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All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Determination of plasma temperatures and luminosities using multiple extreme-ultraviolet and X-ray filters

We carefully examine the techniques used to infer temperatures of stellar coronal plasmas from the count rates of several broadband instruments in the X-ray and extreme-ultraviolet spectral ranges. In particular, we determine to what extent temperatures can be constrained and the corresponding uncertainties in the luminosities and emission measures lowered by fitting simultaneously count rates from the Einstein imaging proportional counter (IPC), the ROSAT Position Sensitive Proportional Counter (PSPC), the ROSAT Wide Field Camera (WFC) (both filters), and the EXOSAT Low Energy Telescope (LET) with the 3-Lex filter. We use published plasma emissivities with solar photospheric abundances. Since it has been found that single-temperature plasmas do not fit IPC data well, we assume a two-temperature plasma model. We find that, even with count rates from all of the above filters and overly optimistic error estimates, it is still not possible to determine a unique two-temperature solution. However, since the use of count rates from many filters can reduce substantially the number of possible solutions, temperature solutions determined by other means can be tested. We carry out such an analysis on a set of 18 nearby late-type stars to determine possible two-temperature solutions using multifilter photometry, and we compare these results with the temperature solutions derived by Schmitt et al. (1990) using IPC spectral data. In general, the two-temperature fits derived from the IPC spectral data are inconsistent with our results, with our data implying that, for many stars, the two temperatures derived by the IPC may be too low by about a factor of 2. The EXOSAT transmission grating Spectrometer (TGS) spectra of capella and sigma(exp 2) CrB support this conclusion. For Procyon and 70 Oph, though, the presence of a temperature component cooler than a million degress (not detected by the IPC) is deduced. While our analysis suggests the existence of more than one temperature in the coronae of late-type stars, in many instances our WFC data appear to be inconsistent with the presence of significant emission measure over a broad temperature distribution. This, together with the success of two-temperature plasmas in fitting IPC and TGS data, implies that for many stars, the coronal emission measure distribution may in fact be dominated by two distinct temperature regimes.

Wood, Brian E.↗
NASA NTRS2025

An Efficient GPU-Accelerated Multi-Source Global Fit Pipeline for LISA Data Analysis

The large-scale analysis task of deciphering gravitational wave signals in the LISA data stream will be difficult, requiring a large amount of computational resources and extensive development of computational methods. Its high dimensionality, multiple model types, and complicated noise profile require a global fit to all parameters and input models simultaneously. In this work, we detail our global fit algorithm, called “Erebor,” designed to accomplish this challenging task. It is capable of analysing current state-of-the-art datasets and then growing into the future as more pieces of the pipeline are completed and added. We describe our pipeline strategy, the algorithmic setup, and the results from our analysis of the LDC2A Sangria dataset, which contains Massive Black Hole Binaries, compact Galactic Binaries, and a parameterized noise spectrum whose parameters are unknown to the user. The Erebor algorithm includes three unique and very useful contributions: GPU acceleration for enhanced computational efficiency; ensemble MCMC sampling with multiple MCMC walkers per temperature for better mixing and parallelized sample creation; and special online updates to reversible-jump (or trans-dimensional) sampling distributions to ensure sampler mixing and accurate initial estimates for detectable sources in the data. We recover posterior distributions for all 15 (6) of the injected MBHBs in the LDC2A training (hidden) dataset. We catalog ∼12000 Galactic Binaries (∼8000 as high confidence detections) for both the training and hidden datasets. All of the sources and their posterior distributions are provided in publicly available catalogs.

LISA global fit↗
NASA NTRS1990

Spectroscopic analysis of global tide gauge sea level data

Yearly and monthly global tide-gage sea-level data are fitted to numerically generated tidal data in order to search for the 18.6-yr lunar nodal tide and 14-month pole tide. Both of these tides are clearly evident, with amplitudes and phases that are consistent with a global equilibrium response. The ocean's response to atmospheric pressure is studied with the least-squares fit technique. Consideration is given to the global rise in sea level, the effects of postglacial rebound, and the possible causes of the enhanced pole tides in the North Sea, the Baltic Sea, and the Gulf of Bothnia. The results support O'Connor's (1986) suggestion that the enhanced pole tide in these regions is due to meteorological forcing rather than a basin-scale resonance. Also, the global average of the tide-gage data show an increase in sea level over tha last 80 yr of between 1.1 and 1.9 mm/yr.

