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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 1,765 records · Page 98
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NASA NTRS1979

Rocket studies of solar corona and transition region

The XSST (X-Ray Spectrometer/Spectrograph Telescope) rocket payload launched by a Nike Boosted Black Brant was designed to provide high spectral resolution coronal soft X-ray line information on a spectrographic plate, as well as time resolved photo-electric records of pre-selected lines and spectral regions. This spectral data is obtained from a 1 x 10 arc second solar region defined by the paraboloidal telescope of the XSST. The transition region camera provided full disc images in selected spectral intervals originating in lower temperature zones than the emitting regions accessible to the XSST. A H-alpha camera system allowed referencing the measurements to the chromospheric temperatures and altitudes. Payload flight and recovery information is provided along with X-ray photoelectric and UV flight data, transition camera results and a summary of the anomalies encountered. Instrument mechanical stability and spectrometer pointing direction are also examined.

Acton, L. W.↗
NASA NTRS1980

Spectrum synthesis of EUV solar flare line profiles

A classic double ribbon flare of importance 1B occurred at approximately 1405 UT on June 15, 1973, reached an H alpha maximum at 1413 UT, and ended at 1455 UT. The flare occurred in an old and simplifying bipolar region at N18 W32. This flare was studied due to the extensive temporal data available. A total of 136 spectra of wavelength ranges from 1100 to 3000 A were taken during the flare's duration by the Naval Research Laboratory normal incidence slit spectrograph. Using this data the nature of the solar chromosphere of a flare event as a function of time was determined.

Tripp, D. A.↗
NASA NTRS1979

Collective plasma effects associated with the continuous injection model of solar flare particle streams

A modified continuous injection model for impulsive solar flares that includes self-consistent plasma nonlinearities based on the concept of marginal stability is presented. A quasi-stationary state is established, composed of a hot truncated electron Maxwellian distribution confined by acoustic turbulence on the top of the loop and energetic electron beams precipitating in the chromosphere. It is shown that the radiation properties of the model are in accordance with observations.

Vlahos, L.↗
NASA NTRS1979

Slowly moving disturbances in the X-ray corona

Sequences of soft X-ray pictures, taken aboard Skylab between May and November, 1973, have made it possible to detect slowly moving disturbances originating in disrupted filaments and causing subsequent brightenings of distant coronal structures. With speeds decreasing from approximately 400 km/sec shortly after the filament disruption to approximately 10 km/sec four or five hours later, these disturbances appear to be identical with slow waves earlier inferred by Bruzel (1952, 1969), Oehman (1953), and Yajima (1971) from chromospheric observations.

Rust, D. M.↗
NASA NTRS1980

An overview of the solar maximum mission

The Solar Maximum Mission (SMM), devoted to the study of active solar phenomena is expected to be launched in February 1980 and operate throughout the peak of the current maximum of solar activity. The SMM observatory consists of two main sections: the instrument module which houses the solar payload instruments and the Fine Pointing Sun Sensor System, and the Multimission Modular Spacecraft (MMS) which carries the spacecraft subsystem modules. The entire observatory is 4m long and 2.3m in diameter. The SMM will carry a payload of six instruments specifically selected to study the short wavelength and coronal manifestations of flares. These include: gamma ray spectrometer, hard X-ray burst spectrometer, hard-X-ray imaging spectrometer, soft X-ray polychromator, UV spectrometer and polarimeter, coronagraph/polarimeter and solar constant monitoring package which will measure the total solar irradiance to an accuracy of 0.1 percent. Specific scientific objectives will include: chromospheric evaporation, thermalization, electron acceleration and flare build-up. Complementary studies will be made as part of an SMM Guest Investigator Program. The SMM observation program will be operated on a 24 hour cycle.

Chipman, E. C.↗
NASA NTRS1980

Outer atmospheres of cool stars. IV - A discussion of cool stellar wind models

Possible wind models for late-type stars which appear not to have hot coronae and transition regions are investigated; taking Arcturus and the prototypical star, models with T less than approximately 20,000 K are considered, and solutions with mass loss rates of 10 to the -9th solar masses per year are sought. The radiation pressure of L-alpha resonance scattering can exceed the force of gravity in the chromosphere and initiate a net outflow, but is insufficient to sustain a wind, except perhaps in the presence of an additional momentum input term such as Alfven wave pressure. It is concluded that L-alpha radiation-pressure-initiated winds can occur in stars to the right of the Linsky-Haisch dividing line in the H-R diagram between stars with and without transition regions and presumably hot coronae, and that the existence of these winds may explain energetically the absence of hot coronae in these stars.

