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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 NTRS2018

G-band FMCW Radar for Humidity Profiling Inside Boundary Layer Clouds

We are developing a G-band FMCW radar for remote sensing of vertical water vapor profiles and total column water vapor. The radar utilizes the frequency-dependent absorption near the 183 GHz water absorption line to obtain a differential signal from which we can derive range-resolved humidity measurements. This proof-of-concept instrument will eventually be tested from an airborne platform. In this report, we discuss recent measurements and a humidity profile retrieval algorithm based on an absorption line shape fitting model

Monje, Raquel↗
NASA NTRS1990

Small-scale structure in the diffuse interstellar medium

The initial results of a study to probe the small-scale structure in the diffuse interstellar medium (ISM) through IUE and optical observations of interstellar absorption lines toward both components of resolvable binary stars is reported. The binaries (Kappa CrA, 57 Aql, 59 And, HR 1609/10, 19 Lyn, and Theta Ser) observed with IUE have projected linear separations ranging from 5700 to 700 Au. Except for Kappa CrA, the strengths of the interstellar absorption lines toward both components of these binaries agree to within 10 percent. In the case of Kappa CrA, the optically thin interstellar Mg I and Mn II lines are about 50 percent stronger toward Kappa-2 CrA than Kappa-1 CrA. Higher resolution observations of interstellar Ca II show that this difference is concentrated in the main interstellar component at V(LSR) = 9 + or - 2 km/s. Interestingly, this velocity corresponds to an intervening cloud that may be associated with the prominent Loop I shell in the local ISM. Given the separation (23 arcsec) and distance (120 pc) of Kappa CrA, the line strength variations indicate that this cloud has structure on scales of 2800 AU or less.

Meyer, David M.↗
NASA NTRS1992

Discovery of neutral hydrogen 21 centimeter absorption at redshift 0.25 toward PKS 1413+135

A strong H I 21-cm absorption line is identified toward PKS 1413+135 at the redshift of the host galaxy and argued to indicate that the IR-optical cutoff of the BL Lac object's spectrum is caused by extinction. The BL Lac object is shown to have strong neutral 21-cm absorption at the redshift range z = 0.24671 +/- 0.00001, and the implied H I column density is derived. The H I covering factor is assumed to be not more than 0.1, suggesting that a high degree of extinction exists in the galaxy. The host galaxy is theorized to be a spiral of type later than S0 based on the redshift of the H I absorption line and the host. The statistical and observational conclusions are found to support the theories of Stock et al. (1992) regarding the red spectrum of the object.

Carilli, C. L.↗
NASA NTRS2011

Analysis of Oxygen Spectral Lines in the 1.27 Micron Band for the ASCENDS Mission

The ASCENDS mission requires simultaneous laser remote sensing of CO2 and O2 in order to convert CO2 column number densities to average column CO2 mixing ratios (XCO2). As such, the CO2 column number density and the O2 column number density will be utilized to derive the average XCO2 column. NASA Langley Research Center, working with its partners, is developing O2 lidar technology in the 1.26-1.27- m band for surface pressure measurements. The O2 model optical depth calculation is very sensitive to knowledge of the transmitted wavelengths and to the choice of Voigt input parameters. Modeling using the HITRAN database is being carried out to establish the evolution of candidate O2 absorption lines as a function of atmospheric parameters such as altitude, temperature, and pressure. Preliminary results indicate limitations of the Voigt profile and the need to utilize more advanced models which take into account line mixing, line narrowing, and speed dependence. In this paper, we evaluate alternative lineshape models to establish the optimum lineshapes which better account for the variability of individual O2 absorption lines at various atmospheric conditions. The combination of our modeling efforts with accurate laboratory measurements is anticipated to aid in achieving the desired CO2 mixing ratio measurement accuracy requirement of for the ASCENDS mission.