Trupin, A.↗
NASA NTRS2017

Raising the Albedo of 2010 GY6: Fitting ATPM to Wise Data

Near-Earth Asteroid 462775 (2010 GY6) is in the Apollo orbit-family with a 1.46 year orbital period. 2010 GY6 was measured by WISE and fitted with NEATM, yielding NEATM model parameters of D=1.1 km, pv=0.028 and eta=2.3.The NEATM-derived geometric albedo of 2010 GY6 is lower than the surface of comet 67P/C-G. The eta value is considerably higher than typical for its phase angle of 33 deg, indicating a cooler surface due to non-zero thermal inertia and/or surface roughness are important. If the thermal inertia and surface roughness are constrained by fitting the Advanced Thermophysical Model (ATPM) to the WISE data, what would the resulting geometric albedo? We find pv=0.06-0.08, in the same range as B- or C-type NEAs like Bennu or JU3.

Near-Earth Asteroid 462775↗
NASA NTRS2006

Using Quasiparticle Poisoning To Detect Photons

According to a proposal, a phenomenon associated with excitation of quasiparticles in certain superconducting quantum devices would be exploited as a means of detecting photons with exquisite sensitivity. The phenomenon could also be exploited to perform medium-resolution spectroscopy. The proposal was inspired by the observation that Coulomb blockade devices upon which some quantum logic gates are based are extremely sensitive to quasiparticles excited above the superconducting gaps in their leads. The presence of quasiparticles in the leads can be easily detected via the charge states. If quasiparticles could be generated in the leads by absorption of photons, then the devices could be used as very sensitive detectors of electromagnetic radiation over the spectral range from x-rays to submillimeter waves. The devices in question are single-Cooper-pair boxes (SCBs), which are mesoscopic superconducting devices developed for quantum computing. An SCB consists of a small superconducting island connected to a reservoir via a small tunnel junction and connected to a voltage source through a gate capacitor. An SCB is an artificial two-level quantum system, the Hamiltonian of which can be controlled by the gate voltage. One measures the expected value of the charge of the eigenvectors of this quantum system by use of a radio-frequency single-electron transistor. A plot of this expected value of charge as a function of gate voltage resembles a staircase that, in the ideal case, consists of steps of height 2 e (where e is the charge of one electron). Experiments have shown that depending on the parameters of the device, quasiparticles in the form of "broken" Cooper pairs present in the reservoir can tunnel to the island, giving rise to steps of 1 e. This effect is sometimes called "poisoning." Simulations have shown that an extremely small average number of quasiparticles can generate a 1-e periodic signal. In a device according to the proposal, this poisoning would be turned to advantage. Depending on the wavelength, an antenna or other component would be used to couple radiation into the reservoir, wherein the absorption of photons would break Cooper pairs, thereby creating quasiparticles that, in turn, would tunnel to the island, creating a 1-e signal. On the basis of conservative estimates of device parameters derived from experimental data and computational simulations that fit the data, it has been estimated that the noise equivalent power of a device according to the proposal could be as low as 6 10(exp -22) W/Hz(exp 1/2). It has also been estimated that the spectroscopic resolution (photon energy divided by increment of photon energy) of such a device in visible light would exceed 100.

Echternach, Pierre↗
NASA NTRS2005

Spectral Photometric Properties of the Moon

We modeled the solar phase curves of the moon at a series of wavelengths using the full disk telescopic observations [1]. We endeavored to keep the database self-contained, that is, to use the values derived for the solar magnitude and phase curves of the disk-integrated [1]. These observations were made in a suite of 10 narrowband filters between 0.315 microns and 1.06 microns, and in the broad band Johnson UBV filters, as part of a larger program to obtain photoelectric photometry of the larger planets. Two aspects of the lunar observations are unique. First, the observations cover phase angles from 6deg through 120deg. More importantly, the observers used a special 20-mm diameter f/15 fused quartz lens constructed solely for this purpose. The lens reduced the whole lunar image in the focal plane to a size comparable to the planets observed as part of the same program. This image was fed directly into the photometer. Thus, these observations constitute the only existing set of phase curves of the entire lunar disk over a range of wavelengths. Table 1 lists the values of the Hapke model parameters which fit the data. Figure 1 is an example of the model fits to the data.

