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Landman, D. A.

Publications and source records attributed to Landman, D. A..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Proton collisional excitation in the lowest lying 3P terms of ions in the Be and Mg isoelectronic sequences

Proton collisional excitation cross sections and rate constants are presented for transitions between the 3P(J) fine-structure levels of the lowest-lying sp configurations in a number of astrophysically important ions belonging to the Be and Mg isoelectronic sequences. The calculations were made by direct integration of the Schroedinger equation resulting from semiclassical Coulomb excitation theory. The cross sections and rate constants for the 3P(J) transitions in the lowest-lying P(2) configurations are expected to be similar to those for the corresponding sp configuration transitions, and this is illustrated for C III. For the high-temperature ion Ca XVII alpha particle excitation is shown to be unimportant for situations involving ordinary values of the He/H abundance ratio. A simple, but apparently accurate method for determining certain radial integrals for low-lying excited configurations is proposed.

Landman, D. A.↗
NASA NTRS1979

Radiation transfer through a model sunspot

A cylindrically symmetric model for a sunspot atmosphere using the similarity principle of Schlueter and Temesvary for the magnetic field configuration is presented. The equations of magnetostatic equilibrium are used, augmented by a radial Evershed flow. The LTE radiative transfer equations for the Stokes vector were solved under a variety of conditions for a ray emerging from a typical penumbral point. The contribution from isolated lines to the broadband circular polarization in sunspot penumbrae is evaluated using a more realistic model sunspot atmosphere than has hitherto been considered. Results indicate that the inclusion of a velocity field along the magnetic field vector is unable to give a net circular polarization of sufficient magnitude, although the variation with the angle between the line-of-sight and the magnetic field vector is in qualitative agreement with observations. The corresponding results for the net linear polarization are satisfactory.

Landman, D. A.↗
NASA NTRS1979

The middle Balmer decrement in quiescent prominences

Measurements of the middle Balmer decrement (n = 10-22) in a number of quiescent prominences are presented. The average decrement continues smoothly the trend of the decrement determined in our previous work on the earlier Balmer lines. The range of T sub ex is found to be 3450-11000 K, consistent with the generally accepted range of values for T sub e. In addition, some values for the hydrogen-to-metal integrated line intensities are given.

Landman, D. A.↗
NASA NTRS1979

H-alpha and H-beta emission in quiescent prominences

High-resolution H-alpha and H-beta line profiles in a number of quiescent prominences were measured at positions of weak to moderate brightness (for H-alpha integrated intensity of not less than 1.35 x 10 to the 5th ergs/sq cm/s/sr). Those profiles that appear to originate primarily in a single physical element can be accurately fitted with a two-component model, each component being characterized by a temperature, a Gaussian microturbulence distribution, and a constant source function. The various values of integrated intensity, optical thickness, and Doppler width are compared with previous measurements and recent theoretical calculations; several discrepancies are noted and discussed.

Landman, D. A.↗
NASA NTRS1979

Some recent results in quiescent prominence spectrometry

This paper describes some recent results of a quiescent-prominence spectrometry program. The observations were made with a 25-cm coronagraph/coude spectrograph system using a silicon vidicon detector. This detector consists of 500 contiguous channels covering approximately 6 or 80 A, depending on the grating used. The instrument is interfaced to a computer system and has the important advantages of wide spectral response, linearity, and signal averaging with real-time display. Its principal drawback is the relatively small target size. For the present work, the aperture was about 3 x 5 arcsec. Absolute intensity calibrations were made by measuring quiet regions near the center of the sun.

Landman, D. A.↗
NASA NTRS1978

Further measurements of quiescent prominence spectra

Measurements of the integrated intensity of H-alpha, H-gamma, H-delta, He 10,830-A and 4471-A, Ca II H and K, and Sr II 4078-A in a number of quiescent prominences are presented. The observations were made using a multichannel coronal spectrophotometer and 25-cm coronagraph/coude spectrograph instrument systems. The data are discussed with reference both to other observations and to recent theoretical developments in the field.

Landman, D. A.↗
NASA NTRS1978

Proton collisional excitation in the ground configuration of Fe/11+/

Proton collisional excitation cross sections at solar coronal energies for the Fe(11+) /3S(2)3p(3)/ ground-configuration transitions are presented. Semiclassical Coulomb excitation theory is used with direct integration of the resulting Schroedinger equation. The rate constants at coronal temperatures are compared with the corresponding ones for electron impact excitation.

