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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Evidence for a Significant Intermediate-Age Population in the M31 Halo from Main Sequence Photometry

We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M3l), 51 arcmin (11 kpc) from the nucleus. These observations, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, are the deepest optical images yet obtained, attaining 50% completeness at m(sub v) = 30.7 mag. The CMD, constructed from approx. 3 x 10(exp 5) stars, reaches more than 1.5 mag fainter than the old main-sequence turnoff. Our analysis is based on direct comparisons to ACS observations of four globular clusters through the same filters, as well as chi square fitting to a finely-spaced grid of calibrated stellar-population models. We find that the M31 halo contains a major (approx. 30% by mass) intermediate-age (6-8 Gyr) metal-rich ([Fe/H] greater than -0.5) population, as well as a significant globular-cluster age (11-13.5 Gyr) metal-poor population. These findings support the idea that galaxy mergers played an important role in the formation of the M31 halo.

Brown, Thomas M.↗
NASA NTRS2016

MBSE-Driven Visualization of Requirements Allocation and Traceability

In a Model Based Systems Engineering (MBSE) infusion effort, there is a usually a concerted effort to define the information architecture, ontologies, and patterns that drive the construction and architecture of MBSE models, but less attention is given to the logical follow-on of that effort: how to practically leverage the resulting semantic richness of a well formed populated model to enable systems engineers to work more effectively, as MBSE promises. While ontologies and patterns are absolutely necessary, an MBSE effort must also design and provide practical demonstration of value (through human-understandable representations of model data that address stakeholder concerns) or it will not succeed. This paper will discuss opportunities that exist for visualization in making the richness of a well-formed model accessible to stakeholders, specifically stakeholders who rely on the model for their day-to-day work. This paper will discuss the value added by MBSE-driven visualizations in the context of a small case study of interactive visualizations created and used on NASA’s proposed Europa Mission. The case study visualizations were created for the purpose of understanding and exploring targeted aspects of requirements flow, allocation, and comparing the structure of that flow-down to a conceptual project decomposition. The work presented in this paper is an example of a product that leverages the richness and formalisms of our knowledge representation while also responding to the quality attributes SEs care about.

Model Based Systems Engineering↗
NASA NTRS2012

ORDEM 3.0 and MASTER-2009 Modeled Small Debris Population Comparison

The latest versions of the two premier orbital debris engineering models, NASA's ORDEM 3.0 and ESA's MASTER-2009, have been publicly released within the last year. Both models have gone through significant advancements since inception, and now represent the state-of-the-art in orbital debris knowledge of their respective agencies. The purpose of these models is to provide satellite designers/operators and debris researchers with reliable estimates of the artificial debris environment in near-Earth orbit. The small debris environment within the size range of 1 mm to 1 cm is of particular interest to both human and robotic spacecraft programs. These objects are much more numerous than larger trackable debris but are still large enough to cause significant, if not catastrophic, damage to spacecraft upon impact. They are also small enough to elude routine detection by existing observation systems (radar and telescope). Without reliable detection the modeling of these populations has always coupled theoretical origins with supporting observational data in different degrees. This paper describes the population generation and categorization of both ORDEM 3.0 and MASTER-2009; their sources (both known and presumed), current supporting data and theory, and methods of population verification. Fluxes on spacecraft for chosen orbits are presented and discussed. Future collaborative analysis is noted.

Krisko, P. H.↗
NASA NTRS2016

MBSE-Driven Visualization of Requirements Allocation and Traceability

In a Model Based Systems Engineering (MBSE) infusion effort, there is a usually a concerted effort to define the information architecture, ontologies, and patterns that drive the construction and architecture of MBSE models, but less attention is given to the logical follow-on of that effort: how to practically leverage the resulting semantic richness of a well-formed populated model to enable systems engineers to work more effectively, as MBSE promises. While ontologies and patterns are absolutely necessary, an MBSE effort must also design and provide practical demonstration of value (through human-understandable representations of model data that address stakeholder concerns) or it will not succeed. This paper will discuss opportunities that exist for visualization in making the richness of a well-formed model accessible to stakeholders, specifically stakeholders who rely on the model for their day-to-day work. This paper will discuss the value added by MBSE-driven visualizations in the context of a small case study of interactive visualizations created and used on NASA's proposed Europa Mission. The case study visualizations were created for the purpose of understanding and exploring targeted aspects of requirements flow, allocation, and comparing the structure of that flow-down to a conceptual project decomposition. The work presented in this paper is an example of a product that leverages the richness and formalisms of our knowledge representation while also responding to the quality attributes SEs care about.