Haisch, B. M.↗
NASA NTRS1980

The Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission

The Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission spacecraft is described, including the experiment objectives, system design, performance, and modes of operation. The instrument operates in the wavelength range 1150-3600 A with better than 2 arcsec spatial resolution, raster range 256 x 256 sq arcsec, and 20 mA spectral resolution in second order. Observations can be made with specific sets of four lines simultaneously, or with both sides of two lines simultaneously for velocity and polarization. A rotatable retarder can be inserted into the spectrometer beam for measurement of Zeeman splitting and linear polarization in the transition region and chromosphere.

Woodgate, B. E.↗
NASA NTRS1980

A model for sunspot associated emission at 6 cm wavelength

Two-dimensional maps of total intensity and circular polarization of a sunspot region at 6 cm have been calculated using a simple model for the chromosphere-corona transition region and observations of the longitudinal component of the photospheric magnetic field. The calculations are in good agreement with the high resolution observations of the same sunspot region at 6 cm, obtained with the Westerbork Synthesis Radio Telescope. It is shown that the 6 cm radiation is predominantly due to gyroresonance absorption process at the second and third harmonics of the gyrofrequency (H = 900-600 G). Estimates of the conductive flux and the electron density in the transition region above the sunspot are also given.

Alissandrakis, C. E.↗
NASA NTRS1980

A model of active prominences

A one-dimensional numerical model of active loop prominences is investigated. The model includes the effects of gravity, the geometry of the magnetic field, and conduction losses to the chromosphere. Calculations indicate that, as originally proposed by Goldsmith, the thermal instability mechanism is, by itself, sufficient to account for the appearance of bright H-alpha knots in postflare loops. Under certain conditions, initial perturbations in the loop temperature and density profiles of small, but finite, amplitude (approximately 5%) and large size scale (greater than or approximately equal to 10 to the 9th cm) can grow into condensations with temperature and density differences of over an order of magnitude and size scales of less than 10 to the 8th cm. In agreement with observations, the conditions that must be satisfied are such that loop prominence systems are likely to occur only in large flares and such that knots preferentially form at the tops of loops. The velocities, densities, and lifetimes calculated for the loop material are also in agreement with observations. It is concluded that in order for H-alpha knots to occur, heating of some form must continue into the late cooling phase of a flare loop, and that this heating is more intense near the loop base than near the apex.

Antiochos, S. K.↗
NASA NTRS1980

Dynamics of flare sprays

During solar cycle No. 20 new insight into the flare-spray phenomenon has been attained due to several innovations in solar optical-observing techniques (higher spatial resolution cinema-photography, tunable passband filters, multislit spectroscopy and extended angular field coronagraphs). From combined analysis of 13 well-observed sprays which occurred between 1969-1974 it is concluded that (1) the spray material originates from a preexisting active region filament which undergoes increased absorption some tens of minutes prior to the abrupt chromospheric brightening at the 'flare-start', and (2) the spray material is confined within a steadily expanding, loop-shaped (presumable magnetically controlled) envelope with part of the materials draining back down along one or both legs of the loop.

Tandberg-Hanssen, E.↗
NASA NTRS1980

6 cm observations of a solar active region and bursts with approximately 6 arcsec resolution

The paper examines the solar active region located near N04E49, that was mapped at a 6 cm wavelength over a period of 12 hours, employing the Westerbork synthesis radio telescope. Two impulsive radio bursts were recorded during this time, one of which was associated with a chromospheric flare. One-dimensional fan beam scans of the burst sources were synthesized in order to display their time history with regard to intensity, polarization, position and size.

Erskine, F. T.↗
NASA NTRS1980

Singly-ionized helium in the driver gas of an interplanetary shock wave

The interplanetary shock wave observed on Jan. 29, 1977 by the HELIOS-1 plasma instruments shows an unusual feature: in the cold tenuous piston plasma following this shock, there appears a third peak in the energy per charge (E/q) spectra, in addition to the normal proton and alpha-particle peaks. The peak is located at E/q ? 4 and persists for about 14 hours, with slowly varying intensities. Independent simultaneous measurement of these particles' charge yields a value of approximately 1. These ions are thought to be He-4(+) ions travelling with the same speed as protons and alpha particles. The occurrence of He-4(+) indicates the possibility that during eruptive prominences or other solar transients, 'cold' chromospheric plasma might escape from the sun without undergoing the normal coronal heating process.

Schwenn, R.↗
NASA NTRS1980

HEAO 1 observations of active coronae in main-sequence and subgiant stars

The HEAO 1 data has been searched for evidence of X-ray emission from 105 bright late-type stars of luminosity classes IV and V, selected on the basis of indirect optical evidence of the presence of a hot corona. Six of the target stars were detected at the 3-standard deviation level and 15 were coincident with 2-standard deviation X-ray sources. On a statistical basis no more than 5 of these 21 sources are spurious, and the probability that the identification with the class of active chromosphere stars is spurious is less than 0.00001. The sources lie near a line of X-ray/bolometric luminosity ratio = 0.0001, similar to a solar plage, and it is concluded that the most active coronae of late-type stars which are not members of close binary systems are being observed. The RS CVn systems discovered to date seem to form a distinct class of coronal X-ray sources, but the lowest X-ray luminosity members of the group, of which Capella may be the prototype, appear to overlap the domain of these single stars with active coronae. The data do not fit the coronal model of Gorenstein and Tucker (1976), but they are consistent with the coronal loop model of Rosner et al. (1978) as extended by Walter et al. (1980).

