Donald A. Landman

High-frequency coronal oscillations and coronal heating

At the 1980 total solar eclipse, we searched for high-frequency (0.1–2 Hz) oscillations in the intensity of the 5303-Å coronal green line, as a test of predictions of theories of coronal heating via magnetohydrodynamic waves. Portions of the image 2.5- or 5-arc sec across were fed to cooled photomultipliers using fiber-optic probes. We detected excess power in Fourier transforms of the data for the region between 0.5 and 2 Hz at the level of 1% or 2% of the incident power. Such oscillations could be associated with Alfvén waves that are trapped on loops a few thousand kilometers long or with fast waves that are trapped on loops a few thousand kilometers in diameter. Additional observations at the 1983 eclipse are planned to resolve atmospheric and instrumental contributions.

OBSERVATIONS OF HELIUM AND HYDROGEN EMISSION IN QUIESCENT PROMINENCES

Observations of a number of helium triplet (λλ 10830, 4713, 4471, 3889, 4026) and hydrogen (Hγ, δ, η, θ) 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 instrumental field of view was 5″ × 20″. The results are compared with previous observations and theory. In particular, the intensity of the λ 10830 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.

Proton collisional excitation among the 2p5 3s configuration levels in the Ne isoelectronic sequence ions Na II-Ni XIX

Abstract Proton collisional excitation cross-sections and rate constants are presented for transitions among the 2p5 3s configuration levels in the Ne isoelectronic sequence ions Na II-Ni XIX. The calculations are made according to symmetrized semiclassical impact parameter theory in which the truncated Schrodinger equation for quadrupole excitation is integrated directly. Various single configuration Hartree-Fock results are also given. The density and temperature regimes for which this process can have useful plasma diagnostic applications for these ions is discussed.

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

Observations of the He λ 10830 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 23P − 23S excitation temperature of 4020 K. The results are compared with those of previous observational and theoretical research.

Theoretical intensity ratios for some Fe XIII coronal lines

Theoretical values for the relative intensities of the Fe XIII lines λ110747, λ110798, and λ3388 are presented as functions of electron density using recent values of the cross-section for collisionl excitation by protons. Our results are compared with those of Chevalier and Lambert.

The middle Balmer decrement in quiescent prominences

We present measurements of the middle Balmer decrement (n = 10–22) in a number of quiescent prominences. The average decrement continues smoothly the trend of the decrement determined in our previous work on the earlier Balmer lines. The range of Tex is found to be 3450–11 000 K, consistent with the generally accepted range of values for Te. In addition, some values for the hydrogen-to-metal (Fe, Ti+) integrated line intensities are given.

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 (3s23p2) transitions are presented. These were obtained by direct computer integration of the Schroedinger equation (with the states expressed in intermediate coupling) resulting from the semi-classical 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. Some cross-section values for the Fe+13 3s23p2P1/2→2P3/2 excitation are also presented.

Additional measurements of the high-latitude sunspot rotation rate

We report measurements of the sunspot rotation rate at high sunspot latitutdes for the years 1966–1968. Ten spots at ¦latitude¦ ≳ 28 deg were found in our Mees Solar Observatory Hα patrol records for this period that are suitable for such a study. On the average we find a sidereal rotation rate of 13.70 ± 0.07 deg day-1 at 31.05 ± 0.01 deg. This result is essentially the same as that obtained by Tang (1980) for the succeeding solar cycle, and significantly larger than Newton and Nunns (1951) results for the 1934–1944 cycle. Taken together, the full set of measurements in this latitude regime yield a rotation rate in excellent agreement with the result ω=14°.377−2°.77 sin2φ, derived by Newton and Nunn from recurrent spots predominatly at lower latitudes throughout the six cycles from 1878–1944.

Radiation transfer through a model sunspot

We present a cylindrically symmetric model for a sunspot atmosphere using the similarity principle of Schlüter and Temesvary for the magnetic field configuration. 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 B is unable to give a net circular polarization of sufficient magnitude, although the variation with the angle between the line-of-sight and B is in qualitative agreement with observations. The corresponding results for the net linear polarization are satisfactory.