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NASA NTRS1980

Significance of major and minor element variations in plagioclase in sodic ferrogabbro and breccia matrix in lunar highlands sample 67915

Attention is given to the significance of the results of a study of Ca, K, Ti, Fe, Mn, and Mg variations in plagioclase in highlands sample 67915,84. This polymict breccia from Outhouse Rock station 11 at the Apollo 16 site has been selected for study because it contains a wide variety of clast types, including a differentiated type-sodic ferrogabbro. It is found that the data on Ca, K, Ti, Fe, Mn, and Mg in plagioclase show no evidence of reaction between sodic ferrogabbro and breccia matrix clasts. Two groups of plagioclase compositions have been recognized in the breccia matrix. The data suggest that the prebreccia characteristics of plagioclase compositions have been preserved in 67915. Data on Mg/(Mg+FE) ratios suggest that the sodic ferrogabbro and the intermediate-Ca plagioclase clasts could be related to the Mg-rich plutonic rock suite and the high-Ca plagioclase clasts to the ferroan anorthosites.

Weiblen, P. W.↗
NASA NTRS1982

Effects of fractional crystallization and cumulus processes on mineral composition trends of some lunar and terrestrial rock series

A plot of Mg of mafic minerals versus An of plagioclase in cumulate rocks from various lunar and terrestrial rock series shows each series to have a distinct curvilinear trend. The slopes of these trends vary from nearly vertical in the case of lunar anorthosites and Mg-norites to nearly horizontal in the case of gabbros from the mid-Atlantic ridge. Calculations based upon known major element partitioning between mafic minerals, plagioclase and subalkaline basaltic liquids indicate that fractional crystallization coupled with cotectic accumulation of mafic minerals and plagioclase will produce mineral composition trends on the Mg versus An diagram with slopes greater than 1 for cases where An is approximately greater than Mg. Furthermore, fractional crystallization of basaltic magmas with alkali concentrations approaching zero will produce near vertical Mg versus An trends. Therefore, the steep slopes of the lunar rock series are consistent with relatively simple fractionation processes. The relatively flat slope of mineral compositions from gabbros collected from the mid-Atlantic ridge at 26 deg N is inconsistent with simple fractionation processes, and calculations show that periodic refilling of a fractionating magma chamber with picritic magma cannot simply explain this flat slope either.

Longhi, J.↗
NASA NTRS1983

Origin of lunar meteorite ALHA 81005 - Clues from the presence of terrae clasts and a very low-titanium mare basalt clast

Attention is given to the endogenous (or primary) lithologies of the lunar crust that can be inferred from the terrae clasts and to the significance of a fragment of very low titanium (VLT) mare basalt in thin section, ALHA 81005,9. Fragments of the norite and harzburgite have mineral compositions similar to that of ferroan anorthosite, and a clast of ferroan anorthosite has pyroxenes with lower molar Mg/(Mg+Fe) than in known pristine rocks. It is inferred that the Mg-suite protoliths for the clasts of intermediate composition are magnesian troctolites, spinel troctolites, and feldspathic lherzolites. Whereas clasts of these lithologies are not present in ALHA 81005,9, mineral fragments from them are. Based on the molar Mg/(Mg+Fe) ratio and Cr content of its pyroxenes, a single basaltic clast is determined to be of mare origin. The composition of its plagioclase and the molar Ti/(Ti+Cr) ratios of its pyroxenes suggest that the clast is a fragment of VLT mare basalt. It is noted that if this basalt is significantly younger than the last basin-forming impact event, which was approximately 3.9 x 10 to the 9th years ago, then its presence probably constrains the source crater for ALHA 81005 to be within a hundred kilometers of a VLT mare basalt flow.

