Browsing by Author "Dufour, Reginald J."
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Item A 3.0 meter liquid mirror telescope(2000) Mulrooney, Mark; Dufour, Reginald J.We constructed a 3.0 meter diameter f/1.5 Liquid Mirror Telescope (LMT) between 1990 and 1994 at the NASA Johnson Space Center, Houston, Texas. We have subsequently operated it since 1995 at the NASA Orbital Debris Observatory (NODO), Cloudcroft, NM. Employing an inexpensive rotating container of mercury as its primary parabolic mirror, the NASA LMT is a cost-effective alternative to telescopes utilizing glass mirrors. We detail criteria for mirror construction including environmental considerations via Hg vapor emission analysis. We describe performance optimization to the NODO site seeing limit of 0.8 arcseconds FWHM via analysis of perturbations to image quality from mirror angular velocity stability, dynamic balance, rotational axis tilt, and prime focus lateral and tilt displacements. We detail the behavior of the two prominent mirror surface wave phenomena---spiral and concentric forms. We demonstrate that the former probably results from vorticity in the air boundary layer above the mirror and show diffraction effects from the latter. We describe mirror stabilization in terms of boundary layer theory. The prime focus NASA-LMT utilizes corrective optics yielding a field of 46 arcminute diameter. Utilizing Micro-Channel-Plate (MCP) intensified video cameras we have obtained 750 hours of zenith staring orbital object event data with a limiting object diameter of approximately 1 cm at 1000 km altitude and 0.1 albedo. We have extended to 17.75 the lower magnitude limit of optical detections among the telescopes employed for orbital object surveys, further demonstrated the incompleteness of the SATCAT, and corroborated results of RADAR employed in orbital object detection. Utilizing CCDs we have conducted a 135 night broadband and multi-narrowband survey of 20 square degrees of sky at high galactic latitude down to a limiting magnitude of ∼22.0. The survey data will yield information on object morphology, spectral classifications, and large-scale structure to a redshift (z) of 0.5 with an accuracy of Deltaz ≤ 0.02. Broadband images from this survey are presented, demonstrating that the NASA-LMT optical performance is comparable to conventional telescopes of equivalent size located at a similar site.Item A study of the dusty SMC HII region N88A(1998) Kurt, Cindy Marie; Dufour, Reginald J.Results from the analysis of HST FOS, WFPC1, IUE, and CTIO 4m observations of the morphology, physical conditions, and chemical abundances in the unusually dusty H II region N88A in the Small Magellanic Cloud are presented. HST WFPC1 imagery of N88A indicate the nebula is bi-lobed due to a dark dust lane cutting across the center of the nebula. The presence of a high ionization arc, apparently connecting two semi-stellar objects within the nebula, is reported. The derived reddening curve for the nebula is flatter in the UV than the general SMC extinction curve, suggesting the presence of large grains. Carbon and possibly nitrogen abundances are enriched in the nebula. The conclusion is that SMC N88A is a very young H II region forming out of a small dusty C- and N-rich molecular cloud which is being disrupted by star formation in a larger OB association in the area.Item A study of the H II region populations of M101, M51 and NGC 4449(1992) Scowen, Paul Andrew; Dufour, Reginald J.An optical study of the HII region populations evident in three galaxies, M101, M51 and NGC 4449, has been made. Using narrow-band filters, emission line imagery has been taken using a CCD focal-reducing camera, at wavelengths covering the emission from H $\alpha,$ H $\beta,$ (O III) $\lambda$5007 and (S II) $\lambda\lambda$6716+6731. Using several identification techniques to spatially select the HII regions, emission line properties have been derived for 625 HII regions in M101, 465 in M51 and 163 in NGC 4449, making this the most complete study of its kind to date. Several trends have been discovered concerning the properties of the HII regions with radial position within their galaxy. M101 exhibits a large gradient in excitation, and oxygen abundance, as well as a gradient in the line-of-sight reddening. No positional variation in the derived ionization parameter for each HII region was found. Local variations in the effective collapse density