Pliutau, Denis↗
NASA NTRS1982

Intensity changes in the UV spectrum of Beta Cephei

Fifty eight short wavelength International Ultraviolet Explorer spectra were taken over a 152 day period. Variations in the absorption lines of C IV (1550 A), Si IV (1393 and 1404 A) and N V (1239 and 1243 A) and a Cr III feature (1208 to 1211 A) were observed. A data reduction technique was developed in order to compare the changes in the equivalent widths of these absorption lines. Periods were determined by least squares fit to a sinusoid using several combinations of the data. In one case eighteen spectra for each ion taken at approximately one day intervals were used; in another, all 58 measurements of each were used; and in a third all measurements from all the ions wee combined. Using both variable metric and interactive algorithms it was determined that for all combinations mentioned a period of 6.10 + or - .06 days is the best fit to the vector of equivalent widths versus time. No other period, with or without the 6.10 day period removed from the data, was found. Analysis of the Cr III feature near 1210 A gives the same period as the others, but in antiphase.

Fahey, R. P.↗
NASA NTRS1985

The gaseous component of the disk around Beta Pictoris

Optical spectra of alpha Lyr, alpha PsA, and beta Pic have been obtained at a velocity resolution of 3 km/s. No circumstellar absorption lines of Ca II or Na I are detected toward alpha Lyr or alpha PsA at sensitive limits. In the favorable case of beta Pic, where the circumstellar disk imaged by Smith and Terrile (1984) is seen nearly edge-on, a strong, narrow, circumstellar Ca II K absorption line previously reported by Slettebak (1982) and weaker, still narrower circumstellar Na I D lines are detected. Negative results of high sensitivity also are obtained for the Ca I 4226 A and CH(+) 4232 A lines, along with upper limits on the Zn II 2026, 2062 A doublet from archival IUE spectra. Under assumptions which agree with other well-established observations of the gaseous abundances of calcium and zinc, the total gaseous column density of hydrogen along a radius of the circumstellar disk is between 10 to the 18th and 4 x 10 to the 20th/sq cm. Within the boundaries of the dust disk detected by Smith and Terrile (1984) the total gaseous mass then is less than about 2, or less than 1 percent of the mass of the planetary system. A simplified model of the density distribution in the gaseous disk yields a characteristic total density n(H) of about 100,000/cu cm, which exceeds that of all interplanetary gas at earth's position by a factor of about 10,000.

Hobbs, L. M.↗
NASA NTRS1978

The line-locking hypothesis, absorption by intervening galaxies, and the z = 1.95 peak in redshifts

The controversy over whether the absorption spectrum in QSOs is intrinsic or extrinsic is approached with attention to the peak of redshifts at z = 1.95. Also considered are the line-locking and the intervening galaxy hypotheses. The line locking hypothesis is based on observations that certain ratios found in absorption line QSOs are preferred, and leads inevitably to the conclusion that the absorption line systems are intrinsic. The intervening galaxy hypothesis is based on absorption redshifts resulting from given absorption cross-sections of galactic clusters and the intergalactic medium, and would lead to the theoretical conclusion that most QSOs show strong absorption, a conclusion which is not supported by empirical data. The 1.95 peak, on the other hand, is most probably an intrinsic property of QSOs. The peak is enhanced by redshift, and it is noted that both an emission and an absorption redshift peak are seen at 1.95.

Burbidge, G.↗
NASA NTRS2011

Analysis of Pulsed Airborne Lidar Measurements of Atmospheric CO2 Column Absorption from 3-13 km Altitudes