Treiman, A. H.↗
NASA NTRS1985

HEAO 3 upper limits to the expected 1634 KeV line from SS 483

A model based on 24 Mg(1369) was developed as the source of the lines in which refractory grains in the jets, containing Mg and 0, are bombarded, by ambient protons in the local ISM. The narrowness of the features results because the recoil Mg nucleus is stopped in the grain before the 1369 keV excited state decays. A consequence of the 24 Mg interpretation is the expected appearance of other emission lines, due to 20 Ne and 20 Na, which are produced by proton bombardment of 24 Mg at the 33 MeV/nucleon energy corresponding to the velocity of the jets. These lines appear at rest energies of 1634 keV and 1636 keV, respectively, and should have essentially the same total flux as that emited at 1369 keV. The HEAO 3 data are examined to search for the 1634 keV (rest) emission. The observation and analysis, the results, and the implications for the understanding of SS 433 are discussed.

Wheaton, W. A.↗
NASA NTRS1986

Arousal and stability - The effects of five new sympathomimetic drugs suggest a new principle for the prevention of space motion sickness

Sympathomimetic agents are frequent components in antimotion-sickness drug combinations because of their usefulness in counteracting the sedation caused by stressful motion or resulting from the administration of other antimotion-sickness drugs. The noradrenergic neurochemistry of the brain's arousal-attentional systems prompted us to evaluate the efficacy of five new sympathomimetic drugs and to further define the role of arousal in susceptibility to motion. Subjects were orally administered methamphetamine (20 mg), phenmetrazine (25 mg), phentermine (37.5 mg), methylphenidate (20 mg), or pemoline (75 mg) 2 h prior to taking a Staircase Profile Test. All of the drugs increased resistance to stressful coriolis stimulation by 80-120 percent. Methylphenidate and pemoline showed fewer side effects. These findings, interpreted in conjunction with the documented inefficacy of most anticholinergic and antihistaminergic drugs tested to date, suggest that sympathomimetic drugs or a generalized state of arosusal can inhibit the development of motion sickness.

Kohl, R. L.↗
NASA NTRS1986

Atmospheric methane sources - Alaskan tundra bogs, an alpine fen, and a subarctic boreal marsh

Methane (CH4) flux measurements from Alaska tundra bogs, an alpine fen, and a subarctic boreal marsh were obtained at field sites ranging from Prudhoe Bay on the coast of the Arctic Ocean to the Alaskan Range south of Fairbanks during August 1984. In the tundra, average CH4 emission rates varied from 4.9 mg CH4 per sq m per day (moist tundra) to 119 mg CH4 per sq m per day (waterlogged tundra). Fluxes averaged 40 mg CH4 per sq m per day from wet tussock meadows in the Brooks Range and 289 mg Ch4 per sq m per day from an alpine fen in the Alaskan Range. The boreal marsh had an average CH4 emission rate of 106 mg CH4 per sq m per day. Significant emissions were detected in tundra areas where peat temperatures were as low as 4 C, and permafrost was only 25 cm below the ground surface. Emission rates from the 17 sites sampled were found to be logarithmically related to water levels at the sites. Extrapolation of the data to an estimate of the total annual CH4 emission from all arctic and boreal wetlands suggests that these ecosystems are a major source of atmospheric CH4 and could account for up to 23 percent of global CH4 emissions from wetlands.

Sebacher, D. I.↗
NASA NTRS1987

Size and metabolic properties of fibers in rat fast-twitch muscles after hindlimb suspension

The effect of hind-limb suspension (HS) on single fibers of the medial gastrocnemius (MG) and the tibialis anterior (TA) muscles were studied in rats. Fiber area and the activities of succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPD) were determined in tissue sections using an image analysis system. After 28 days of HS, the MG atrophied 28 percent, whereas the TA weight was maintained. Both dark- and light-ATPase fibers in the deep region of the MG had decreased cross-sectional areas following HS, with the atrophic response being twice as great in the light-ATPase fibers than in the dark-ATPase fibers. Following HS, mean SDH activities of both fiber types were significantly lower in the MG and TA than in the CON; by contrast, mean GPD activities were either maintained at the CON level or were higher in both MG and TA muscles. The data suggest an independence of the mechanisms determining the muscle fiber size and the metabolic adaptations associated with HS.

