K. B. Gebbie

The detection of mesogranulation on the sun

Time averages of velocity measurements at disk center on the quiet Sun reveal the presence of a fairly stationary pattern of cellular flow with a spatial scale of 5--10 Mm. Such mesogranulation has a spatial rms vertical velocity amplitude of about 60 ms/sup -1/ superposed on the larger scale supergranular flows. The lifetimes of mesogranules appear to be at least 2 hr.

Steady flows in the solar transition region observed with SMM

Steady flows in the quiet solar transition region have been observed with the Ultraviolet Spectrometer and Polarimeter (UVSP) experiment on the Solar Maximum Mission (SMM) satellite. The persistent vertical motions seen at disk center have spatial rms amplitudes of 1.4 km s/sup -1/ in the C II line, 3.9 km s/sup -1/ in Si IV, and 4.2 km s/sup -1/ in C IV. The amplitudes of the more horizontal flows seen toward the limb tend to be somewhat higher. Plots of steady vertical velocity versus intensity seen at disk center in Si IV and C IV show two distinct branches.

On Spatial Variations in the Intensity of Chromospheric HA

Investigation of the formation of patterns in H-alpha spectroheliograms and filtergrams. Introducing a source-sink-control diagram, it is concluded that the H-alpha line source function in the quiet solar chromosphere is indirectly controlled by the photospheric radiation fields in the Balmer and Paschen continua. It is demonstrated that in producing the observed patterns, horizontal spatial variations in the shape of the absorption profile are extremely effective compared to changes in the source and sink terms. Applying this mechanism, asymptotic values are computed for the contrasts and visibilities in chromospheric H-alpha.

The height variation of supergranular velocity fields determined from simultaneous OSO 8 satellite and ground-based observations

Simultaneous satellite and ground-based observations of supergranular velocities in the Sun were made using the University of Colorado UV Spectrometer on OSO 8 and the Sacramento Peak Observatory diode array instrument. We compare our observations of the steady Doppler velocities seen toward the limb in the middle chromosphere and the photosphere: the observed Si II lambda1817 and Fe I lambda5576 spectral lines differ in height of formation by about 1400 km.The striking results of these observations are that supergranular motions are able to penetrate at leas 11 density scale heights and that, in doing so, the motion increases from about 800 m s/sup -/1 in the photosphere to at least 3000 m s/sup -1/ in the middle chromosphere. Further, a distinct change appears to occur in the flow structure: whereas the horizontal component of the velocity predominates in low photosphere, suggesting strong braking of vertical momentum, the motions higher in the atmosphere are more isotropic. These observations imply that supergranular velocities should be evident in the transition region.The strong horizontal shear layers in supergranulation must produce turbulence and internal gravity waves. These smaller scale motions have bearing on chromospheric heating and nonthermal line broadening.

The Menzel symposium on solar physics, atomic spectra, and gaseous nebulae

A symposium in honor of Donald H. Menzel 1 s contributions to astrophysics was held on his 70th birthday at the Harvard College Observatory, Cambridge, Massachusetts, 8-9 April 19 71. Menzel and his school have made distinguished contributions to the theory of atomic physics, solar physics, and gaseous nebulae. The work on planetary nebulae represented the first investi gations of non-equilibrium thermodynamic conditions in astronomy; the solar work extended these investigations to stellar atmospheres. The applied atomic physics laid the basis for what we now call laboratory astrophysics and, together with work on non-equilibrium ther modynamics, inspired the founding of the Joint Institute for Laboratory Astrophysics. Menzel has served as a distinguished consultant to the National Bureau of Standards, and publication of this volume represents a grateful acknowledgment of his service to the Bureau. The papers summarize the current status of work in the three fields he pioneered.

A mechanism for the production of light and dark contrasts in radiatively controlled lines.

It is argued that visible contrasts can arise even in a line that is controlled wholly by an external radiation field. Lateral differences in the local shapes of the line absorption profile are shown to account for such contrasts. Two cases are treated explicitly: (a) a profile locally broadened by mass flow, and (b) a profile locally narrower due to the suppression of turbulent velocities, as might result from the presence of magnetic fields.

The embedded feature model for the interpretation of chromospheric contrast profiles

Contrast profiles obtained from chromospheric filtergrams and spectra of bright and dark mottles have to date been interpreted almost exclusively in terms of Beckers cloud model. Here we demonstrate the failure of this model to account in a physically consistent way for the observed contrasts. As an alternative, we introduce an embedded-feature model, restricting our discussion in this paper to stationary features. Our model is then characterized by three independent parameters: the density of absorbing atoms, the geometrical depth, and the profile of the absorption coefficient. An analytic approximation to the contrast resulting from such a model reproduces well the observed behavior of all types of contrast profiles.

The Temperature Control Bracket

Temperature control bracket energy equation as measure of temperature distribution in pure hydrogen stellar atmosphere, considering electron energy and radiation field

On the Dependence of T_{e} upon Quantity Versus Quality of the Radiation Field in a Stellar Atmosphere

Stellar atmosphere radiation field quantity vs quality, deriving electron temperature as function of tau

Helium resonance lines in the flare of 15 June, 1973

Time sequences of He i and He ii resonance line intensities at several sites within the flare of 15 June, 1973 are derived from observations obtained with the Naval Research Laboratorys Slitless Spectroheliograph on Skylab. The data are compared with predictions in six model flare atmospheres based on two values for the heating rate and three for the flux of photoionizing coronal X-rays and EUV. A peak ionizing flux more than 103 times that in the quiet Sun is indicated. For most conditions in flare kernels the He ii Lα and Lβ lines are found to be formed by collisional excitation, thereby contributing to the local cooling of the plasma at temperatures above 6 × 104 K. Emission in the higher Lyman lines is generally the result of a mixture of collisional excitation at these temperatures and photoionization and recombination at temperatures near 2.5 × 104 K. We discuss implications for the common practice of deriving stellar coronal fluxes from He ii 1640 Å fluxes assuming dominance of the recombination mechanism.