Engineering topics

Bartoe, J.-D. F.

Publications and source records attributed to Bartoe, J.-D. F..

At least 19 records

NASA NTRS1991

An ultraviolet spectral atlas of a sunspot and an active region 1190-1730 A

An ultraviolet spectral atlas of a sunspot with high spectral and spatial resolution in the wavelength region 1190-1730 A is presented. The atlas contains spectra of three different areas in the sunspot and also of an active region and a quiet region. The selected areas are averaged over several arcsec, ranging from 3.5 arcsec in the sunspot to 18 arcsec in the quiet region. Brief descriptions of the data reduction and calibration procedures are given. The absolute intensities are determined with an accuracy of + or - 30 percent and the wavelength scale is accurate to better than 0.01 A. The transition region lines show the most extreme example known of downflowing gas above a sunspot, a phenomenon which seems to be commonly connected to sunspots.

Brekke, P.↗

NASA NTRS1991

Multiple flow velocities in the transition region

Observations with the High Resolution Telescope and Spectrograph (HRTS) of the C IV lines at 1550 A above sunspots reveal the coexistence of several distinct high velocity gas components within the instrument resolution element of 1 x 1 arcsec. A further investigation of the HRTS material demonstrates that such multiple gas velocities are not restricted to the temperature region around 100,000 K, where the C IV lines are formed, but that the gas flows with essentially unchanged speed through all temperature layers from 250,000 K to 10,000 K. Furthermore, the phenomenon is not restricted to sunspots, but occurs also in other solar regions, often most easily distinguished in active regions. The characteristics of the velocity fields are described. The mass fluxes are analyzed, and the requirements they place on the resolving power of future space instruments are discussed.

Brekke, P.↗

NASA NTRS1989

Correspondence between solar fine-scale structures in the corona, transition region, and lower atmosphere from collaborative observations

The Soft X-Ray Imaging Payload and the High Resolution Telescope and Spectrograph (HRTS) instrument were launched from White Sands on 11 December 1987 in coordinated sounding rocket flights to investigate the correspondence of coronal and transition region structures, especially the relationship between X-ray bright points (XBPs) and transition region small spatial scale energetic events. The coaligned data from X-ray images are presented along with maps of sites of transition region energetic events observed in C IV (100,000 K), HRTS 1600 A spectroheliograms of the T sub min region and ground based magnetogram and He I 10830 A images.

Moses, J. Daniel↗

NASA NTRS1988

Plasma motions in an emerging flux region

Ultraviolet spectra of C IV show large nonthermal broadening in an area of emerging flux. These nonthermal motions are observed at a very early stage of reconnecting field lines. The spectra can be traced to small, rapidly changing surge or filament-like features which are seen in the center, blue, and red wing of H-alpha. They seem to have the characteristics of macrospicules or explosive events. They are precursors of the reconnection process. Plasma turbulence and/or plasma waves in the reconnecting plasma may cause the broad C IV line profiles. The activity in the transition zone precedes the formation of a bright chromospheric loop system.

Brueckner, G. E.↗

NASA NTRS1986

HRTS results from Spacelab 2

The High Resolution Telescope and Spectrograph (HRTS) instrument flew on the Spacelab 2 mission and consisted of a 30-cm Gregorian telescope, a slit spectrograph covering the 1190-1680 A region with 0.05-A spectral resolution, a broadband (90 A FWHM) spectroheliograph tuned to 1550 A, and an H-alpha filter system. The spectrograph slit was 920 arcsec, approximately in length. Subarcsecond spatial resolution along the slit is possible, but because of jitter in the Spacelab Instrument Pointing System, good exposures actually achieved 1-2 arcsec resolution.

Brueckner, G. E.↗

NASA NTRS1983

Observations of high-energy jets in the corona above the quiet sun, the heating of the corona, and the acceleration of the solar wind

High spatial resolution observations of the ultraviolet solar spectrum which reveal high-energy events in the quiet sun are presented. The tandem Wadsworth spectrograph used to make the observations is described along with the observing techniques, and a brief description of the characteristics of high-resolution transition zone spectra is given. The sizes, velocities, line profiles, time behavior, temperature range, differential emission measures, densities, masses, energies, and birthrates of turbulent events and jets in the quiet sun are derived from the observations and discussed. Possible accelerating mechanisms for these events are discussed, and the consequences of these events for the heating of the solar corona are discussed. A cloud model of the solar wind is proposed and possible correlations between the high-energy events and other solar fine-structure features are discussed.