Landman, D. A.↗
NASA NTRS1977

Measurements of H-beta, He D3, and Ca/+/ 8542-A line emission in quiescent prominences

Measurements of H-beta, He D3, and Ca(+) 8542-A line emission in 18 quiescent prominences are presented which were performed with a 25-cm coronagraph/coude spectrograph system and an optical multichannel analyzer utilizing a Si-vidicon detector assembly mounted at the single-pass spectrograph port. The data obtained show that the line profiles deviate in the wings from those calculated on the basis of an isothermal atmosphere and a Gaussian absorption coefficient. Both a non-Gaussian microturbulence component and a temperature gradient from prominence-core to coronal values can successfully account for this phenomenon. The line widths from a given line of sight of prominence material are reduced on the basis of a common core emitting region with a temperature of 7500 to 11,600 K and a microturbulent velocity of 4.5 to 7.1 km/s for the isothermal model (these values are 5% to 10% less for the two-temperature model). It is noted that long-period low-amplitude oscillations in the D3 line width and intensity were observed when a specific line of sight in a quiescent prominence was followed. These oscillations are found to remain coherent for as many as 3 or 4 cycles and to be associated with prominence structural activation.

Landman, D. A.↗
NASA NTRS1977

Measurements of line emission in quiescent prominences - Ca/+/, H and He

The paper presents observations of Ca(+) H, K, and infrared-triplet integrated line intensities, as well as H-beta, H-gamma and He 5876-A throughout eight quiescent prominences. The data were obtained with a multichannel coronal spectrophotometer system. The presently available theoretical models appear to be insufficient to provide a consistent basis for the interpretation of the data.

Landman, D. A.↗
NASA NTRS1976

A study of the He 10,830-A line emission from quiescent prominences

Observations of the He 10,830-A line emission in a number of quiescent prominences are presented. The line shapes are analyzed to obtain values for the Doppler widths and optical thicknesses, leading to a determination of the 2(3)P-2(3)S excitation temperature as 4020 K. The results are compared with those of previous observational and theoretical research.

Landman, D. A.↗
NASA NTRS1975

Observations of helium and hydrogen emission in quiescent prominences

Observations of a number of helium triplet (10830, 4713, 4471, 3889, 4026 A) and hydrogen (H-gamma, delta, eta, and theta) emission-line intensities in six quiescent prominences are presented. The regions of prominence and neighboring corona were raster-scanned by the telescope, and all lines were measured concurrently at each point. The results are compared with previous observations and theory. In particular, the intensity of the 10830-A emission relative to the other triplets is found to differ strongly from the predictions of the recent detailed calculations of Heasley et al. (1974) for model quiescent prominences.

Illing, R. M. E.↗
NASA NTRS1975

Proton collisional excitation in the ground configurations of Fe/+12/ and Fe/+13/. III - Transitions between magnetic sublevels

Values of proton collisional cross-sections at coronal energies have been computer for all transitions between magnetic sublevels of the Fe(+12) and Fe(+13) ground configurations. Semiclassical Coulomb excitation theory was used with the resulting truncated Schroedinger equations being directly integrated. The corresponding rate constants for coronal temperatures are presented and comparison is made with previous results.

Landman, D. A.↗
NASA NTRS1973

Proton collisional excitation in the ground configuration of Fe/+12/. II

Improved values of the proton impact excitation cross sections at coronal energies for all the Fe(+12) ground configuration transitions are presented. These were obtained by direct computer integration of the Schroedinger equation (with the states expressed in intermediate coupling) resulting from the semiclassical Coulomb excitation theory formulation of the process. Comparison is made with previous results. The associated rate constants at coronal temperatures are given and compared with the corresponding electron impact excitation rate constants.

Landman, D. A.↗
NASA NTRS1973

Proton collisional excitation in the ground configuration of Fe/+12/.

Using semiclassical Coulomb excitation theory, proton collisional excitation and deexcitation cross sections are calculated for all transitions between the Fe(+12) ground configuration levels. Rate constants pertaining to these processes are then derived for coronal temperatures. These rates are shown to be comparable in all cases to the corresponding electron rate constants.

Landman, D. A.↗
NASA NTRS1973

Theoretical intensity ratios for some Fe XIII coronal lines.

Using cross section values for collisional excitation by protons recently calculated by Landman (1973), theoretical values for the relative intensities of the Fe XIII 10747-, 10798-, and 3388-A lines are determined as functions of electron density. The obtained results are compared with those of Chevalier and Lambert (1969).

Finn, G. D.↗