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Nicolas, K. R.

Publications and source records attributed to Nicolas, K. R..

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

HRTS II EUV observations of a solar ephemeral region

HRTS II has been used to observe the EUV emission of a small bipolar magnetic feature or ephemeral region, where strong EUV line enhancement exhibits contrasts (measured relative to the quiet sun) which range from 10 to 70. The substantiality of the Lyman-alpha and C II-O V emission, and the absence of any measurable emission in coronal forbidden lines, sets a temperature range for the loop's active part of the order of 16,000-300,000 K. The use of the ratios of allowed lines as temperature diagnostics yields temperatures that are very near ionization equilibrium temperatures, and the use of chromospheric lines to form a wavelength standard yields absolute velocities ranging in magnitude from zero to 12 km/sec for C IV, N IV, and O V. This flow is interpreted as a siphon flow.

Roussel-Dupre, R.↗
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 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 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

Solar C III line intensity ratios observed from Skylab

Solar observations of C III line intensity ratios are analyzed which were obtained by the Naval Research Laboratory extreme-ultraviolet slit spectrograph on Skylab from quiet and active regions, coronal holes, prominences, and a flare. Electron densities are determined by comparing the observed intensity ratios to their theoretical variation as a function of electron density and temperature. Both isothermal line ratios that are evaluated at a characteristic emitting temperature and ratios that are integrated through the temperature and density structure of a model solar atmosphere are calculated. The density-sensitive ratios R(Si IV 1402/C III 1908) and R(Si III 1892/C III 1908) are also used to derive additional values of electron density. It is found that the ratios R(C III 1247/C III 1908), R(Si IV 1402/C III 1908), and R(Si III 1892/C III 1908) give consistent values of electron density for each feature. The C III 1908-A, Si III 1892-A, and Si IV 1402-A lines have recently been observed from the IUE satellite in spectra of late-type stars, and can serve as practical density diagnostics that are independent of assumptions about the stellar surface gravity.

Cook, J. W.↗
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 NTRS1977

Emission measures, electron densities, and nonthermal velocities from optically thin UV lines near a quiet solar limb

Calibrated intensities and line widths are presented for 45 optically thin chromospheric and transition-zone UV lines observed in a quiet area near the solar limb. The observations were made over the wavelength range from 1175 to 1915 A with the slit spectrograph on the Skylab Apollo Telescope Mount. Three nonthermal-velocity components are derived from the transition-zone line widths: a main component of 23 km/s and two high-velocity components of 45 and 75 km/s, respectively, which contribute 5% to 10% of the averaged intensity. Absolute intensities are determined as a function of height, emission measures are obtained as functions of height as well as temperature, and electron densities are estimated from density-sensitive line ratios. The densities estimated from different sets of lines are found not to agree with each other, but the values obtained from the Si III multiplet between 1297 and 1301 A are considered to be the most reliable. An atmospheric model with inhomogeneous structures extending high above the solar surface is suggested.

Moe, O. K.↗
NASA NTRS1976

Far ultraviolet excitation processes in comets

Recent observations of atomic oxygen and carbon in the far ultraviolet spectrum of comet Kohoutek have demonstrated the existence of these atomic species in the cometary coma. However, in order to identify the source of their origin, it is necessary to relate the observed ultraviolet flux to the atomic production rate. Analyses of observed OI wavelength 1304 and CI wavelength 1657 A multiplets have been carried out using high resolution solar spectra. Also examined is the possibility of observing ultraviolet fluorescence from molecules such as CO and H2, as well as resonance scattering either from atomic ions for which there are strong corresponding solar lines (CII) or from atoms for which there is an accidental wavelength coincidence (SI).

Feldman, P. D.↗