for neutral gas have been detected for both M101 and M51. No such analysis was possible for NGC 4449 due to a lack of available data. M51 shows systematic emission variations only in the brightest cores of its largest HII regions, an effect attributed to a larger influence of the local ISM on the properties of the fainter, and more obscured, HII regions. M51 exhibits a spiral pattern that does not follow a single mathematical description, departing most dramatically at the corotation radius. A variation in the evolutionary time from peak local compression to peak star formation with radius has been detected for one of the arms in the galaxy, but not the other. NGC 4449 displays no systematic variations in the derived emission properties of its HII region population. This is attributed to a star formation mechanism that is independent of the radial ordinate, contrasting with the spiral density wave mechanism dominant in spiral galaxies. Unprecedented deep CCD imagery of this galaxy is presented, revealing the complicated structure of ionized filaments between the HII regions. The emission properties of these filaments are studied.Item Acceleration of ambient ions in the Lunar atmosphere(1981) Bulgher, Debra Lynn; Freeman, John W.; Dufour, Reginald J.; Michel, F. CurtisThe Apollo Suprathermal Ion Detector Experiments (SIDEs) deployed on the lunar surface observe sporadic bursts of positive ions throughout the local lunar night. Evidence exists that the source of these events is most likely the dayside lunar atmosphere. Ionization of the neutral lunar atmosphere by photoionization or chargeexchange produces a population of ions over the sunlit portion of the moon. These ions are accelerated by the interplanetary electric field, executing cycloidal trajectories that may bring them onto the nightside hemisphere of the moon. A nightside surface electric field directed radially inward can then further accelerate these ions onto the lunar surface, altering their energies and trajectories such that they are detected by the SIDE. It is possible to obtain ion trajectories that intersect various positions on the nightside of the moon in this manner. For several nighttime ion events, synthetic particle data have been produced with this model which are in agreement with the observed data. Parameters of the nightside surface potential distribution are determined for the selected events. A profile of the expected surface potential over the nightside hemisphere of the moon indicates a variable surface potential. The height distribution over which the potential is effective becomes increasingly larger, while the magnitude of the surface potential becomes increasingly negative, when approaching local lunar midnight. Assuming an exponential neutral nimber density profile for all atmospheric constituents, indirect observations of the neutral lunar atmosphere can be made by the SIDE. Combined with the effect of the surface potential on the height distribution of these ions, number densities for various species in the lunar atmosphere determined in this manner are in agreement with reported values from various other experiments also deployed on the lunar surface.Item An analysis of the WN shell nebula NGC 6888 using CCD imagery and spectrophotometry(1991) Mitra, Patralekha; Dufour, Reginald J.We present a model describing the morphology and physical processes in NGC 6888, a 'wind-blown' nebula around the WN6 star HD192163. CCD imagery with the Palomar 1.5m revealed distinct morphological features that were further probed with spectrophotometry using the KPNO #2 telescope + Intensified Reticon Scanner. Distinctions in morphology in (O III) compared to H$\alpha$ led to a parametrization into two physical systems: (1). An inner ionized shell observable in all the emission lines, with (N II) T$\sb{\rm e}$ = 8000 $\sp\circ$K, (O III) T$\sb{\rm e}$ = 14,000 $\sp\circ$K and (S II) N$\sb{\rm e}$ = 400 cm$\sp{-3.