We have developed a pulsed lidar technique for measuring the tropospheric CO2 concentrations as a candidate for NASA's ASCENDS space mission [1]. It uses two pulsed laser transmitters allowing simultaneous measurement of a CO2 absorption line in the 1575 nm band, O2 extinction in the Oxygen A-band, surface height and backscatter profile. The lasers are precisely stepped in wavelength across the CO2 line and an O2 line region during the measurement. The direct detection receiver measures the energies of the laser echoes from the surface along with the range profile of scattering in the path. The column densities for the CO2 and O2 gases are estimated from the ratio of the on- and off-line signals via the integrated path differential absorption (IPDA) technique. The time of flight of the laser pulses is used to estimate the height of the scattering surface and to reject laser photons scattered in the atmosphere. We developed an airborne lidar to demonstrate an early version of the CO2 measurement from the NASA Glenn Lear-25 aircraft. The airborne lidar stepped the pulsed laser's wavelength across the selected CO2 line with 20 wavelength steps per scan. The line scan rate is 450 Hz, the laser pulse widths are 1 usec, and laser pulse energy is 24 uJ. The time resolved laser backscatter is collected by a 20 cm telescope, detected by a NIR photomultiplier and is recorded on every other reading by a photon counting system [2]. During August 2009 we made a series of 2.5 hour long flights and measured the atmospheric CO2 absorption and line shapes using the 1572.33 nm CO2 line. Measurements were made at stepped altitudes from 3-13 km over locations in the US, including the SGP ARM site in Oklahoma, central Illinois, north-eastern North Carolina, and over the Chesapeake Bay and the eastern shore of Virginia. Although the received signal energies were weaker than expected for ASCENDS, clear CO2 line shapes were observed at all altitudes, and some measurements were made through thin clouds. The Oklahoma and east coast flights were coordinated with a LaRC/ITT CO2 lidar on the LaRC UC-12 aircraft, and in-situ measurements were made using its CO2 sensor and radiosondes. We have conducted an analysis of the ranging and IPDA lidar measurements from these four flights. Most flights had 5-6 altitude steps with 200-300 seconds of recorded measurements per step. We used a cross-correlation approach to process the laser echo records. This was used to estimate the range to the scattering surface, to define the edges of the laser pulses and to determine echo pulse energy at each wavelength. We used a minimum mean square approach to fit an instrument response function and to solve for the best-fit CO2 absorption line shape. We then calculated the differential optical depth (DOD) of the fitted CO2 line. We computed its statistics at the various altitude steps, and compare them to the DODs calculated from spectroscopy based on HITRAN 2008 and the column conditions calculated from the airborne in-situ readings. The results show the lidar and in-situ measurements have very similar DOD change with altitude and greater than 10 segments per flight where the scatter in the lidar measurements are less than or equal to 1ppm. We also present the results from subsequent CO2 column absorption measurements, which were made with stronger detected signals during three flights on the NASA DC-8 over the southwestern US in during July 2010.

Abshire, James B.↗
DOE OSTI2015

DIFFUSE ATOMIC AND MOLECULAR GAS IN THE INTERSTELLAR MEDIUM OF M82 TOWARD SN 2014J

We present a comprehensive analysis of interstellar absorption lines seen in moderately high resolution, high signal-to-noise ratio optical spectra of SN 2014J in M82. Our observations were acquired over the course of six nights, covering the period from ∼6 days before to ∼30 days after the supernova reached its maximum B-band brightness. We examine complex absorption from Na I, Ca II, K I, Ca I, CH{sup +}, CH, and CN, arising primarily from diffuse gas in the interstellar medium (ISM) of M82. We detect Li I absorption over a range in velocity consistent with that exhibited by the strongest Na I and K I components associated with M82; this is the first detection of interstellar Li in a galaxy outside of the Local Group. There are no significant temporal variations in the absorption-line profiles over the 37 days sampled by our observations. The relative abundances of the various interstellar species detected reveal that the ISM of M82 probed by SN 2014J consists of a mixture of diffuse atomic and molecular clouds characterized by a wide range of physical/environmental conditions. Decreasing N(Na I)/N(Ca II) ratios and increasing N(Ca I)/N(K I) ratios with increasing velocity are indicative of reduced depletion in the higher-velocity material. Significant component-to-component scatter in the N(Na I)/N(Ca II) and N(Ca I)/N(Ca II) ratios may be due to variations in the local ionization conditions. An apparent anti-correlation between the N(CH{sup +})/N(CH) and N(Ca I)/N(Ca II) ratios can be understood in terms of an opposite dependence on gas density and radiation field strength, while the overall high CH{sup +} abundance may be indicative of enhanced turbulence in the ISM of M82. The Li abundance also seems to be enhanced in M82, which supports the conclusions of recent gamma-ray emission studies that the cosmic-ray acceleration processes are greatly enhanced in this starburst galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Computational Modeling of Exciton-Bath Hamiltonians for Light Harvesting 2 and Light Harvesting 3 Complexes of Purple Photosynthetic Bacteria at Room Temperature

