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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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NASA NTRS1984

The origin of low-velocity absorption components in the Mg II resonance lines of hybrid-chromosphere stars

It is argued that the low-velocity absorption features seen in the Mg II resonance lines of seven confirmed and three probable hybrid-chromosphere stars are interstellar rather than circumstellar in origin. From a comparison of radial velocities based on all available spectra in the International Ultraviolet Explorer (IUE) archives with estimates of the interstellar velocity along each line of sight, a good correlation between the observed position of the low-velocity component and the predicted interstellar feature is found. It is also shown that previous arguments in favor of the circumstellar origin of the low-velocity absorption features are either incorrect or implausible. The conclusion of the present study may modify previously proposed models of hybrid star winds which have assumed a priori that both Mg II absorption components are circumstellar.

Drake, S. A.↗
NASA NTRS1984

On interstellar Fe X forbidden line absorption toward Cepheus OB2

A weak interstellar absorption line which can be identified as the forbidden line of Fe X 6375 A is observed in the spectrum of the A2 Ia star Nu Cep, which is a member of the Cepheus OB2 association. The equivalent width, width, and radial velocity of the line differ indistinguishably from those of similar absorption previously detected uniquely toward the O6f star Lambda Cep, another association member located at a projected distance of about 50 pc from Nu Cep. The absorption may reveal a particularly dense, low-latitude concentration of hot, foreground interstellar gas of the kind generally responsible for the observed soft X-ray background.

Hobbs, L. M.↗
NASA NTRS1985

Voyager 1 imaging and IRIS observations of Jovian methane absorption and thermal emission - Implications for cloud structure

Images from three filters of the Voyager 1 wide angle camera are used to measure the continuum reflectivity and spectral gradient near 6000 A and the 6190 A band methane/continuum ratio for a variety of cloud features in Jupiter's atmosphere. The dark barge features in the North Equatorial Belt have anomalously strong positive continuum spectral gradients suggesting unique composition. Methane absorption is shown at unprecedented spatial scales for the Great Red Spot and its immediate environment, for a dark barge feature in the North Equatorial Belt, and for two hot spot and plume regions in the North Equatorial Belt. Methane absorption and five micrometer emission are correlated in the vicinity of the Great Red Spot but are anticorrelated in one of the plume hot spot regions. Methane absorption and simultaneous maps of five micrometer brightness temperature are quantitatively compared to realistic cloud structure models which include multiple scattering at five micrometer as well as in the visible. Variability in H2 quadrupole lines are also investigated.

West, R. A.↗
NASA NTRS1985

Formation of the H-alpha absorption line in the chromospheres of cool stars

The theory of the formation of the H-alpha absorption line in the chromospheres of cool stars is discussed and a number of results are presented which demonstrate that observations of this line can provide valuable information on certain properties of stellar chromospheres. It is shown that the widespread existence of strong H-alpha absorption in cool stars indicates the equally widespread existence of stellar chromospheres. The calculations also reinforce the idea that the great widths of H-alpha absorption lines in late-type giant stars are due to nonthermal chromospheric velocity fields.

Cram, L. E.↗
NASA NTRS1985

O VIII resonant absorption in PKS 2155 - 304 - A hot wind

The broad X-ray absorption feature in PKS 2155 - 304 could be due to O VIII Ly-alpha resonant absorption in a wind with outflow speeds up to about 30,000 km/s. The properties of such a wind are calculated. A homogeneous, spherically symmetric wind would involve a mass flux of about a 1000 solar masses/year, but this estimate could be greatly reduced if the outflow were beamed, and/or the absorbing gas were clumped into small clouds. In the latter case, the O VIII absorption offers clues to the physical state of thermal material closer to the central energy source than the clouds which produce optical emission lines in quasars.

Krolik, J. H.↗
NASA NTRS1985

Low-frequency absorption of sound in air

Thirty sets of sound absorption measurements in air at a pressure of 1 atmosphere are presented at temperatures from 10 C to 50 C, relative humidities from 0 to 100 percent, and frequencies from 10 to 2500 Hz. The measurements were conducted by the method of free decay in a resonant tube having a length of 18.261 m and bore diameter of 0.152 m. Background measurements in a gas consisting of 89.5 percent N2 and 10.5 percent Ar, a mixture which has the same sound velocity as air, permitted the wall and structural losses of the tube to be separated from the constituent absorption, consisting of classical rotational and vibrational absorption, in the air samples. The data were used to evaluate the vibrational relaxation frequencies of N2 and/or O2 for each of the 30 sets of meteorological parameters. Over the full range of humidity, the measured relaxation frequencies of N2 in air lie between those specified by ANSI Standard S1.26-1978 and those measured earlier in binary N2H2O mixtures. The measured relaxation frequencies could be determined only at very low values of humidity, reveal a significant trend away from the ANSI standard, in agreement with a prior investigation.

