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At least 1,243 records · Page 69
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NASA NTRS1971

Analysis of solar ultraviolet lines

The formation of the strongest ultra-violet emission lines of Mg II, O I, C II, and C III in the solar atmosphere is studied in detail. The equations of statistical equilibrium and radiative transfer for each ion are solved using a general computer program that is capable of solving non-LTE line-formation problems for arbitrary atmospheric and atomic models. Interpreting the results in terms of the structure of the solar atmosphere, it is concluded that the HSRA atmosphere has a temperature too low by about 500 K near h = 1100 km and that a temperature plateau with T sub e approximately = 18,000 K and width close to 60 km exists in the upper chromosphere. The structure of the solar atmosphere in the range 20,000 to 100,000 K and the effects of microturbulence on the formation of lines are also investigated. Approximate analytic line-formation problems are solved, and more exact solutions are derived later. An attempt is made to make the best possible fit to the Ca II K line center-to-limb profiles with a one-component atmosphere, with an assumed source function and microturbulent velocity.

Chipman, E.↗
NASA NTRS1971

Observations of interstellar Ca I lines.

Evaluation of interferometric, photoelectric scans of the interstellar Ca I line at 4226 A for four stars having strong interstellar Ca II K-lines. The Ca I line is detected in three, and possibly all four, cases, of which one was kn*wn previously. Negative Ca I results are also obtained for six stars with weaker K-lines. The significance of the resulting electron densities deduced from the Ca I and Ca II lines is discussed.

Hobbs, L. M.↗
NASA NTRS1971

Coronagraphic observations of an enhanced coronal region. I - Fe XIII and Ni XV emission line data.

Observation of nine coronal emission lines representing five stages of Fe ionization and one stage of Ni in an enhanced coronal region. The data from these observations are presented along with a density model of the enhanced region obtained from the Fe XIII and Ni XV emission line ratios as a function of position angle. The electron densities obtained from Fe XIII lines range from 10 to the 8th to 10 to the 9th per cu cm, and are slightly lower for Ni XV line data. Estimates of the variation of temperature over the enhanced region are inferred from the observed line intensities.

Fisher, R.↗
NASA NTRS1972

Line shape parameters for HCl and HF in a CO2 atmosphere.

Results of high-resolution (0.1 cm/cm) on several CO2-broadened lines in the fundamentals of HCl35 and HCl37. Line intensities, half-widths, and shapes were determined at room temperature. Half-widths in HCl-CO2 collisions were computed for several temperatures, employing Anderson's (1949) theory. The measured shapes of HCl lines broadened by CO2 are described by a semiempirical super-Lorentzian shape. The curve-of-growth for this line shape is derived in terms of a function similar to the Ladenburgh-Reiche function. Absorption between R(0) and P(1) is affected by the appearance of several pressure-induced Q-branch lines, at the pressures from 1 to 10 atm used in the present study.

Varanasi, P.↗
NASA NTRS1972

Photoelectric line profiles in umbral spectra.

Umbral line profiles of H-alpha, NaD2 and HeI 10830 have been observed photoelectrically with a pressure scanning spectrometer. The H-alpha line profile shows, in a medium-sized spot, a pronounced weakening in the wings but a persistence of the line core in agreement with the results of Fricke and Elsaesser (1965). The profile of the HeI 10830 line shows an unexpected strengthening over the umbra of the two spots which have been observed. The NaD2 line profile together with continuum observations at 4260, 5890, and 6530 A have been accounted for with an empirical (T, tau) relation by one of us (Yun, 1971). The wavelength dependence and the absolute values from 4000 to 14,000 A of the intensity curve generated by this relation shows very good agreement with the intensities observed by Woehl et al. (1970) in a spot of similar diameter.

Fay, T. D.↗
NASA NTRS1972

The last Balmer line and H gamma in model B stars

Profiles of the last few Balmer lines (H12-H27) and the full profiles of the H gamma line were computed for a grid of hydrogen line blanketed model atmospheres. The use of the last hydrogen line and the equivalent width of H gamma provide a quick means of estimating the effective temperature and surface gravity of B stars. Regression curves relating the quantum number of the last hydrogen line to the electron density in the model atmosphere are given. Futhermore, it is shown that the difference in the gravity determination deduced from H gamma equivalent widths using the Edmonds-Schuter-Wells formalism and the Griem wing formulae is, at worst, 0.18 in the common logarithm.

Fischel, D.↗
NASA NTRS1973

Theory of satellite structures on spectral-line profiles.

A systematic comparison with experiment of various explanations for the problem of satellite-band formation on spectral-line profiles was initiated. The experiments were performed under a variety of conditions in an effort to construct a consistent model of entire line shapes. A composite theory is detailed which is the result of the insights of many individuals. The calculations indicate that the main features of the problem, the line, the high-intensity red satellites, and the blue satellite can be described simultaneously. The results also indicate that widely different potentials can lead to very similar line profiles. Ancillary conclusions are presented concerning the role of Lennard-Jones potentials in line-shape calculations.

