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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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At least 37 records · Page 2
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NASA NTRS1989

Three very cool degenerate stars in Luyten common proper motion binaries - Implications for the age of the galactic disk

During the course of a spectroscopic study of Luyten common proper motion (CPM) stars, spectrophotometric observations have been obtained of three binaries containing degenerate stars with estimated absolute magnitudes M(V) of about 16. Each of the three pairs consists of a yellow degenerate star primary and a DC 13 + secondary 1.4-2.3 mag fainter. One of the primary stars is spectral class DC 7, another is a sharp-lined DA 8, and the third shows peculiar broad absorption features which we interpret as pressure-shifted C2 Swan bands. The LP 701 - 69/70 system has survived for over 8 billion years without disruption by passing stars, despite its 1500 a.u. orbital major axis. The three cool degenerate companions nearly double the available sample of stars at the low-luminosity terminus of the white dwarf cooling sequence. These findings appear consistent with the conclusion that degenerate stars in the old disk population have not had time to evolve to a luminosity fainter than M(V) about 16.2.

Hintzen, Paul↗
NASA NTRS2023

Electrification Within Wintertime Stratiform Regions Sampled During the 2020/2022 NASA IMPACTS Field Campaign

Two nor'easter events—sampled during the NASA Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign—were examined to characterize the microphysics in relation to the underlying electrification processes within wintertime stratiform regions. A theoretical model was developed to determine whether accretion or diffusion growth regimes were preferential during periods of greatest electrification. Model simulation with electrification parameterization was used to provide supplemental context to the physical processes of in-cloud microphysics and electrification. The strongest electric fields (i.e., ∼80 V m −1 at 20 km) during the 2020 NASA IMPACTS deployment was associated with large non-rimed ice crystals colliding with each other. During the 29–30 January 2022 science flight, the NASA P-3 microphysical probe data demonstrated that non-inductive charging was possible off the coastline of Cape Cod, Massachusetts. Later in the science flight, when the NASA P-3 and ER-2 were coordinating with each other, measured electric fields consistently were less than 8 V m −1 and electrification was subdued owing to reduced concentrations of graupel and large ice hydrometeors. Altogether, the in-situ observations provide evidence for the non-riming collisional charging mechanism and demonstrates that graupel and supercooled liquid water may not be necessary for weak electrification within wintertime stratiform regions. Model output from simulation of both events suggested that the main synoptic snowbands were associated with elevated hydrometeor snow charge density and electric fields.

snowfall↗
NASA NTRS2019

Contribution of ULF Wave Activity to the Global Recovery of the Outer Radiation Belt During the Passage of a High‐Speed Solar Wind Stream Observed in September 2014

Energy coupling between the solar wind and the Earth's magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how ultralow frequency (ULF) wave activity during the passage of Alfvenic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on 22 September 2014, which coincides with the corotating interaction region preceding a high‐speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground‐ and space‐based observational data and global magnetohydrodynamic simulations and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L‐shells. Magnetohydrodynamic simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfven modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by phase space density calculations for this global recovery period.

Silva, L. A. Da↗
NASA NTRS1989

The binary companion of the classical Cepheid AW Per

An analysis of IUE spectra of the companion of AW Per shows it to be an extreme BpSi/HeW star with a spectral type of B7 V to B8 V. The flux of the composite spectrum from 1200 A through V is found to be well matched by F7 Ib and B8 V standard stars with Delta M(V) = 3.1 mag. The results suggest that the mass of the Cepheid must be greater than 4.7 solar masses. The flux distribution of the star and the mass limits from the orbit are consistent with a companion that is itself a binary.

Evans, Nancy Remage↗
NASA NTRS1983

Microcrystalline silicon growth for heterojunction solar cells

A total of sixteen runs of e-beam vacuum deposition of p type microcrystalline Si (m-Si) films were attempted on n type or p-n junction single crystalline Si (C-Si) substrates. The m-Si film thickness varied from .15 to .7 um and metal contacts were deposited after plasma hydrogenation. The p-m-Si on n-c-Si structure had a Voc of up to 490 m V while no Voc improvements were observed in the p-m-Si on p-n C-Si structure against p-n controls. Both CFF and Jsc were lower than control. Possible problem areas were interfaced between m-Si and C-si and the back contacts due to lack of sintering for fear of dehydrogenation.

