Search NASA⌕ Search

Engineering topics

Edgar, R. J.

Publications and source records attributed to Edgar, R. J..

16 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Orbital Verification of the CXO High-Resolution Mirror Assembly Alignment and Vignetting

Prior to launch, the High Resolution Mirror Assembly (HRMA) of the Chandra X-ray Observatory underwent extensive ground testing at the X-ray Calibration Facility (XRCF) at the Marshall Space Flight Center in Huntsville. Observations made during the post-launch Orbital Activation and Calibration period, allow the on-orbit condition of the X-ray optics to be assessed. Based on these ground-based and on-orbit data, we examine the alignment of the x-ray optics based on the PSF, and the boresight and alignment of the optical axis alignment relative to the detectors. We examine the vignetting and the single reflection ghost suppression properties of the telescope. Slight imperfections in alignment lead to a small azimuthal dependence of the off-axis area; the morphology of off-axis images also shows an additional small azimuthal dependence varying as 1/2 the off-axis azimuth angle.

Gaetz, T. J.↗
NASA NTRS2000

Orbital Measurement and Verification of the Chandra X-Ray Observatory's PSF

The recently launched Chandra x-ray Observatory (CXO) was designed to have the sharpest angular resolution yet of any x-ray telescope. Detailed modeling and metrology of the optics followed by extensive testing at the X-ray Calibration Facility at the Marshall p Space Flight Center in Huntsville, Alabama, indicated that the optics were performing exceedingly well, within our ability to account for distortion of the mirrors due to gravity, and the effects of finite distance and size of the x-ray generator. Thus it was only on-orbit that we expected to directly observe the specified half arcsecond performance. We present here results of the on-orbit calibration of the point spread function (PSF), comparing it with our predictions. We discuss how the PSF varies with source location in the telescope field of view, as well as with the spectral energy distribution of the source.

Jerius, D.↗
NASA NTRS2000

Absolute Effective Area of the Chandra High-Resolution Mirror Assembly

The Chandra X-ray Observatory was launched in July 1999, and is returning exquisite sub-arcsecond x-ray images of star groups, supernova remnants, galaxies, quasars, and clusters of galaxies. In addition to being the premier X-ray observatory in terms of angular and spectral resolution, Chandra is the best calibrated X-ray facility ever flown. We discuss here the calibration of the effective area of the High Resolution Mirror Assembly. Because we do not know the absolute X-ray flux density of any celestial source, this must be based primarily on ground measurements and on modeling. In particular, we must remove the calibrated modeled responses of the detectors and gratings to obtain the mirror area. For celestial sources which may be assumed to have smoothly varying spectra, such as the Crab Nebula, we may verify the continuity of the area calibration as a function of energy. This is of significance in energy regions such as the Ir M-edges, or near the critical grazing angle cutoff of the various mirror shells.

Schwartz, D. A.↗
NASA NTRS1997

High minor ion outflow speeds in the inner corona and observed ion charge states in interplanetary space

The study carried out in order to demonstrate that high minor ion outflow speeds of the order of O(5+) outflow speed are consistent with charge state observations is presented. The calculations were based on atomic data, observational constraints concerning electron temperatures, electron densities and flow speeds. Minor ion charge state observations were used in order to place limits on solar wind acceleration and heating mechanisms. The charge states of C, O, Fe and Si ions measured in situ were compared to those calculated from two solar wind models. The use of the planned ultraviolet and charge state observations in order to constrain both the ion outflow speeds and electron temperature is discussed.

Esser, R.↗
NASA NTRS1997

Predictions of the On-Orbit Performance of AXAF's Optics

The AXAF optics and science instruments have recently undergone a battery of tests at the Marshall Space Flight Center X-Ray Calibration Facility to determine their spatial and spectral performance. We have combined these data, detailed maps of the optics, surfaces, precise measurements of surface roughness and reflectivity, and detailed mechanical models of the optics and their support structures to arrive at predictions of the optics' on-orbit performance. We present on- and off-axis effective areas, encircled energies, and PSFS.

Jerius, D.↗
NASA NTRS1996

DXS spectra of the 0.25 keV diffuse background

Data from the diffuse X-ray spectrometer (DXS) experiment, a Shuttle payload that flew in January 1993, were analyzed. The DXS measured spectra from the local hot bubble component of the diffuse X-ray background. The soft X-ray diffuse background spectra contain emission lines and emission-line blends, indicating that the source of the low latitude diffuse background is thermal (a hot phase of the interstellar medium). The measured spectra do not resemble the model spectra of cosmic abundance or depleted abundance coronal plasmas at any temperature in the range of 10(exp 5) K to 10(exp 7) K.

Sanders, W. T.↗
NASA NTRS1992

The Diffuse X-ray Spectrometer Experiment

The Diffuse X-ray Spectrometer Experiment, or 'DXS', is designed to measure the spectrum of the low-energy diffuse X-ray background with about 10 eV energy resolution and 15-deg spatial resolution. During a 5-day Space Shuttle mission, DXS is to measure the spectrum of ten 15 x 15 deg regions lying along a single 150-deg-long great circle arc on the sky. DXS carries two large-area X-ray Bragg spectrometers for the 44-84 A wavelength range; these permit measurement of the wavelength spectrum of the cosmic low-energy diffuse X-ray background with good spectral resolution.