}$, (2) The (O III) bubble and rim, visible only in (O III) and characterized by a higher (O III) T$\sb{\rm e}$ = 50,000 $\sp\circ$K. The nebula is found to have 5-10 M$\sb\bigodot$ of ionized mass. An extrapolation of (O III) $\lambda$5007 fluxes to IR emission line intensities led to revised values of neutral mass $\sim$40 M$\sb\bigodot$ for the nebula. Of this 3-6 M$\sb\bigodot$ is found to be enriched mass, 0.5 M$\sb\bigodot$ contributed by stellar wind mass loss and wind swept ISM mass is determined to be $\sim$20-60 M$\sb\bigodot$. Photoionization models demonstrate that the shell is enriched in N and He and depleted in O compared to Galactic H II regions. These results collectively indicate a scenario that is a combination of several physical processes. A slow wind ejected in an asymmetric fashion from the star is swept up by a fast stellar wind together with the ambient medium, creating the ionized shell. This interaction also creates Rayleigh Taylor instabilities which are determined to be plausible formation mechanisms for the observed knots. The hot gas ($\sim$ 10$\sp7 \sp\circ$K) penetrates the nebular material in the NW and SE as there is less ejecta pressure opposing it along the polar axis, and creates the observed (O III) bubbles in the NW and lattice in the SE.Item Chemical abundances in planetary nebulae in NGG 6822(1984) Kirsch, Russell Gary; Dufour, Reginald J.; Reiff, Patricia H.; Stebbings, Ronald F.; O'Dell, Charles R.The results of an investigation of the optical spectra of five planetary nebulae and two H II regions are presented. The nebulae, located in NGC 6822, a Local Group Irregular Galaxy at a distance of .557 Mpcs, were examined using the Richey-Cretien spectrograph and the Silicon Intensified (SIT) Vidicon, on the 4-meter telescope at the Cerro Tololo Interamerican Observatory. From the measurement of selected emission line strengths in the XX37 - XX71 spectral ranges, the relative abundances of He, N, , Ne, S are calculated with respect to H (Log (H) = 12.) for each nebula. Electron densities are derived for the planetary nebulae from the ratio of the Cs IlU line intensities, I(6716)/I(6731), while their temperatures are obtained from theiatio of the Co IIlH line intensities, 1(4363), 1(4959), 1(57). The derived chemical abundances are examined in the context of possible Nitrogen enrichment of the Interstellar Medium and the possible age of the galaxy. Type I planetaries exhibited a He and N enrichment of factors of up to 2 and 31, respectively. The high N enrichment indicates it is a product of Primary Nucleosynthesis, and Type I planetaries are probably significant in N enrichment of the ISM. Type II planetaries exhibit a He and N enrichment of a lesser magnitude than Type I; factors of 1.4 and 5, respectively. This lower enrichment indicates N is a product of Secondary Nucleosynthesis. The age of NGC 6822 is probably similar to that of the Milky Way Galaxy, about 1^1 years, whereas the Magellanic Clouds are younger, a few 1^9 years.Item Comparison of clusters with and without detectable Wolf-Rayet stars in starburst galaxies using optical, near-infrared imagery and spectroscopy(2003) Buckalew, Brent Alan; Dufour, Reginald J.This optical, near-infrared observational study compares the properties of clusters with and without Wolf-Rayet (W-R) stars in starburst galaxies. Previous studies looked only at the galactic properties. Because this work identifies the specific locations of W-R stars, comparisons of clusters with and without W-R stars are possible and enable us to understand the impact of massive stars on their environment, to gain knowledge of the cosmic formation and evolution of chemical abundances, to constrain the parameters for modeling these systems, and to apply this knowledge to observations of starburst galaxies at higher redshifts. BHK and Ha imagery as well as spectroscopic observations over lambdalambda3500--7000 were taken of 48 clusters in 20 galaxies. Using standard reduction techniques, we calibrated the data to provide the locations of W-R stars and to derive 35 cluster and interstellar medium properties such as age and elemental abundances. These 35 properties of clusters with and without W-R stars are compared for similarities and differences in stellar populations, nebular morphology, and elemental abundances. Most stellar populations of clusters with and without W-R stars confirm current evolutionary theory of massive stars. Clusters with W-R stars are currently younger, bluer clusters which will later evolve into clusters without W-R stars. A few young non W-R clusters may indicate that the IMF/Upper Stellar Mass Limit is not universal; further work to determine the presence of W-R stars in these young clusters is therefore critical. Clusters with and without W-R stars show significant differences in nebular morphology, differences best explained evolutionarily. The clusters with W-R stars typically have a