SEARCH · Search NASA

Results for “21”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6

All sources NASA NTRS DOE OSTI

NASA NTRS1982

Comparison of the thermal and nonthermal radiation characteristics of Jupiter at 6, 11, and 21 cm with model calculations

Four different data sets on Jupiter, one at 6, one at 11, and two at 21 cm, are compared to each other and with the synchrotron radiation model of the magnetosphere developed by de Pater (1981). The model agrees with all these data sets, and hence was used to derive and interpret the characteristics of the thermal radiation component at all three wavelengths. The disk temperatures are 233 + or - 17, 280 + or - 20, and 340 + or - 26 K at 6, 11, and 21 cm, respectively. A comparison of the data with atmospheric model calculations strongly suggests that the disk is uniform at 6 and 11 cm near the center of the disk, where mu is greater than 0.6-0.7. This may indicate a nonuniform distribution of ammonia at layers at and above the visible cloud layers.

De Pater, I.↗

NASA NTRS1983

Solar flare particle fluences during solar cycles 19, 20 and 21

Satellite data for solar flare particle events during solar cycle 21 (up to July 1982) have been analyzed to obtain event-integrated fluxes of energetic protons and alpha particles. Thirty nine events with proton fluences (E greater than 10 MeV) greater than 10-million/sq cm occurred during 1976-1982. The average flux of protons with kinetic energy greater than 10 MeV is 65 per sq cm/s for this period. The event averaged alpha to proton ratio, in the energy interval 1-22 MeV/n, varies between 0.006 to 0.04, with an average value of about 0.02 for the whole cycle. The flux of protons (with energies greater than 10 MeV) averaged over cycle 21 is lower than those for solar-cycle 20 per sq cm/s based on satellite data, and for solar-cycle 19 378 per sq cm/s based on lunar sample data. There is no definitive correlation between solar-cycle averaged proton fluxes and sunspot numbers.

Mcguire, R. E.↗

NASA NTRS1985

Vortex creep and the internal temperature of neutron stars The Crab pulsar and PSR 0525 + 21

The behavior of the Crab pulsar following the 1969 and 1975 glitches and the postglich behavior of the old pulsar PSR 0525 + 21 are explained as resulting from internal torques due to the thermal creep of vortex lines in pinned superfluid regions. An overview of vortex creep theory is first given, and the immediate postglitch behavior of the Crab pulsar is calculated and compared with observation. The persistent shift in the spin-down rate observed for the Crab pulsar following the 1975 glitch is considered, and the internal and surface temperatures of this pulsar are deduced. The postglich behavior expected for very old pulsars is examined, showing that PSR 0525 + 21 falls into this category. It is concluded that the behavior of the Crab pulsar following both glitches can be characterized by the same two pinning regions. A comparison of the internal temperature for the Crab and Vela pulsars provides a significant constraint on the cooling of neutron stars.

Alpar, M. A.↗

NASA NTRS1985

The molecular core associated with DR 21

DR 21 has been observed in the J = 1-0 line of HCN with a resolution of 12.5 by 15.5 arcsec using the mm-wave interferometer at the Hat Creek Observatory. The HCN line is seen in both emission and absorption as an isolated clump immediately adjacent to the compact H II regions of DR 21. The full extent of the clump is about 30 arcsec in R.A. and 60 arcsec in decl. which corresponds to 0.3 by 0.6 pc for an assumed distance of 2 kpc. The mass of the clump is estimated to be about 200 solar masses. Two velocity components are present: the more intense one at -5 km/s is only seen in emission, and the other at -2.4 km/s is seen in emission in the northwest and mostly in absorption against the continuum source. The component at -5.0 km/s is identified to have higher excitation, and the one at -2.4 km/s to have greater column density.

