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At least 307 records · Page 17
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NASA NTRS1970

Scientific Rationale Summaries for Apollo Candidate Lunar Exploration Landing Sites - Case 340

A summary of the scientific rationale for each Apollo landing site listed by the Group for Lunar Exploration Planning on February 7, 1970 is presented. These sites include the Fra Mauro Formation, Littrow, Censorinus, Davy crater chain, Marius Hills, Descartes, Tycho, Copernicus central peaks, and Hadley-Apennines. In addition, a summary of the scientific rationale for Flamsteed P, the Apollo 13 backup site, and Hyginus is presented.

Head, J. W.↗
NASA NTRS1980

Outer satellite atmospheres: Their extended nature and planetary interactions

Highly developed numerical models are applied to interpret extended-atmosphere data for the sodium cloud of Io and the hydrogen torus of Titan. Solar radiation pressure was identified and verified by model calculations as the mechanism to explain two different east-west asymmetries observed in the sodium cloud. Analysis of sodium line profile data, suggesting that a Jupiter magnetospheric wind may be responsible for high speed sodium atoms emitted from Io, and preliminary modeling of the interaction of the Io plasma torus and Io's sodium cloud are also reported. Models presented for Titan's hydrogen torus are consistent both with the recent Pioneer 11 measurements and earlier Earth-orbiting observations by the Copernicus satellite. Progress is reported on developing models for extended gas and dust atmospheres of comets.

Smyth, W. H.↗
NASA NTRS1979

Observations of emission lines in M supergiants

Copernicus observations of Mg 2 h and k emission lines from M giants and supergiants are described. Supergiants with extensive circumstellar gas shells show an asymmetric k line. The asymmetry is ascribed to superimposed lines of Fe 1 and Mn 1. The Mg 2 line width fit the Wilson-Bappu relation derived from observations of G and K Stars. Results of correlated ground-based observations include (1) the discovery of K 1 fluorescent emission from the Betelgeuse shell; (2) extimates of the mass-loss rates; and (3) the proposal that silicate dust grains must account for the major fraction of the Si atoms in the Betelgeuse shell.

Lambert, D. L.↗
NASA NTRS1980

The rate of mass loss and variations in the wind from the Be star delta Centauri

Copernicus ultraviolet scans of the Be star delta Centauri obtained in 1976 and 1979, show a significant variation in the Si III lambda 1206 profile, The strong asymmetry that was present in 1976 had disappeared by 1979. The Si IV lambda 1400 doublet was also asymmetric in 1976, but was not observed in 1979. A quantitative fit of the line shapes to theoretical wind profiles shows that the mass-loss rate in 1976 was 2 x 10 to the minus 8th power/yr, and that the rate of mass loss in Si III was at least one order of magnitude less in 1979. It is not possible to determine whether the variation represented an overall change in the lass-loss rate, or whether it was due to a change in the ionization balance. The profile fitting procedure resulted in the adoption of assumed underlying photospheric Si III and Si IV profiles, and the equivalent widths measured from these profiles are most consistent with T sub eff between 30,000 and 35,000 K, somewhat hotter than implied by the spectral classification normally assigned to this star. The ultraviolet photospheric line widths, coupled wit published theoretical analyses of rotational gravitational darkening, imply an intrinsic equatorial velocity of about 310 km/sec and an angle of inclination of the rotational axis to the line of sight of i is less than or equal to 44 deg.

Snow, T. P., Jr.↗
NASA NTRS1979

Simultaneous ultraviolet and X-ray observations of the massive binary V861 Scorpii /=OAO 1653-40/

Results are reported for simultaneous Copernicus UV and X-ray observations of the massive binary system V861 Sco (possibly associated with the X-ray source OAO 1653-40) over a period of five orbital cycles from April to September 1978. It is found that the UV spectrum of V861 Sco is similar to that of a normal supergiant and that the X-ray flux from OAO 1653-40 is highly variable. A simultaneous change in the C III 1176-A line and the 3.8-8.8-keV X-ray flux is discussed which was detected when V861 Sco was observed in September 1978. The close correlation between the X-ray and UV events is taken to imply that the X-ray source OAO 1653-40 is coincident with V861 Sco. The event energetics and physical conditions in the region responsible for the C III 1176-A emission are considered. It is concluded that the most likely X-ray production mechanism is accretion by a gas stream onto a black hole.

Polidan, R. S.↗
NASA NTRS1979

A non-LTE treatment of beryllium lines - Misidentification of the solar Be I feature at 2650 A

The formation of beryllium lines, with particular reference to the solar Be spectrum, is investigated in a non-LTE context with a 25-level model atom in which 15 levels are allowed to depart from LTE. In some transitions, particularly the Be I 2650-A line, the non-LTE effects can be quite dramatic, changing the deduced abundances by a factor of 4. Based on the non-LTE calculations and Copernicus observations of other stars, it is found that a solar spectral feature at 2650 A, previously identified by numerous investigators as a Be I line, cannot be produced by Be I. Non-LTE effects on the Be II 3131-A line, used for most Be abundance determinations in the literature, are small by comparison.