Brueckner, G. E.↗

NASA NTRS1983

High resolution telescope and spectrograph observations of solar fine structure in the 1600 A region

High spatial resolution spectroheliograms of the 1600 A region obtained during the HRTS rocket flight of 1978 February 13 are presented. The morphology, fine structure, and temporal behavior of emission bright points (BPs) in active and quiet regions are illustrated. In quiet regions, network elements persist as morphological units, although individual BPs may vary in intensity while usually lasting the flight duration. In cell centers, the BPs are highly variable on a 1 minute time scale. BPs in plages remain more constant in brightness over the observing sequence. BPs cover less than 4 percent of the quiet surface. The lifetime and degree of packing of BPs vary with the local strength of the magnetic field.

Cook, J. W.↗

NASA NTRS1982

High resolution EUV structure of the chromosphere-corona transition region above a sunspot

Rocket observations are reported for a sunspot at high spatial and spectral resolution in the extreme ultraviolet region (EUV) between 1170 and 1715 A. The instrument and data reduction are described, and the appearance of the sunspot features in EUV emission lines is presented together with a correlation of the nonthermal velocity field with the Doppler velocity field. For sunspots the shape of the differential emission measure curve shows that the minimum is shifted to lower temperatures by over a factor of two, while the slope on a log-log scale near log of effective temperature equal to 5.3 is increased by a factor of two. This means that the energy balance is dominated by radiative losses from the large amount of transition region plasma, and an upper limit of a million K exists on the extrapolated temperature above the umbra. Static energy balance models of the umbra show that the observed enthalpy flux can balance radiative losses above 30,000 K for a fill factor greater than 0.1. An umbral model is compared with the chromospheric sunspot model of Kneer and Mattig (1978).

Nicolas, K. R.↗

NASA NTRS1982

An image drift compensation system for a solar pointed space telescope

Two sounding rocket test flights have been conducted in the development of an image drift compensation system designed for a solar-pointed space telescope. The system, whose scientific results are presented, employs limb-sensing photodiodes at the telescope focal plane and provides drift compensation to better than + or - 0.1 arcsec. A variation of this device will be employed by the Space Shuttle/Spacelab 2 flight of the High Resolution Telescope and Spectrograph (HRTS) Instrument. The data gathered by the rocket flights of the drift compensation system have revealed high velocity ejecta traveling through the transition zone and corona at velocities up to 400 km/sec. The HRTS configuration and its constitutive instruments' optical parameters are described.

Bartoe, J.-D. F.↗

NASA NTRS1981

A high precision Solar Ultraviolet Spectral Irradiance Monitor for the wavelength region 120-400 nm

There exists a growing need to improve the accuracy of measurement of the absolute solar flux within the wavelength range 120-400 nm. Although full-disk solar fluxes and variations thereof in the 120-400 nm region are required to model the solar atmosphere, current increased interest in the measurements arises from their importance in modeling the terrestrial atmosphere. The Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) experiment under development for flight aboard the Space Shuttle and the Upper Atmospheric Research Satellite is described. SUSIM will monitor the solar flux in the 120-144 nm region with high precision, using an in-flight calibration system to reduce absolute error to less than 10%, and error relative to the 400 nm continuum to less than 1%.

Vanhoosier, M. E.↗

NASA NTRS1981

The sunspot chromosphere-corona transition region

Data from simultaneous readings of the line intensities, Doppler shifts, and line widths of a sunspot ion emission lines between 1170-1700 A are reported. Subsonic and supersonic flows were observed in the same line of sight above the umbra. A reduction of coronal plasma over sunspots with an electron temperature exceeding 1,000,000 K was confirmed, concurrent with enhanced emission from the transition region plasma in the temperature range 200,000-1,000,000 K. The differential emission measure is noted to have been caused to shift because of the enhancement of the transition region plasma emission, where radiative losses dominated the energy balance. Calculations of the energy balance also indicated that a detected divergence in the enthalpy flux for the umbral downflows could balance the radiative losses in the electron temperature range 30,000-200,000 K.

Nicolas, K. R.↗

NASA NTRS1980

Stark effect at the Si I series limit

Small redshifts and weakenings of high n lines in members of the Si series observed over a sunspot are interpreted as due to the Stark effect. Other origins, including Doppler motions, appear to be excluded. The spectra were obtained with high spatial resolution using the NRL high-resolution telescope and spectrograph. The origin of the Stark effect is not yet certain. An interpretation in terms of a quasi-static quadratic effect would require rather high perturber densities. An alternative interpretation would be a motional Stark effect, arising perhaps through the presence of magnetohydrodynamic waves.