Dickel, H. R.↗

NASA NTRS1985

Helios 1 energetic particle observations of the solar gamma-ray/neutron flare events of 1982 June 3 and 1980 June 21

The characteristics of the energetic particles associated with the solar gamma-ray/neutron flare events of June 3, 1982 and June 21, 1980 observed by the Goddard cosmic-ray experiment on Helios 1 (at heliocentric distances of 0.57 and 0.54 AU, respectively) differ in several important respects from typical sonar particle increases. In particular, the June 3, 1982 event has a proton energy spectrum which fits a remarkable flat power law in kinetic energy with a spectral index of 1.2, an electron/proton ratio of 1 at 4 MeV, and a small but well-defined precursor event that began some 3 hr before the impulsive flare increase. Similar energetic particle precursors were observed for the gamma-ray associated 1980 June 21 and June 7 flare events. At energies less than about 40 MeV, the particle onset time measured for the June 3, 1982 event is anomalous, suggesting that these lower energy particles may have been released at the sun about 1-2 minutes before the higher energy particles.

Mcdonald, F. B.↗

NASA NTRS1985

Ionization frequencies for solar cycle 21 - Revised

Detailed spectra of the extreme ultraviolet solar flux at the earth were provided by instruments on the Atmosphere Explorer satellites. These data have been used for aeronomical purposes in a large number of studies. An important parameter for such studies is the rate of production of various ions through the photoionization process. This parameter, known as an ionization frequency, is the integral over wavelength of the product of the solar flux and the cross section for the ionization of the particular constituent. Thus, the determination of the ionization rate is dependent on a good knowledge of the solar EUV intensities for the solar period in question. Over the past few years the EUV solar spectra that have been developed for use by aeronomers as reference spectra for such photochemical and ionospheric studies have been improved. The results of a redetermination of the most important ionization frequencies using the revised solar fluxes are reported. The impact is found to be more significant at solar maximum, amounting to a reduction of 12-21 percent in the ionization frequencies of the major terrestrial thermospheric constituents for solar-minimum conditions and 21-33 percent for solar-maximum conditions. The corrections are apart from the ongoing debate concerning the absolute intensity of EUV solar-flux measurements for the solar-cycle 21 maximum period.

Torr, M. R.↗

NASA NTRS1987

Infrared radiometry of Uranus and Neptune at 21 and 32 microns

Mauna Kea's NASA IRTF has been used to obtain 21- and 32-cm radiometric measurements of Uranus and Neptune; brightness temperatures of 54.1 + or - 0.3 K for Uranus and 58.1 + or 0.3 K for Neptune were obtained by calibrating the 21-cm data against Alpha Boo. A calibration of the 32-cm data against Callisto and Ganymede yielded respective temperatures of 51.8 + or - 1.5 K and 55.6 + or - 1.2 K. The general decrease of brightness temperatures with wavelength from 20 to 30 microns is confirmed. The two planets are noted to appear as bodies sufficiently different to depart from the hypothesis of smooth planetary bulk property variation as a function of heliocentric distance.

Orton, Glenn S.↗

NASA NTRS1988

Variation of the quiet sun at 21 cm - 1981-1987

The sun was imaged at a wavelength of about 21 cm during 1981-1987 using the VLA, the Green Bank 91-m telescope, the Arecibo 305 m telescope, and powerful maximum entropy image reconstruction techniques. There was a systematic decrease in the quiet sun's brightness temperature at 21 cm as the sun declined from sunspot maximum to sunspot minimum; this was accompanied by a systematic decrease in the sun's radius. The two-fold decrease in the electron number density in the solar transition region and low corona could have been the cause of these variations.

Bastian, T. S.↗

NASA NTRS1990

The hot DOA1 degenerate HZ 21 - A search for circumstellar/photospheric metals and peculiar absorption at He II

A high-resolution IUE spectrum of the hot DO1 degenerate HZ 21 was obtained by combining US1 + European 2 low-background observing shifts. The SWP image reveals a rich spectrum of interstellar absorption lines with an average velocity in the line of sight to HZ 21 of -30 km/s. However, there is no clear evidence of any highly or lowly ionized metal features which could be attributed to circumstellar, wind, or photospheric absorption. There is, however, a broad absorption trough at He II (1640) which was not unexpected, given the clear presence of He II (4686) absorption in this star's optical spectrum. The velocity width of He II (1640) appears consistent with photospheric absorption wings which appear to flank the geocoronal Ly-alpha emission feature. The He II (1640) feature reveals what appears to be a broad (310 km/s) emission reversal. Evidence is provided that the emission reversal is probably real.

