F5 IV-V star Procyon (Alpha CMi, d = 3.5 pc) has been measured using the high-resolution Princeton spectrometer aboard NASA's Copernicus satellite. L-alpha absorption lines of interstellar deuterium and hydrogen are distinctly present. The average number density of interstellar hydrogen along the line of sight is found to be 0.11 + or - 0.02 per cu cm, similar to the densities that have been found in the directions of the stars Epsilon Eri, Epsilon Ind, and Alpha Cen A. These stars are all within 3.5 pc of the earth. The ratio of deuterium to hydrogen in the direction of Procyon is found to be 1.3 (+1.2, -0.5) x 10 to the -5th.

Anderson, R. C.↗
NASA NTRS1978

The abundance of boron in B- and A-type stars

Results are reported for Copernicus observations of the 1362.46-A resonance line of B II in 16 normal B and A stars. An average for the stars in which a boron abundance has been determined yields a B/H abundance ratio of 2 x 10 to the -10th; this value is taken to be the cosmic abundance of boron. The observed abundances are compared with those predicted by the galactic-cosmic-ray (GCR) spallation theory for the 'best fit' GCR flux, and remarkably good agreement is obtained. The value derived for the cosmic boron abundance is shown to support the theory that spallation reactions by high-energy GCRs on atoms of C, N, and O in the interstellar gas are responsible for the origin of B and Be as well as at least some Li. It is noted that the meteorite boron abundance is an order of magnitude greater than the cosmic abundance derived from stars, which implies an anomalous local enrichment in boron and possibly in the B-11/B-10 ratio during the formation of carbonaceous chondrites.

Boesgaard, A. M.↗
NASA NTRS1979

Rotationally excited HD toward Zeta Ophiuchi

Copernicus satellite measurements of HD in J-double prime = 1 and J-double prime = 0 toward Zeta Oph are reported. The ratio of the number densities of HD in the J = 0 and J = 1 states is determined to be 0.15 + or - 0.02 at the 1-sigma level. A value of approximately 24 x 10 to the -17th erg/cu cm per A at 1000 A is obtained for the UV energy density at the Zeta Oph cloud, and the mechanisms for excitation of HD are examined. A tight upper limit is derived for the abundance of HCl, which has been predicted to be present due to the interaction of ionized chlorine with neutral hydrogen. A calculation is performed which indicates that the cloud is 28 pc from the star. It is shown that the two-component cloud model of Black and Dalgarno (1977) with densities of 500 and 2500 H nuclei per cu cm for the outer regions and core, respectively, is in excellent agreement with the observations.

Wright, E. L.↗
NASA NTRS1979

Ultraviolet and optical spectroscopic studies of Lambda Andromedae - The chromosphere and interstellar medium

Chromospheric lines of, and interstellar lines toward, the spectroscopic binary Lambda And (primary component G7-G8 III-IV) have been observed in the ultraviolet with the spectrometer and telescope on board the Copernicus satellite. An extensive, high-resolution spectroscopic study of the Ca II H and K profiles has also been undertaken. Some of these optical spectra were obtained simultaneously with the ultraviolet data. The ultraviolet emission lines of Lamba And are compared to the sun and to stars of similar spectral type. The star Lamba And resembles the active sun in surface brightness of chromospheric emissions and in appearance of the Mg II and Ca II profiles. The largest variations in the integrated calcium emission cores amount to an 80% increase in the K core and a corresponding 40% increase in the H core between observations two years apart. Variations in the cores may show a dependence on spectroscopic phase, and may be contributed to by circumstellar matter in the binary system. Previously unreported, transient emission features have also been observed, at a velocity of -70 km/s with respect to the Ca II emission cores.

Baliunas, S. L.↗
NASA NTRS1979

Interstellar absorption lines in the spectrum of Gamma Velorum

Copernicus scans of selected interstellar absorption lines in the UV spectrum of Gamma Vel are analyzed, together with ground-based data, to obtain column densities for various ion states of C, N, O, Na, Mg, Al, Si, P, S, Cl, Ar, Ca, Mn, Fe, and CO. N I and O I are fitted to a single empirical curve of growth with a velocity parameter (b) of 8 km/s; Mg II, Si II, P II, S II, Mn II, and Fe II are fitted to another curve with b between 3 and 9 km/s. Abundance determinations relative to H I show that: (1) C, N, P, S, and Ar are probably close to their solar values; (2) O may be depleted by about a factor of 2; (3) Mg, Al, Si, Cl, Mn, and Fe are depleted by a factor of 4 or more: (4) Al is depleted by at least a factor of 10 in the H II region; and (5) both N V and O VI are present, but not C IV. The N V/O VI ratio implies that the electron temperature in the H II region is about 275,000 K.