Roy, Roland R.↗
NASA NTRS1991

Development of a pressure based multigrid solution method for complex fluid flows

In order to reduce the computational difficulty associated with a single grid (SG) solution procedure, the multigrid (MG) technique was identified as a useful means for improving the convergence rate of iterative methods. A full MG full approximation storage (FMG/FAS) algorithm is used to solve the incompressible recirculating flow problems in complex geometries. The algorithm is implemented in conjunction with a pressure correction staggered grid type of technique using the curvilinear coordinates. In order to show the performance of the method, two flow configurations, one a square cavity and the other a channel, are used as test problems. Comparisons are made between the iterations, equivalent work units, and CPU time. Besides showing that the MG method can yield substantial speed-up with wide variations in Reynolds number, grid distributions, and geometry, issues such as the convergence characteristics of different grid levels, the choice of convection schemes, and the effectiveness of the basic iteration smoothers are studied. An adaptive grid scheme is also combined with the MG procedure to explore the effects of grid resolution on the MG convergence rate as well as the numerical accuracy.

Shyy, Wei↗
NASA NTRS1992

Terrestrial magma ocean and core segregation in the earth

According to the recent theories of formation of the earth, the outer layer of the proto-earth was molten and the terrestrial magma ocean was formed when its radius exceeded 3000 km. Core formation should have started in this magma ocean stage, since segregation of metallic iron occurs effectively by melting of the proto-earth. Therefore, interactions between magma, mantle minerals, and metallic iron in the magma ocean stage controlled the geochemistry of the mantle and core. We have studied the partitioning behaviors of elements into the silicate melt, high pressure minerals, and metallic iron under the deep upper mantle and lower mantle conditions. We employed the multi-anvil apparatus for preparing the equilibrating samples in the ranges from 16 to 27 GPa and 1700-2400 C. Both the electron probe microanalyzer (EPMA) and the Secondary Ion Mass spectrometer (SIMS) were used for analyzing the run products. We obtained the partition coefficients of various trace elements between majorite, Mg-perovskite, and liquid, and magnesiowustite, Mg-perovskite, and metallic iron. The examples of the partition coefficients of some key elements are summarized in figures, together with the previous data. We may be able to assess the origin of the mantle abundances of the elements such as transition metals by using the partitioning data obtained above. The mantle abundances of some transition metals expected by the core-mantle equilibrium under the lower mantle conditions cannot explain the observed abundance of some elements such as Mn and Ge in the mantle. Estimations of the densities of the ultrabasic magma Mg-perovskite at high pressure suggest existence of a density crossover in the deep lower mantle; flotation of Mg-perovskite occurs in the deep magma ocean under the lower mantle conditions. The observed depletion of some transition metals such as V, Cr, Mn, Fe, Co, and Ni in the mantle may be explained by the two stage process, the core-mantle equilibrium under the lower mantle conditions in the first stage, and subsequent downwards separation of the ultrabasic liquid (and magnesiowustite) and flotation of Mg-perovskite in the lower mantle.

Ohtani, Eiji↗
NASA NTRS1991

Emission-line and continuum properties of 92 bright QSOs - Luminosity dependence and differences between radio-selected and optically selected samples

The emission line and continuum properties of new spectra of 92 QSOs are investigated. A detailed deconvolution of the semiforbidden C III 1909 A blend reveals that the secondary feature is almost certainly Al III 1859 A. A study of the Mg II 2800 A emission-line profiles suggests that the broad 'shoulders' often observed are probably intrinsic to the Mg II emission line. It is shown that the QSOs discovered by slitless spectroscopic methods do not differ significantly from those discovered by UV excess surveys. Significant correlations with luminosity are found for W(Mg II), W(semiforbidden C III), I(C III)/I(Mg II), and the continuum ratio fv(1909 A)/fv(2800 A). All of the significant correlations are substantially stronger for a radio-selected subsample compared to a radio-quiet subsample. The C IV and semiforbidden C III emission lines each have a mean blueshift relative to Mg II of 450 km/s while semiforbidden C IV has a mean blueshift relative to semiforbidden C III of 200 km/s.