Fritz, M. L.↗

NASA NTRS1990

Astrotech 21 - A technology program for future astrophysics missions

Cutts, James A.↗

NASA NTRS1991

A 21 centimeter line survey of a region around four outer galaxy open clusters

To investigate the role of atomic gas in the interaction of massive stars with the interstellar medium, a 21 cm survey was made of a region surrounding four young, outer Galaxy open clusters, NGC 281, 433, 436, and 457. A rectangular area ranging in Galactic longitude from 115 to 133 deg, and in latitude from -10 to -1 deg, was observed with the NRAO 140 foot telescope. Most of this region was fully sampled, resulting in spatial resolution equal to the telescope's 21 arcmin beamwidth. The data are presented as longitude-latitude and latitude-velocity contour maps. A catalog of atomic gas features (e.g., clouds, filaments, and shells) is given.

Leisawitz, David↗

NASA NTRS1991

Astrotech 21 program overview

This brief report describes the initiation and development of the Astrotech 21 Program. The scope of the included workshop discusses sensor technology and how this may be utilized in the overall scheme of the Astrotech 21 Program.

Cutts, J.↗

NASA NTRS1991

X-ray observations of filament eruption in the 1980 May 21 flare

X-ray and H-alpha observations of an erupting filament and other observations of the associated flare on May 21, 1980 suggest that an erupting filament played a major role in the X-ray flare. While Antonucci et al. (1985) analyzed the May 21 flare as one of the best cases of chromospheric evaporation, the possible contribution from X-ray emitting erupting plasma has been ignored. It is that preheated plasma existed and may have contributed part of the blue-shifted X-ray emission observed in the Ca XIX line, which was formerly attributed solely to chromospheric evaporation. Thus it remains an open question - in two-ribbon flares in particular - just how important chromospheric evaporation is in flare dynamics.

Batchelor, D. A.↗

NASA NTRS1991

Astrotech 21: A technology program for future astrophysics missions

The Astrotech 21 technology program is being formulated to enable a program of advanced astrophysical observatories in the first decade of the 21st century. This paper describes the objectives of Astrotech 21 and the process that NASA is using to plan and implement it. It also describes the future astrophysical mission concepts that have been defined for the twenty-first century and discusses some of the requirements that they will impose on information systems for space astrophysics.

Cutts, James A.↗

NASA NTRS1992

Discovery of neutral hydrogen 21 centimeter absorption at redshift 0.25 toward PKS 1413+135

A strong H I 21-cm absorption line is identified toward PKS 1413+135 at the redshift of the host galaxy and argued to indicate that the IR-optical cutoff of the BL Lac object's spectrum is caused by extinction. The BL Lac object is shown to have strong neutral 21-cm absorption at the redshift range z = 0.24671 +/- 0.00001, and the implied H I column density is derived. The H I covering factor is assumed to be not more than 0.1, suggesting that a high degree of extinction exists in the galaxy. The host galaxy is theorized to be a spiral of type later than S0 based on the redshift of the H I absorption line and the host. The statistical and observational conclusions are found to support the theories of Stock et al. (1992) regarding the red spectrum of the object.

Carilli, C. L.↗

NASA NTRS1994

The solar cycle variation of coronal temperature and density during cycle 21-22

In this paper we characterize the temperature and the density structure of the corona utilizing co-spatial spectrophotometric observations during the descending phase of cycle 21 through the ascending phase of cycle 22. The data include ground-based intensity observations of the green (5303A Fe XIV) and red (6374A Fe X) coronal forbidden lines from Sacramento Peak and synoptic maps of white-light K-coronal polarized brightness, pB from the High Altitude Observatory, and photospheric magnetographs from the National Solar Observatory, Sacramento Peak. A determination of plasma temperature T can be derived unambiguously from the intensity ratio Fe X/Fe XIV, since both emission lines come from ionized states of Fe, and the ratios are only weakly dependent on density. The latitudinal variation of the temperature and the density within the descending and the ascending phases of solar cycle 21 and 22 are presented. There is a large-scale organization of the inferred coronal temperature distribution; these structures tend to persist through most of the magnetic activity cycle. This distribution differs in spatial and temporal characterization from the traditional picture of sunspot and active region evolution over the range of sunspot cycle.

