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Evidence for the presence of thallium in the sun is presented. Umbral spectra were found to contain an absorption feature at or near the predicted position for the Tl I 5350 A line. Analysis of the 5350 A line indicated that the solar thallium abundance is given by log N(Tl) values ranging from 0.72 to 1.07 on the standard scale log N(H) = 12.00. Unidentified blends, however, limit the accuracy of the abundance determination.
The existence of 'holes' in the corona is reported characterized by abnormally low densities and temperatures. It was found that such coronal holes appear to be the source of high-velocity, enhanced-density streams in the solar wind as observed at the earth's orbit. It was further noted that coronal holes appear to be associated with regions of diverging magnetic fields in the corona. Models were developed to accomplish the objective for the principal energy flows in the transition region and corona.
The paper describes qualitatively the spatial distribution of UV emission obtained from high resolution spectroheliograms in the UV emission lines He I, He II, O IV, O V, and Ne VII photographed during a sounding rocket flight. Broad band filtergrams of the far UV solar corona were also obtained. The results confirmed that spicules are the location of UV emission. Most of the UV emission in the temperature range from 100,000 to 200,000 K is concentrated in and around the spicules and this concentration decreases with increasing temperatures. Four different areas of UV emission are discussed. The He I and He II spectroheliogram observations showed He to be suppressed in the coronal holes, polar caps, and sunspots.
The theoretical electron density sensitive emission-line ratio R = I(1718.56 a)/I(1486.51 A) in N IV is presented for a range of N(sub e)(approximately equals 10(exp 10) - 10(exp 12)/cu cm) applicable to higher density solar plasmas, such as active regions. A comparison of these calculations with the observed values of R of several solar features obtained with the Naval Research Laboratory's S082B spectrograph on board Skylab reveals general agreement between theory and observation at pointings just above the limb, where line blends with N IV 1718.56 A should be insignificant, which provides experimental support for the accuracy of the line ratio calculations.
Recent high-resolution and high-cadence extreme-ultraviolet (EUV) imaging has revealed a new phenomenon, impacting prominence debris, where prominence material from failed or partial eruptions can impact the lower atmosphere, releasing energy. We report a clear example of energy release and EUV brightening due to infalling prominence debris that occurred on 2011 September 7-8. The initial eruption of material was associated with an X1.8-class flare from AR 11283, occurring at 22:30 UT on 2011 September 7. Subsequently, a semicontinuous stream of this material returned to the solar surface with a velocity v greater than 150 km/s, impacting a region remote from the original active region between 00:20 and 00:40 UT on 2011 September 8. Using the Solar Dynamics Observatory/Atmospheric Imaging Assembly, the differential emission measure of the plasma was estimated throughout this brightening event. We found that the radiated energy of the impacted plasma was L(sub rad) approx. 10(exp 27) erg, while the thermal energy peaked at approx.10(exp 28) erg. From this we were able to determine the mass content of the debris to be in the range 2 x 10(exp 14) less than m less than 2 x 10(exp 15) g. Given typical prominence masses, the likely debris mass is toward the lower end of this range. This clear example of a prominence debris event shows that significant energy release takes place during these events and that such impacts may be used as a novel diagnostic tool for investigating prominence material properties.
High-resolution images of the sun in the soft-X-ray/XUV range have been obtained with normal-incidence multilayer coated optics (MCOs) during a sounding-rocket flight on October 23, 1987 from White Sands. MCOs were used in two Cassegrain telescopes, as off-axis primary mirrors, and as tertiary mirrors operating with a Wolter-Schwarzschild (WS) grazing-incidence mirror. The inherent energy-selective property of MCOs allowed distinct groups of emission lines to be isolated in the solar corona and the transition region. Images were recorded at 173 and 256 A with the Cassegrain telescopes, at 256 A with a Herschelian telescope, and at 44, 173, and 256 A with the WS hybrid telescope. In addition, soft-X-ray images in the 8-18-A bandpass were obtained at the prime focus of the WS optics. The images show many features of the solar corona and transition region, including magnetically confined loops of hot solar plasma, coronal plumes, polar coronal holes, supergranulation, and features associated with overlying cool prominences.
Although spicules hae been obseved for many years, very little is known about their role in the transport of mass and energy between the chromosphere and the higher layers of the atmospere. Athay and Holzer (1982) demonstrated that the rise and fall of spicular material can supply the thermal energy required for heating the upper chromosphere, transition, and possibly corona. The proposed mechanism depends upon assumptions about the fate of spicules after they disappear from view in the visual spectrum where observations are limited to spectral lines formed at chromospheric temperatures. The present investigation is concerned with an analysis of meaurements of the spatial and temporal variations of EUV emission near the solar limb. The obtained results place empirical constraints on the fate of spicules after they disappear from view in the visible spectrum and thereby place constraints on their role in the transport of mass and energy between the chromosphere and corona.
It is noted in the present investigation of Alfven wave propagtion in a simple medium consisting of three uniform layers, each of which is characterized by a different Alfven speed value, that the central layer can, under general conditions, act as a resonant cavity. When this cavity is externally driven by an incident wave on one of the outer layers, resonant transmission peaks are generated which allow large energy fluxes to enter the cavity from outside. Two types of resonance are distinguished: one which occurs when the cavity has the largest or the smallest of the three Alfven speeds, as in coronal loops, and another which is generated when the cavity Alfven speed is intermediate between the two outer Alfven speed values, as may occur on solar spicules. It is also shown that if the energy lost to heat exceeds that lost through leakage out of the cavity, cavity heating can be independent of the damping rate.
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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.
The temporal characteristics of coronal loops are described using a number of unique time-lapse sequences of Ne VII 465 A, Mg IX 368 A, and Fe XV 284 A spectroheliograms. These sequences were obtained with the NRL Skylab/ATM slitless spectrograph during the final Skylab mission (November 1973-February 1974). In the first sequence, Ne VII and Mg IX images were obtained simultaneously at 1.5-mm intervals for a 27-min duration on Nov. 28, 1973. In the second sequence, simultaneous Ne VII-Mg IX pairs were obtained at approximately 3-hr intervals (on alternate satellite orbits) for a 36-hr duration on Jan. 19-20, 1974. The intervening orbits were used to obtain a third sequence which consisted of Fe XV images at 3-hr intervals for the same 36-hr duration. The results place severe constraints on theoretical models of coronal heating and mass flow.
A simple model is presented to describe fast plasma heating by anomalous and inertial resistivity effects. It is noted that a small fraction of the plasma contains strong currents that run parallel to the magnetic field and are driven by an exponentiating electric field. The anomalous character of the current dissipation derives from the excitation of electrostatic ion-cyclotron and/or ion-acoustic waves. The possible role of resistivity deriving from geometrical effects ('inertial resistivity') is also considered. Using a marginal stability analysis, equations for the average electron and ion temperatures are derived and numerically solved. No loss mechanisms are taken into account. The evolution of the plasma is described as a path in the drift velocity diagram, where the drift velocity is plotted as a function of the electron to ion temperature ratio.