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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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At least 145 records · Page 8
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NASA NTRS1975

Detection of the O III 88.16-micron forbidden line in M17

This paper reports the detection of the fine-structure forbidden line of O III at 88.16 microns in emission from M 17 (the Omega Nebula), which is an optically bright galactic H II region and a strong thermal radio source. The observations were made using an airborne 30-cm telescope and a liquid helium-cooled grating spectrometer with Ge:Ga photoconductive detectors. The line intensity is found to be 2.2 (+1.0, -0.7) by 10 to the -15th power W/sq cm. The results are compared with those of a search for the present line in M 42 as well as with theoretical predictions of the line intensity.

Ward, D. B.↗
NASA NTRS1990

H2 line emission in three Seyfert nuclei: Evidence against UV-excitation

Line emission from vibrationally excited molecular hydrogen has been detected in a considerable number of active galactic nuclei (AGNs), including those generally believed to contain compact and luminous central engines (e.g., Seyfert nuclei) and those in which the luminosity is believed to arise from massive bursts of star formation (starburst nuclei). In most of these AGNs, only the bright 1-0 S(1) line (rest wavelength 2.12 microns) has been searched for and detected to date. Line-emitting H2 can be excited directly either by energetic collisions created by shock waves or by absorption of UV radiation. Each of these excitation mechanisms has been clearly identified in galactic and extragalactic regions. In active galactic nuclei strong sources of UV and (in some case) x rays are present. If the nuclear molecular matter is quiescent (i.e., isolated from the active nucleus and not set into motion by episodes of star formation) the H2 line emission will be dominated by fluorescence, or possibly by thermal emission due to heating by x rays (Krolik, this conference). However, it is expected or indeed observed that a significant fraction of the interstellar medium in and near these nuclei is undergoing rapid motions; either generated by the central engine or by a nuclear starburst, which are capable of producing strong shock phenomena in nearby molecular gas. Thus, a priori it is not obvious which mechanism is responsible for the H2 line emission from the nucleus of an active galaxy.

Geballe, T. R.↗
NASA NTRS1980

A search for FeH in M and S giants

The strongest lines of FeH in the visible spectrum fall in the domain of TiO and ZrO bands. Analysis exists for TiO, but nothing is yet available for the weak but important ZrO lines. Using plate measurements and microphotometer tracings, high dispersion spectra of the following cool stars have been searched for FeH lines: Beta Peg, Mu UMa, Alpha Her, Omicron Cet, Chi Cyg, HR 105, HR 8714, R And, R Cyg, R Cam, T Sgr, R CMi, Cy Cyg, and RU Cam. The strongest FeH lines are unimpressive in R Cyg, where the strong infrared bands of FeH have already been identified. Identification of the blue-green FeH lines in other spectra must be considered inconclusive until a rotational analysis of the FeH spectrum is available.

Davis-Locanthi, D.↗
NASA NTRS1990

A search for evidence of past and ongoing mass loss in the hot DO degenerates PG 1159 - 035, PG 1034 + 001, and KPD 0005 + 5106

The results are reported of a search for evidence of mass loss from three very hot, helium-rich degenerate stars, PG 1034 + 001, PG 1159 - 035, and KPD 0005 + 5106, based upon a search for weak, velocity-displaced line features in high-resolution IUE spectra. The search was entirely negative for PG 1159 - 035 and resulted in the detection of Si IV in PG 1034 + 001 at the same redshifted velocity as the other detected far-ultraviolet resonance doublets. The presence of photospheric silicon in a DO star at 80,000 K is not predicted by current radiative acceleration theory. For KPD 0005 + 5106 there is no convincing far-ultraviolet spectroscopic detection of either past or ongoing mass loss. The high-ionization resonance doublets of C IV, Si IV, and N v share the same velocity broadening as the interstellar lines but are velocity displaced by + 10 km/s relative to the local interstellar medium. Their origin is ascribed to an expanding, photoionized H II region around KPD 0005 + 5106.