Zuckerwar, A. J.↗
NASA NTRS1985

Laboratory evaluation and application of microwave absorption properties under simulated conditions for planetary atmospheres

Radio absorptivity data for planetary atmospheres obtained from spacecraft radio occultation experiments and Earth-based radio astronomical observations can be used to infer abundances of microwave absorbing atmospheric constituents in those atmospheres, as long as reliable information regarding the microwave absorbing properties of potential constituents is available. The use of theoretically-derived microwave absorption properties for such atmospheric constituents, or laboratory measurements of such properties under environmental conditions which are significantly different than those of the planetary atmosphere being studied, often lead to significant misinterpretation of available opacity data. Steffes and Eshleman showed that under environmental conditions corresponding to the middle atmosphere of Venus, the microwave absorption due to atmospheric SO2 was 50 percent greater than that calculated from Van Vleck-Weiskopff theory. Similarly, the opacity from gaseous H2SO4 was found to be a factor of 7 greater than theoretically predicted for conditions of the Venus middle atmosphere. The recognition of the need to make such measurements over a range of temperatures and pressures which correspond to the periapsis altitudes of radio occultation experiments, and over a range of frequencies which correspond to both radio occultation experiments and radio astronomical observations, has led to the development of a facility at Georgia Tech which is capable of making such measurements.

Steffes, P. G.↗
NASA NTRS1986

In situ stratospheric ozone measurements by long path UV absorption - Developments and interpretation

A high-sensitivity, in situ UV absorption ozone sensor has been developed for use in the stratosphere. The instrument couples 254-nm radiation from a low-pressure mercury discharge lamp into a 40-pass White cell to attain a high-sensitivity ozone absorption measurement. Preflight/postflight laboratory tests utilizing an ozone source coupled to a laboratory UV ozone photometer in a fast-flow system as well as in-flight diagnostics verify the successful operation of the instrument. Evidence is presented to verify that in situ UV absorption ozone photometers can measure stratospheric ozone with better than 3 percent precision and 5 percent accuracy, provided proper attention is given to both the thermal field surrounding the gondola and the ambient pressure measurements. Ozone data are compared with modeled profiles in the 28- to 40-km region. An assessment of the disagreement between observations and modeled profiles is given along with suggestions for future experiments designed to constrain photochemical models.

Weinstock, E. M.↗
NASA NTRS1986

Correlation of QSO absorption lines in universes dominated by cold dark matter

Theoretical predictions for the redshift correlations between QSO absorption-line systems are investigated in the context of 'cold dark matter' cosmological models. Particles in 'particle-mesh' N-body simulations are interpreted as absorbing clouds at epochs corresponding to mean redshifts, z, of 0.0, 1.25, and 3.0. The velocity correlation function for absorbing clouds is found by passing lines-of-sight through the systems and computing velocity differences for those particles which lie close to the lines. It depends strongly on z and Omega but only weakly, if at all, on the number density, diameter or mass of the clouds. Two interpretations are possible: (1) the heavy element absorption systems are associated with galaxies which are an unbiased sample of the mass distribution in an Omega(0) = 0.2 universe or (2) the Lyman-alpha absorbers are an unbiased sample of the mass in an Omega(0) = 1 universe and the heavy-element absorption systems, like galaxies, are more strongly clustered than the mass.

Salmon, J.↗
NASA NTRS1986

Moderate spectral resolution observations of 3 micron absorption features in highly obscured objects

The 3 micron absorption spectra of sources seen in or behind molecular clouds generally show a variety of absorption features. Three separate absorptions are used to explain these features. The cooled-grating array spectrometer (CGAS) at the NASA Infrared Telescope Facility was used to obtain spectra of the late-type mass-loss star OH 0739-12 and the protostars MonR2 IRS-2 and IRS-3 (solid circles). The differences between the spectra are discussed.

Smith, R. G.↗
NASA NTRS1986

OH radical measurements by optical absorption spectroscopy

The long path absorption spectroscopy (LPA) measurement of OH utilizes the strong UV absorption spectrum of the molecule with well resolved rotational lines around 308 nm. The light source consists of an Ar ion laser pumped CW dye laser, the output of which is frequency doubled to emit a spectrally smooth light profile of 0.1 nm FWHM at 308 nm. This is considerably broader than the sharp (0.0018 nm wide) absorption features of OH and also wider than the total spectral region (0.06 nm) scanned around the OH lines. For field measurements a Cassegrain-type telescope expands the small diameter of the original laser beam by a factor of 50 to about a 0.25-m diameter in order to reduce the divergence of the beam as well as its mean photon flux density, thus reducing the maximum self-generated OH concentration to 40,000 cu. cm. The light is passed into the open atmosphere and reflected at about 5 km distance resulting in a 10-km light path length. A telescope focuses the returning light onto the entrance slit of a monochromator the single exit slit of which is replaced by a mechanical scanning device operating at a scan repetition rate of 6.6 KHz. For a typical measurement (1h duration) some 20,000,000 scans are averaged, rendering the contribution of atmospheric turbulence to the spectral noise negligible.

Platt, U.↗
NASA NTRS1987

A method of predicting the energy-absorption capability of composite subfloor beams

A simple method of predicting the energy-absorption capability of composite subfloor beam structure was developed. The method is based upon the weighted sum of the energy-absorption capability of constituent elements of a subfloor beam. An empirical data base of energy absorption results from circular and square cross section tube specimens were used in the prediction capability. The procedure is applicable to a wide range of subfloor beam structure. The procedure was demonstrated on three subfloor beam concepts. Agreement between test and prediction was within seven percent for all three cases.