gas configuration similar to a Stromgren sphere so that the dust is heated, causing red H-K colors. Around the clusters without W-R stars, the gas expands into a superbubble configuration because of longer influence from stellar winds. The dust in these superbubbles obscures the stellar light, causing red B-H colors. Neither N/O nor S/O shows enhancements due to Wolf-Rayet stars. Future work will expand these studies into X-ray, ultraviolet, and infrared wavelengths.Item Digital analysis of narrow band imagery of the Cygnus loop(1983) Hester, John Jeffrey; Dufour, Reginald J.; Clayton, Donald W.; Few, Arthur A.Digital analysis of narrow passband direct imagery of a field in the southeast part of the Cygnus Loop SNR is presented. Calibrated surface brightness and spectral line ratio maps involving emission lines from six different ionic species are shown. The detailed morphology of the remnant and correlations between various line ratios are discussed in the context of recent shock model calculations. The spatial structure is categorized on the basis of the presence or absence of features in images isolating different emission lines, and the correlation or lack thereof between these features and features in the maps of spectral line ratios such as [ III] 57/Ha. For a common type of structure, features present in line ratio maps are not associated with surface brightness features. These same structures also demonstrate spectral behavior consistent with that predicted by steadyflow shock calculations, indicating the presence of steady-flow shocks with velocities from <= 6 km/sec to ≈ 12 km/sec. Differences in the morphologies of the remnant as viewed in different emission lines and gradients in spectral line ratios are interpreted as a continuous transition with distance behind the blast wave from non-steady-flow shocks with velocities >= 13 km/sec to steady-flow shocks with velocities ≈ 6 km/sec .Item Estimation of repetition rate from signal and texture features(1983) Tagare, Hemant D.; Figueiredo, Rui J. P. de; Parks, Thomas W.; Dufour, Reginald J.This thesis develops relevant definitions and a theoretical basis for estimating the repetition rate of a random repetitive signal. The repetition rate is estimated by looking for repetition amongst local features of the signals. These features have to satisfy a uniqueness condition, and we have shown that the derivatives of a signal constitute a set of such features. The estimator has been shown to be asymptotically unbiased. The estimation algorithm can not only be tuned to the waveshape information of the signal (by a proper choice of features), but also to the extent of non-stationarity expected in the input signal class. A set of features has been obtained for applying this algorithm to repetitive textured images and voiced speech signals. Vith these features, it has been possible to extract the repetition rate in both the above classes of signals. In the case of voiced speech this rate corresponds to its pitch.Item Instantaneous recycling approximation in chemical evolution of galaxies(1985) Pantelaki, Irini A.; Clayton, Donald W.; Wolf, Richard A.; Dufour, Reginald J.The purpose of this study is to determine the range of validity of the instantaneous recycling approximation (IRA) in the models for the chemical evolution of galaxies. To achieve this and in order to be able to follow the evolution of the gas mass and the gas metallicity with time without making the instantaneous recycling assumption, I constructed a simple numerical code. This same code was later converted to a form assuming the instantaneous recycling approximation and the two groups of solutions (with and without IRA) were compared. The results show that in the case of a star formation rate which at early times builds up to a maximum and later declines, a physically important departure from the instantaneous recycling approximation is observed in: a) The evolution of the gas mass at late times when the remaining gas mass density becomes a small fraction of the total density and b) the time evolution of the abundances in the interstellar gas of the elements contributed by the low mass stars. A less significant discrepancy between the two solutions (with and without IRA) appears at late times in the cases of the abundances of the elements whose origin are the intermediate and high mass stars.Item Observations of selected Perseus Arm H II regions(1979) Talent, David