Walter, F. M.↗
NASA NTRS1980

Outer atmospheres of cool stars. VI - Models for Epsilon Eridani based on IUE spectra of C II, Mg II, Si II, and Si III

Observations of the ultraviolet line spectrum of the active chromosphere star, Epsilon Eridani, obtained with the IUE satellite have been analyzed. The coupled statistical equilibrium and radiative transfer equations for the prominent transitions of C II, Mg II, Si II, and Si III. A satisfactory fit to all of the line strengths can be achieved with a model similar to that recently proposed to explain bright points on the quiet sun. A surface pressure at the base of the transition region of 0.5 dynes/sq cm is derived, which is a factor of 3 higher than the quiet sun value, but a factor of 3 smaller than predicted by scaling laws, assuming a conductively heated stellar transition region. It is found that the surface fluxes of the C II 1334, 1335 and Si III 1892 emission lines are good diagnostics of pressure at the base of the transition region, but line ratio techniques using the 1892 line for estimating electron densities may be valid.

Simon, T.↗
NASA NTRS1980

Analysis of the solar magnesium lines

The observed quiet-sun profiles for a number of Mg I and II lines are compared with theoretical spectra computed for two upper-photosphere lower-chromosphere models published by Ayres and Linsky (1976). Both the Mg I and the Mg II resonance line wings, observed with the University of Hawaii Echelle Rocket Spectrographs, favor a model with a higher temperature in the upper photosphere than required to match the visible region lines 4571 and 5172. Neither model atmosphere reproduces the observed shapes in the cores of the strong lines or the limb darkening of the 4571 A intercombination line. The wings of the ultraviolet lines in plages can be reproduced either with a mean one-component atmosphere or by a two-component model with an ad hoc filling factor.

Heasley, J. N.↗
NASA NTRS1980

Depth-dependence of turbulence in stellar atmospheres

Recent observations concerning the depth dependence of motions in stellar atmospheres are reviewed. With regard to turbulence in stellar photospheres, attention is given to evidence from the sun and Arcturus for an increase in the total micro- plus macro-velocities with height, starting at mid-photospheric levels. Concerning stellar chromospheric velocity fields, it is noted that Mg II data point to changes in the hydrodynamic structure of the upper atmosphere. Ca II and Mg II asymmetry observations and other studies are used to describe the upper atmospheric structure of cool evolved stars, particularly coronae and circumstellar envelopes, revealing a depth dependent effect of velocity fields among a wide range of such stars.

Stencel, R. E.↗
NASA NTRS1980

Mass ejections

Observations and model simulations of solar mass ejection phenomena are examined in an investigation of flare processes. Consideration is given to Skylab and other observations of flare-associated sprays, eruptive prominences, surges and coronal transients, and to MHD, gas dynamic and magnetic loop models developed to account for them. Magnetic forces are found to confine spray material, which originates in preexisting active-region filaments, within steadily expanding loops, while surges follow unmoving, preexisting magnetic field lines. Simulations of effects of a sudden pressure pulse at the bottom of the corona are found to exhibit many characteristics of coronal transients associated with flares, and impulsive heating low in the chromosphere is found to be able to account for surges. The importance of the magnetic field as the ultimate source of energy which drives eruptive phenomena as well as flares is pointed out.

Rust, D. M.↗
NASA NTRS1980

The thermal X-ray flare plasma

Following a review of current observational and theoretical knowledge of the approximately 10 to the 7th K plasma emitting the thermal soft X-ray bursts accompanying every H alpha solar flare, the fundamental physical problem of the plasma, namely the formation and evolution of the observed X-ray arches, is examined. Extensive Skylab observations of the thermal X-ray plasmas in two large flares, a large subflare and several compact subflares are analyzed to determine plasma physical properties, deduce the dominant physical processes governing the plasma and compare large and small flare characteristics. Results indicate the density of the thermal X-ray plasma to be higher than previously thought (from 10 to the 10th to 10 to the 12th/cu cm for large to small flares), cooling to occur radiatively as much as conductively, heating to continue into the decay phase of large flares, and the mass of the thermal X-ray plasma to be supplied primarily through chromospheric evaporation. Implications of the results for the basic flare mechanism are indicated.

Moore, R.↗