Steidel, Charles C.↗
NASA NTRS1993

Ignition and combustion of lunar propellants

The ignition and combustion of Al, Mg, and Al/Mg alloy particles in 99 percent O2/1 percent N2 mixtures is investigated at high temperatures and pressures for rocket engine applications. The 20 micron particles contain 0, 5, 10, 20, 40, 60, 80, and 100 weight percent Mg alloyed with Al, and are ignited in oxygen using the reflected shock in a shock tube near the endwall. Using this technique, the ignition delay and combustion times of the particles are measured at temperatures up to 3250 K as a function of Mg content for oxygen pressures of 8.5, 17, and 34 atm. An ignition model is developed which employs a simple lumped capacitance energy equation and temperature and pressure dependent particle and gas properties. Good agreement is achieved between the measured and predicted trends in the ignition delay times. For the particles investigated, the contribution of heterogeneous reaction to the heating of the particle is found to be significant at lower temperatures, but may be neglected as gas temperatures above 3000 K. As little as 10 percent Mg reduces the ignition delay time substantially at all pressures tested. The particle ignition delay times decrease with increasing Mg content, and this reduction becomes less pronounced as oxidizer temperature and pressure are increased.

Burton, Rodney L.↗
NASA NTRS1995

Probing the galactic disk and halo. 2: Hot interstellar gas toward the inner galaxy star HD 156359

We present Goddard High Resolution Spectrograph intermediate-resolution measurements of the 1233-1256 A spectral region of HD 156396, a halo star at l = 328.7 deg, b = -14.5 deg in the inner Galaxy with a line-of sight distance of 11.1 kpc and a z-distance of -2.8 kpc. The data have a resolution of 18 km/s Full Width at Half Maximum (FWHM) and a signal-to-noise ratio of approximately 50:1. We detect interstellar lines of Mg II, S II, S II, Ge II, and N V and determine log N/(Mg II) = 15.78 +0.25, -0.27, log N(Si II) greater than 13.70, log N(S II) greater than 15.76, log N(Ge II) = 12.20 +0.09,-0.11, and log N(N v) = 14.06 +/- 0.02. Assuming solar reference abundances, the diffuse clouds containing Mg, S, and Ge along the sight line have average logarithmic depletions D(Mg) = -0.6 +/- 0.3 dex, D(S) greater than -0.2 dex, and D(Ge) = -0.2 +/- 0.2 dex. The Mg and Ge depletions are approximately 2 times smaller than is typical of diffuse clouds in the solar vicinity. Galactic rotational modeling of the N v profiles indicates that the highly ionized gas traced by this ion has a scale height of approximately 1 kpc if gas at large z-distances corotates with the underlying disk gas. Rotational modeling of the Si iv and C iv profiles measured by the IUE satellite yields similar scale height estimates. The scale height results contrast with previous studies of highly ionized gas in the outer Milky Way that reveal a more extended gas distribtion with h approximately equals 3-4 kpc. We detect a high-velocity feature in N v and Si II v(sub LSR) approximately equals + 125 km/s) that is probably created in an interface between warm and hot gas.

Sembach, Kenneth R.↗
NASA NTRS1995

A multiparametric analysis of the Einstein sample of early-type galaxies. 2: Galaxy formation history and properties of the interstellar medium