Leroy; Dufour, Reginald J.; Talbot, Raymond J.; Cloutier, Paul A.The results of an investigation of the optical spectra of four galactic H II regions: NGC 7635, NGC 7538, NGC 2359, and NGC 1624 are presented. The nebulae, located in the Perseus Arm of the Galaxy at distances ranging from 11 to 14 kpc from the galactic center (3.5 to 5. kpc from the sun), were examined using the Intensified Image Dissector Scanner (IIDS) on the 2.1-meter telescope at Kitt Peak National Observatory (KPNO). From the measurement of selected emission-line strengths in the XX37-41 and XA46-74 spectral ranges, the relative abundances of He, N, O, Ne, S, and Ar are calculated with respect to H (log(H) = 12.) for each nebula. Electron densities are derived for the H II regions from the ratio of the [S II] line intensities, I (6716)/I (6731) , while their temperatures are obtained from the ratio of the [N II] line intensities, 1(5759/1(6583). The effects of temperature fluctuations on the abundance calculations are also discussed. The derived chemical abundances are examined in the context of possible chemical abundance gradients in the Galaxy. Significant radial gradients are found for oxygen and nitrogen: dlog(/H)/dR = -.12+.3 kpc-1 and dlog(N/H)/dR = -.16+.3 kpc-1. In each nebula several positions were observed. In this paper particular attention is given to an examination of the condensations in NGC 7635, while an overabundance of nitrogen in NGC 2359 is discussed in the context of its association with the Wolf-Rayet star HD 56925 (WN5).Item Solar radiation pressure perturbations on satellite hydrogen atoms in the Earth's exosphere(1981) Stentz, Henry Valentine; Chamberlain, Joseph W.; Dessler, A. J.; Dufour, Reginald J.The following study investigates the effects of radiation pressure on H-atoms in the earth's exosphere. The exosphere is regarded as collisionless, permitting the atoms to be treated as particles in orbit about the earth obeying the laws of celestial mechanics. Attention is restricted to a class of atoms called satellites, whose initial orbital parameters place them in Keplerian satellite orbits, as distinguished from captive atoms whose orbits intersect the exobase (ballistic particles) and those which escape on hyperbolic trajectories. The evolution of these satellite orbits under the perturbing force of radiation pressure is determined by numerically integrating the classical perturbation equations for the orbital elements. These equations express the rates of change of the standard orbital elements in terms of the other elements and the vector components of a perturbing force. Results are presented graphically and compared with analytical results from a paper by Chamberlain (1979).Item Surface reconstruction from surface contours(1983) Simar, Laurence Ray; Figueiredo, Rui J. P. de; Clark, John W.; Dufour, Reginald J.Surface reconstruction from surface contours has become increasingly important in the medical field. Given a set of serial cross sections, it is shown that a structural technique of reconstruction can be developed. The motivation is to analyze the structure of the cross sections so as to represent the surface more faithfully than conventional techniques. The procedure involves syntactic and semantic techniques which allow the algorithm to analyze the cross sections at a high level. This information can then be used to recognize features on adjacent contours and then reproduce the surface which generated the cross sections.Item The dust distribution and ionization structure of the Orion nebula(1991) Walter, Donald Kim; Dufour, Reginald J.Presented are the results of an empirical study of the scattering of starlight in the UV and optical continuum by dust in Orion, plus the distribution of the ionic species of CNO across the face of the nebula. Spectra from the IUE have been combined with ground-based spectrophotometry and CCD imagery. This study of M42 is the most extensive to date. The distribution of dust and its effects on the scattering of starlight are examined. The variation of scattered light with distance and wavelength has been parameterized and a functional relationship determined. Abundances for ionic species of carbon, oxygen and nitrogen have been calculated. Several results were uncovered. The C/H abundance in Orion must be lowered by a factor of 3-5 compared to past results. The C/H abundance is constant across the inner 5 arcmin of the nebula as is the