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At least 487 records · Page 27
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NASA NTRS1991

Measurement of self-broadening of the ozone nu(3) transitions

Self-broadening coefficients have been measured for a number of rovibrational lines in the nu(3) band of ozone, in the frequency range 1015-1058/cm, with J values between 0 and 27, and over a range of K(a) values. A multiparameter nonlinear least-squares fitting procedure is used to reduce the data, and the sensitivity of the procedure to instrument line width, weak satellite features, and absolute intensity has been examined. The retrieved coefficients are compared with millimeter-wave broadening coefficients, direclty measured rotational relaxation times, and recently suggested empirical representations.

Flannery, C.↗
NASA NTRS1991

An observation of annihilation radiation from the Galactic center region

Results are reported from observations of the 511 MeV annihilation gamma-ray line from the Galactic center, made on May 22, 1989 with a high-resolution gamma-ray spectrometer on board a balloon launched from Alice Springs (Australia). The observations were made at about 4 gm/sq cm atmospheric depth for 6 hrs in a series of target and background pointings lasting 20 min each. The results obtained from multiparameter Gaussian fits to the data were as follows: 511 keV flux = 0.00089 + or - 0.00027 ph/sq cm per sec-rad, line width of about 1.1 keV, and less than 3.2 keV FWHM at 95 percent confidence.

Matteson, J.↗
NASA NTRS1991

Gamma-ray lines from SN1987A

Results of gamma-ray observations of SN1987A conducted over a period of 800 days using balloon-borne high-resolution germanium detectors are discussed. Most of the measurements show red-shifted line centroids (about 500 km/s) and broadened profiles, contradicting the standard homogeneous and spherically symmetric models, which predict blue-shifted lines and narrower line widths. To explain this apparent contradiction, it may be necessary to invoke fragmentation and nonspherical geometries.

Teegarden, B. J.↗
NASA NTRS1991

New measurements of the 6190-A band of methane

The present paper reports new laboratory measurements that were made of the absorption coefficient of the visible methane band at 6190 A. Data were obtained using a tunable dye laser system operating with a line width of 0.067/cm. Spectra were recorded at approximately 1-A intervals with the beam coupled to a 22-m base length White-type absorption cell adjusted for an optical path of 1584 km and filled to a density of 0.884 amagats. Errors in pressure, temperature, and path length amounted to an uncertainty in the abundance of no more than 0.4 percent. Fourteen data sets were recorded and coadded. The final signal-averaged methane data were divided by a similar set of signal-averaged empty cell scans to remove the transmittance of the White cell and system optics. The results are compared with previous low-resolution measurements in the spectral region from 6000 to 6400 A.

Mickelson, M. E.↗
NASA NTRS1992

A high-performance Hg(+) trapped ion frequency standard

A high-performance frequency standard based on (199)Hg(+) ions confined in a hybrid radio frequency (RF)/dc linear ion trap is demonstrated. This trap permits storage of large numbers of ions with reduced susceptibility to the second-order Doppler effect caused by the RF confining fields. A 160-mHz-wide atomic resonance line for the 40.5-GHz clock transition is used to steer the output of a 5-mHz crystal oscillator to obtain a stability of 2 x 10(exp -15) for 24,000-second averaging times. Measurements with a 37-mHz line width for the Hg(+) clock transition demonstrate that the inherent stability for this frequency standard is better than 1 x 10(exp -15) at 10,000-second averaging times.

Prestage, J. D.↗
NASA NTRS1991

Nonequilibrium ionization effects in asymmetrically heated loops

The effects of nonequilibrium ionization on magnetic loop models with a steady siphon flow that is driven by a nonuniform heating rate are investigated. The model developed by Mariska (1988) to explain the observed redshifts of transition region emission lines is examined, and the number densities of the ions of carbon and oxygen along the loop are computed, with and without the approximation of ionization equilibrium. Considerable deviations from equilibrium were found. In order to determine the consequences of these nonequilibrium effects on the characteristics of the EUV emission from the loop plasma, the profiles and wavelength positions of all the important emission lines due to carbon and oxygen were calculated. The calculations are in broad agreement with Mariska's conclusions, although they show a significant diminution of the Doppler shifts, as well as modifications to the line widths. It is concluded that the inclusion of nonequilibrium effects make it more difficult to reproduce the observed characteristics of the solar transition region by means of the asymmetric-heating models.