Model Based Systems Engineering↗
NASA NTRS2020

The Fast Radio Burst Luminosity Function and Death Line in the Low-Twist Magnetar Model

We explore the burst energy distribution of fast radio bursts(FRBs)in the low-twist magnetar model ofWadiasingh & Timokhin(WT19). Motivated by the power-lawfluence distributions of FRB121102, we proposean elementary model for the FRB luminosity function of individual repeaters with an inversion protocol thatdirectly relates the power-law distribution index of magnetar short burstfluences to that for FRBs. The protocolindicates that the FRB energy scales virtually linearly with crust/field dislocation amplitude, if magnetar shortbursts prevail in the magnetoelastic regime. Charge starvation in the magnetosphere during bursts(required inWT19)for individual repeaters implies the predicted burstfluence distribution is narrow,3 decades for yieldingstrains and oscillation frequencies feasible in magnetar crusts. Requiring magnetic confinement and chargestarvation, we obtain a death line for FRBs, which segregates magnetars from the normal pulsar population,suggesting only the former will host recurrent FRBs. We convolve the burst energy distribution for individualmagnetars to define the distribution of luminosities in evolved magnetar populations. The broken power-lawluminosity function’s low-energy character depends on the population model, while the high-energy index tracesthat of individual repeaters. Independent of the evolved population, the broken power-law isotropic-equivalentenergy/luminosity function peaks at∼1037–1040erg with a low-energy cutoff at∼1037erg. Lastly, we considerthe localfluence distribution of FRBs andfind that it can constrain the subset of FRB-producing magnetarprogenitors. Our model suggests that improvements in sensitivity may reveal aflattening of the global FRBfluencedistribution and saturation in FRB rates.

Cosmology↗
NASA NTRS1977

'Chain pooling' model selection as developed for the statistical analysis of a rotor burst protection experiment

A statistical decision procedure called chain pooling had been developed for model selection in fitting the results of a two-level fixed-effects full or fractional factorial experiment not having replication. The basic strategy included the use of one nominal level of significance for a preliminary test and a second nominal level of significance for the final test. The subject has been reexamined from the point of view of using as many as three successive statistical model deletion procedures in fitting the results of a single experiment. The investigation consisted of random number studies intended to simulate the results of a proposed aircraft turbine-engine rotor-burst-protection experiment. As a conservative approach, population model coefficients were chosen to represent a saturated 2 to the 4th power experiment with a distribution of parameter values unfavorable to the decision procedures. Three model selection strategies were developed.

Holms, A. G.↗
NASA NTRS1996

A Conservation Strategy for the Florida Scrub-Jay on John F. Kennedy Space Center/Merritt Island National Wildlife Refuge: An Initial Scientific Basis for Recovery

The Florida Scrub-Jay (Aphelocoma coerulescens) is an indicator of ecosystem integrity of Florida scrub, an endangered ecosystem that requires frequent fire. One of the largest populations of this federally threatened species occurs on John F. Kennedy Space Center/Merritt Island National Wildlife Refuge. Population trends were predicted using population modeling and field data on reproduction and survival of Florida Scrub-Jays collected from 1988 - 1995. Analyses of historical photography indicated that habitat suitability has been declining for 30 years. Field data and computer simulations suggested that the population declined by at least 40% and will decline by another 40% in 1 0 years, if habitat management is not greatly intensified. Data and computer simulations suggest that habitat suitability cannot deviate greatly from optimal for the jay population to persist. Landscape trajectories of vegetation structure, responsible for declining habitat suitability, are associated with the disruption of natural fire regimes. Prescribed fire alone can not reverse the trajectories. A recovery strategy was developed, based on studies of Florida Scrub-Jays and scrub vegetation. A reserve design was formulated based on conservation science principles for scrub ecosystems. The strategy emphasizes frequent fire to restore habitat, but includes mechanical tree cutting for severely degraded areas. Pine thinning across large areas can produce rapid increases in habitat quality. Site-specific strategies will need to be developed, monitored, and modified to achieve conditions suitable for population persistence.