C/O ratio.Item The photoklystron(1980) Simons, Sedgwick Lewis; Freeman, John W.; Dufour, Reginald J.; Few, Arthur A.The photoklystron is a photoelectric vacuum tube designed to convert broadband light energy directly into monochromatic high frequency AC power. It requires a DC reflecting voltage (which draws no power) and the first model works best with a DC accelerating voltage (which represents an additional input energy) but has been shown to operate with only light energy. With the accelerating voltage, frequencies from 4 to over 2 MHz. have been produced, and electrical efficiencies near 2% have been measured. Computer analysis of the electron trajectories revealed that unlike a reflex klystron the photoklystron works by extracting the kinetic energy of the electrons over a period of several cycles. For net energy output the accelerating and reflecting voltages are adjusted so that the electron trajectories have a period which is a multiple of the period of the RF output desired. Any electrons which are improperly phased are quickly eliminated by collision with the photocathode or repeller. Conditions for optimum interaction of the electrons with the RF field have been investigated both analytically and numerically using a Tektronix 452 computer. Although some aspects of the photoklystron are not fully understood at this time, it has been shown to be a fundamentally new and simple oscillator, offering a wide variety of applications.Item The physical diagnostics and ionization structure of the Orion Nebula(1993) Walter, Donald Kim; Dufour, Reginald J.The most detailed study to date of the physical diagnostics and ionization structure of the core of M42 (the Orion Nebula) is presented using new long slit spectra and existing CCD imagery. Cospatial temperature and density diagnostics are presented for distances out to $\sim$5 arcminutes from the Trapezium and clearly show gradients in $T\sb{e}$ and $N\sb{e}.$ Temperatures are derived using S$\sp+,$ O$\sp+,$ N$\sp+,$ O$\sp{++}$ and the Balmer Discontinuity, T(Bac). Values for T(S$\sp+)$ in the range 11,000-14,500 K are presented and suggest shock heating at the ionization front as predicted by some models. A gradient in T(Bac) is derived with temperatures as low as 3000 K and is left open to interpretation. Density gradients for S$\sp+,$ O$\sp+$ and Cl$\sp{++}$ are also presented and are consistent with model predictions for an H scII region in the champagne phase of evolution. Using imagery we have constructed a picture of the core of Orion, including previously unknown features. Ratio maps show a high ionization cavity centered on the Trapezium and a low ionization region to the southwest. Ripples and bends in the background molecular cloud are detected. Further to the southwest the ionization begins to increase with distance, which is interpreted as the molecular cloud curving back toward the observer. Additional features in the imagery include a bar-like structure to the northeast of the Trapezium and a high density knot and ellipse of material believed to be a Herbig Haro object. Our diagnostics provide unprecedented detail as to the variation of temperature fluctuations with position. The mean square temperature fluctuation, $t\sp2,$ for the ions O$\sp{++}$ and N$\sp+$ is similar on a global scale, with a value in the range 0.03-0.05 for an assumed constant recombination temperature. Using a gradient in T(Bac) predicts $t\sp2$ values of 0.01-0.15 with values increasing outward. The ion S$\sp+$ gives unusually high values of $t\sp2$ and is not a reliable indicator of fluctuations in the H$\sp+$ zone since some of the (S II) emission arises from beyond the ionization front.Item The quiescent rotator(1982) Polstorff, Juergen; Michel, F. Curtis; Wolf, Richard A.; Dufour, Reginald J.The problem of a physically self-consistent pulsar magnetosphere has existed since the introduction of the Goldreich and Julian model. This work presents a method for creating a self consistent charge-separated finite magnetosphere which would surround a pulsar with magnetic dipole and spin axis aligned. The finite magnetosphere configuration is allowed due to the existence of vacuum gaps and acts to make the pulsar surface emission free. This produces a quiescent rotator that is electrically static. Two examples using discrete charges to model the magnetosphere are presented and the magnetospheric configuration associated with them is examined.