Engineering topics

Maran, S. P.

Publications and source records attributed to Maran, S. P..

At least 37 records · Page 2

NASA NTRS1982

The ultraviolet spectrum of the Crab Nebula

Ultraviolet spectroscopy of the Crab Nebula done by the International Ultraviolet Explorer satellite is described, and an estimate of the carbon abundance is made, noting data reduction to remove spectral defects caused by radiation hits. The important C IV 1549, He II 1640, and semiforbidden C III 1908 emission line intensities were measured and upper limits placed on other ultraviolet features for the brightest filamentary region in the Nebula. The emission lines imply an average ionic abundance ratio n(C+2)/n(O+2) in the range from 0.4 to 1.5 in the observed gaseous condensations. The elemental abundance ratio of carbon to oxygen is probably in the same range. Analysis shows that there is no perceptible excess of carbon due to presupernova nucleosynthesis in the observed region. The large helium abundance, small carbon and oxygen abundances, and presence of a neutron star in the Crab Nebula suggest that the presupernova star had a mass close to eight solar masses.

Davidson, K.↗

NASA NTRS1982

Ultraviolet spectroscopy of planetary nebulae in the Magellanic Clouds

Ultraviolet spectra of the high excitation planetary nebulas LMC P40, SMC N2, and SMC N5 are presented in an investigation of their chemical composition in an effort to make reliable estimates of the carbon abundance in extragalactic planetary nebulas. The carbon abundance is found to be almost 40 times more abundant in the SMC planetaries than in the SMC interstellar medium, and is about 6 times more abundant in the LMC planetary than in the LMC interstellar medium. The net result of carbon synthesis and convective dredgeup in the progenitors of planetary nebulas as reflected in the nebular carbon abundance is roughly the same in the Galaxy, the LMC, and the SMC.

Maran, S. P.↗

NASA NTRS1982

Telescopes and space exploration

Progress in contemporary astronomy and astrophysics is shown to depend on complementary investigations with sensitive telescopes operating in several wavelength regions, some of which can be on the Earth's surface and others of which must be in space.

Brandt, J. C.↗

NASA NTRS1982

IUE observations of planetary nebulae and their central stars in the Magellanic Clouds

The planetary nebulae LMC P40, SMC N2, and SMC N5 and their central stars were observed with IUE. The C abundances in the nebulae, compared with those in galactic planetaries, indicate that convective dredgeup of locally nucleosynthesized C has occurred. The progenitors of the nebulae were C stars at the theoretical upper luminosity threshold, thus such stars do occur as predicted, although none so bright have been found in the Clouds. The central stars of the nebulae have masses approximately 1 solar mass, luminosities approximately 40,000 solar luminosity, and radii approximately 0.7 solar radius; they have probably not yet reached their maximum luminosities. With M(subv) 19.1-19.8, they may be the visually faintest stars yet observed by UV spectroscopy. Clearly, it is not true that planetary nebulae nuclei all have masses M = (0.6 + or - 0.1) solar mass.

Maran, S. P.↗

NASA NTRS1982

The High Resolution Spectrograph for the Space Telescope

The High Resoltuion Spectrograph (HRS) in conjunction with the Space Telescope (ST), extends ultraviolet astronomical spectroscopy to higher spectra, spatial, and time resolutions than previously achieved, as well as to fainter and more distant celestial objects. Other significant advances inherent in the instrument are high photometric accuracy and efficient operation via exposure meter control and real time rejection of bad data. These capabilities are provided to accomplish the scientific programs of the HRS investigation definition team, which concern the interstellar medium, stellar winds, and evolutionary aspects of stellar atmosphere studies; the determination of chemical abundances relevant to stellar evolution; the investigation of quasars and Seyfert galaxy nuclei; and the analysis of the atmospheres of solar system objects, including comets.

Brandt, J. C.↗

NASA NTRS1981

Millimeter wave radiometry as a means of determining cometary surface and subsurface temperature

Thermal emission spectra for a variety of cometary nucleus models were evaluated by a radiative transfer technique adapted from modeling of terrestrial ice and snow fields. It appears that millimeter wave sensing from an interplanetary spacecraft is the most effective available means for distinguishing between alternate models of the nucleus and for evaluating the thermal state of the layer which is below the instantaneous surface where modern theories of the nucleus indicate that sublimation of the cometary volatiles actually occurs.

