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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 NTRS1994

A six year timing solution for PSR B1951 + 32

Six years of pulse time-of-arrival measurements have been collected from observations of the young, fast pulsar PSR B1951 + 32 in the CTB 80 supernova remnant using the Jodrell Bank and Arecibo radio telescopes. The combined data allow for the determination of a phase connected solution between 1987 August 21 and 1993 September 21. This solution provides an accurate rotational ephemeris for high energy x-ray and gamma-ray observations of this source made during the six years of radio timing observations to an accuracy of better than one tenth of a pulse period (4 ms). The pulsar has an activity parameter comparable with the value seen in the Crab pulsar.

Foster, R. S.↗
NASA NTRS2005

"Dynamics and Structure of Planetary Rings"

This document reports on the research carried out under this grant for the funding period ending December 31, 2004. During this period, we concentrated our efforts on acquiring and interpreting observations of Saturn's rings and small satellites, using Hubble Space Telescope observations, Arecibo radar results, and Earth-based stellar occultations. A total of ll peer reviewed papers and 27 meeting abstracts were published during this period. We highlight these accomplishments.

French, Richard G.↗
NASA NTRS1995

Astrophysics with Pulsar/Main Sequence Star Binaries

Until very recently, all known radio pulsars in binary orbits had as companions old, degenerate stars, either neutron stars or white dwarfs. In this talk we introduce a new class of binary radio pulsars having as companions young, massive stars. Concentrating on one system in particular, we show that these systems open a new phase space for studying a variety of physical phenomena, including post-Keplerian dynamics, physics of stellar winds and interiors, and binary evolution theory.

Arecibo Telescope↗
DOE OSTI2024

Characterizing the Gamma-Ray Emission Properties of the Globular Cluster M5 with the Fermi-LAT

Abstract We analyzed the globular cluster M5 (NGC 5904) using 15 yr of gamma-ray data from the Fermi Large Area Telescope (LAT). Using rotation ephemerides generated from Arecibo and FAST radio telescope observations, we searched for gamma-ray pulsations from the seven millisecond pulsars (MSPs) identified in M5. We detected no significant pulsations from any of the individual pulsars. In addition, we searched for possible variations of the gamma-ray emission as a function of orbital phase for all six MSPs in binary systems, but we did not detect any significant modulations. The gamma-ray emission from the direction of M5 is well described by an exponentially cutoff power-law spectral model, although other models cannot be excluded. The phase-averaged emission is consistent with being steady on a timescale of a few months. We estimate the number of MSPs in M5 to be between 1 and 10, using the gamma-ray conversion efficiencies for well-characterized gamma-ray MSPs in the Third Fermi-LAT Catalog of Gamma-ray Pulsars, suggesting that the sample of known MSPs in M5 is (nearly) complete, even if it is not currently possible to rule out a diffuse component of the observed gamma rays from the cluster.

Astronomy & Astrophysics↗
NASA NTRS1983

The NASA SETI Program - Objectives of the R&D activity

The current activity in NASA's SETI Program is a research and development program jointly carried out by the NASA Ames Research Center and the Jet Propulsion Laboratory. The purpose of this R&D phase is to develop all prerequisites for a well defined microwave observing program. The specific objectives include the development of a prototype search system which will ultimately be capable of processing data rates up to 10 gigabytes/second. Specialized signal detection algorithms and automated search procedures will be developed and tested with the prototype hardware. A series of field tests will be carried out with the NASA Deep Space Network facilities at Goldstone, CA and with the 305-m radio telescope at the Arecibo Ionospheric Observatory in Puerto Rico.

Klein, M. J.↗
NASA NTRS1990

An isolated, well-defined infrared cirrus cloud

High spatial resolution H I measurements of a high-latitude FIR cirrus cloud (l = 9 deg, b = 51 deg) were obtained with the Arecibo 310 m telescope. The cloud is well isolated spatially and has a velocity well-separated from other H I clouds, providing an ideal laboratory for studying diffuse interstellar clouds. The Iv(100)/N(H) and Iv(60)/Iv(100) ratios are consistent with the Draine and Anderson model which includes a distribution of grain sizes down to 3 A. The small grains undergo transient heating and affect the 60 micron FIR continuum emission. Current models, however, underpredict Iv(12)/Iv(100) and Iv(25)/Iv(100) by more than a factor of 2. The effects small grains have on the thermal equilibrium of diffuse interstellar clouds are discussed.