Iles, P. A.↗
NASA NTRS1999

Nozomi Cis-Lunar Phase Orbit Determination

Japan's Institute of Space and Astronautical Science (ISAS) launched Nozomi, its first mission to the planet Mars using the newly developed M-V launch vehicle on July 3, 1998.

orbit↗
NASA NTRS1993

The mass-luminosity relation for stars of mass 1.0 to 0.08 solar mass

Mass-luminosity relations determined at IR wavelengths are presented for stars with masses 1.0 to 0.08 solar mass. Using IR speckle imaging techniques on a sample of nearby binaries, we have been able to concentrate on the lower main sequence, for which an accurate mass-luminosity calibration has remained problematic. In addition, the mass-visual luminosity relation for stars with 2.0-0.08 solar mass is produced by implementing new photometric relations linking V to JHK wavelengths for the nearby stars, supplemented with eclipsing binary information. These relations predict that objects with masses of about 0.08 solar mass have M(K) of about 10 and M(V) of about 18.

Henry, Todd J.↗
NASA NTRS1983

The distribution of stars in the Galaxy

A discussion is presented of the basic ideas underlying the use of star counts to determine galactic parameters. Previous work using star counts is reviewed, and possible future observational programs that will be important in increasing the knowledge of the stellar content of the galaxy are indicated. The techniques used in star counts are illustrated by applications to the differential number-magnitude counts in SA 57, the frequency-color diagrams in SA 57 and SA 68, the paucity of intermediate population stars in the range M(V) = 5-8, and the M/L ratio for the unseen matter in the halo.

Bahcall, J. N.↗
NASA NTRS2002

The Luminosity Function of QSO Host Galaxies

We present some results from our HST archival image study of 71 QSO host galaxies. The objects are selected to have z less than or equal to 0.46 and total absolute magnitude M(sub v) less than or equal to -23 in our adopted cosmology (H(sub 0) = 50 kilometers per second Mpc(sup-1), q(sub 0) = 0.5, lambda = 0)). The aim of this initial study is to investigate the composition of the sample with respect to host morphology and radio loudness, as well as derive the QSO host galaxy luminosity function. We have analyzed available WFPC2 images in R or I band (U in one case), using a uniform set of procedures. The host galaxies span a narrow range of luminosities and are exceptionally bright, much more so than normal galaxies, usually L greater than L*(sub v). The QSOs are almost equally divided among three subclasses: radio-loud QSOs with elliptical hosts, radio-quiet QSOs with elliptical hosts, and radio-quiet QSOs with spiral hosts. Radio-loud QSOs with spiral hosts are extremely rare. Using a weighting procedure, we derive the combined luminosity function of QSO host galaxies. We find that the luminosity function of QSO hosts differs in shape from that of normal galaxies but that they coincide at the highest luminosities. The ratio of the number of quasar hosts to the number of normal galaxies at a luminosity L*(sub v) is R = (Lv/11.48L*(sub v))(sup 2.46), where L*(sub v) corresponds to M*(sub v)= -22.35, and a QSO is defined to be an object with total nuclear plus host light M(sub v) less than or equal to -23. This ratio can be interpreted as the probability that a galaxy with luminosity L(sub V) will host a QSO at redshift z approximately equal to 0.26.

Hamilton, Timothy S.↗
NASA NTRS1985

An analysis of the Basel star catalog

The standard Bahcall-Soneira (1980) Galaxy model is compared with the data from the 12 fields in the Basel star catalog that are at Galactic latitudes above 20 deg and have E(B-V) of less than 0.1 mag. Good agreement is found between the calculated and observed color distributions, as well as star counts, for all the fields. The globular cluster feature that is observed in the luminosity function of globular clusters near M(v) = +1 to +4 mag is also present in the spheroid field stars. It is possible to assign some of the spheroid stars from the standard two-component Galaxy model (thin disk plus de Vaucouleurs spheroid) to a third stellar component (a thick disk with a spheroid luminosity function) without disturbing the agreement with observations.