Hobbs, R. W.↗

NASA NTRS1981

Millimeter-wave experiments for cometary space missions

Predicted brightness temperatures, computed by means of radiative transfer techniques adapted from the modeling of terrestrial ice and snow fields, are given for cometary nucleus models consisting of homogeneous layers of water ice and refractory grain mixtures presented as functions of wavelength. The computed millimeter-wave spectra are sensitive to the values of such physically significant nucleus parameters as (1) crust thickness, (2) subsurface temperature gradient, and (3) sublimating surface boundary temperature. Although antenna beam dilution is a major obstacle for ground-based molecular spectral line radio observations of comets, a millimeter-wave radiometer in the vicinity of the comet would be immune to this effect and able to make observations of several candidate parent molecules in the gas phase.

Hobbs, R. W.↗

NASA NTRS1981

Preliminary report on IUE spectra of the Crab Nebula

The Crab Nebula is marginally observable with the IUE. Observations of the optically brightest filamentary regions, made with IUE in August 1979, show the C IV lambda 1549, He II lambda 1640, and C III lambda 1909 emission lines. The intensities of these lines were compared with the visual wavelength data. It appears that carbon is not overabundant in the Crab; carbon/oxygen is approximately normal and oxygen is slightly scarcer than normal as a fraction of the total mass.

Davidson, K.↗

NASA NTRS1981

Application of millimeter-wave remote sensing to the investigation of comets

It is pointed out the despite years of investigation, the solid, quasi-permanent component of comets, the nucleus, remains largely a mystery. The composition and thermal properties of the nucleus determine the evolution of the more familiar and often spectacular cometary features, the coma and tail. Under certain circumstances, the nucleus may be obscured by a dust cloud of much higher temperature. The most appropriate technology for the investigation of the surface and subsurface layers of the nucleus is considered to be millimeter-wave sensing from an interplanetary spacecraft. Simple radiative transfer models, adapted from methods employed for the interpretation of remote-sensing data on terrestrial ice and snow fields, are used to predict the millimeter-wave spectra of representative model nuclei. The spectra determine the choice of the minimum set of observing frequencies that is required. An instrument configuration driven by these requirements and guided by available technology and the restraints of a proposed NASA spacecraft is then derived.

Hobbs, R. W.↗

NASA NTRS1981

A meeting with the universe: Science discoveries from the space program

A general history of space exploration is presented. The solar system is discussed. The Sun-Earth relationship is considered, including magnetic fields, solar wind, the magnetosphere, and the Sun-weather relationship. The universe beyond the solar system is discussed. Topics include stellar and galactic evolution, quasars and intergalactic space. The effects of weightlessness and ionizing radiation on human beings are considered. The possibility of extraterrestrial life is discussed. Lunar and planetary exploration, solar-terrestrial physics, astrophysics, biomedical research and exobiology are reviewed. Numerons color illustrations are included.

French, B. M.↗

NASA NTRS1981

Relativistic astrophysics - The view from Texas in Baltimore /Review/

Recent observational and theoretical work presented at the Tenth Texas Symposium on Relativistic Astrophysics held in Baltimore, Maryland from December 15-19, 1980, is outlined. Areas covered include the theoretical foundations of relativistic astrophysics in general relativity, quantum gravitational theory and the association of grand unification with astronomical and cosmological issues, the cosmic microwave, X-ray, gamma-ray, UV, cosmic ray and gravitational wave backgrounds, the current expansion rate and average mass-energy density of the universe, and mechanisms of galaxy formation. Also discussed are the characteristics of active galaxies and clusters emitting in the gamma-ray and X-ray regions, and compact objects formed from supernova explosions, including pulsars, X-ray-emitting neutron stars, Sco X-1 and SS 433, gamma-ray sources, and X-ray and gamma-ray bursters.

Trimble, V. L.↗

NASA NTRS1981

Progress report on the high resolution spectrograph for the Space Telescope

The instrument design is complete and many components and subsystems have been manufactured and tested. Solar-blind, multichannel, pulse counting detectors for two ultraviolet spectral bands have been developed and satisfactory flight units have been chosen. A large, lightweight graphite-epoxy optical bench, utilizing fingerplate joints with no metallic parts in order to minimize thermal expansion, has been built. Tests of the engineering model torque-motor-driven grating carrousel indicate that this critical system exceeds tight specifications for accurate and repeatable angular positioning. A complement of large, high-frequency gratings and an echelle is being completed in several laboratories. Software resident in a computer on the spacecraft will control the spectrograph with the capability to alter procedures in response to real-time evaluation of the data.