Herter, T.↗
NASA NTRS1990

Dynamic spectra of radio bursts from flare stars

The Arecibo 305 m telescope has been used to observe radio bursts from flare stars at 430 and 1415 MHz. Dynamic spectra of the emission with bandwidths of 10 MHz in the former case and 40 MHz in the latter are recorded. For AD Leo, the microwave burst emission was 100 percent right circularly polarized, achieved brightness temperatures near 10 to the 16th K, was generally broadband in character, but was superposed with finite structures in both frequency and time. Quasi-periodic pulsations were clearly present as well as a sudden reduction feature. For YZ CMi, the emission was 100 percent left circularly polarized and was relatively broadband with fine structures. Instabilities driven by anisotropies in the electron distribution, particularly the loss-cone distribution, are considered to account for the coherent radiation.

Bastian, T. S.↗
NASA NTRS1994

An H I survey of high-velocity clouds in nearby disk galaxies

We observed 14 nearly face-on disk galaxies with the Arecibo 305 m telescope and found the double-horned H I profiles to have high-velocity wings in 10 of these galaxies. Such wings can be caused by high-velocity clouds, similar to those observed in our own Galaxy. Disk galaxy models were constructed that include both high-velocity clouds (modeled as a component of galactic gas with a velocity dispersion of either 30 or 50 km/s) and warped H I disks. We find that the high-velocity wings can be reproduced by models with high-velocity clouds but not by models with warps that are similar to those observed in other galaxies. If these wings are due to high-velocity clouds, then the mass of neutral hydrogen in high-velocity clouds for the 10 galaxies ranges from 6 X 10(exp 7) solar mass to 4 x 10(exp 9) solar mass, which corresponds to 4% - 14% of the total H I in these galaxies. The galaxies with no detected high-velocity wings are also those with the lowest far-infrared fluxes as measured by Infrared Astronomy Satellite (IRAS), which is consistent with the galactic fountain model in which the young stellar population (responsible for most of the far-infrared emission produces supernovae which then provide the kinetic energy of the high-velocity clouds.

Schulman, Eric↗
NASA NTRS1993

Radar Investigations of Earth-Approaching Asteroids

Much useful information about physical and dynamical properties can be obtained from radar observations of near-Earth asteroids that come within reach of the Arecibo and Goldstone telescopes.

resolution of echoes Doppler frequency synthesize ↗
NASA NTRS1999

Radar Reconnaissance of Near-Earth Asteroids

Groundbased radar observations of NEAs can help identify space resources with commercial potential and can dramatically reduce the cost and risk of the initial spacecraft missions to those objects. The near-Earth asteroid (NEA) population is thought to contain approximately 1500 objects as large as a kilometer, approximately 300,000 as large as 100 meters, and more than 100,000,000 as large as 10 meters. More than 10% of the NEAs are more accessible in terms of mission delta-V (i.e., fuel required) than the Moon, Mars, or the moons of Mars. Fewer than 1000 NEAs have been found, but the discovery rate is increasing rapidly. Once an asteroid is discovered (necessarily by wide-field optical telescopes), radar can provide otherwise unavailable information about its size, shape, spin state, and surface properties if it approaches within the range of the Goldstone (California) or Arecibo (Puerto Rico) radar telescopes. Asteroids generally appear as unresolved points through groundbased optical telescopes, but radar measurements of the distribution of echo power in time delay (range) and Doppler frequency (radial velocity) can yield images with resolution as fine as a decameter. Image sequences that furnish adequate orientational coverage can be inverted to construct geologically detailed 3-D models, to define the rotation state precisely, and to constrain the object's internal density distribution. Estimates of radar scattering properties characterize the surface's cm-to-m-scale roughness as well as its bulk density, which for asteroids depends primarily on porosity and metal concentration. A useful spin-off of radar detection is orbit refinement that simplifies navigation of flyby and rendezvous spacecraft.