Spadaro, D.↗
NASA NTRS1991

Measurements of Lorentz-broadening coefficients and pressure-induced line shift coefficients in the nu2 band of D2(O-16)

Lorentz-broadening and pressure-induced line-shift coefficients are determined experimentally for 126 transitions in the nu2 band of D2(O-16) from laboratory spectra with a Fourier-transform spectrometer. A nonlinear least-squares fitting procedure is employed to measure transitions up to J double-prime = 12 in the buffer gases air, nitrogen, and oxygen. The N2-broadening/O2-broadening coefficient ratio is correlated with the magnitude of the O2-broadening coefficient, and the pressure coefficients are not correlated with line widths.

Rinsland, Curtis P.↗
NASA NTRS1991

Observations of the Galactic center 511 keV line

A review of observations of the positron annihilation 511 keV line from the Galactic center and plane is presented. Emphasis is given to the new data from balloon observations in 1988 and 1989. The positron annihilation source in the direction of the center was found to be turned on again in 1988 October after being observed in a quiescent state since the early 1980s. There is evidence for variability between May and October in 1988. The new observations give the first data in which the line is spectrally resolved and in which the Galactic center and plane components of the annihilation radiation are independently measured. These data support the two-component model of the emission with a variable point source near the center and a steady-state source distributed along the galactic plane. Comparing measurements of narrow and wide field instruments in the 1980s gives a flux of about 8 x 10 exp -4 photons/sq cm/s for the point source in its high state and a flux of about 1.2 x 10 exp-3 photons/sq cm/s/rad for the galactic plane component with a relatively flat distribution over the central radian. The line width for the point source component is about 3 keV FWHM.

Gehrels, Neil↗
NASA NTRS1992

Measurement of CO overtone line profiles in SVS 13

High-resolution spectra of the CO overtone emission in the infrared source SVS 13 are obtained and the individual vibration-rotation lines are resolved for the first time in a young stellar object. The observed FWHM velocity of the lines in the v = 2-0 band is 40 km/s. A fit of the v = 2-0 band head with a single temperature LTE slab model yields an optical depth of 0.3 in the R(51) line and a rotational temperature of about 3500 K. Given the best estimates for the orientation of the SVS 13 outflow, the observed line widths are much smaller than expected for either of the two most favored interpretations for the CO emission: a circumstellar disk or a high-velocity neutral wind.

Carr, John S.↗
NASA NTRS1992

Diode injection - seeded, 940 nanometer (nm), titanium - sapphire laser for H2O DIAL (differential absorption lidar), measurements

Differential absorption of laser radiation by various molecular species represents both a selective and a sensitive method of measuring specific atmospheric constituents. DIAL measurements can be carried out via two different means. Both involve using two laser pulses with slightly different wavelengths (lambda), (one lambda at a strong absorption line of the molecule of interest, the other detuned into the wing of the line), and comparing the attenuation of the pulses. One approach relies on scattering of the radiation from some conveniently located topographical target. In the other technique elastic scattering from atmospheric aerosols and particulates is used to return the radiation to the lidar receiver system. This case is referred to as the differential absorption and scattering technique, and is the technique we are interested in to measure water vapor at 940 nm. The 940 nm wavelength is extremely desirable to atmospheric scientist interested in accurate DIAL measurements of H2O in the upper and lower troposphere. Simulated measurements using approximately 940 nm and 815 nm lasers at a range of altitudes and experimental conditions are shown. By offering access to larger absorption cross-sections, injected seeded, 940 nm DIAL laser transmitters would allow for more accurate water profile measurements at altitudes from 6 to 16 km than is currently possible with 730 nm and 815 nm DIAL laser transmitters. We have demonstrated the operation of an injected seeded titanium-sapphire (TS) laser operating at approximately 940 nm with an energy of more than 90 mJ per pulse. The TS laser is pumped by a commercial, 600 mJ, 532 nm, 10 Hz Nd:YAG laser. The slope efficiency of the laser using a flat 50 percent R output coupler and a 10 m end-mirror is shown. The laser was injected seeded with a CW, AlGaAs, semiconductor diode laser which had an output of 83 mW. The CW diode seed beam was introduced into the TS laser cavity through a HR end-mirror. When the diode beam is aligned to the TS resonator, it controls the TS laser output wavelength and its spectral line width with the required resolution for DIAL applications. This work supports the need for the development of 940 nm, titanium-sapphire DIAL transmitters.

