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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

IUE observations of the chromospheric activity-age relation in young solar-type stars

Ultraviolet data obtained with the IUE spacecraft are presented for a dozen solar-type stars in the field. The stars are of spectral type F6 V - G1 V; on the basis of their high Li content, they range in age from 0.1 to 2.8 Gyr. The evolution of transition regions and chromospheric emission with stellar age is studied along with the surface distribution of magnetically active regions as revealed by rotational modulation of UV emission line fluxes.

Simon, T.↗
NASA NTRS1973

Helium abundance of the sun.

Critical review of the four methods that have been used to estimate the ratio of helium to hydrogen in the sun - the solar neutrino flux, spectral intensity of helium lines in prominences and the chromosphere, elemental abundance of solar cosmic rays, and variations of solar wind He/H. At present the measured value for the neutrino flux cannot be explained by any of the theoretical models of the sun, and thus the neutrino measurements cannot yield an estimate of He/H. Helium line intensity measurements give the most accurate values for He/H now available - i.e., 5 to 8% helium by number. However, these results refer to the chromosphere and prominences only, and questions of spatial and temporal variations of the observed quantities and of the inferred helium abundances have not yet been dealt with adequately.

Hirshberg, J.↗
NASA NTRS1987

Evidence for gentle chromospheric evaporation during the gradual phase of large solar flares

The Multichannel Subtractive Double Pass Spectrograph of the Meudon solar tower is used to obtain high spatial resolution H-alpha line profiles during the gradual phase of three solar flares. In all cases, small blueshifts lasting for several hours are observed in the flare ribbons. By contrast, the region between the two ribbons exhibits large redshifts that are typical of H-alpha post flare loops. The blueshifts in the ribbons is interpreted as upward chromospheric flows of 0.5-10 km/s, and the possible ambiguities of the interpretation are discussed. A preliminary analysis indicates that such upflows are sufficient to supply the greater than 10 to the 16th g of mass needed to maintain a dense H-alpha postflare loop system in the corona.

Schmieder, B.↗
NASA NTRS1978

The collisional interaction of a beam of charged particles with a hydrogen target of arbitrary ionization level

The classical theory of scattering under the Coulomb potential of both charged and neutral particles is used to derive formulae for the energy deposition rate and mean scattering of a beam of charged particles interacting with a cold hydrogen target of arbitrary ionization level as a function of the column density traversed by the beam. These general results hold for any form of stable injection energy spectrum, and their relevance to the existing literature on chromospheric heating during solar flares is discussed.

Emslie, A. G.↗
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 NTRS1989

Two-dimensional magnetohydrodynamic model of emerging magnetic flux in the solar atmosphere

The nonlinear undular mode of the magnetic buoyancy instability in an isolated horizontal magnetic flux embedded in a two-temperature layered atmosphere (solar corona-chromosphere/photosphere) is investigated using a two-dimensional magnetohydrodynamic code. The results show that the flux sheet with beta of about 1 is initially located at the bottom of the photosphere, and that the gas slides down the expanding loop as the instability develops, with the evacuated loop rising as a result of enhanced magnetic buoyancy. The expansion of the magnetic loop in the nonlinear regime displays self-similar behavior. The rise velocity of the magnetic loop in the high chromosphere (10-15 km/s) and the velocity of downflow noted along the loop (30-50 km/s) are consistent with observed values for arch filament systems.

Shibata, K.↗
NASA NTRS1981

Chromospheric and photospheric evolution of an extremely active solar region in solar cycle 19

a comprehensive investigation was made of phenomena attending the disk passage, July 7 to 21, 1959, of active solar center HAO-59Q. At the photospheric level that comprised an aggregate of groups of sunspots of which one group, Mt. Wilson 14284, showed all the attributes deemed typical of solar regions associated with the production of major flares. A special characteristic of 59Q was its capability to eject dark material. Part of this material remained trapped in the strong magnetic fields above group 14284 where it formed a system of interrelated arches, the legs of which passed through components of the bright chromospheric network of the plage and were rooted in various underlying umbrae. Two apparently diffeent kinds of flare were identified in 59Q; namely, prominence flares (which comprised brightenings within part of the suspended dark prominence) and plage flares (which comprised brightenings within part of the chromospheric network). Prominence flares were of three varieties described as 'impact', 'stationary' and 'moving' prominence flares. Plage flares were accompanied in 3 percent of cases by Type III bursts. These latter radio events indicate the associated passage through the corona of energetic electrons in the approximate energy range 10 to 100 keV. At least 87.5 percent, and probably all, impulsive brightenings in 59Q began directly above minor spots, many of which satellites to major umbrae. Stationary and moving prominence flares were individually triggered at sites beneath which magnetic changes occurred within intervals which included each flare's flash phase.