Ostro, S. J.↗
NASA NTRS1999

Radar Reconnaissance of Near-Earth Asteroids

Groundbased radar observations of NEAs can help identify space resources with commercial potential and can dramatically reduce the cost and risk of the initial spacecraft missions to those objects. The near Earth asteroid (NEA) population is thought to contain approx. 1500 objects as large as a kilometer, approx. 300,000 as large as 100 meters, and more than 100,000,000 as large as 10 meters. More than 10% of the NEAs are more accessible in terms of mission delta-V (i.e., fuel required) than the Moon, Mars, or the moons of Mars. Fewer than 1000 NEAs have been found, but the discovery rate is increasing rapidly. Once an asteroid is discovered (necessarily by wide-field optical telescopes), radar can provide otherwise unavailable information about its size, shape, spin state, and surface properties if it approaches within the range of the Goldstone (California) or Arecibo (Puerto Rico) radar telescopes. Asteroids generally appear as unresolved points through groundbased optical telescopes, but radar measurements of the distribution of echo power in time delay (range) and Doppler frequency (radial velocity) can yield images with resolution as fine as a decameter. Image sequences that furnish adequate orientational coverage can be inverted to construct geologically detailed 3-D models, to define the rotation state precisely, and to constrain the object's internal density distribution. Estimates of radar scattering properties characterize the surface's cm-to-m-scale roughness as well as its bulk density, which for asteroids depends primarily on porosity and metal concentration. A useful spin-off of radar detection is orbit refinement that simplifies navigation of flyby and rendezvous spacecraft.

Ostro, S. J.↗
NASA NTRS1990

Identifying galaxies in the zone of avoidance

A set of IR color criteria was applied to sources in the IRAS Point Source Catalog at low Galactic latitudes in order to select candidate galaxies. A total of 371 of the selected sources within a Galactic latitude range (b) = 2-16 deg were searched for H I with the Arecibo 305 m radio telescope. Twenty-six percent (97) were detected, including 36 galaxies previously known only as IRAS sources. The H I spectra of the detected galaxies are presented together with their observed redshifts and velocity widths.

Lu, N. Y.↗
NASA NTRS1990

H I in the giant elliptical galaxy NGC 4406

The Arecibo 305-m radio telescope was used to make 21-cm measurements of NGC 4406, an elliptical galaxy containing 10 to the 10th solar mass of hot diffuse gas. The H I decreases by a factor of 3 one beamwidth from the center and by an order of magnitude two beam widths from the center. Excess H I emission is seen in the X-ray tail, but not in dust-rich regions. The H I measurements do not support the suggestion that the X-ray tail is hot gas being stripped from the galaxy.

Bregman, Joel N.↗
NASA NTRS1992

Discovery of two planets around a millisecond pulsar

By timing the arrival of radio signals from a rapidly spinning pulsar at the Arecibo Observatory's radio/radar telescope, the most convincing evidence so far for a planetary system outside our own has been found: two or possibly three planets that orbit the neutron star called PSR1257+12. This finding indicates that planet formation may be a more common process than previously anticipated and that the formation of disks of gas and dust that are sufficiently massive to condense into Earth-sized planets orbiting their central bodies can take place under surprisingly diverse conditions.

Wolszczan, A.↗
NASA NTRS1974

Meter-wavelength observations of pulsars using very long baseline interferometry

The results of an investigation of the angular structure imposed on pulsar radiation due to scattering in the interstellar medium are presented. The technique of very-long-baseline interferometry was used to obtain the necessary high angular resolution. The interferometers formed by the Arecibo, NRAO, and Sugar Grove telescopes were used at radio frequencies of 196, 111, and 74 MHz during seven separate observing sessions between November 1971 and February 1973. A crude visibility function for the Crab nebular pulsar was obtained along with the correlated pulse profile. The technique of differential fringe phase was used to show that the pulsar and the compact source in the Crab nebula are coincident to within 0.001 arcsec which corresponds to aproximately 2 a.u. at the distance to the nebula. The ratio of pulsing to total flux, and the fringe visibility of the time-averaged pulsing flux are also discussed, and apparent angular sizes of the pulsars were measured.