We have conducted bivariate and multivariate statistical analysis of data measuring the integrated luminosity, shape, and potential depth of the Einstein sample of early-type galaxies (presented by Fabbiano et al. 1992). We find significant correlations between the X-ray properties and the axial ratios (a/b) of our sample, such that the roundest systems tend to have the highest L(sub x) and L(sub x)/L(sub B). The most radio-loud objects are also the roundest. We confirm the assertion of Bender et al. (1989) that galaxies with high L(sub x) are boxy (have negative a(sub 4)). Both a/b and a(sub 4) are correlated with L(sub B), but not with IRAS 12 um and 100 um luminosities. There are strong correlations between L(sub x), Mg(sub 2), and sigma(sub nu) in the sense that those systems with the deepest potential wells have the highest L(sub x) and Mg(sub 2). Thus the depth of the potential well appears to govern both the ability to reatin an ISM at the present epoch and to retain the enriched ejecta of early star formation bursts. Both L(sub x)/L(sub B) and L(sub 6) (the 6 cm radio luminosity) show threshold effects with sigma(sub nu) exhibiting sharp increases at log sigma(sub nu) approximately = 2.2. Finally, there is clearly an interrelationship between the various stellar and structural parameters: The scatter in the bivariate relationships between the shape parameters (a/b and a(sub 4)) and the depth parameter sigma(sub nu) is a function of abundance in the sense that, for a given a(sub 4) or a/b, the systems with the highest sigma(sub nu) also have the highest Mg(sub 2). Furthermore, for a constant sigma(sun nu), disky galaxies tend to have higher Mg(sub 2) than boxy ones. Alternatively, for a given abundance, boxy ellipticals tend to be more massive than disky ellipticals. One possibility is that early-type galaxies of a given mass, originating from mergers (boxy ellipticals), have lower abundances than 'primordial' (disky) early-type galaxies. Another is that disky inner isophotes are due not to primordial dissipation collapse, but to either the self-gravitating inner disks of captured spirals or the dissipational collapse of new disk structures from the premerger ISM. The high measured nuclear Mg(sub 2) values would thus be due to enrichment from secondary bursts of star formation triggered by the merging event.

Eskridge, Paul B.↗
NASA NTRS1994

Interactive effects of growth hormone and exercise on muscle mass in suspended rats

Measures to attenuate muscle atrophy in rats in response to simulated microgravity (hindlimb suspension (HS)) have been only partially successful. In the present study, hypophysectomized rats were in HS for 7 days, and the effects of recombinant human growth hormone (GH), exercise (Ex), or GH+Ex on the weights, protein concentrations, and fiber cross-sectional areas (CSAs) of hindlimb muscles were determined. The weights of four extensor muscles, i.e., the soleus (Sol), medial (MG) and lateral (LG) gastrocnemius, and plantaris (Plt), and one adductor, i.e., the adductor longus (AL), were decreased by 10-22% after HS. Fiber CSAs were decreased by 34% in the Sol and by 1 17% in the MG after HS. In contrast, two flexors, i.e., the tibialis anterior (TA) and extensor digitorum longus (EDL), did not atrophy. In HS rats, GH treatment alone maintained the weights of the fast extensors (MG, LG, Plt) and flexors (TA, EDL) at or above those of control rats. This effect was not observed in the slow extensor (Sol) or AL. Exercise had no significant effect on the weight of any muscle in HS rats. A combination of GH and Ex treatments yielded a significant increase in the weights of the fast extensors and in the CSA of both fast and slow fibers of the MG and significantly increased Sol weight and CSA of the slow fibers of the Sol. The AL was not responsive to either GH or Ex treatments. Protein concentrations of the Sol and MG were higher only in the Sol of Ex and GH+Ex rats. These results suggest that while GH treatment or intermittent high intensity exercise alone have a minimal effect in maintaining the mass of unloaded muscle, there is a strong interactive effect of these two treatments.

Grindeland, Richard E.↗
NASA NTRS1992

Prostaglandin E2 Prevents Ovariectomy-Induced Cancellous Bone Loss in Rats

The object of this study was to determine whether prostaglandin E2, (PGE2) can prevent ovariectomy induced cancellous bone loss. Thirty-five 3-month-old female Sprague-Dawley rats were divided into two groups. The rats in the first group were ovariectomized (OVX) while the others received sham operation (sham-OVX). The OVX group was further divided into three treatment groups. The daily doses for the three groups were 0,1 and 6 mg PGE2/kg for 90 days. Bone histomorphometric analyses were performed on double-fluorescent-labeled undecalcified proximal tibial metaphysis (PTM). We confirmed that OVX induces massive cancellous bone loss (-80%) and a higher bone turnover (+143%). The new findings from the present study demonstrate that bone loss due to ovarian hormone deficiency can be prevented by a low-dose (1 mg) daily administration of PGE2. Furthermore, a higher-dose (6 mg) daily administration of PGE2 not only prevents bone loss but also adds extra bone to the proximal tibial metaphyses. PGE, at the 1-mg dose level significantly increased trabecular bone area, trabecular width, trabecular node density, density of node to node, ratio of node to free end, and thus significantly decreased trabecular separation from OVX controls. At this dose level, these same parameters did not differ significantly from sham-OVX controls. However, at the 6-mg dose level PGE2, there were significant increases in trabecular bone area, trabecular width, trabecular node density, density of node to node, and ratio of node to free end, while there was significant decrease in trabecular separation from both OVX and sham-operated controls. The changes in indices of trabecular bone microanatomical structure indicated that PGE2 prevented bone loss as well as the disconnection of existing trabeculae. In summary, PGE2, administration to OVX rats decreased bone turnover and increased bone formation parameters resulting in a positive bone balance that prevented bone loss (in both lower and higher doses) and added extra bone to metaphyses of OVX rats (in higher dose). These findings support the strategy of the use of bone stimulation agents in the prevention of estrogen depletion bone loss (postmenopausal osteoporosis).