Breininger, D. R.↗
NASA NTRS2013

NASA Orbital Debris Baseline Populations

The NASA Orbital Debris Program Office has created high fidelity populations of the debris environment. The populations include objects of 1 cm and larger in Low Earth Orbit through Geosynchronous Transfer Orbit. They were designed for the purpose of assisting debris researchers and sensor developers in planning and testing. This environment is derived directly from the newest ORDEM model populations which include a background derived from LEGEND, as well as specific events such as the Chinese ASAT test, the Iridium 33/Cosmos 2251 accidental collision, the RORSAT sodium-potassium droplet releases, and other miscellaneous events. It is the most realistic ODPO debris population to date. In this paper we present the populations in chart form. We describe derivations of the background population and the specific populations added on. We validate our 1 cm and larger Low Earth Orbit population against SSN, Haystack, and HAX radar measurements.

Krisko, Paula H.↗
NASA NTRS2003

Global Properties of Local Star Forming Galaxies (ADP 2000)

We performed an archival study of the Hopkins Ultraviolet Telescope (HUT) Astro-2 database. Nineteen spectra of star-forming regions and starburst galaxies were retrieved, reprocessed, and analyzed. The spectra cover the wavelength region 912- 1800 A, providing access to the domain of peak luminosity from a young stellar population. We created an atlas of galaxy spectra documenting the continuum and line properties with an emphasis on the relatively unexplored spectral region below 1200 A. The dust obscuration law was derived from a comparison of the HUT spectra with synthetic population models. The law is similar to the commonly adopted starburst reddening curve at longer wavelengths and approaches the Milky Way law near the Lyman break. A simple power-law parameterization is given, which allows users to express the reddening law in terms of the stellar or nebular color excess at ultraviolet or optical wavelengths. We studied the effect of time-dependent dust obscuration on synthetic ultraviolet line profiles of a young stellar population. If the youngest and most massive stars are more obscured than the older, less massive stars, the C IV 1550 and other stellar wind lines are significantly diluted with respect to a simple foreground screen model for the dust. We propose to use stellar wind lines as a probe of the dust-obscuration model instead of the previously employed nebular emission lines. Since purely stellar diagnostics are utilized, uncertain assumptions on the nebular properties are unnecessary. Photoionization models demonstrate that the C IV 1550 emission is typically dominated by stellar winds and nebular contamination is negligible. A first comparison with the galaxy sample observed with the Hopkins Ultraviolet Telescope favors a dust geometry affecting ionizing and nonionizing stars equally. We point out the need for higher quality data for a more rigorous comparison. The Hubble Space Telescope is capable of obtaining such data in the future.

Leitherer, Claus↗
NASA NTRS1982

Line shape of the non-thermal 6300 A O/1D/ emission

The two-population model of Schmitt, Abreu and Hays (1981) is used to calculate the line shape of the atomic oxygen metastable state, nonthermal O(1D) 6300 A emission, in order to simulate observations made from a space platform at different zenith angles and altitudes. The Addition theorem, for spherical harmonics of a Legendre polynomial expansion of the nonthermal population distribution function, is used to obtain nonthermal line shapes observed at zenith angles other than the local vertical one.

Schmitt, G. A.↗
NASA NTRS1973

The V-K colours of the nuclei of bright galaxies

Photometric observations of the nuclei of the galaxies M32, M33, M51, NGC5195 and M101 are reported. These give U-B, B-V, H-K and V-K colours for each object and the K-L colour for M32. No short-wavelength infra-red excesses are found. For M32, published population models (Spinrad & Taylor) predict a V-K colour too red to be compatible with the observations.

Penston, M. V.↗
NASA NTRS1979

Population statistics of faint stellar and non-stellar objects

A disc and halo population model is constructed to fit star counts and color data down to V approximately 23 at absolute value of b = 90 deg. This model is used to predict star counts and colors down to V approximately 30. Deviations from these extrapolated relationships provide constraints on the number of faint quasars and black dwarf stars. It is shown that extra-galactic globular clusters start contributing significantly to star counts at V approximately 25 and are more numerous than stars for V 31. Morphological studies of galaxies with approximately 0.5, were made with the space telescope. Significant constraints on theoretical models that describe the evolution of clusters of galaxies are provided.

Vandenbergh, S.↗
NASA NTRS1989

UV Observations of NGC 205

Low resolution IUE observations of the dwarf elliptical galaxy NGC 205 show that the UV spectral energy distribution (SED) of the galaxy is relatively flat. Spectra centered on the nucleus and on a region north of the nucleus show evidence of recent bursts of star formation which contribute strongly to the UV spectral energy distribution. The UV spectra was fit with a composite spectrum based on a Miller-Scalo initial mass function, an underlying older population (modelled using the UV spectrum of 47 Tuc), and an extinction based on a SMC-like extinction cure. This fit implies that the total mass of young stars (with M equal to or greater than 1 solar mass) in the galaxy is approx. 7x10(5) solar mass, which can be compared to the total mass of globular cluster like stars in the galaxy of approx. 8x10(7) solar mass.