Miller, George E.↗
NASA NTRS1992

Observations of comet Levy 1990c in the (OI) 6300-A line with an imaging Fabry-Perot

We have observed the comet Levy 1990c during 16-25 August 1990 using the MPAE focal reducer system based Fabry-Perot etalon coupled with the 1 meter telescope of the Observatory of Hoher List. The free spectral range and resolution limit of the interferometer was approximately 2.18 A and approximately 0.171 A respectively. Classical Fabry-Perot fringes were recorded on a CCD in the cometary (OI) 6300 A line. They are well resolved from telluric air glow and cometary NH2 emission. Our observations indicate that the (OI) is distributed asymmetrically with respect to the center of the comet. In this paper we report the spatial distribution of (OI) emission and its line width in the coma of comet Levy.

Prasad, C. Debi↗
NASA NTRS1992

Tests of shock chemistry in IC 443G

Eight molecular species, in the hot dense clump IC 443G, believed to be impacted by the shock wave from the SNR IC 443, are investigated. The clump consists of two distinct regions, one relatively cool, and one hotter and denser. Region 1 contains CO, HCO(+), HCN, and CN, whose abundances may be explained either by ion-molecule chemistry, or by a D shock of 60-90 km/s, passing through a clump of about 100,000/cu cm. Region 2 gives rise to SiO, CS, SO, and H2CO, and requires an ND shock of 5-15 km/s passing through a region of about 1,000,000/cu cm. Observed fractional abundances fit ND shock models if L is about 6.6 x 10 exp 15 cm. In general, observed line widths vary inversely with derived excitation density, while centroid velocities of all species are essentially identical.

Turner, B. E.↗
NASA NTRS1993

An interpretation of the narrow positron annihilation feature from X-ray nova Muscae 1991

The physical mechanism responsible for the narrow redshifted positron annihilation gamma-ray line from the X-ray nova Muscae 1991 is studied. The orbital inclination angle of the system is estimated and its black hole mass is constrained under the assumptions that the annihilation line centroid redshift is purely gravitational and that the line width is due to the combined effect of temperature broadening and disk rotation. The large black hole mass lower limit of 8 solar and the high binary mass ratio it implies raise a serious challenge to theoretical models of the formation and evolution of massive binaries.

Chen, Wan↗
NASA NTRS1993

GRIS detections of the 511 keV line from the Galactic center region in 1992

The Gamma Ray Imaging Spectrometer (GRIS) was flown on balloons over Alice Springs, Australia on 1992 April 26 and May 7. A full Galactic center transit (about 12 hr) was achieved on both flights with the instrument working normally. The electron/positron annihilation line was detected on both flights. The line fluxes and line widths were found to be (7.7 +/- 1.2) x 10 exp -4 and (8.9 +/- 1.1) x 10 exp -4 photons/sq cm per sec and 1.3 +/- 0.7 and 3.6 +/- 1.0 keV, respectively. These results are compared to each other and earlier (1988) GRIS results to produce suggestive evidence for source variability. Near-contemporaneous OSSE/CGRO Galactic center observations indicate that the GRIS results cannot be due solely to a single point source like IE 1740.7-2942 within a few degrees of the Galactic center. The GRIS 1992 results represent the first time that successive high-resolution balloon measurements have been achieved on a time scale of days.