Dominque, D.↗
NASA NTRS2025

Efficient GPU-Accelerated MultiSource Global Fit Pipeline for LISA Data Analysis

The large-scale analysis task of deciphering gravitational-wave signals in the LISA data stream will be difficult, requiring a large amount of computational resources and extensive development of computational methods. Its high dimensionality, multiple model types, and complicated noise profile require a global fit to all parameters and input models simultaneously. In this work, we detail our global fit algorithm, called “Erebor,” designed to accomplish this challenging task. It is capable of analyzing current state-of-the-art datasets and then growing into the future as more pieces of the pipeline are completed and added. We describe our pipeline strategy, the algorithmic setup, and the results from our analysis of the LDC2A Sangria dataset, which contains massive black hole binaries, compact galactic binaries, and a parametrized noise spectrum whose parameters are unknown to the user. The Erebor algorithm includes three unique and very useful contributions: GPU acceleration for enhanced computational efficiency; ensemble Markov Chain Monte Carlo (MCMC) sampling with multiple MCMC walkers per temperature for better mixing and parallelized sample creation; and special online updates to reversible-jump (or transdimensional) sampling distributions to ensure sampler mixing and accurate initial estimates for detectable sources in the data.We recover posterior distributions for all 15 (6) of the injected massive black hole binaries (MBHB) in the LDC2A training (hidden) dataset. We catalog ∼12000 galactic binaries (∼8000 as high confidence detections) for both the training and hidden datasets. All of the sources and their posterior distributions are provided in publicly available catalogs.

LISA↗
NASA NTRS1994

Detection of the SO2 atmosphere on Io with the Hubble Space Telescope

Observations of the trailing hemisphere of Io made with the Faint Object Spectrograph of the Hubble Space Telescope (HST) in March 1992 have resulted in the first detection of atmospheric SO2 absorption bands in the ultraviolet. These observations represent only the third positive means of detection of what is widely believed to be Io's primary atmospheric constituent. Below approximately 2130 A the geometric albedo of the satellite is dominated by SO2 gas absorption band signatures, which have been analyzed using models that include the effects of optical thickness, temperature, and spatial distribution. The disk-intergrated HST data cannot resolve the spatial distribution, but it is possible to define basic properties and set constraints on the atmosphere at the time of the observations. Hemispheric atmospheres with average column density N = 6 - 10 x 10(exp 15)/sq sm and T(gas) = 110 - 500 K fit the data, with preference for temperatures of approximately 200 - 250 K. Better fits are found as the atmosphere is spatially confined, with a limit of approximately 8% hemispheric areal coverage and N approximately equal to 3 x 10(exp 17)/sq cm with colder 110 - 250 K temepratures. A dense (N greater than or equal to 10(exp 16)/sq cm), localized component of SO2 gas, such as that possibly associated with active volcanoes, can generate the observed spectral constrast only when the atmosphere is cold (110 K) and an extended component such as Pele is included. The combination of a dense, localized atmosphere with a tenuous component (N less than 10(exp 16)/sq cm, either patchy or extended) also fits the data. In all cases the best fit models imply a disk-averaged column density larger than exospheric but approximately 10 - 30 times less than the previous upper limit from near-UV observations.

Ballester, G. E.↗
NASA NTRS1985

Improved mapping of radio sources from VLBI data by least-square fit

A method is described for producing improved mapping of radio sources from Very Long Base Interferometry (VLBI) data. The method described is more direct than existing Fourier methods, is often more accurate, and runs at least as fast. The visibility data is modeled here, as in existing methods, as a function of the unknown brightness distribution and the unknown antenna gains and phases. These unknowns are chosen so that the resulting function values are as near as possible to the observed values. If researchers use the radio mapping source deviation to measure the closeness of this fit to the observed values, they are led to the problem of minimizing a certain function of all the unknown parameters. This minimization problem cannot be solved directly, but it can be attacked by iterative methods which we show converge automatically to the minimum with no user intervention. The resulting brightness distribution will furnish the best fit to the data among all brightness distributions of given resolution.

Rodemich, E. R.↗
NASA NTRS1977

Silicon vidicon imaging of Jupiter - 4100- to 8300-A absolute reflectivities and limb darkening of spatially resolved regions

Jupiter was observed in six continuum wavelength channels in the region 4100-8300 A, using a silicon vidicon imaging photometer. Spectral reflectivities and high spatial resolution limb-darkening curves for several belts and zones have been extracted from the data. Simple model fits to the data yield information regarding spectral and spatial variations in single-scattering albedos and shape of particle single-scattering phase functions. Belts appear to be more backscattering than zones, particularly in the blue. The data are in moderate agreement with limb-darkening predicted by models derived from the center-to-limb variation in equivalent width of the H2 4-0 S(1) quadrupole line (Cochran, 1976) in the South Tropical Zone, but strongly disagree with the results of such models for the North Equatorial Belt.

