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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Further high-resolution Na I observations of the local interstellar medium

High-resolution absorption measurements of the interstellar Na I D lines at 5890 A observed toward 27 early-type stars in the local interstellar medium (LISM) are presented. These results are combined with other high-resolution sodium measurements to map the space distribution of neutral sodium column density for some 118 stars out to less than 200 pc. These measurements indicate an upper limit to the neutral sodium column density of log N(Na I) less than 10.0/sq cm can be inferred out to a distance of 50 pc in most directions in the LISM. Also, the rarefield region of the Local Bubble may extend beyond 60 pc in at least 35 percent of the directions sampled thus far. Evidence is shown for a ubiquitous, comoving vector for neutral NaI gas clouds in the LISM which is in a different direction to LISM vectors previously reported for more ionized local gas clouds. A comparison of the measured sodium columns with those of interstellar Ca II for a sample of 12 stars within 95 pc results in a ratio of Na I/Ca II less than 0.5 for most stars. This value implies that there could be warm, neutral gas with T of about 12,500 K beyond 50 pc in the LISM.

Welsh, B. Y.↗
NASA NTRS1993

Maintaining the Na atmosphere of Mercury

The possible sources of the Na atmosphere of Mercury are calculatively studied. The likely structure, composition, and temperature of the planet's upper crust is examined along with the probable flux of Na from depth by grain boundary diffusion and by Knudsen flow. The creation of fresh regolith is considered along with mechanisms for supplying Na from the surface to the exosphere. The implications of the calculations for the probable abundances in the regolith are discussed.

Killen, Rosemary M.↗
NASA NTRS1993

Optical studies of interstellar material in low density regions of the Galaxy. I - A survey of interstellar Na I and Ca II absorption toward 57 distant stars

We present high-resolution spectra of the Na I D and Ca II K lines toward 57 late-O and early-B stars along extended (d greater than 1 kpc) low-density paths through the Milky Way disk and halo. The sight lines preferentially sample diffuse gas in the interstellar medium (ISM) along interarm, Galactic center, and high latitude directions. We measure equivalent widths, apparent column densities, and absorption component structure. The Ca II to Na I ratios presented as a function of velocity for each sight line exhibit variations due to elemental depletion, ionization, and density enhancements. Absorption along high latitude sight lines is kinematically simpler than it is along interarm and Galactic center sight lines. Galactic rotation noticeably broadens the absorption profiles of distant stars located in these latter directions. Along several sight lines, we see Ca II absorption at velocities corresponding to large distances (/z/ about 1 kpc) from the Galactic plane. The effects of differences in the Ca II and Na I scale heights and nonzero velocity dispersions are readily apparent in the data. Brief notes are given for several sight lines with interesting absorption properties.

Sembach, K. R.↗
NASA NTRS1994

Semi-volatiles at Mercury: Sodium (Na) and potassium (K)

Several lines of evidence now suggest that Mercury is a planet rich in moderately-volatile elements such as Na and K. Recent mid-infrared spectral observations of Mercury's equatorial and mid-latitude region near 120 degrees mercurian longitude indicate the presence of plagioclase feldspar. Spectra of Mercury's surface exhibit spectral activity similar to labradorite (plagioclase feldspar with NaAlSi3O8: 30-50 percent) and bytownite (NaAlSi3O8: 10-30 percent). These surface studies were stimulated by the relatively large abundance of Na and K observed in Mercury's atmosphere. An enhanced column of K is observed at the longitudes of Caloris Basin and of the antipodal terrain. Extreme heating at these 'hot' longitudes and severe fracturing suffered from the large impact event could lead to enhanced outgassing from surface or subsurface materials. Alternatively, sputtering from a surface enriched in K could be the source of the observed enhancement. Recent microwave measurements of Mercury also give indirect evidence of a mercurian regolith less FeO-rich than the Moon. An anomalously high index of refraction derived from the whole-disk integrated phase curve of Danjon may also be indicative of surface sulfides contributing to a regolith that is moderately volatile-rich. The recent exciting observations of radar-bright spots at high latitudes also indicate that a substance of high volume scattering, like ice, is present in shadowed regions. Other radar-bright spots have been seen at locations of Na enhancements on the atmosphere. All combined, these pieces of evidence point to a planet that is not severely depleted in volatiles or semi-volatiles.