Morton, D. C.↗
NASA NTRS1979

Variable outflow in the O6ef star Lambda Cephei

The paper analyzes spectroscopic data from the UV region using the Copernicus satellite on six consecutive days in September, 1975. It is found that the P Cygni lines of C III at 1175 A and of N V at 1238 and 1242 A show little or no variation in their profiles. The results indicate that the changes in the 4686-A H II and H-alpha can be interpreted as a variable outflow near the surface of the star, either due to random density inhomogeneities propagating outward, or the effects of rotation of a nonspherical star, or both. Insufficient data exist at present to distinguish between periodic and random fluctuations.

Leep, E. M.↗
NASA NTRS1979

A survey of ultraviolet circumstellar absorption lines in the spectra of early Be and shell stars

Copernicus UV data are used to examine the rich shell absorption spectra between 1120 and 1140 A in 17 Be and shell stars. Previous observations of the program stars are reviewed, the general appearance of the shell spectra between 1120 and 1140 A is described, and the shell spectra are compared with the spectra of four bright B-type supergiants in the same wavelength region. The line strengths are analyzed to determine quantitative shell strengths and shell column densities; the shell line velocities are discussed in the context of different models. It is shown that UV shell lines can exist in stars with no visible-wavelength shell features, that Fe III shell lines dominate the spectra between 1120 and 1140 A in Be and shell stars with circumstellar absorption features, and that the spectra of Be and shell stars in this region strongly resemble those of supergiants of similar effective temperature.

Snow, T. P., Jr.↗
NASA NTRS1979

The depletion of interstellar gaseous iron

The Copernicus UV telescope was used to measure equivalent widths of interstellar Fe II resonance lines toward 55 early-type stars; the measurements permit the determination of Fe II column densities. The depletion of interstellar gaseous iron was obtained by combining these measurements with the results from a previous atomic and molecular hydrogen survey program; the derived depletions refer mostly to matter in H I regions. As an example, the nearly normal gaseous iron abundance in the distant high-latitude intermediate-velocity cloud toward HD 93521 is consistent with the idea that these clouds are produced by galactic supernova explosions.

Savage, B. D.↗
NASA NTRS1979

Four UV observations of the interstellar wind by Mariner 10 - Analysis with spherically symmetric solar radiation models

Four Mariner 10 observations of interplanetary hydrogen 1216-A and helium 584-A emissions are analyzed by using radiation models that employ spherically symmetric solar radiation fields. It is shown that the measured 584-A intensities can be represented with a statistical accuracy of about 10% by a model that assumes spherical symmetry for the 584-A solar radiation and that the 1216-A intensities can be represented to within 15% by a model based on spherically symmetric solar corpuscular and EUV radiation. An interstellar wind velocity of 22 km/s, a helium number density of 0.008 per cu cm, and an interstellar neutral-gas temperature of 1500 K near the solar system are obtained from Copernicus satellite measurements.

Ajello, J. M.↗
NASA NTRS1979

The ultraviolet flux distribution of Alpha-2 Canum Venaticorum

Intermediate- and narrow-band UV spectrophotometry from Copernicus, OAO 2, the S2-68 experiment on TD 1, and a sounding-rocket experiment are combined with ground-based observations to define the absolute flux distribution of the bright magnetic Ap star Alpha-2 CVn over the wavelength range from 1030 to 7580 A. Two flux distributions are presented which coincide more or less with the rare-earth maximum and minimum in the star's cycle. The results are compared with those for two normal stars, the UV variability of Alpha-2 CVn is characterized as a function of wavelength, and non-LTE effects on the UV continua of C I and Si I are analyzed. Some physical properties of Alpha-2 CVn are estimated, and the evolutionary age of the star is estimated to be between 220 million and 300 million years. It is concluded that Alpha-2 CVn is old enough to have been magnetically braked to its current rotational velocity by either the centrifugal-wind or the accretion mechanism and to have developed its chemical peculiarities by either mechanism.