Jordan, C.↗

NASA NTRS1979

The energy balance and pressure in the solar transition zone for network and active region features

The electron pressure and energy balance in the solar transition zone are determined for about 125 network and active region features on the basis of high spectral and spatial resolution extreme ultraviolet spectra. Si III line intensity ratios obtained from the Naval Research Laboratory high-resolution telescope and spectrograph during a rocket flight are used as diagnostics of electron density and pressure for solar features near 3.5 x 10 to the 4th K. Observed ratios are compared with the calculated dependence of the 1301 A/1312 A and 1301 A/1296 A line intensity ratios on electron density, temperature and pressure. Electron densities ranging from 2 x 10 to the 10th/cu cm to 10 to the 12th/cu cm and active region pressures from 3 x 10 to the 15th to 10 to the 16th/cu cm K are obtained. Energy balance calculations reveal the balance of the divergence of the conductive flux and turbulent energy dissipation by radiative energy losses in a plane-parallel homogeneous transition zone (fill factor of 1), and an energy source requirement for a cylindrical zone geometry (fill factor less than 0.04).

Nicolas, K. R.↗

NASA NTRS1979

Lyman-alpha rocket spectra and models of the quiet and active solar chromosphere based on partial redistribution diagnostics

Absolute intensity Lyman-alpha profiles with a spatial resolution of 0.8 min and a spectral resolution of 50 mA were obtained for network and cell regions in the quiet sun, umbral and penumbral areas of a sunspot, two plages, and a quiescent prominence of the limb. Weak limb brightening shown by the Lyman-alpha cores and wings are consistent with predictions derived from partial redistribution line transfer calculations. Through use of a comoving two-level partial redistribution code which conserves mass flux, unequal red and blue Lyman-alpha peak intensities may be interpreted as flow velocities near 20,000 K. Outflows in the plages and downflows in the network are also noted. A model of a mean quiet sun chromosphere consistent with the Lyman-alpha integrated intensity, the Lyman continuum slope, and the millimeter continuum is presented.

Basri, G. S.↗

NASA NTRS1979

H2 emission in the solar atmosphere

New identifications of emission lines of molecular hydrogen in the EUV spectrum of sunspots are reported. The spectra were obtained during the first and second flights of the Naval Research Laboratory's High Resolution Telescope and Spectrograph (HRTS). While most of the lines originate in the Lyman bands, fluorescence from the Werner bands has been found for the first time in the solar atmosphere. H2 fluorescent emission has also been identified in the spectra of a solar flare observed with NRL's normal incidence spectrograph on Skylab. Column densities for H2 are derived from intensities of lines in the sunspot spectra.

Bartoe, J.-D. F.↗

NASA NTRS1979

CO emission lines in the solar atmosphere

New identifications of CO emission lines in the EUV spectrum of a sunspot are reported. The spectra were obtained with the Naval Research Laboratory's High Resolution Telescope and Spectrograph. The emission is from the CO fourth positive system and is excited by the strong lines of C IV, Si IV and O IV. Transitions in the 0-3 band which lie above 1700 A and other lines at shorter wavelengths have been identified from the spectrum of the June 15, 1973 flare, obtained with the Naval Research Laboratory's normal incidence spectrograph on Skylab. The observed intensities in the sunspot are used to derive the CO column density.

Jordan, C.↗

NASA NTRS1979

Measurements of spectrally integrated atmospheric transmittance in the O2 Schumann-Runge bands and derived oxygen column densities - 76-102 km

Atmospheric transmittances integrated over wavelength intervals corresponding approximately to the (15-0) through (4-0) Schumann-Runge bands of O2 have been determined from EUV solar spectra (wavelengths between 1768 and 1948 A) photographed at seven altitudes between 102 and 76 km with a rocket-borne spectrograph having a resolution of 0.07 A. The observed transmittances are compared with atmospheric transmittances predicted from three models of the O2 absorption cross section. The predicted transmittances have also been used to derive column densities of atmospheric O2 from the observations. The results are compared with values calculated from the U.S. Standard Atmosphere (1976) and with oxygen column densities determined by Prinz and Brueckner (1977) from EUV solar spectra of the Schumann-Runge continuum (wavelength below 1750 A) and of the H-Lyman alpha line (1216 A) recorded on the same films used in the present research. The comparisons test the utility of the models for studies of atmospheric photochemistry, suggest which models may be best for this purpose, and indicate how the models can be improved.

Longmire, M. S.↗

NASA NTRS1978

Emission lines of H2 in the extreme-ultraviolet solar spectrum

A sunspot EUV spectrum covering the wavelength range from 1175 to 1714 A with high spatial and spectral resolution is examined which contains about 200 lines not previously reported in solar spectra. Many of the lines are identified as transitions in the Lyman bands of H2. It is shown that the H2 lines are photoexcited not only by H L-alpha, as reported previously, but also by the strong transition-region lines of C II, Si IV, and O IV. The line intensities are analyzed as far as is possible at present, and differences between the quiet chromosphere and the sunspot chromosphere are deduced. The polarization of the observed lines is briefly discussed, the importance of the H L-alpha fluorescence mechanism for the excitation of the H2 Lyman bands is demonstrated, and it is concluded that the H2 lines could also be observable in stars of spectral type later than the sun.

Jordan, C.↗