Vandenberg, N. R.↗
NASA NTRS2018

The NANOGrav 11-year Data Set: High-Precision Timing of 45 Millisecond Pulsars

We present high-precision timing data over time spans of up to 11 years for 45 millisecond pulsars observed as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project, aimed at detecting and characterizing low-frequency gravitational waves. The pulsars were observed with the Arecibo Observatory and/or the Green Bank Telescope at frequencies ranging from 327 MHz to 2.3 GHz. Most pulsars were observed with approximately monthly cadence, and six high-timing-precision pulsars were observed weekly. All were observed at widely separated frequencies at each observing epoch in order to fit for time-variable dispersion delays. We describe our methods for data processing, time-of-arrival (TOA) calculation, and the implementation of a new, automated method for removing outlier TOAs. We fit a timing model for each pulsar that includes spin, astrometric, and (for binary pulsars) orbital parameters; time-variable dispersion delays; and parameters that quantify pulse-profile evolution with frequency. The timing solutions provide three new parallax measurements, two new Shapiro delay measurements, and two new measurements of significant orbital-period variations. We fit models that characterize sources of noise for each pulsar. We find that 11 pulsars show significant red noise, with generally smaller spectral indices than typically measured for non-recycled pulsars, possibly suggesting a different origin. A companion paper uses these data to constrain the strength of the gravitational-wave background

Arzoumanian, Zaven↗
NASA NTRS2004

Multi-Wavelength Observations of Asteroid 2100 Ra-Shalom: Visible, Infrared, and Thermal Spectroscopy Results

The August 2003 apparition of asteroid 2100 Ra-Shalom brought together a collaboration of observers with the goal of obtaining rotationally resolved multiwavelength spectra at each of 5 facilities: infrared spectra at the NASA Infrared Telescope Facility (Clark and Shepard), radar images at Arecibo (Shepard and Clark), thermal infrared spectra at Palomar (Lim, McConnochie and Bell), visible spectra at McDonald Observatory (Vilas, Lederer and Jarvis), and visible lightcurves at Ondrojev Observatory (Pravec). The radar data was to be used to develop a high spatial resolution physical model to be used in conjunction with spectral data to investigate compositional and textural properties on the near surface of Ra Shalom as a function of rotation phase. This was the first coordinated multi-wavelength investigation of any Aten asteroid. There are many reasons to study near-Earth asteroid (NEA) 2100 Ra-Shalom: 1) It has a controversial classification (is it a C- or K-type object)? 2) There would be interesting dynamical ramifications if Ra-Shalom is a K-type because most K-types come from the Eos family and there are no known dynamical pathways from Eos to the Aten population. 3) The best available spectra obtained previously may indicate a heterogeneous surface (most asteroids appear to be fairly homogeneous). 4) Ra-Shalom thermal observations obtained previously indicated a lack of regolith, minimizing the worry of space weathering effects in the spectra. 5) Radar observations obtained previously hinted at interesting surface structures. 6) Ra-Shalom is one of the largest Aten objects. And 7) Ra-Shalom is on a short list of proposed NEAs for spacecraft encounters and possible sample returns. Preliminary results from the visible, infrared, and thermal spectroscopy measurements will be presented here.

Clark, Beth Ellen↗
NASA NTRS1987

Observations of Comet Halley at H-alpha and 6300 A

High spectral resolution measurements of Comet Halley at H-alpha and OD-1 were obtained in March, 1986 using a small aperture telescope with the Fabry-Perot interferometer at the Arecibo Observatory. It is suggested that the highly structured spectral signature observed at H-alpha is due to collimation of atomic hydrogen in the inner hydrogen corona, following photodissociation of parent species, and that the emission is due to resonance fluorescence of solar Lyman-beta radiation. A feature at 6300.8 A accompanying the OD-1 emission at 6300.3 A is attributed to NH2. For a 6-arcmin field of view, a brightness for the OD-1 emission of 260 + or - 50 rayleighs is found for both March 15 and 17.

Kerr, R. B.↗