Light harvesting 2 (LH2) complex is the primary component of the photosynthetic unit of purple bacteria that is responsible for harvesting and relaying excitons. The electronic absorption line shape of LH2 contains two major bands at 800 and 850 nm wavelength regions. Under low light conditions, some species of purple bacteria replace LH2 with light harvesting 3 (LH3), a variant form with almost the same structure as the former but with distinctively different spectral features. The major difference between the absorption line shapes of LH2 and LH3 is the shift of the 850 nm band of the former to a new 820 nm region. The microscopic origin of this difference has been the subject of some theoretical/computational investigations. However, the genuine molecular level source of such a difference is not clearly understood yet. This work reports a comprehensive computational study of LH2 and LH3 complexes so as to clarify different molecular level features of LH2 and LH3 complexes and to construct simple exciton-bath models with a common form. All-atomistic molecular dynamics simulations of both LH2 and LH3 complexes provide detailed molecular level structural differences of bacteriochlorophylls (BChls) in the two complexes, in particular, in their patterns of hydrogen bonding (HB) and torsional angles of the acetyl group. Time-dependent density functional theory calculation of the excitation energies of BChls for structures sampled from the MD simulations suggests that the observed differences in the HB and torsional angles cannot fully account for the experimentally observed spectral shift of LH3. Potential sources that can explain the actual spectral shift of LH3 are discussed, and their magnitudes are assessed through fitting of experimental line shapes. Furthermore, these results demonstrate the feasibility of developing simple exciton-bath models for both LH2 and LH3, which can be employed for large-scale exciton quantum dynamics in their aggregates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2010

Fiber-Coupled Planar Light-Wave Circuit for Seed Laser Control in High Spectral Resolution Lidar Systems

Precise laser remote sensing of aerosol extinction and backscatter in the atmosphere requires a high-power, pulsed, frequency doubled Nd:YAG laser that is wavelength- stabilized to a narrow absorption line such as found in iodine vapor. One method for precise wavelength control is to injection seed the Nd:YAG laser with a low-power CW laser that is stabilized by frequency converting a fraction of the beam to 532 nm, and to actively frequency-lock it to an iodine vapor absorption line. While the feasibility of this approach has been demonstrated using bulk optics in NASA Langley s Airborne High Spectral Resolution Lidar (HSRL) program, an ideal, lower cost solution is to develop an all-waveguide, frequency-locked seed laser in a compact, robust package that will withstand the temperature, shock, and vibration levels associated with airborne and space-based remote sensing platforms. A key technology leading to this miniaturization is the integration of an efficient waveguide frequency doubling element, and a low-voltage phase modulation element into a single, monolithic, planar light-wave circuit (PLC). The PLC concept advances NASA's future lidar systems due to its compact, efficient and reliable design, thus enabling use on small aircraft and satellites. The immediate application for this technology is targeted for NASA Langley's HSRL system for aerosol and cloud characterization. This Phase I effort proposes the development of a potassium titanyl phosphate (KTP) waveguide phase modulator for future integration into a PLC. For this innovation, the proposed device is the integration of a waveguide-based frequency doubler and phase modulator in a single, fiber pigtail device that will be capable of efficient second harmonic generation of 1,064-nm light and subsequent phase modulation of the 532 nm light at 250 MHz, providing a properly spectrally formatted beam for HSRL s seed laser locking system. Fabrication of the integrated PLC chip for NASA Langley, planned for the Phase II effort, will require full integration and optimization of the waveguide components (SHG waveguide, splitters, and phase modulator) onto a single, monolithic device. The PLC will greatly reduce the size and weight, improve electrical- to-optical efficiency, and significantly reduce the cost of NASA Langley s current stabilized HSRL seed laser system built around a commercial off-the-shelf seed laser that is free-space coupled to a bulk doubler and bulk phase modulator.