Farley, Gary L.↗
NASA NTRS1985

Absorption Cross-Sections of Sodium Diatomic Molecules

The absorption cross sections of sodium dimers were studied using a heat pipe over operating in the non-heat-pipe mode. Three wavelength regions were observed. They are in the red, the green-blue, and the near ultraviolet regions. The absorption cross section depends on the wavelength of the incident light. Representative peak values for the v"=0 progression in the red and green-blue regions are 2.59 A sup 2 (average value) and 11.77 A sup 2 (T sub ave=624 K). The value for the C greater than X transitions is several tenths A sup 2. The cross sections were measured from absorption spectra taken as a function of temperature.

Fong, Zeng-Shevan↗
NASA NTRS1987

Atlas of Absorption Lines from 0 to 17900 Cm (sup)-1

Plots of logarithm (base 10) of absorption line strength versus wavenumber from 0 to 17900/cm(sup)-1 are shown for the 28 atmospheric gases (H2O, CO2, O3, N2O, CO, CH4, O2, NO, SO2, NO2, NH3, HNO3, OH, HF, HCl, HBr, HI, ClO, OCS, H2CO, HOCl, N2, HCN, CH3Cl, H2O2, C2H2, C2H6, PH3), which appear in the 1986 Air Force Geophysics Laboratory high-resolution transmission molecular absorption data base (HITRAN) compilation, and for O(P-3), O-18 isotopic ozone, and HO2 from the 1984 JPL compilation in the 0- to 200/cm(sup)-1 region, and infrared solar CO lines at 4500 K. Also shown are plots of logarithm (base 10) of approximate infrared absorption cross sections of 11 heavy molecules versus wavenumber. The cross-section data cover 700 to 1800/cm(sup)-1 and are included as a separate data file in the 1986 HITRAN database.

Park, J. H.↗
NASA NTRS1986

Parameterization of near infrared absorption by atmospheric gases

An absorption coefficient (k) distribution model is presented for fast calculation of atmospheric transmittances based solely on essential data from line-by-line (LBL) calculations. The absorption at any site is summed over the spectra obtained by LBL calculations. Application of the scaling model is illustrated with sample calculations for 0.72 micron emissions and the 1.36 micron water vapor band. LBL absorption spectra are calculated for the pressure levels 260 mb, 400 mb and 1000 mb.

Ridgway, W. L.↗
NASA NTRS1986

Absorption cross section measurements of oxygen in the wavelength region 195-241 nm of the Herzberg continuum

The continuous absorption cross section of oxygen in the region 205-241 nm is studied as a function of path length and oxygen pressure. The technique used to study the continuous absorption cross section is described. Cross section measurements of oxygen in the wavelength region 193-205 nm obtained by Cheung et al. (1984) are applied in this experiment. The measured cross section is analyzed in terms of a Herzberg continuum and a pressure-dependent continuum. The total measured continuum cross section, the cross section involving two molecules of O2, and the Herzberg continuum absorption cross section values are calculated. It is observed that the Herzberg continuum cross section of oxygen values measured at 1 nm intervals in the region 195-241 nm, increase from 6.3 x 10 to the -24th sq cm at 195 nm to a maximum of 6.6 x 10 to the -24th sq cm at 201 nm and then decrease to 0.85 x 10 to the -24th sq cm at 241 nm. The Herzberg values are compared with data from previous investigations and the values correlate well.

Cheung, A. S.-C.↗
NASA NTRS1987

A method of predicting the energy-absorption capability of composite subfloor beams

A simple method of predicting the energy-absorption capability of composite subfloor beam structure has been developed. The method is based upon the weighted sum of the energy-absorption capability of constituent elements of a subfloor beam. An empirical data base of energy absorption results from circular and square cross section tube specimens were used in the prediction capability. The procedure is applicable to a wide range of subfloor beam structure. The procedure was demonstrated on three subfloor beam concepts. Agreement between test and prediction was within seven percent for all three cases.

Farley, Gary L.↗
NASA NTRS1987

Satellite sensing of aerosol absorption

A method is developed for remote sensing of aerosol absorption from satellite images of the earth's surface. The method is based on the measurement of the change in the upward radiances between a clear and a hazy day over a varying surface reflectance. For a zero change balance between brightening due to scattering and darkening due to absorption and scattering is reached. This balance is utilized via a radiative transfer model to derive the aerosol single-scattering albedo. A sensitivity study is performed, and the method is tested against laboratory measurements. It is suggested that for the case of haze introduced on top of an existing background aerosol and with a fair estimate of the scattering phase function, the error in the remotely sensed single-scattering albedo is in the range of 0.03-0.05. The main errors in the method arise from variations in the surface reflectance between the clear and the hazy days, uncertainty in the scattering phase function, and variation of the aerosol and gaseous absorption between these two days. If the satellite calibration varies with time, the measurements of single-scattering albedo can be substantially affected.

Kaufman, Yoram J.↗