Brandt, J. C.↗

NASA NTRS1980

IUE observations of the hot components in two symbiotic stars

Recent IUE observations reveal striking differences in the UV spectra of two symbiotic stars, R Aqr and RW Hya. RW Hya is found to be an unexpectedly intense source of UV radiation. The measurements reported demonstrate the presence of a hot component in each star, supporting the view that each is a binary system with a luminous red primary and a hot, subluminous companion. In one case, the hot companion manifests itself by exciting a compact nebulosity; in the other case the continuous spectrum of the hot star is directly detected, while the continuum of nebulosity excited by the hot star is detected at longer wavelengths.

Michalitsianos, A. G.↗

NASA NTRS1980

150 GHz observations of three radio galaxies

Radio galaxies were observed for the first time at 150 GHz. The central sources in Cyg A and 3C 111 were detected, as were the two radio lobes of Cyg A. No emission was found from the central source in 3C 236. The millimeter-wavelength emission from the central sources in Cyg A and 3C 111 is probably due in each case to a compact component that is optically thin to synchrotron radiation above about 35 GHz. These components are similar, although the compact component in 3C 111 is more luminous at both radio and X-ray wavelengths than the one in Cyg A. The 3C 111 central source was much weaker than anticipated on the basis of prior observations at 90 GHz, perhaps due to variability. Even at 150 GHz, there is no evidence of a high-frequency cutoff in the spectrum of the central source in Cyg A, and variability of this source also is expected. The flux densities of the Cyg A lobes are consistent with the power laws derived at lower frequencies, indicating that no steepening occurs in their spectra out to at least 150 GHz. There is no evidence for a compact, optically thick component in 3C 236.

Kafatos, M.↗

NASA NTRS1979

High resolution spectrograph for the Space Telescope

The high resolution spectrograph (HRS) for ultraviolet astronomy with the Space Telescope will provide a spectral resolution of approximately 120,000 over a nominal wavelength range of 110-320 nm, together with a spatial resolution of about 0.25 arc seconds. The two detectors will consist of 512-element Digicons with cesium telluride and cesium iodide photocathodes, respectively. Photoelectrons in transit between the photocathodes and the diodes within the Digicons can be deflected in two axes with 12-bit resolution. This feature facilitates a design that emphasizes reliability since (once a hermetic seal is opened in orbit), only two moving parts, a grating carrousel and a shutter, are required for regular operation of the HRS. The instrument will be controlled by a computer in the spacecraft. The scientific objectives of the HRS investigation relate to interstellar matter in our own and nearby galaxies, physical processes of stellar mass loss and mass transfer, chemical abundances, bright quasars and Seyfert galaxy nuclei, and solar system phenomena.

Brandt, J. C.↗

NASA NTRS1979

Distribution of astronomical sources in the second Equatorial Infrared Catalogue

Measurements of infrared (2.7-micron) source positions and flux densities have been derived based on an additional 60.6 hours of satellite observations beyond those considered in the preparation of the Equatorial Infrared Catalogue No. 1 (EIC-1). These data have been processed together with the EIC-1 data to produce EIC-2. The new catalog differs from EIC-1 as follows: there are 1278 sources; there is a larger percentage of unidentified sources; there are increased numbers of sources identified with Two-Micron Sky Survey sources, AFGL sources, AGK3 stars and SAO stars.

Nagy, T. A.↗

NASA NTRS1978

Preliminary results of linear polarization measurements at 99 GHz

The results of the first linear polarization measurements of extrasolar radio sources at a frequency above 35 GHz are presented. For the quasars 3C 273 and 3C 345, the observed position angles are in accord with the predictions of Inoue, and the measurements are consistent with the suggestion that the compact components responsible for the high-frequency emission are affected by high degrees of internal Faraday depolarization. For the radio galaxy 3C 274 (Virgo A) the observed position angle and degree of polarization are consistent with the model of Hobbs and Waak.

Hobbs, R. W.↗

NASA NTRS1978

Upconversion of broadband infrared spectra

An experimental device successfully upconverts IR radiation in the 3.2-5.0 micron wavelength range simultaneously to visible light at 0.80-0.88 microns, while preserving frequency coding and is thus applicable to IR spectroscopy. The 1.8-micron bandwidth of IR radiation that is upconverted without temperature or phase match tuning is the largest yet reported. The over-all system quantum efficiency of the upconverter/spectrometer system is 0.01% and could be improved to 0.4%.

Gurski, T. R.↗