Mckenna-Lawlor, S. M. P.↗
NASA NTRS1998

A Multiplicity Survey of Chromospherically Active and Inactive Stars

Surveys of the three samples of solar-type stars, segregated by chromospheric emission level, were made to determine their multiplicity fractions and to investigate the evolution of multiplicity with age. In total, 245 stars were searched for companions with DeltaV <= 3.0 and separations of 0.035" to 1.08" using optical speckle interferometry, By incorporating the visual micrometer survey for duplicity of the LamontHussey Observatory, the angular coverage was extended to 5.0" with no change in in the DeltaV limit. This magnitude difference allows mass ratios of 0.63 and larger to be detected throughout a search region of 2-127 AU for the stars observed. The 84 primaries observed in the chromospherically active sample are presumably part of a young population and are found to have a multiplicity fraction of 17.9% +/- 4.6%. The sample of 118 inactive, presumably older, primaries were selected and observed using identical methods and are found to have a multiplicity fraction of only 8.5% +/- 2.7%. Given the known link between chromospheric activity and age, these results tentatively imply a decreasing stellar multiplicity fraction from 1 to 4 Gyr, the approximate ages of the two samples. Finally, only two of the 14 very active primaries observed were found to have a companion meeting the survey detection parameters. In this case, many of the systems are either very young, or close, RS CVn type multiples that are unresolvable using techniques employed here.

Mason, Brian D.↗
NASA NTRS1982

The vertical propagation of waves in the solar atmosphere. II Phase delays in the quiet chromosphere and cell-network distinctions

The differences in the phase of the velocity oscillations between a pair of chromospheric Ca II lines was measured using the Vacuum Tower Telescope at the Sacramento Peak Observatory. The observed phase differences indicate that the acoustic modes are trapped or envanescent, rather than propagating, in the chromosphere. Systematic distinctions are found in the phase delays between quiet network and cell interior regions for both intensity and velocity oscillations in photospheric and chromospheric lines. The theory of linear perturbations in an isothermal atmosphere is invoked to interpret these differences. From this analysis it is found that one or more of the following explanations is possible: (1) the radiative damping is more effective in the network than in the cell interior; (2) the network features exclude oscillations of large horizontal wavenumber; or (3) the scale height of the chromosphere is larger in the network than in the cell interior.

Lites, B. W.↗
NASA NTRS1989

Solar and stellar coronal plasmas

Progress in observational, theoretical, and radio studies of coronal plasmas is summarized. Specifically work completed in the area of solar and stellar magnetic fields, related photospheric phenomena and the relationships between magnetism, rotation, coronal and chromospheric emission in solar-like stars is described. Also outlined are theoretical studies carried out in the following areas, among others: (1) neutral beams as the dominant energy transport mechanism in two ribbon-flares; (2) magneto hydrodynamic and circuit models for filament eruptions; and (3) studies of radio emission mechanisms in transient events. Finally, radio observations designed for coronal activity studies of the sun and of solar-type coronae are described. A bibliography of publications and talks is provided along with reprints of selected articles.

Golub, Leon↗
NASA NTRS2015

Solar Lyman-Alpha Polarization Observation of the Chromosphere and Transition Region by the Sounding Rocket Experiment CLASP