Cook, Anthony↗
NASA NTRS2013

BD-22deg3467, a DAO-type Star Exciting the Nebula Abell 35

Spectral analyses of hot, compact stars with non-local thermodynamical equilibrium (NLTE) model-atmosphere techniques allow the precise determination of photospheric parameters such as the effective temperature (T(sub eff)), the surface gravity (log g), and the chemical composition. The derived photospheric metal abundances are crucial constraints for stellar evolutionary theory. Aims. Previous spectral analyses of the exciting star of the nebula A35, BD-22deg3467, were based on He+C+N+O+Si+Fe models only. For our analysis, we use state-of-the-art fully metal-line blanketed NLTE model atmospheres that consider opacities of 23 elements from hydrogen to nickel. We aim to identify all observed lines in the ultraviolet (UV) spectrum of BD-22deg3467 and to determine the abundances of the respective species precisely. Methods. For the analysis of high-resolution and high signal-to-noise ratio (S/N) far-ultraviolet (FUSE) and UV (HST/STIS) observations, we combined stellar-atmosphere models and interstellar line-absorption models to fully reproduce the entire observed UV spectrum. Results. The best agreement with the UV observation of BD-22deg3467 is achieved at T(sub eff) = 80 +/- 10 kK and log g = 7.2 +/- 0.3. While T(sub eff) of previous analyses is verified, log g is significantly lower. We re-analyzed lines of silicon and iron (1/100 and about solar abundances, respectively) and for the first time in this star identified argon, chromium, manganese, cobalt, and nickel and determined abundances of 12, 70, 35, 150, and 5 times solar, respectively. Our results partially agree with predictions of diffusion models for DA-type white dwarfs. A combination of photospheric and interstellar line-absorption models reproduces more than 90% of the observed absorption features. The stellar mass is M approx. 0.48 Solar Mass. Conclusions. BD.22.3467 may not have been massive enough to ascend the asymptotic giant branch and may have evolved directly from the extended horizontal branch to the white dwarf state. This would explain why it is not surrounded by a planetary nebula. However, the star, ionizes the ambient interstellar matter, mimicking a planetary nebula.

Ziegler, M.↗
DOE OSTI2016

The Lyman continuum escape fraction of the cosmic horseshoe: a test of indirect estimates

High-redshift star-forming galaxies are likely responsible for the reionization of the universe, yet direct detection of their escaping ionizing (Lyman continuum [LyC]) photons has proven to be extremely challenging. In this study, we search for escaping LyC of the Cosmic Horseshoe, a gravitationally lensed, star-forming galaxy at z = 2.38 with a large magnification of ∼24. Transmission at wavelengths of low-ionization interstellar absorption lines in the rest-frame ultraviolet suggests a patchy, partially transparent interstellar medium. This makes it an ideal candidate for direct detection of the LyC. We obtained a 10-orbit Hubble near-UV image using the Wide Field Camera 3 (WFC3)/UVIS F275W filter that probes wavelengths just below the Lyman limit at the redshift of the Horseshoe in an attempt to detect escaping LyC radiation. After fully accounting for the uncertainties in the opacity of the intergalactic medium (IGM) and accounting for the charge transfer inefficiency in the WFC3 CCDs, we find a 3σ upper limit for the relative escape fraction of f{sub esc,rel}<0.08. This value is a factor of five lower than the value (0.4) predicted by the 40% transmission in the low-ion absorption lines. Though possible, it is unlikely that the nondetection is due to a high-opacity line of sight through the IGM (<20% chance). We discuss several possible causes for the discrepancy between the escape fraction and the covering fraction and consider the implications for future attempts at both direct LyC detection and indirect estimates of the escape fraction.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

Metal abundances of RR Lyrae stars in galactic globular clusters

Results are reported for image-tube scanner measurements of Preston's (1959) metal-abundance indicator and metallic-line absorption in the G-band region (4285 to 4317 A) of 47 RR Lyrae stars in 12 galactic globular clusters and 67 RR Lyrae field stars. The relationship (Fe/H) is defined and determined from curve-of-growth analyses of 13 RR Lyrae field stars, while a comparison of metal-abundance vs metallic-line absorption relationships derived for the field and cluster stars indicates that both groups can be calibrated in the same way. Based on this calibration, (Fe/H) values are deduced for the globular-cluster stars and the clusters themselves. It is found that the alpha-rich phenomenon is present in these stars and is confined to calcium and titanium.