Wilcots, Eric M.↗
NASA NTRS1990

Galaxy evolution and large-scale structure in the far-infrared. II - The IRAS faint source survey

The new IRAS Faint Source Survey data base is used to confirm the conclusion of Hacking et al. (1987) that the 60 micron source counts fainter than about 0.5 Jy lie in excess of predictions based on nonevolving model populations. The existence of an anisotropy between the northern and southern Galactic caps discovered by Rowan-Robinson et al. (1986) and Needham and Rowan-Robinson (1988) is confirmed, and it is found to extend below their sensitivity limit to about 0.3 Jy in 60 micron flux density. The count anisotropy at f(60) greater than 0.3 can be interpreted reasonably as due to the Local Supercluster; however, no one structure accounting for the fainter anisotropy can be easily identified in either optical or far-IR two-dimensional sky distributions. The far-IR galaxy sky distributions are considerably smoother than distributions from the published optical galaxy catalogs. It is likely that structure of the large size discussed here have been discriminated against in earlier studies due to insufficient volume sampling.

Lonsdale, Carol J.↗
NASA NTRS1992

How old is the z = 3.4 radio galaxy B2 0902+34?

The redshift 3.395 radio galaxy B2 0902+34 has been observed at K and in a 0.09 micron wide 2.21 micron filter which includes the redshifted forbidden O III 4959 and 5007 A emission lines. A value of m(K) = 19.9 +/- 0.3 is found in a 4 arcsec aperture, a magnitude fainter than Lilly's (1988) value, while the narrow-band image reveals that most of this flux is actually due to line emission. After correcting for forbidden O III 4959 and 5007A, a color is found which is consistent with the flat F(v) spectrum considered characteristic of a protogalaxy. Ages for the galaxy derived from stellar population models based on the limit R - K less than 3.8 are much younger than those for the I - K = 4.5 value reported by Lilly.

Eisenhardt, Peter↗
NASA NTRS1992

The metal-rich globular cluster NGC 6553 - Clump morphology and age

Stellar evolutionary tracks for metal-rich HB stars have been used to construct synthetic population models for the peculiar HB clump in NGC 6553. Although the uncertainties are large, it is possible to derive an age for NGC 6553 in the range 8-13 Gyr, which supports the idea that the disk globular cluster system is younger than the oldest stars in the Galactic halo and bulge.

Demarque, P.↗
NASA NTRS1992

RR Lyrae stars as standard candles

Recent developments in our understanding of RR Lyrae variables are discussed, with special emphasis on their role as distance indicators. The dependence of RR Lyrae luminosity on metallicity and horizontal-branch (HB) morphology is now well understood with many pieces of supporting evidence. This allows the determination of distances to several Local Group galaxies (LMC, M31, and M33) by constructing HB population models that reproduce the observed luminosity functions of RR Lyraes in these galaxies. The new RR Lyrae distances to M31 and M33 are some 15-37 percent larger than those adopted by de Vaucouleurs (1986) and by Aaronson et al. (1986), while they are in reasonable agreements with the recent results based on multicolor CCD photometry of classical Cepheids. This indicates that the large value of Hubble constant (90-100 km/s/Mpc) suggested by these authors may be due, at least in part, to the errors in distances to nearby calibrating galaxies.

Lee, Young-Wook↗
NASA NTRS1992

BATSE spectroscopy results

We present preliminary analyses of gamma-ray burst spectra from the BATSE Spectroscopy Detectors. Our conclusions are: (1) No spectral lines have yet been detected in BATSE data from any cosmic gamma-ray burst. This is not surprising as the data for few bright bursts is available, and previous experiments saw lines in only a small fraction of the bursts. (2) Burst spectra show emission up to 20 MeV, with four of eight examined bursts having significant spectral breaks from 1 to 2 MeV. These breaks are consistent with opacity effects due to the interaction of photons with a high magnetic field. (3) Various distance independent parameters from burst spectra and time histories have no correlation with parameters related to distance. In other words, bright bursts look the same as faint bursts. This places a strong constraint on two population models of bursts. (4) The detection time of individual photons is not correlated from detector to detector, as predicted by Mitrofanov's pulsed emission model.

Schaefer, Bradley E.↗