Sprague, A.↗
NASA NTRS1994

The local distribution of Na I interstellar gas

We present high-resolution absorption measurements (lambda/Delta lambda approximately 75,000) of the interstellar Na I D lines at 5890 A toward 80 southern hemisphere early-type stars located in the local interstellar medium (LISM). Combining these results with other sodium measurements taken from the literature, we produce galactic maps of the distribution of neutral sodium column density for a total of 293 stars generally lying within approximately 250 pc of the Sun. These maps reveal the approximate shape of the mid-plane contours of the rarefied region of interstellar space termed the Local Bubble. Its shape is seen as highly asymmetric, with a radius ranging from 30 to 300 pc, and with an average radius of 60 pc. Similar plots of the Galactic mid-plane distribution of sources emitting extreme ultraviolet radiation show that they also trace out similar contours of the Local Bubble derived from Na I absorption measurements. We conclude that the Local Bubble absorption interface can be represented by a hydrogen column density, Nu(sub ETA) = 2 x 10(exp 19) cm(exp -2), which explains both the local distribution of Na I absorption and the observed galactic distribution of extreme ultraviolet sources. The derived mid-plane contours of the Bubble generally reproduce the large-scale features carved out in the interstellar medium by several nearby galactic shell structures.

Welsh, B. Y.↗
NASA NTRS1974

On the velocity dependence of the interstellar Na I/Ca II ratio

The correlation noted by Routly and Spitzer (1952) between the ratio of the column densities of interstellar Na I and Ca II and radial velocity in the spectra of 21 early-type stars is reinvestigated on the basis of more recent data for 64 stars. The original result is confirmed, and it is further demonstrated that the low values of Na I/Ca II are associated with large peculiar velocities relative to the local standard of rest. It is proposed that the bulk of the high-velocity components can be interpreted as old supernova remnants. A statistical analysis of the distribution with velocity of interstellar Ca II K lines observed by Adams (1949) in the directions of some 300 early-type stars is found to be consistent with this hypothesis.

Siluk, R. S.↗
NASA NTRS1974

Cosmogenic Al-26 and Na-22 in Luna-16 lunar regolith

The activities of cosmogenic isotopes Al-26 and Na-22 in two samples taken from different depths of the lunar regolith core returned by the Luna 16 automatic station were measured by scintillation gamma spectrometer. The measured activities, when recalculated to the time of sampling of the lunar surface material, are: Al-26 - 62 + or - 8 and 54 + or - 9; Na-22 - 42 + or - 8 and 48 + or - 9. Depthwise distributions of the activities of these isotopes in lunar rocks of different types indicate the presence of a considerable depth gradient of activity near the surface caused by the fall off in the fluxes of primary and secondary cosmic radiation. The absence of this gradient in the measured samples, along with data on the tracks and content of inert gases, as well as the granulometric characteristics of the regolith indicate that the surficial layer of the regolith at the sampling site underwent mixing.

Vinogradov, A. P.↗
NASA NTRS1975

Interstellar K I and Na I absorption lines near rho Ophiuchi

Results are reported for photoelectric interferometric scans of the interstellar K I (7699 A) and Na I D1 absorption lines toward rho Oph AB and omicron Sco in the complex of dark clouds near rho Oph. The scans are found to reveal a well-marked line multiplicity toward both stars. It is shown that the resolved components of the line profiles can provide a natural explanation for the difference between the radial velocity of the strongest atomic lines of Na I and Ca II and that of the much weaker molecular lines of CH(+), CH, and CN that was previously observed toward rho Oph. The less saturated 7699-A lines toward both stars yield K I column densities roughly consistent with the calculated interstellar reddening.