Sanders, W. T.↗
NASA NTRS1990

The SHEAL Diffuse X-ray Spectrometer experiment

The paper describes the Diffuse X-ray Spectrometer (DXS) experiment which will be carried on board the NASA's SHEAL 2 mission, scheduled to be launched as an attached Shuttle payload in 1992. The SHEAL DXS is designed to measure the spectrum of the low-energy (0.15 to 0.28 keV) diffuse X-ray background with the energy resolution better than 0.01 keV. The results of calculations of the anticipated data are presented together with diagrams of the DXS assembly.

Sanders, W. T.↗
NASA NTRS1986

The soft X-ray background as a supernova blast wave viewed from inside - Solar abundance models

A model of the soft X-ray background is presented in which the sun is assumed to be inside an active supernova blast wave. The blast wave evolves in a preexisting cavity. The broad band surface brightnesses is explained by such a blast wave with an explosion energy of E sub approximately 5 x 10 to the 50th power ergs and radius 80 to 100 pc, using solar abundances. An approach to treating the problem of large anisotropies in the ambient medium is also explored, accommodating the observed anticorrelation between the soft X-ray surface brightness and the 21 cm column density. It is found that only for post shock temperatures below 10 to the 6 power K a shock propagating into a density enhancement will be dimmer than a similar shock in a lower density region.

Edgar, R. J.↗
NASA NTRS1986

Highly ionized atoms in cooling gas

The ionization of low density gas cooling from a high temperature was calculated. The evolution during the cooling is assumed to be isochoric, isobaric, or a combination of these cases. The calculations are used to predict the column densities and ultraviolet line luminosities of highly ionized atoms in cooling gas. In a model for cooling of a hot galactic corona, it is shown that the observed value of N(N V) can be produced in the cooling gas, while the predicted value of N(Si IV) falls short of the observed value by a factor of about 5. The same model predicts fluxes of ultraviolet emission lines that are a factor of 10 lower than the claimed detections of Feldman, Brune, and Henry. Predictions are made for ultraviolet lines in cooling flows in early-type galaxies and clusters of galaxies. It is shown that the column densities of interest vary over a fairly narrow range, while the emission line luminosities are simply proportional to the mass inflow rate.

Edgar, R. J.↗
NASA NTRS1984

A Model of the Soft X-ray Background as a Blast Wave Viewed from Inside

The suggestion that the soft X-ray background arises in part from the Sun which is inside a large supernova blastwave was examined by models of spherical blastwaves. The models can produce quantitative fits to both surface brightnesses and energy band ratios when t = 10 to the 5th power E sub o = 5 x 10 to the 50th power ergs, and n sub approx. 0.004 cm to the -3 power. The models are generalized by varying the relative importance of factors such as thermal conduction, Coulomb heating of electrons, and external pressure; and to allow the explosions to occur in preexisting cavities with steep density gradients, or by examination of the effects of large obstructions or other anisotrophies in the ambient medium.

Edgar, R. J.↗
NASA NTRS1984

The time development of a blast wave with shock-heated electrons

Accurate approximations are presented for the time development of both edge conditions and internal structures of a blast wave with shock heated electrons, and equal ion and electron temperatures at the shock. The cases considered evolve in cavities with power law ambient densities (including the uniform ambient density case) and have negligible external pressure. Account is taken of possible saturation of the thermal conduction flux. The structures evolve smoothly to the adiabatic structures.

Edgar, R. J.↗
NASA NTRS1984

The soft X-ray background as a supernova blast wave viewed from inside: Solar abundance models

A model of the soft X-ray background is presented in which the Sun is assumed to be inside an active supernova blast wave. The blast wave evolves in a preexisting cavity. The broad band surface brightnesses is explained by such a blast wave with an explosion energy of E sub approx. 5 x 10 to the 50th power ergs and radius 80 to 100 pc, using solar abundances. An approach to treating the problem of large anisotropies in the ambient medium is also explored, accommodating the observed anticorrelation between the soft X-ray surface brightness and the 21 cm column density. It is found that only for post shock temperatures below 10 6 K a shock propagating into a density enhancement will be dimmer than a similar shock in a lower density region.

Edgar, R. J.↗
NASA NTRS1983

The time development of a blast wave with shock heated electrons

Accurate approximations are presented for the time development of both edge conditions and internal structures of a blast wave with shock heated electrons, and equal ion and electron temperatures at the shock. The cases considered evolve in cavities with power law ambient densities (including the uniform ambient density case) and have negligible external pressure. Account is taken of possible saturation of the thermal conduction flux. The structures evolve smoothly to the adiabatic structures.

Edgar, R. J.↗
NASA NTRS1982

Another self-similar blast wave: Early time asymptote with shock heated electrons and high thermal conductivity

Accurate approximations are presented for the self-similar structures of nonradiating blast waves with adiabatic ions, isothermal electrons, and equation ion and electron temperatures at the shock. The cases considered evolve in cavities with power law ambient densities (including the uniform density case) and have negligible external pressure. The results provide the early time asymptote for systems with shock heating of electrons and strong thermal conduction. In addition, they provide analytical results against which two fluid numerical hydrodynamic codes can be checked.

Cox, D. P.↗