We are planning an international rocket experiment Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is (2015 planned) that Lyman α line (Ly(alpha) line) polarization spectroscopic observations from the sun. The purpose of this experiment, detected with high accuracy of the linear polarization of the Ly(alpha) lines to 0.1% by using a Hanle effect is to measure the magnetic field of the chromosphere-transition layer directly. For polarization photometric accuracy achieved that approx. 0.1% required for CLASP, it is necessary to realize the monitoring device with a high throughput. On the other hand, Ly(alpha) line (vacuum ultraviolet rays) have a sensitive characteristics that is absorbed by the material. We therefore set the optical system of the reflection system (transmission only the wavelength plate), each of the mirrors, subjected to high efficiency of the multilayer coating in accordance with the role. Primary mirror diameter of CLASP is about 30 cm, the amount of heat about 30,000 J is about 5 minutes of observation time is coming mainly in the visible light to the telescope. In addition, total flux of the sun visible light overwhelmingly large and about 200 000 times the Ly(alpha) line wavelength region. Therefore, in terms of thermal management and 0.1% of the photometric measurement accuracy achieved telescope, elimination of the visible light is essential. We therefore, has a high reflectivity (> 50%) in Lyα line, visible light is a multilayer coating be kept to a low reflectance (<5%) (cold mirror coating) was applied to the primary mirror. On the other hand, the efficiency of the polarization analyzer required chromospheric magnetic field measurement (the amount of light) Conventional (magnesium fluoride has long been known as a material for vacuum ultraviolet (MgF2) manufactured ellipsometer; Rs = 22%) about increased to 2.5 times were high efficiency reflective polarizing element analysis. This device, Bridou et al. (2011) is proposed "that is coated with a thin film of the substrate MgF2 and SiO2 fused silica." As a result of the measurement, Rs = 54.5%, to achieve a Rp = 0.3%, high efficiency, of course, capable of taking out only about s-polarized light. Other reflective optical elements (the secondary mirror, the diffraction gratingcollector mirror), subjected to high-reflection coating of Al + MgF2 (reflectance of about 80%), less than 5% in the entire optical system by these (CCD Science was achieved a high throughput as a device for a vacuum ultraviolet ray of the entire system less than 5% (CCD of QE is not included).

Narukage, Noriyuki↗
NASA NTRS1994

Electron beams in solar flares

A list of publications resulting from this program includes 'The Timing of Electron Beam Signatures in Hard X-Ray and Radio: Solar Flare Observations by BATSE/Compton Gamma-Ray Observatory and PHOENIX'; 'Coherent-Phase or Random-Phase Acceleration of Electron Beams in Solar Flares'; 'Particle Acceleration in Flares'; 'Chromospheric Evaporation and Decimetric Radio Emission in Solar Flares'; 'Sequences of Correlated Hard X-Ray and Type 3 Bursts During Solar Flares'; and 'Solar Electron Beams Detected in Hard X-Rays and Radiowaves.' Abstracts and reprints of each are attached to this report.

Aschwanden, Markus J.↗
NASA NTRS1984

Extreme Limb Profiles of the Sun at Far Infrared and Submillimeter Wavelengths

Limb intensity profiles at 30, 50, 100, and 200 microns, determined from Kuiper airborne observatory (KAO) observations of the occultation of the solar limb during the total eclipse of July 31, 1981, are presented. Significant but gradual limb brightening was found at the longer wavelengths consistent with the 6000 K temperature-plateau structure of the model chromospheres of Vernazza, Avrett, and Loeser. The 100 and 200 micrometers limbs are extended significantly further above the visible limb than the Vernazza, Avrett, and Loeser model predicts. These results show that the solar chromosphere is strongly perturbed from gravitational-hydrostatic equilibrium to heights as low as 1000 km. These profiles can serve as a powerful diagnostic for modeling the temperature and density of chromospheric structure free from the assumption of gravitational-hydrostatic equilibrium.

Becklin, E. E.↗
NASA NTRSDate not supplied

Even Small Events Involve the Entire Solar Atmosphere

The connection between the photosphere, chromosphere, and corona is essential for understanding the energy flows throughout the solar atmosphere. Here we discuss and analyze observations centered on a bipolar region of enhanced-network magnetic flux near disk center on SOL2017-03-17T14:00-17:00. The comprehensive data set comprises observations from SDO: HMI, AIA; Hinode: SOT, XRT; DST: IBIS, FIRS; ALMA; and IRIS; thus providing a variety of plasma diagnostics spanning the photosphere to the corona. Numerous transient brightenings were observed across the data set, and here we highlight transient brightenings within a set of thin filamentary features. One interesting event shows initial heating in the cooler (ALMA, 7000 K) before showing in the hotter (XRT, 3 MK) data series. These brightenings showcase how even small events involve large ranges of the solar atmosphere.

chromosphere↗