Hobbs, L. M.↗
NASA NTRS1975

Interstellar Na I and Ca II absorption in intercloud regions

The weak interstellar absorption lines of Na I, Ca II, and H I formed in the intercloud medium toward eight nearly unreddened stars are analyzed. Compared with the corresponding column densities within a standard cloud, the Na I/H column-density ratio is smaller by a factor probably in excess of 17, while the Ca II/H column-density ratio is about normal. These results imply that the local intercloud medium extensively contains low-density H I regions in which the temperature is at least about 2500 K and the depletion of calcium is less severe than in the clouds, by a factor of 20.

Hobbs, L. M.↗
NASA NTRS1980

Na + Xe collisions in the presence of two nonresonant lasers

Na+Xe collisions in the presence of two distinct laser fields (rhodamine 110 and Nd:glass) are investigated with reference to the response to nonresonant radiation of alkali metals collisionally perturbed by a buffer gas. It is found that the excited Na-asterisk (4s)+Xe state is produced with a measurable cross section due to two-photon absorption with field intensities as low as 10 MW/sq cm.

De Vries, P. L.↗
NASA NTRS1980

Volatile element chemistry in the solar nebula - Na, K, F, Cl, Br, and P

The results of the most extensive set to date of thermodynamic calculations on the equilibrium chemistry of several hundred compounds of the elements Na, K, F, Cl, Br, and P in a solar composition system are reported. Two extreme models of accretion are investigated. In one extreme complete chemical equilibrium between condensates and gases is maintained because the time scale for accretion is long compared to the time scale for cooling or dissipation of the nebula. Condensates formed in this homogeneous accretion model include several phases such as whitlockite, alkali feldspars, and apatite minerals which are found in chondrites. In the other extreme complete isolation of newly formed condensates from prior condensates and gases occurs due to a time scale for accretion that is short relative to the time required for nebular cooling or dissipation. The condensates produced in this heterogeneous accretion model include alkali sulfides, ammonium halides, and ammonium phosphates. None of these phases are found in chondrites. Available observations of the Na, K, F, Cl, Br, and P elemental abundances in the terrestrial planets are found to be compatible with the predictions of the homogeneous accretion model.

Fegley, B., Jr.↗
NASA NTRS1980

Computational study of alkali-metal-noble gas collisions in the presence of nonresonant lasers - Na + Xe + h/2/pi/omega sub 1 + h/2/pi/omega sub 2 system

The collision of Na with Xe in the presence of both the rhodamine-110 dye laser and the Nd-glass laser is investigated within a quantum-mechanical close-coupled formalism, utilizing ab initio potential curves and transition dipole matrix elements. Both one- and two-photon processes are investigated; the Na + Xe system is not asymptotically resonant with the radiation fields, so that these processes can only occur in the molecular collision region. The one-photon processes are found to have measurable cross sections at relatively low intensities; even the two-photon process has a significant section for field intensities as low as 10 MW/sq cm.

Devries, P. L.↗
NASA NTRS1981

Possible selective adsorption of enantiomers by Na-montmorillonite

Racemic amino acids including (D,L) alpha-alamine, (D,L) alpha-aminobutyric acid, (D,L) valine, and (D,L) norvaline were incubated with Na-montmorillonite at 100% CEC at three hydrogen ion concentrations, and amino acid adsorption was determined by ion exchange chromatography. Enantiomers were analyzed by gas chromatography. Differences in the quantities of D and L enantiomers in any of the fractions was no larger than a few percent. Although a large difference in the adsorption of the amino acid enantiomers was not observed, the analysis may indicate a small preferential adsorption (0.5-2%) of L-amino acids by Na-montmorillonite.