Guhathakurta, M.↗

NASA NTRS1994

Optical imaging and high spatial resolution 21 cm H I observations of the peculiar galaxy NGC 2782 (Arp 215)

We have used the Very Large Array (VLA) B and C Arrays to make 21 cm H I observations of the peculiar galaxy NGC 2782 (Arp 215). These observations are complementary to previously published D Array VLA data, which revealed the presence of a long (5 min to 54 kpc) H I plume near the western side of this galaxy. We have also obtained BVRI H alpha images of the main body of this galaxy using the McDonald Observatory 30 inch telescope. The optical images of this galaxy show a strong stellar tail extending to the east, opposite the H I plume. Within the disk of NGC 2782, unsharp masking of the optical images at all 4 broadband wavelengths reveals three bright 'ripples', separated by approximately 15 sec. The light profiles across these ripples are symmetric, without a sharp outer edge. H alpha is strong at the starburst nucleus and along the northern and western sections of the inner ripple. The new higher resolution H I data show that the atomic gas is very clumpy. We have identified ten H I clumps in the long western plume, with H I masses of approximately 10(exp 8) solar mass, similar to those of dwarf galaxies, and column densities of approximately 10(exp 21) cm(exp -2) over surface areas of approximately 10 kpc(exp 2). No CO (1-0) emission has been detected from this plume, suggesting that it is material stripped from the outer edge of a disk galaxy. The H alpha peaks, in contrast, are generally not coincident with H I peaks. No H I is seen at the tip of the eastern extension. The H I distribution near this structure is ring-like rather than tail-like as in the optical data. We have detected redshifted H I absorption toward the central continuum source, indicating gas infall into the nuclear region. Using a restricted 3-body dynamical model, we have successfully reproduced the basic properties of NGC 2782 with an off-center collision between two galaxies, where a lower mass disk companion (M(sub 2)/M(sub 1) approximately 0.25) collides almost head-on with a larger disk galaxy. In this scenario, the companion becomes the eastern extension, and the long western tail is material pulled out from the larger galaxy. The lack of H I at the tip of the eastern tail may be due to stripping during the collision. Alternative formation scenarios include a merger or interaction between two disk galaxies, where the ripples may be due to a disturbed spiral density wave or galactic winds due to the central starburst.

Smith, Beverly J.↗

NASA NTRS1994

Tests of the Tully-Fisher relation. 1: Scatter in infrared magnitude versus 21 cm width

We examine the precision of the Tully-Fisher relation (TFR) using a sample of galaxies in the Coma region of the sky, and find that it is good to 5% or better in measuring relative distances. Total magnitudes and disk axis ratios are derived from H and I band surface photometry, and Arecibo 21 cm profiles define the rotation speeds of the galaxies. Using 25 galaxies for which the disk inclination and 21 cm width are well defined, we find an rms deviation of 0.10 mag from a linear TFR with dI/d(log W(sub c)) = -5.6. Each galaxy is assumed to be at a distance proportional to its redshift, and an extinction correction of 1.4(1-b/a) mag is applied to the total I magnitude. The measured scatter is less than 0.15 mag using milder extinction laws from the literature. The I band TFR scatter is consistent with measurement error, and the 95% CL limits on the intrinsic scatter are 0-0.10 mag. The rms scatter using H band magnitudes is 0.20 mag (N = 17). The low width galaxies have scatter in H significantly in excess of known measurement error, but the higher width half of the galaxies have scatter consistent with measurement error. The H band TFR slope may be as steep as the I band slope. As the first applications of this tight correlation, we note the following: (1) the data for the particular spirals commonly used to define the TFR distance to the Coma cluster are inconsistent with being at a common distance and are in fact in free Hubble expansion, with an upper limit of 300 km/s on the rms peculiar line-of-sight velocity of these gas-rich spirals; and (2) the gravitational potential in the disks of these galaxies has typical ellipticity less than 5%. The published data for three nearby spiral galaxies with Cepheid distance determinations are inconsistent with our Coma TFR, suggesting that these local calibrators are either ill-measured or peculiar relative to the Coma Supercluster spirals, or that the TFR has a varying form in different locales.

Bernstein, Gary M.↗