Ke, Hua Zhu↗
NASA NTRS1996

Short-Term Chromospheric Variability in alpha Tauri (K5 III): Results from IUE Time Series Observations

We evaluate time series observations of chromospheric lines (Mg II, Mg I, and C II) for the K giant alpha Tau obtained using the IUE LWP camera at high dispersion. These observations cover a time span of about 2 weeks in 1994 February-March and were designed to resolve variations occurring within hours, days, and weeks. We consider the observational results in relation to theoretical acoustic heating models, motivated by the fact that alpha Tau may exhibit a basal (i.e., minimum) level of chromospheric activity. The data reveal flux variations between the extremes of 8% in Mg II h+k and 15% in each emission component. These variations occur on timescales as short as 8 hr but not on timescales longer than approx.3 days. For the h and k components, flux variations occurring on a timescale as short as 1.5 hr are also found. These changes are often not correlated (and are sometimes even anticorrelated), leading to remarkable differences in the h/k ratios. We argue that these results are consistent with the presence of strong acoustic shocks, which can lead to variable Mg II line emission when only a small number of strong shocks are propagating through the atmosphere. We deduce the electron density in the C II lambda 2325 line formation region to be log(base e) of N. approx. equals 9.0, in agreement with previous studies. Our data provide evidence that the Mg II basal flux limit for K giants might be a factor of 4 higher than suggested by Rutten et al.

Cuntz, Manfred↗
NASA NTRS1996

AB Initio Characterization of MgCCH, MgCCH(+), and MgC2, and Pathways to their Formation in the Interstellar Medium

A study of Mg-bearing compounds has been performed in order to determine molecular properties which are critical for planning new astronomical searches and laboratory studies. The primary focus of the work is on MgCCH, MgCCH(+), and the isomers of MgC2. Only MgCCH has been identified in laboratory studies. Additional calculations have been carried out on MgH, MgNC, MgCN, and their cations in an effort to evaluate pathways to the formation of MgCCH and MgCCH(+) in the InterStellar Medium (ISM) or in circumstellar envelopes. Correlated ab initio methods and correlation-consistent basis sets have been employed. Properties including structures, rotational constants, dipole moments, and harmonic frequencies are reported. A transition state between linear MgCC and cyclic MgC2 has been characterized and was found to yield a minimal barrier (approx. 0.5 kcal/mole), indicating easy interconversion to the cyclic form. Direct reactions in the ISM between Mg or Mg(+) and HCCH are precluded by energetic considerations, but a number of ion- molecule or neutral-neutral exchange reactions between CCH and various Mg-containing species offer plausible pathways to MgCCH or MgCCH(+). Weakly bound MgH may react with CCH to form MgCCH, but MgH has not been detected. Both MgNC and MgCN have been observed, but reactions with CCH are slightly endothermic by 1-3 kcal/mole. Although MgH(+), MgNC(+), and MgCN(+) have not been detected, their reactions with CCH to form MgCCH(+) are all exothermic. With only a small barrier separating linear MgCC and cyclic MgC2, the dissociative recombination of MgCCH(+) with an electron is expected to yield cyclic MgC2, and regenerate Mg and CCH. New astronomical searches for MgCCH, MgCCH(+), cyclic MgC2, MgNC(+), and MgCN(+) will provide further insight into organo-magnesium astrochemistry.