Butler, D.↗
NASA NTRS1991

First results from the Goddard High-Resolution Spectrograph - The Galactic halo and the Ly-alpha forest at low redshift in 3C 273

Results of initial spectroscopy using the Goddard High-Resolution Spectrograph and the Hubble Space Telescope on the bright low-redshift quasar 3C 273 are presented. Absorption lines produced by gas in the disk and halo of the Galaxy from numerous neutral and weakly ionized atoms and also from highly ionized atoms are detected. The detection of N v provides additional strong support for the existence of gas with T about 200,000 K at large distances away from the disk of the Galaxy. Ten absorption lines with EW greater than 50 mA, and four possible lines with EW between 25 and 50 mA, are also found in the region between 1235 and 1406 A. These cannot be identified with any lines in the galactic interstellar medium and must therefore all be Ly-alpha systems at very low redshifts. This number of lines is 5-10 times larger than expected from a simple extrapolation of the high-redshift evolution derived from ground-based observations and is consistent with no evolution in cloud properties since z = 2.

Morris, Simon L.↗
NASA NTRS1996

High Redshift Quasars

The report for this period includes three papers: 'Associated Absorption at Low and High Redshift'; 'Strong X-ray Absorption in a Broad Absorption Line Quasar: PHL5200'; and 'ASCA and ROSAT X-ray Spectra of High-Redshift Radio-Loud Quasars'. The first gives examples from both low and high redshift for combining information on absorbing material in active galactic nuclei from both x-ray and the UV. The second presents ASCA observations of the z = 1.98 prototype broad absorption line quasar (BALQSO): PHL 5200, detected with both the solid-state imaging spectrometers and the gas imaging spectometers. The third paper presents results on the x-ray properties of 9 high-redshift radio-loud quasars observed by ASCA and ROSAT, including ASCA observations of S5 0014+81 (z = 3.38) and S5 0836+71 (z = 2.17) and ROSAT observations of PKS 2126-158.

Elvis, Martin S.↗
NASA NTRS1995

The cooling of the white dwarf in U Geminorum following heating by two different outbursts

We present the analysis of 13 orbital phase-resolved IUE (large and small aperture) SWP spectra, sampling the quiescent intervals of the proptotype dwarf nova U Geminorum following two individual outbursts, the outburst of 1992, 29 August-14 September, and the outburst of 1993, 19 March-5 April. The quiescent interval following the outburst 29 August 1992 is the longest ever recorded. During quiescence, the photospheric radiation of the exposed white dwarf dominates the far ultrviolet. The variations in absorption line strengths and continum flux levels are analyzed as a function of both orbital phase and elapsed time, since the return to optical quiescence, by fitting the IUE spectra with a grid of high gravity, LTE, model atmospheres with solar composition constructed with TLUSTY and SYNSPEC (Hubeny, I. Tlusty and Synnspec: A Users Guide (1994)). We present evidence from both absorption line variations and continuum variations, as a function of time since the outbursts, that the white dwarf photosphere has cooled by several thousand degrees. Within the signal-to-noise limitations, we find no evidence of a difference in heating and cooling between the two outbursts.

Huang, Min↗
DOE OSTI2020

White dwarf pollution by hydrated planetary remnants: hydrogen and metals in WD J204713.76–125908.9

ABSTRACT WD J204713.76–125908.9 is a new addition to the small class of white dwarfs with helium-dominated photospheres that exhibit strong Balmer absorption lines and atmospheric metal pollution. The exceptional abundances of hydrogen observed in these stars may be the result of accretion of water-rich rocky bodies. We obtained far-ultraviolet and optical spectroscopy of WD J204713.76–125908.9 using the Cosmic Origin Spectrograph on-board the Hubble Space Telescope and X-shooter on the Very Large Telescope, and identify photospheric absorption lines of nine metals: C, O, Mg, Si, P, S, Ca, Fe, and Ni. The abundance ratios are consistent with the steady-state accretion of exo-planetesimal debris rich in the volatile elements carbon and oxygen, and the transitional element sulphur, by factors of 17, 2, and 4, respectively, compared to the bulk Earth. The parent body has a composition akin to Solar system carbonaceous chondrites, and the inferred minimum mass, 1.6 × 1020 g, is comparable to an asteroid 23 km in radius. We model the composition of the disrupted parent body, finding from our simulations a median water mass fraction of 8 per cent.

Hoskin, Matthew J.↗