Bahcall, J. N.↗
NASA NTRS1991

Electrostatic fields in a dusty Martian environment

While there have been several studies suggesting the possibility of electrical activity on Mars, to date there have been no measurements to search for evidence of such activity. In the absence of widespread water clouds and convective storm systems similar to those on the Earth and Jupiter, the most likely candidate for the creation of electrostatic charges and fields is triboelectric charging of dust, i.e., the friction between blown dust and the ground, and of dust particles with each other. Terrestrial experience demonstrates that electric fields 5 to 15 kV-m(exp -1) are not uncommon in dust storms and dust devils in desert regions, where the polarity varies according to the chemical composition and grain size. Simple laboratory experiments have demonstrated that modest electrostatic fields of roughly 5,000 V-m(exp -1) may be produced, along with electrical spark discharges and glow discharges, in a simulation of a dusty, turbulent Martian surface environment. While the Viking landers operated for several years with no apparent deleterious effects from electrostatic charging, this may have been at least partly due to good engineering design utilizing pre-1976 electronic circuitry to minimize the possibility of differential charging among the various system components. However, free roaming rovers, astronauts, and airborne probes may conceivably encounter an environment where electrostatic charging is a frequent occurrence, either by way of induction from a static electric field or friction with the dusty surface and atmosphere. This raises the possibility of spark discharges or current surges when subsequent contact is made with other pieces of electrical equipment, and the possibility of damage to modern microelectronic circuitry. Measurements of electrostatic fields on the surface of Mars could therefore be valuable for assessing this danger. Electric field measurements could also be useful for detecting natural discharges that originate in dust storms. This detection could be performed at distances ranging from 10s of km in the case of J-charge-like discharge signatures, to planetary distances if there exists a global electrical circuit or Schumann resonance spectrum.

Sentman, D. D.↗
NASA NTRS1993

An Optical Study of the Faint End of the Stellar Luminosity Function

We implement a new method by which to study the faint end of the field star luminosity function. The method relies on deep, multicolor photometry of fields projected against highly obscured, nearby molecular clouds. The clouds act as nearly opaque screens and delimit a well- defined survey volume which is in principle free of the problem of distinguishing nearby, intrinsically faint dwarf stars from more distant red giants. This study is based upon deep photographic and CCD photometry at optical (V,R,I) bandpasses towards the most highly obscured portions of the Taurus and Ophiuchus molecular clouds. The total volume delimited by the clouds is similar 200 pc^3. Within this region our survey is complete for all stars brighter than M_v = 16 - 17 mag; at R and I, the survey is complete down to the lowest mass stars capable of sustaining core hydrogen burning...

Herbst, W.↗
NASA NTRS2016

Outer Radiation Belt Dropout Dynamics Following the Arrival of Two Interplanetary Coronal Mass Ejections

Magnetopause shadowing and wave-particle interactions are recognized as the two primary mechanisms for losses of electrons from the outer radiation belt. We investigate these mechanisms, sing satellite observations both in interplanetary space and within the magnetosphere and particle drift modeling. Two interplanetary shocks sheaths impinged upon the magnetopause causing a relativistic electron flux dropout. The magnetic cloud (C) and interplanetary structure sunward of the MC had primarily northward magnetic field, perhaps leading to a concomitant lack of substorm activity and a 10 day long quiescent period. The arrival of two shocks caused an unusual electron flux dropout. Test-particle simulations have shown 2 to 5 MeV energy, equatorially mirroring electrons with initial values of L 5.5can be lost to the magnetosheath via magnetopause shadowing alone. For electron losses at lower L-shells, coherent chorus wave-driven pitch angle scattering and ULF wave-driven radial transport have been shownto be viable mechanisms.