Diner, D. J.↗
NASA NTRS1988

Optical to mid-infrared polarimetry of OH 0739-14

Optical and mid-IR polarimetry and optical photometry are presented for OH 0739 - 14 (= OH 231.8 + 4.2), and previous NIR polarimetry is confirmed. The wavelength dependence of the polarization is modeled. A model using 50-nm silicate grains fits the data at optical and NIR wavelengths but does not do well at the 10-micron silicate feature. The model with 100-nm ice grains fits the data well except at the L band, which is near the 3.08-micron ice absorption feature. The source is most likely to contain a mixture of these two grain species.

Heckert, Paul A.↗
NASA NTRS1994

Atmospheric effects on the risetime and waveshape of sonic booms

Accurate prediction of human response to sonic booms from proposed HSCT aircraft depends on a knowledge of the waveshape and risetime of the boom at the ground. In previous work, we have developed a numerical technique to predict the combined effects of molecular absorption and finite wave distortion on the sonic boom as it propagates from the aircraft to the top of the turbulent boundary layer. We have more recently developed a scattering center based model to calculate the effects of turbulence on the sonic boom waveform as it propagates through this boundary layer. Calculations have been performed using single scales of turbulence and compared to measurements at Edwards AFB in the late 1960's. A model of the atmosphere involving two scales each for convective and mechanical turbulence has been developed and fit to meteorological data collected during JAPE 2. Scattering calculations employing this model underpredict the number of unperturbed waveforms. In order to develop a more realistic model of the atmosphere, the JAPE 2 meteorological data has been fit to a von Karman spectrum. Results of scattering using this multi-scale model will be presented. The combination of finite wave effects with turbulent scattering predictions includes the principal effects of the atmosphere on the sonic boom from the HSCT.

Raspet, Richard↗
NASA NTRS2000

The BATSE Gamma-Ray Burst E-Peak Distribution

Gamma-ray burst observed by BATSE are found to have approximately the same characteristic energy, denoted as E_p. We examine whether instrumental effects can give rise to this observation. We simulate the derivation of E-p and determine that the values in the BATSE sample are accurate and complete above a minimum fluence. We simulate the triggering of BATSE on gamma-ray bursts, deriving the efficiency of detecting bursts as a function of characteristic energy. From this simulation, we model the observed E_p distribution function expected when the intrinsic distribution function is a power-law. We find that this distribution produces poor fits to the observations. We find that a log-normal intrinsic distribution with a power-law tail gives a good fit to the data. From these fits, we conclude that instrumental effects cannot produce the observed E_p distribution, and that the observed distribution is a consequence of a narrow intrinsic distribution of E_p in gamma-ray bursts.

Brainerd, Jerome J.↗
NASA NTRS2003

Termolecular ion-molecule reactions in Titan's atmosphere. IV. A search made at up to 1 micron in pure hydrocarbons

The results of a study of ion-molecule reactions occurring in pure methane, acetylene, ethylene, ethane, propyne, propene, propane, and diacetylene at pressures up to 40 microns of pressure are reported. A variety of experimental methods are used: The standard double resonance in an ICR, for determination of the precursor ions and the modulated double resonance ejection in an ICR, for the determination of the daughter ions. The FA-SIFT technique was used for validation and examination of termolecular reactions with rate coefficients that are less than 10(-26) cm(6) s(-1). An extensive database of reaction kinetics already exists for many of these reactions. The main point of this study was the determination of the accuracy of this database and to search for any missing reactions and reaction channels that may have been omitted from earlier investigations. A specific objective of this work was to extend the study to the highest pressures possible to find out if there were any important termolecular reaction channels occurring. A new approach was used here. In the pure hydrocarbon gases the mass spectra were followed as a function of the pressure changes of the gas. An initial guess was first made using the current literature as a source of the reaction kinetics that were expected. A model of the ion abundances was produced from the solution of the partial differential equations in terms of reaction rate coefficients and initial abundances. The experimental data was fitted to the model for all of the pressures by a least squares minimization to the reaction rate coefficients and initial abundances. The reaction rate coefficients obtained from the model were then compared to the literature values. Several new channels and reactions were discovered when the modeled fits were compared to the actual data. This is all explained in the text and the implications of these results are discussed for the Titan atmosphere.