Leckrone, D. S.↗
NASA NTRS1979

The ratio of deuterium to hydrogen in interstellar space. IV - The lines of sight to Delta, Epsilon, and Iota Orionis

Deuterium absorption features in spectra of Delta, Epsilon, and Iota Ori obtained with Copernicus are analyzed. The Iota Ori line-of-sight analysis, which is quite detailed because of the high-velocity H I components superposed on the deuterium features, gives a D/H ratio (which is uncertain because of a complex profile) of 0.000014. A D/H ratio of the order of 7 millionths is determined for Delta and Epsilon Ori. For the complex line profiles involved, one may regard this as a formal lower limit. Several attempts were made to increase the ratio N(D I)/N(H I) in the context of reasonable models for the line of sight, but with no success; the derived values are therefore regarded as actual values, not lower limits. Since the derived value is an average on the line of sight, the possibility cannot be ruled out that the true ratios N(D I)/N(H I) in individual nearby components differ from the mean values. The mean value for these two directions is lower by a factor of 4 than the best value for the Zeta Pup line of sight (the highest yet derived for path lengths greater than 50 pc).

Laurent, C.↗
NASA NTRS1979

Deep photospheric flows in Tau Scorpii

From analysis of weak, unblended, ultraviolet lines observed in Tau Scorpii by Copernicus, the same line widths and the same slightly blue-depressed wings as found in the upper photospheric lines of the visual region are found. In addition, a radial-velocity discrepancy of about 6 km/s between weak and strong lines in the 1000-1300-A region is found. These results are in quantitative agreement with one another and with the results of the visual region. They imply that a flow of material is present even in the deep photosphere of this star. However, one cannot yet specify the geometry of the flow (outward-radial versus temperature-weighted convection columns). At the least, this flow alters the expected radiation-driven flow solution close to the photosphere. At the most, it could provide the heating of a chromosphere or a corona just outside the photosphere, as required by the imperfect flow model.

Smith, M. A.↗
NASA NTRS1979

Orion's Cloak - A rapidly expanding shell of gas centered on the Orion OB1 association

The structure of the interstellar gas surrounding the Orion OB1 association and the neighboring lambda Orionis association is detailed. UV absorption lime spectra of various ionization stages of C, N, Si and S in the directions of 12 stars were obtained by means of the spectrometer on board the Copernicus satellite. The presence of a shell of material surrounding the two associations and expanding at 100 to 120 km/sec, designated Orion's Cloak, was revealed, together with sporadically occurring higher column density matter at lower velocities. Results are interpreted to indicate the presence of a rapidly moving radiative shock outside the H II region of the association stars and inside this feature, a lower velocity, higher column density cloud which appears to be directly ionized by association stars. It is suggested that the gas features are caused by the effects of a recent supernova and of multiple supernovae, stellar winds and rocket-accelerated clouds in addition to stellar ionization.

Cowie, L. L.↗
NASA NTRS1979

Search for short time-scale periodicity in the X-ray flux of 4U1700-37

The existence of a short-term periodicity in the X-ray light curve of the binary system 4U1700-37 was investigated by recent Copernicus observations. 4U1700-37 was observed for two complete binary cycles in July, 1978, with a sampling interval of 86.5 sec which allowed for the detection of periodicities down to 3 min. No evidence of the periodicity which had been previously reported in the ranges 20 to 30 min or 90 to 100 min was found, nor was there any in other ranges down to 3 min, even when X-ray noise caused by intense flares on 4U1700-37 was taken into account. Possible explanations for the recent absence of periodicity are proposed.

Branduardi, G.↗
NASA NTRS1979

O VI absorption in interstellar cloud surfaces

The velocity profiles of O VI absorption lines of 24 stars, observed in early Copernicus surveys, have been compared with the line profiles of Si III (1206.51 A) and N II (1083.99 A). The velocity structures of the O VI lines appear to be correlated with those of the material in the lower ionization stages. It is argued that the O VI absorption arises in the coronal gas of the conductive interface between hot gas, responsible for extended, soft X-ray emission, and cooler interstellar clouds. The velocity broadening of both sets of lines is attributed to motions of the cloud surfaces induced by pressure fluctuations in the interstellar medium.

Cowie, L. L.↗