Fritz, Matthew L.↗
NASA NTRS1981

Far-infrared observations of shocked CO in Orion

The J = 27-26 and J = 30-29 transitions of CO have been detected in the Orion molecular cloud. These detections, together with an improved measurement of the J = 21-20 transition, allow estimation of the temperature and density of the shocked material and the fractional abundance of CO. By solving the equations of detailed balance for J less than or equal to 50 and fitting the data to a two-component model consistent with earlier 2-micron and 12-micron H2 observations, it is shown that the hot (2000 K) component has a density of approximately 1.0 x 10 to the 6th/cu cm, while the cooler component lies in the range of 400-1000 K and is 2-5 times more dense. Approximately 25% of the carbon is in the form of CO. The spatial extent of the hot CO has also been examined by observing the J = 21-20 transition at a number of positions, and it is found to be distributed similarly to the H2 lines. In addition, a search for J = 21-20 and J = 22-21 CO emission from six other sources has resulted in 3-standard-deviation upper limits of a factor of 10 below the intensity of the Orion lines.

Storey, J. W. V.↗
NASA NTRS1978

On the detectability of millimeter wavelength spectral lines from planetary atmospheres

This paper adopts a simple line-formation model to estimate detection limits on the fractional absorption produced by molecular lines in the spectra of the planets, when observed with the 14-m antenna and low-noise receivers of the Five College Radio Astronomy Observatory. The results, which can readily be adjusted for receiver and telescope characteristics of other observatories, indicate that three kinds of observing programs may prove fruitful: (1) programs to monitor temporal variations of the strong CO absorption in the spectrum of Venus and Mars; (2) searches for weak absorption lines of other molecules, which are particularly promising for Venus: and (3) efforts to measure broad features in the continuous spectra of Venus, and possibly Jupiter, produced by molecules deep in the planetary atmospheres. Except for delineation of broad features of NH3 and possibly H2O near 25 GHz, hardly any useful observations can be made at frequencies less than 60 GHz.

White, R. E.↗
NASA NTRS1995

A search for the C3 carbon cluster in the Interstellar Medium

We have searched for rovibrational emission and absorption transitions arising from the 63 cm(exp -1) nu(sub 2) (pi(sub u)) bending vibration of the C3 carbon cluster in the interstellar medium using the Betz/Boreiko heterodyne receiver on board the Kuiper Airborne Observatory. The Q(4) line at 1896.707 GHz was searched for in the IRc2 Orion/M42 and the W3 sources, and the R(2) transition at 1968.594 GHz was searched for in Sgr B2. No emission lines were observed in any source. However, a weak absorption was detected in Sgr B2 with a LSR velocity of 63.7+/-0.6 km s(exp -1) and a FWHM linewidth of 7.9+/-0.8 km s(exp -1). This absorption is tentatively identified as the R(2) transition of the C(sub 3) bending mode.

Vanorden, A.↗
NASA NTRS2000

Limits on Line Bisector Variability for Stars with Extrasolar Planets

We present an analysis of high-resolution synoptic spectra of ten F- and G-type stars, seven of which exhibit periodic radial velocity variations due to the presence of one or more substellar companions. We searched for subtle periodic variations in photospheric line asymmetry, as characterized by line bisectors. In principle, periodic variations in line asymmetry observed at lower spectral resolution could mimic the radial velocity signature of a companion, but we find no significant evidence of such behavior in our data. Observations were obtained from 1998 March to 1999 February using the National Solar Observatory (NSO) 1.52-m McMath-Pierce Solar Telescope Facility on Kitt Peak in conjunction with the solar-stellar spectrograph, achieving a resolving power of 1.2x10(exp5). To characterize line asymmetry, we first measured line bisectors for the unblended Fe I photospheric line at 625.26 nm. To improve sensitivity to small fluctuations, we then combined points in each bisector to form a velocity displacement with respect to the line core. We searched for periodic variations in this displacement, finding no substantial difference between stars with substellar companions and those without reported companions. We find no correlation between bisector velocity displacement and the known orbital phase of substellar companions around our target stars. Simulations of a periodic signal with noise levels that mimic our measurement errors suggest that we can exclude bisector variations with amplitudes greater than about 20 m/s. These results support the conclusion that extrasolar planets best explain the observed periodic variations in radial velocity.