Woon, David E.↗
NASA NTRS1996

The alpha Centauri Line of Sight: D/H Ratio, Physical Properties of Local Interstellar Gas, and Measurement of Heated Hydrogen (The 'Hydrogen Wall') Near the Heliopause

We analyze high-resolution spectra of the nearby (1.34 pc) stars alpha Cen A (G2 V) and alpha Cen B (K1 V), which were obtained with the Goddard High Resolution Spectrograph on the Hubble Space Telescope. The observations consist of echelle spectra of the Mg II 2800 A and Fe II 2599 A resonance lines and the Lyman-alpha lines of hydrogen and deuterium. The interstellar gas has a velocity (v = - 18.0 +/- 0.2 km/s) consistent with the local flow vector proposed for this line of sight by Lailement & Berlin (1992). The temperature and nonthermal velocity inferred from the Fe II, Mg II, and D I line profiles are T = 5400 +/- 500 K and xi = 1.20 +/- 0.25 km/s, respectively. However, single-component fits to the H I Lyman-alpha lines yield a Doppler parameter (b(sub HI) = 11.80 km/s) that implies a significantly warmer temperature of 8350 K, and the velocity of the H I absorption (v = - 15.8 +/- 0.2 km/s) is redshifted by about 2.2 km/s with respect to the Fe II, Mg II, and D I lines. The one-component model of the interstellar gas suggests natural logarithm N base HI = 18.03 +/- 0.01 and D/H = (5.7 +/- 0.2) x 10(exp -6) . These parameters lead to a good fit to the observed spectra, but this model does not explain the higher temperature and redshift of H I relative to the other interstellar lines. The most sensible way to resolve the discrepancy between H(I) and the other lines is to add a second absorption component to the H(I) lines. This second component is hotter (T approx. equals 30,000 K), is redshifted relative to the primary component by 2-4 km/s, and has a column density too low to be detected in the Fe(II), Mg(II), and D(I) lines. We propose that the gas responsible for this component is located near the heliopause, consisting of the heated H I gas from the interstellar medium that is compressed by the solar wind. This so-called 'hydrogen wall' is predicted by recent multifluid gasdynamical models of the interstellar gas and solar wind interaction. Our data provide the first measurements of the temperature and column density of H(I) in the hydrogen wall. After considering the effects that a corresponding hydrogen wall around alpha Cen would have on our analysis, our best estimates for the parameters of the solar hydrogen wall are natural log N(sup (2))(H(I)) = 14.74 +/- 0.24, b(sup (2))(H(I)) = 21.9 +/- 1.7 km/s (corresponding to T = 29,000 +/- 5000 K), and v(sup (2))(H(I)) greater than -16km/s. Unfortunately, the existence of this heated H(I) reduces our ability to compute the H(I) column density of the interstellar medium accurately because, with slight alterations to our assumed stellar Lyman-alpha profiles, we discovered that acceptable two-component fits also exist with natural log N(H(I))approx. 17.6. We, therefore, quote large error bars for the H I column density along the alpha Cen line of sight, natural log N(H(I)) = 17.80 +/- 0.30. For this range in N(H(I)), n(H(I)) = 0.15 /cu.cm (+/- a factor of 2) and D/H = (0.5-1.9) x 10(exp -5). This is the first direct measurement of the H(I) density in a local cloud and allows us to predict the distance from the Sun to the edge of the local cloud along various lines of sight. This range in D/H is consistent with the value D/H = 1.6 x 10(exp -5) previously derived for the Capella and Procyon lines of sight. We cannot tell whether D/H ratio varies or is constant in the local interstellar medium, but we do find that the D(I)/Mg(II) ratio for the alpha Cen line of sight is about 4 times smaller than for the Capella and Procyon lines of sight. Therefore, either D/H or the Mg depletion varies significantly over distance scales of only a few parsecs.

Linsky, Jeffrey L.↗