Shipman, H. L.↗
NASA NTRS1979

Studies of interstellar absorption lines with IUE

The paper deals with a survey of interstellar absorption lines in the wavelength region from 1150 to 3200 A toward 25 stars. The spectra of 10 of these stars show very strong narrow absorption lines of Si IV and C IV. Lines of N V appear in eight directions. The N V lines can arise in the same gas that is responsible for the ubiquitous interstellar lines of O VI, observed previously with a Copernicus spectrometer, but the lines of Si IV and C IV must be formed in a cooler gas. The measured lines of Si IV and C IV can be produced by normal H II regions photoionized by the observed stars.

Black, J. H.↗
NASA NTRS1979

New observations of interstellar abundances and depletions of boron, vanadium, chromium, and cobalt

New observations of interstellar lines of boron, vanadium, chromium, and cobalt in the spectra of Zeta Oph and Xi Per have been obtained with the Copernicus satellite. Chromium has been detected for the first time toward a reddened star, and cobalt has been seen for the first time in any interstellar line of sight. New limits have been obtained for boron and vanadium. These new data, along with limits on scandium and other species from the literature, have been compared with models for the depletion process. No fully conclusive test of depletion models is yet possible, but the new data on boron appear to favor the hypothesis that the depletions are dominated by accretion of gas-phase particles onto grains, rather than being due to grain condensation under pressure equilibrium. The impact of these new data on the study of grain surface properties is described.

Snow, T. P., Jr.↗
NASA NTRS1980

Changes in the ultraviolet spectrum of the mass-losing Be star 59 Cygni

Observations of a few selected wavelength regions in the ultraviolet spectrum of the Be star 59 Cyg, obtained in 1975 November, are compared with the complete low-resolution Copernicus scan of the same star obtained in 1972 October. Changes in the spectrum between the two times are discussed and interpreted in terms of the two distinct shell episodes revealed by optical data. A wide range of ionization exists from Fe III to N V, with a range in radial velocity of approximately 1000 km/s. Changes in the Si III, Si IV, and N V absorption arising in the stellar wind show that the velocity structure of the wind may have changed, and that the ionization balance also was altered over the 3 year interim.

Marlborough, J. M.↗
NASA NTRS1980

Ultraviolet spectroscopy of the outer layers of stars

Ultraviolet observations of the extended atmospheres and circumstellar envelopes of early-type and cool stars are reviewed. UV spectra of OB stars have shown that mass loss occurs in virtually all these stars and in many Be stars, and the Copernicus satellite has also provided information on the physical conditions and variability of the winds. The winds have been interpreted in terms of hot coronal wind models, imperfect flow models and radiation pressure models, and estimates of mass loss ranging from 10 to the -10th to 9 x 10 to the -6th solar masses/year have been obtained. Further UV data of faint stars, additional wavelengths and time variability are required. Recent UV and X-ray experiments have detected stellar chromospheres, transition regions coronas and winds in cool stars. Semiempirical line-profile and line-flux models and purely theoretical atmospheric models have been constructed to explain chromosphere, corona and wind data, and future observations of the physical properties of stellar chromospheres, coronas and winds, terms in the energy balance equation, stellar activity and its long-term variability and atmospheric modifications due to the presence of companion stars are proposed for such missions as Spacelab.

Snow, T. P., Jr.↗
NASA NTRS1980

Detection of interstellar boron in front of kappa Orionus

The detection of interstellar boron in the direction of kappa Ori, obtained with the Copernicus satellite telescope by observing the B II 1362.46-A resonance line is reported. A B/H concentration ratio of (1.5 + or - 0.7) x 10 to the -10th (2 standard deviation error bar) is obtained. The main uncertainty lies in the determination of the continuum of the star in that wavelength region, dominated by a broad stellar absorption feature. The value inferred for B/H in the interstellar medium is consistent with the solar and stellar values, believed to be the galactic value, and with the theory of the production of B by cosmic rays in the interstellar medium.

Meneguzzi, M.↗
NASA NTRS1980

A search for the reported Ti II 3080 multiplet emission in late-type stars

Gurzadyan (1975), using a low-resolution objective-prism spectrograph, has reported the presence of both the multiplet Ti II 3080 and the doublet Mg II 2800 simultaneously either in emission or in absorption in late-type stars. Using the high-resolution spectrometers onboard Copernicus and BUSS, it is found that stars which display Mg II 2800 strongly in emission do not have a corresponding emission feature at 3080.