Hydrocarbons, Acyclic/analysis↗
NASA NTRS1989

Observational constraints on an embedded cloud model for the soft X-ray diffuse background

The reason for the observed anticorrelation between soft X-ray diffuse background (SXRB) and neutral hydrogen column densities are considered. Using the B and C band data from an all-sky survey of the SXRB, as well as data in the Be band, it is shown that the Jakobsen and Kahn (1986) embedded cloud model, in which several statistical properties of the SXRB in the B and C bands were used to constrain their model parameters, cannot fit the observed band ratios, except in the limit in which virtually all of the emission originates in the near side of the absorbing gas. It was also shown that model parameters corresponding to appreciably mixed emission and absorption, as proposed by Bunner et al. (1969) and Davidsen et al. (1972), do not fit the data. Model parameters corresponding to the absorption models of Bowyer et al. (1968), Bunner et al. (1969), Davidsen et al. (1972), and Yentis et al. (1972), cannot fit the data unless the absorbing material is more strongly clumped than is permitted by 21-cm observations.

Burrows, D. N.↗
NASA NTRSDate not supplied

New Features of the NEQAIR Radiation Code

The longest-lived code for predicting shock layer radiation, NEQAIR, is now in its 5th decade of service. Substantial changes to the code have been made over the previous decade, the most recent report of which was at the 5th Workshop on Radiation in High Temperature Gases in 2014, for the version referred to as NEQAIR14. This paper will review some of the improvements made to the NEQAIR code since then, which is now at v15.2. Some of these features are discussed briefly below. NEQAIR15 and subsequent versions have enabled parallel evaluation of multiple lines of sight. This is accomplished by utilizing the HDF5 file format and placing multiple lines into a single file, LOS.h5, which is used for both input and output. This approach enables straightforward parallel execution both over the number of lines of sight and the number of points per line. For large problems, runtime reduces linearly with the number of nodes deployed since each line is processed independently by a subset of MPI ranks. Three applications of the multi-line solver are discussed. The first has to do with performing loosely coupled radiation-flowfield solutions. In this case the computed absorption and emission coefficients are used to evaluate the total energy absorbed or emitted at each point, allowing evaluation of the volumetric source term in the flowfield. The second computation is for obtaining heat flux from nonuniform flows, which require integration over spherical co-ordinates. These are of particular interest for evaluating radiation on the vehicle backshell. This 3D option improves the angular integration scheme and allows adaptive line selection that together reduce the number of lines required by about an order of magnitude. The final application is for remote observation, which is essentially the 3D integration problem over a small solid angle. For all three of these computations, data can be stored in the HDF5 file which allows a NEQAIR run to be restarted when it times out, or to add atmospheric absorption or instrument scan functions. An additional level of parallelism is enabled in NEQAIR15.2 using GPU routines. The GPU parallelism has realized up to 8x speed-up when running on a single core but diminishes as CPU parallelism is increased. For running multi-line simulations, it may be easier to reserve a large number of CPU nodes than to obtain the number of GPU nodes required for similar performance. A GUI, known as NEQTPY, allows for reading and creating input files, running NEQAIR, and displaying results. A significant feature of NEQTPY is the ability to perform spectral fits to data. The fits can operate on a single line spectrum (radiance vs. wavelength) or a 3D input file with multiple columns of data. Other new features include improved constants, additional species, more detailed non-Boltzmann modelling, advanced user controls, the ability to read and calculate spectra from HITRAN datafiles, photodissociation and photoionization cross-sections. A “fast” automatic grid option may reduce the size and time of spectral calculations while still maintaining good accuracy for total heat flux.

Brett A Cruden↗
NASA NTRS1978

Determination of volume fraction in multiphase systems using incomplete pole figures

The determination of the volume fraction of a second phase in a multiphase sample by X-ray diffraction becomes more difficult if the diffracting planes have a preferred orientation. Lopata and Kula have described a method of treating this problem using complete pole figures for each of the phases. With some samples, it is not always possible or convenient to obtain data over the full hemisphere. Equations and an example are given which require X-ray data over a limited range of approximately 0 to 75 deg. This can be obtained by reflection without a specially cut sample or transmission data. A series of Legendre polynomials are fitted to data collected while spinning the sample about its normal. An extrapolation is made possible by introducing two conditions on the end points which must be satisfied if the extrapolation functions are to be valid.

Houska, C. R.↗