Leventhal, M.↗
NASA NTRS1993

A search for the rotational transitions of H2D+ at 1370 GHz and H3O+ at 985 GHz

A search was made for the 1370 GHz lowest rotational transition of the molecular ion H2D+ in NGC 2264, W3, and the IRc2 region of M42. No emission lines were seen, but an absorption feature was detected toward IRc2. The column density and fractional abundance were calculated using a tentative identification of the line as the transition of para H2D+. The LSR velocity and the measured line width are consistent with the dynamical parameters of the hot core source. Physical parameters deduced from the data differ from those derived from millimeter-wave observations of the hot core condensation. It is suggested that significant amounts of low-density gas are associated with this region and that the material is cold enough for enhanced deuterium fractionation to occur. A search was also made for the 985 GHz transition of ortho H3O+ in W3 and IRc2 with negative results.

Boreiko, R. T.↗
NASA NTRS1993

Measurement of p-mode energy propagation in the quiet solar photosphere

We have measured and analyzed the p-mode oscillations in the profile of the Mg I 4571 A line in a quiet region near disk center. The oscillations are found to be mostly standing waves, in agreement with previous work. However, a small propagating component is measured, and we determine the direction, magnitude, and vertical variation of the energy propagation. The work integral indicates an upward energy flow of about 2 x 10 exp 7 ergs/sq cm/s at a height of 50 km above the base of the photosphere for waves with frequencies of 2-16 mHz. This energy flow decreases exponentially with height and drops below 10 exp 5 ergs/sq cm/s in the uppermost photosphere. The energy flow leaving the upper photosphere is at least an order of magnitude too small to constitute a significant source of heating for the chromosphere. However, the p-mode damping in the lower photosphere approaches levels large enough to account for the measured p-mode line widths. The relative amplitudes and phases of the thermodynamic quantities indicate that the p-mode are neither adiabatic nor isothermal in the photosphere.

Fontenla, J. M.↗
NASA NTRS1993

On the generation of sound by turbulent convection. I - A numerical experiment

Motivated by the problem of the origin of the solar p-modes, we study the generation of acoustic waves by turbulent convection. Our approach uses the results of high-resolution 3D simulations as the experimental basis for our investigation. The numerical experiment describes the evolution of a horizontally periodic layer of vigorously convecting fluid. The sound is measured by a procedure, based on a suitable linearization of the equations of compressible convection that allows the amplitude of the acoustic field to be determined. Through this procedure we identify unambiguously some 400 acoustic modes. The total energy of the acoustic field is found to be a fraction of a percent of the kinetic energy of the convection. The amplitudes of the observed modes depend weakly on (horizontal) wavenumber but strongly on frequency. The line widths of the observed modes typically exceed the natural linewidths of the modes as inferred from linear theory. This broadening appears to be related to the (stochastic) interaction between the modes and the underlying turbulence which causes abrupt, episodic events during which the phase coherence of the modes is lost.

Bogdan, Thomas J.↗
NASA NTRS1993

An ultraviolet spectral atlas of the sun between 1190-1730 A

An ultraviolet spectral atlas of different solar regions in the wavelength region 1190-1730 A is presented. The data were obtained with the High Resolution Telescope and Spectrograph during a rocket flight in 1978. The spectral resolution of the instrument was 0.05 A while a spatial resolution of approximately 1.8 arcsec was achieved. The atlas contains spectra of three different quiet regions including pointings at disk center and the extreme limb. Data from an active region close to the solar limb and a prominence have also been included together with an atlas of a so-called explosive event. The selected areas are averaged over several arcsec, ranging from 3.5 to 220 arcsec. The absolute intensities are determined with an accuracy of +/- 30 percent except for the strongest emission lines that are synthesized from spectra with different exposure times. The atlas is available in a machine-readable form together with an IDL program to interactively measure line widths, total intensities, and solar wavelengths.

Brekke, P.↗