Alves, L. R.↗
NASA NTRS1984

A redshift survey of the poor cluster A1142

A nearly complete redshift survey of the galaxy cluster A1142 over a 2 sq deg region which includes the central 0.7 Mpc of the cluster is presented which includes 63 new redshifts. Of the 60 galaxies in the region brighter than m(v) = 16.5, about 40 percent are either foreground or background to the cluster. For the 35 cluster members, a mass-to-light ratio of 520 solar masses/solar luminosities is derived, consistent with the results for other well-studied systems.

Geller, M. J.↗
NASA NTRS1997

New Constraints on Simultaneous Optical Emission from Gamma-Ray Bursts Measured by the Livermore Optical Transient Imaging System Experiment

LOTIS is a gamma-ray burst optical counterpart search experiment located near Lawrence Livermore National Laboratory in California. Since operations began in 1996 October, LOTIS has responded to five triggers as of 1997 July 30, which occurred during good weather conditions. GR-B 970223 (BATSE trigger 6100) was an exceptionally strong burst, lasting approx. 30 s with a peak at approx. 8 s. LOTIS began imaging the error box approx. 11 s after the burst began and achieved simultaneous optical coverage of 100% of the region enclosed by the BATSE 3 sigma error circle and the interplanetary network annulus. No optical transients were observed brighter than the m{}_{V} approx.11 completeness limit of the resulting images, providing a new upper limit on the ratio of simultaneous optical to gamma-ray fluence of R-{L) less than 1.1 x 10 logical and {-4} and on the ratio of simultaneous optical (at 700 mn) to gamma-ray (at 100 keV) flux density of R-{F} less than 305 for a B-type spectrum and R-{F} less than 475 for an M-type spectrum.

Park, H. S.↗
NASA NTRS1990

Imaging large- and small-scale structures of the far ultraviolet background with the FAUST instrument

The FAUST telescope is an ultraviolet survey instrument that features a wide 8 deg field of view, 1-arcmin angular resolution, and a photon counting detector. Operating in the 1400-1800 A band, it will be sufficiently sensitive to detect blue m(v) = 17 objects in a single 20-minute night. The instrument is part of the ATLAS-1 shuttle mission, presently scheduled for flight in May 1991. A substantial number of high galactic latitude fields will be investigated, with particular emphasis on studies of the origin of the diffuse far UV background.

Lampton, M.↗
NASA NTRS1986

Comet P/Halley 1910, 1986: An objective-prism study

V. M. Slipher of the Lowell Obs. collected a large amount of spectroscopic data during the 1910 apparition of Halley's comet. Three of his post perihelion objective-prism plates were selected, digitized, and subjected to modern digital data reduction procedures. Some of the important steps in the analysis where: (1) Density to intensity conversion for which was used 1910 slit spectra of Fe-arc lamp on similar plates (Sigma) and derived an average characteristic curve; (2) Flux calibration using the fact that during the period June 2 to 7 1910 P/Halley was very close (angular distance) to the bright star Alpha Sex (A0III, V-4.49), and the spectra of both star and comet were recorded on the same plates. The flux distribution of Alpha Sex was assumed to be similar to that of the standard star 58 Aql and derived a sensitivity curve for the system; (3) Atmospheric extinction using the standard curve for the Lowell Obs.; (4) Solar continuum subtraction using the standard solar spectrum binned to the spectral resolution. An example of a flux-calibrated spectrum of the coma (integrated over 87,000km) before the subtraction of solar continuum is presented.

Carsenty, U.↗
NASA NTRS1983

X-rays and rotation among post-T Tauri G stars in Orion Ic

Walter and Kuhi (1981) have shown that at least 10 out of 12 T Tauri stars brighter than m(v) = 12.5 are X-ray emitters. The X-ray luminosities of these stars, L(x), are often close to the detection threshold value. One of the principal results of the present investigation is the evidence for at least a weak correlation between L(x) and V(R) sin i. If it is assumed that results obtained concerning stars in the Orion Ic Association are representative of other stellar fields, it appears that along with the RS CVn stars, pre-main-sequence G stars are among the most X-ray luminous late-type stars on the H-R diagram. A second conclusion is that the X-rays are almost certainly produced by flares and/or thin coronae close to the stellar surface.

Smith, M. A.↗