Povich, M. S.↗
NASA NTRS1976

New upper limits for atmospheric constituents on Io

A spectrum of Io from 0.86 to 2.7 microns with a resolution of 3.36 per cm and a signal to rms noise ratio of 120 is presented. No absorptions due to any atmospheric constituents on Io could be found in the spectrum. Upper limits of 0.12 cm-atm for NH3, 0.12 cm-atm for CH4, 0.4 cm-atm for N2O, and 24 cm-atm for H2S were determined. Laboratory spectra of ammonia frosts as a function of temperature were compared with the spectrum of Io and showed this frost not to be present at the surface of Io. A search for possible resonance lines of carbon, silicon, and sulfur, as well as the 1.08-micron line of helium, proved negative. Upper emission limits of 60, 18, 27, and 60 kilorayleighs, respectively, were established for these lines.

Fink, U.↗
NASA NTRS1979

Recent observations of Hercules X-1 with HEAO-1 and OSO-8

HEAO 1 X-ray observations of Her X-1 near an onset of the high state are discussed. An X-ray light curve is determined which indicates that for about 0.5 day before the X-ray intensity turn-on there was 1.2-sec pulsed emission from the source at a level intermediate between the high- and low-state intensities. These results are taken as demonstrating the stability in the 35-day cycle when compared with previous observations. An inconclusive search for 58-keV line emission from Her X-1 is also reported.

Pravdo, S. H.↗
NASA NTRS1980

Steady flows in the chromosphere and transition-zone above active regions as observed by OSO-8

Two years of data from the University of Colorado ultraviolet spectrometer aboard OSO-8 were searched for steady line-of-sight flows in the chromosphere and transition-zone above active regions. The most conspicuous pattern that emerges from this data set is that many sunspots show persistent blueshifts of transition-zone lines indicating velocities of about 20 km/s with respect to the surrounding plage areas. The data show much smaller shifts in ultraviolet emission lines arising from the chromosphere: the shifts are frequently to the blue, but sometimes redshifts do occur. Plage areas often show a redshift of the transition-zone lines relative to the surrounding quiet areas, and a strong gradient of the vertical component of the velocity is evident in many plages. One area of persistent blueshift was observed in the transition-zone above an active region filament. The energy requirement of these steady flows over sunspots is discussed.

Lites, B. W.↗
NASA NTRS1983

The 12 micron band of ethane: A spectral catalog from 765 cm(-1) to 900 cm(-1)

The high resolution laboratory absorption spectrum of the 12 micro band of ethane gas is studied. The data were obtained using the McMath Solar Telescope 1 meter Fourier Transform interferometer at Kitt Peak National Observatory and tunable diode laser spectrometers at the University of Tennessee and NASA/Goddard Space Flight Center. Over 200 individual vibration rotation transitions were analyzed taking into account many higher order effects including torsional splitting. Line positions were reproduced to better than 0.001/cm. Both ground and upper state molecular constants were determined in the analysis. The experimental details, the analysis procedures and the results are addressed. A list of ethane transitions occurring near (14)CO2 laser lines needed for heterodyne searches for C2H6 in extraterrestrial sources is also included. A spectral catalog of the ethane nu sub g fundamental from 765/cm to 900/cm is provided. A high dispersion (1/cm 12 in.) plot of both the Kitt Peak interferometric data and a simulated spectrum with Doppler limited resolution, a table of over 8500 calculated transitions listed quantum number assignments, frequencies and intensities are provided.

Atakan, A. K.↗
NASA NTRS1985

High-resolution spectrum of Cygnus X-1

A high resolution spectrum of Cygnus X-1 in the 45 to 600 keV range is presented. The measurement was made by the HEAO 3 gamma ray spectrometer during 82 days in the fall of 1979 and spring of 1980, when the source was in its normal low state. Results of a search for narrow emission lines from the source are reported. The spectrum shows no significant narrow features. The 3 delta upper limit to a narrow 511 keV annihilation line is 3 x 0.0001 photons/sq cm/s. There is also no evidence in HEAO 3 broadband data above 500 keV for the broad annihilation feature observed by HEAO 1.