Oegerle, W. R.↗
NASA NTRS1980

Evidence for the degenerate dwarf nature of Cygnus X-2

Observations of Cygnus X-2 using the Copernicus satellite have revealed a novel relationship between the spectral hardness and the intensity of this source in the 3-8 keV band. This behavior is very similar to that predicted for a spherically accreting nonmagnetic degenerate dwarf. The data, interpreted in terms of this model, determine solar mass, luminosity, and the distance for Cyg X-2; these parameters are at variance with the values derived from optical observations of the system. The implications of this discrepancy for the understanding of the source are examined.

Branduardi, G.↗
NASA NTRS1980

Simultaneous X-ray and optical observations of rapid variability in Scorpius X-1

Copernicus and SAS-3 observations of Sco X-1 during very active states show strong and rapid X-ray flickering with time scales as short as 20 sec. Simultaneous optical photometry reveals similar and remarkably well correlated flickering of lower amplitude. The level of correlation decreases when the X-ray source becomes fainter, but optical and X-ray fluxes, averaged over 1 min, are usually well correlated for B magnitudes less than 12.9. Cross-correlation analysis of the data during periods of high activity shows no really significant time delay between X-ray and optical features, although the cross-correlation function peaks systematically for positive lag values (optical following X-rays). The amplitude of the X-ray flickering exhibits a strong energy-dependence consistent with the well-known intensity versus spectral-hardness relation derived from previous observations. The highly correlated optical activity is interpreted as due to reprocessing of X-ray photons in the binary system.

Ilovaisky, S. A.↗
NASA NTRS1980

Mass loss from UW Canis Majoris

The present analysis is an application of the theory described by Lucy (1971) for the calculation of P Cygni resonance line profiles formed by isotropic and coherent scattering in spherically symmetric expanding circumstellar envelopes. Copernicus satellite measurements of resonance features in the FUV spectrum of the O 7 supergiant UW Canis Majoris (= HD 57060) are compared with theoretical P Cygni profiles. Grids of line profiles are computed using four free parameters which contain information about the velocity law, ionization equilibrium, temperature, and envelope density. Thus, with the assumption of a spherically symmetric steady flow, and of solar element abundances, the stellar mass loss rate and the electron temperature of the expanding shell can be derived. The mass flow is treated in a fully transonic way, i.e., the Sobolev approximation is applied.

Drechsel, H.↗
NASA NTRS1980

Radial velocity study of four southern RS CVn candidates and related field stars

Radial velocity variations are demonstrated for four southern RS CVn candidates: HD 39937, 101379, 155555, and 174429. The period of HD 155555 appears to have decreased by about one part in 100,000 over the past 18 yr. In addition, high-resolution observations of the Ca II H and K profiles and the Mg II 2800-A emission doublet are presented. These enhance the likelihood of these being RS CVn objects. Radial velocity data for 15 other late-type bright field stars are presented. Some of these were observed by Copernicus and may exhibit unusual chromospheres, while the rest lack radial velocity information as tabulated in the Bright Star Catalog. All velocity measures have been corrected to the IAU heliocentric system.

Stacy, J. G.↗
NASA NTRS1980

Mercury in a thin layer in HgMn stars - A test of a diffusion model

Lines of the first three states of ionization of mercury have been observed in Mu Leporis and Chi Lupi using the Copernicus satellite. Lines of Hg II and Hg III have been observed in Alpha Andromedae. There appears to be an absorption feature at every wavelength where there is expected to be a mercury line. The presence of all three states of ionization is likely in Mu Lep and Chi Lup. The relative equivalent widths of the lines of the various states of ionization do not depend on the effective temperature of the stars, in contradiction to what is expected if mercury were uniformly distributed in the atmosphere. It is, however, expected if mercury has been concentrated, by diffusion, in a thin layer, where the radiative forces just equal the gravitational forces on mercury. That mercury should be so concentrated is also required by the explanation of the mercury isotope anomaly proposed by Michaud, Reeves, and Charland.

Megessier, C.↗
NASA NTRS1980

Highly-ionized species in the interstellar medium

Interstellar absorption lines have been observed toward 25 stars with the International Ultraviolet Explorer satellite. Results are presented for observations of interstellar lines of C III, C IV, N V, Si III, and Si IV. Strong lines of Si IV or C IV are seen toward 11 stars. The strengths of these lines are inconsistent with their formation in the same hot gas responsible for the interstellar O IV lines observed with the Copernicus ultraviolet spectrometer. Comparison with simple models of the ionization structures of H II regions around hot stars suggests that the observed column densities of Si III, Si IV, and C IV are in harmony with those expected in normal photoionized nebulae. The line of sight to HD 93250, and O3 V star near Eta Carinae, passes through highly ionized gas that shows features spanning 250 km/s in radial velocity. Stellar wind velocities are presented for 21 of the stars observed in this survey of interstellar absorption lines.

Black, J. H.↗