Friebele, E.↗
NASA NTRS1985

Quantitation of Na+, K+-atpase Enzymatic Activity in Tissues of the Mammalian Vestibular System

In order to quantify vestibular Na(+), K(+)-ATPase, a microassay technique was developed which is sufficiently sensitive to measure the enzymatic activity in tissue from a single animal. The assay was used to characterize ATPase in he vestibular apparatus of the Mongolian gerbil. The quantitative procedure employs NPP (5 mM) as synthetic enzyme substrate. The assay relies upon spectrophotometric measurement (410 nm) of nitrophenol (NP) released by enzymatic hydrolysis of the substrate. Product formation in the absence of ouabain reflects both specific (Na(+), K(+)-ATPase) and non-specific (Mg(++)-ATPase) enzymatic activity. By measuring the accumulation of reaction product (NP) at three-minute intervals during the course of incubation, it is found that the overall enzymatic reaction proceeds linearly for at least 45 minutes. It is therefore possible to determine two separate reaction rates from a single set of tissues. Initial results indicate that total activity amounts to 53.3 + or - 11.2 (S.E.M.) nmol/hr/mg dry tissue, of which approximately 20% is ouabain-sensitive.

Kerr, T. P.↗
NASA NTRS1985

Theoretical transition probabilities between the lowest 2S, 2P and 2D states of Na, K, Rb and Cs

Theoretical transition probabilities between the lowest 2S, 2P and 2D states of the alkali atoms Na through Cs have been computed using near Hartree-Fock quality Slater basis sets. The important core-valence correlation effects are incorporated explicitly by a configuration-interaction procedure. For Cs, the calculations were repeated using a Gaussian basis set so that relativistic effects could be incorporated through an effective core potential procedure. The best calculated electric quadrupole Einstein coefficients are Na(196.3/s), K(103.6/s), Rb(72.4/s) and Cs(19.7/s). Core-valence effects become increasingly important down the column, and reduce the quadrupole transition strengths to about the same degree as for the 2P-2S and 2D-2P dipole-allowed transitions. Relativistic effects increase the quadrupole moment of Cs, but less so than in Ba, presumably because the alkali 2D states are more diffuse.

Langhoff, S. R.↗
NASA NTRS1990

PHL 1226 and IC 1746 - A QSO-galaxy pair without Ca II or Na I absorption

Spectroscopic observations of the QSO PHL 1226 show no absorption lines at the expected wavelengths of Ca II H and K and Na I D absorption at the redshift of the nearby galaxy IC 1746 (z = 0.0176). The line of sight to PHL 1226 intercepts IC 1746 near the galaxy major axis at a projected separation from the galaxy nucleus of 28/h50 kpc. The 3-sigma upper limits on equivalent width attained in the spectra are 110 mA for Ca II H or K and 90 mA for either of the Na I D lines. The probable Ca II K line reported by Bergeron et al. (1988) is not confirmed.

Junkkarinen, Vesa T.↗
NASA NTRS1990

Ca II and Na I absorption in the QSO S4 0248 + 430 due to an intervening galaxy

Observations of the QSO S4 0248 + 430 and a nearby anonymous galaxy are presented. Two absorption components are found in both Ca II H and K and Na I D1 and D2 at z(a) = 0.0515, 0.0523. Column densities of log N(Ca II) = 13.29, 13.50, and log N(Na I) = 13.79, 14.18 are found for z(a) = 0.0515, 0.0523 absorption systems, respectively. The column density ratios imply considerable calcium depletion and disk-type absorbing gas. At least one and possibly both absorption components are produced by high-velocity gas. A broadband image of the field shows an asymmetrical armlike feature or possible tidal tail covering and extending past the position of the QSO. The presence of this extended feature and the apparent difference between the absorption velocities and galaxy rotation velocity suggest that the absorbing gas is not ordinary disk gas, but rather is a result of tidal disruption.

Womble, Donna S.↗
NASA NTRS1991

A theoretical study of Na(H2O)n(+) (n = 1-4)

The successive H2O binding energies of Na(H2O)n(+) are in excellent agreement with experiment and are rather insensitive to electron correlation since the bonding is predominantly electrostatic. A point-charge model shows that changes in the successive binding energies are due primarily to ligand-ligand repulsion. Vibrational frequencies and IR intensities are determined for Na(H2O)n(+) (n = 1-4) at the self-consistent-field and second-order Moller-Plesset levels of theory to facilitate experimental study of these ions.

Bauschlicher, Charles W., Jr.↗