Ling, J. C.↗
NASA NTRS1984

Hydrogen cyanide in comets - Excitation conditions and radio observations of comet IRAS-Araki-Alcock 1983d

The HCN emission of the pure rotation and rotation/vibration lines in comet IRAS-Araki-Alcock 1983d is examined. The prevailing excitation mechanism for the emissions was the excitation of the nu-2, 2 nu-2, and nu-3 vibrational bands by the solar infrared field. For the description of inner coma, a dynamical excitation model is presented which includes collisions. It is predicted on the basis of the model that HCN molecules in rotation and rotation vibration lines of IRAS-Araki-Alcock 1983d would be detectable with a large-millimeter wave telescope, and that the strongest infrared lines would be observable from space observatories. Subsequent searches for the J = 1-0 HCN radio lines in comet 1983d with the Five College Radio Astronomy Observatory (FCRAO) proved unsuccessful. An extremely low upper limit was found for HCN production which suggests that HCN might not be the only parent of planetary cometary CN.

Bockelee-Morvan, D.↗
NASA NTRS1989

BBXRT observations of X ray binaries

The Broad Band X Ray Telescope (BBXRT) is a new X ray spectrophotometer scheduled for launch Apr. 26, 1990, for a 10 day mission aboard the Space Shuttle Columbia. High quality spectra between 0.3 and 12 keV of about 100 different sources are expected. BBXRT has the best energy resolution for examining features due to the K-shell of Fe, seen in the spectra of X ray binaries. The resolution is sufficient to make sensitive searches for broadened emission lines, to resolve multiple features, and to determine the ionization state of the emitting plasma by measuring line energies. Simulated spectra of several sources are presented.

Marshall, F. E.↗
NASA NTRS1991

Luminosity function of quasars at large redshifts from grism surveys

We have carried out a systematic search for emission-line objects through photometrically calibrated CCD grism surveys with the Palomar 200-inch telescope in transit mode, covering 62 square degrees. These surveys have yielded 141 quasars detected by their C IV or Ly-alpha emission in the redshift range 2.0 - 4.7. We use this sample and the known flux limits to derive the slope of the luminosity function and the space density above a given line luminosity, as a function of redshift. While space densities are approximately constant at redshifts 2.0 - 3.0, they are declining steeply for redshifts larger than 3.

Schmidt, Maarten↗
NASA NTRS2000

Production of Star-Grazing and Star-Impacting Planetestimals via Orbital Migration of Extrasolar Planets

During the orbital migration of a giant extrasolar planet via ejection of planetesimals (as studied by Murray et al. in 1998), inner mean-motion resonances can be strong enough to cause planetesimals to graze or impact the star. We integrate numerically the motions of particles which pass through the 3:1 or 4:1 mean-motion resonances of a migrating Jupiter-mass planet. We find that many particles can be trapped in the 3:1 or 4:1 resonances and pumped to high enough eccentricities that they impact the star. This implies that for a planet migrating a substantial fraction of its semimajor axis, a fraction of its mass in planetesimals could impact the star. This process may be capable of enriching the metallicity of the star at a time when the star is no longer fully convective. Upon close approaches to the star, the surfaces of these planetesimals will be sublimated. Orbital migration should cause continuing production of evaporating bodies, suggesting that this process should be detectable with searches for transient absorption lines in young stars. The remainder of the particles will not impact the star but can be ejected subsequently by the planet as it migrates further inward. This allows the planet to migrate a substantial fraction of its initial semimajor axis by ejecting planetesimals.

Quillen, A. C.↗
NASA NTRS2008

Heavy Elements and Cool Stars

We report on progress in the analysis of high-resolution near-IR spectra of alpha Orionis (M2 Iab) and other cool, luminous stars. Using synthetic spectrum techniques, we search for atomic absorption lines in the stellar spectra and evaluate the available line parameter data for use in our abundance analyses. Our study concentrates on the post iron-group elements copper through zirconium as a means of investigating the slow neutron-capture process of nucleosynthesis in massive stars and the mechanisms that transport recently processed material up into the photospheric region. We discuss problems with the atomic data and model atmospheres that need to be addressed before theoretically derived elemental abundances from pre-supernova nucleosynthesis calculations can be tested by comparison with abundances determined from observations of cool, massive stars.

Wahlgren, Glenn M.↗