Atakan, A. K.↗
NASA NTRS1973

An investigation of hydraulic-line resonance and its attenuation

An investigation of fluid resonance in high-pressure hydraulic lines has been made with two types of fluid dampers (or filters) installed in the line. One type involved the use of one or more closed-end tubes branching at right angles from a main line, and the other type was a fluid muffler installed in-line. These devices were evaluated in forced vibration tests with oscillatory disturbances over a 1000-Hz range applied to one end of the line and with oscillatory pressures measured at various stations along the main pipe. Limited applications of acoustic-wave theory to the branched systems are also included. Results show varying attenuations of pressure perturbations, depending on the number and location of branches and the type of muffler. Up to three branches were used in the branch-resonator study, and the largest frequency range with maximum attenuation was obtained for a three-branch configuration. The widest frequency ranges with significant attenuations were obtained with two types of fluid mufflers.

Sewall, J. L.↗
NASA NTRS1974

Development of acoustically lined ejector technology for multitube jet noise suppressor nozzles by model and engine tests over a wide range of jet pressure ratios and temperatures

An experimental program comprising model nozzle and full-scale engine tests was undertaken to acquire parametric data for acoustically lined ejectors applied to primary jet noise suppression. Ejector lining design technology and acoustical scaling of lined ejector configurations were the major objectives. Ground static tests were run with a J-75 turbojet engine fitted with a 37-tube, area ratio 3.3 suppressor nozzle and two lengths of ejector shroud (L/D = 1 and 2). Seven ejector lining configurations were tested over the engine pressure ratio range of 1.40 to 2.40 with corresponding jet velocities between 305 and 610 M/sec. One-fourth scale model nozzles were tested over a pressure ratio range of 1.40 to 4.0 with jet total temperatures between ambient and 1088 K. Scaling of multielement nozzle ejector configurations was also studied using a single element of the nozzle array with identical ejector lengths and lining materials. Acoustic far field and near field data together with nozzle thrust performance and jet aerodynamic flow profiles are presented.

Atvars, J.↗
NASA NTRS1975

Emission-line strengths and the chemical compositions of quasi-stellar objects

Estimates of emission-line strengths in 160 QSOs are listed. They are used, together with those for 60 objects published earlier, to compile a table of rest-frame equivalent widths for a composite QSO containing 28 lines seen in objects with z from 0.06 to 3.53. Models are computed for matter partially filling a spherical volume, ionized by ultraviolet flux from a central object and optically thick with absorption from heavy elements taken into account. Constant temperature and density are taken for the He II region, where most of the important lines are emitted. Allowance is made for lower and higher temperatures in the H I and He III regions. Emergent emission-line equivalent widths are computed and compared with the observations. An abnormally low helium abundance is not needed to achieve a fit, since the only anomalously weak line is He II 4686 A whose upper level may be depopulated by stimulated emission of He II 1215 A caused by very strong L-alpha 1216 A flux.

Chan, Y.-W. T.↗
NASA NTRS1975

The He II lines in the spectrum of zeta Puppis

The observed He II line spectrum in zeta Pup is compared with that predicted from model atmospheres in an attempt to establish the parameters (effective temperature, log g) which characterize the model that best represents this star's atmosphere. The study is conducted by compiling equivalent widths of the He II lines in the series (n = 2,3,4,5) and comparing them with predictions from plane-parallel static model atmospheres using a non-LTE theory of line formation. Good agreement between observation and prediction for a model atmosphere with an effective temperature of 50,000 K and log of 4.0 is found for the upper members of the n = 3 and n = 5 series, but discrepancies are found for the two lines of the n = 2 series and the upper members of the n = 4 series. It is shown that the n = 4 level appears to be more overpopulated at moderate atmospheric depths than the non-LTE calculations with plane-parallel layers indicate. It is suggested that this may be due to an overlap of the H and He II lines in the even-even series caused by macroturbulent velocities of the hydrogen and helium atoms.

Snijders, M. A. J.↗
NASA NTRS1976

External tank gaseous oxygen line simulated lightning tests

Tests were made to evaluate the effects of lightning strikes on the shuttle external tank gaseous oxygen pressurization line. This line, designed to conduct gaseous oxygen may also act as a lightning conductor. Questions have been raised as to the potential hazard of this line as a lightning conductor with speculation as to the damage that might occur to the pressurization line, and the adjacent thermal protective surfaces, from a lightning strike. The region of investigation was from above the cone of the launch tower lightning protection to 15.24 km (50, 000 ft) altitude. Tests were performed on samples of thin wall stainless steel tubing filled with gaseous oxygen under simulated flight conditions. No specimen malfunctions occurred when the tests were conducted according to JSC specifications. Based on the JSC specifications and the results of these tests, it is concluded that a lightning strike will not cause a malfunction of the shuttle external tank gaseous oxygen line made of the representative material tested.

Smith, H. E.↗
NASA NTRS1975

VLF line radiation in the earth's magnetosphere and its association with power system radiation

In a recent experiment, discrete VLF emissions from the magnetosphere were triggered by a transmitter at Siple Station in Antarctica. Spectrograms of these signals as received at the conjugate point, Roberval, Quebec, showed changes in slope, entrainments, and cutoffs at frequencies (several kilohertz) close to the harmonic induction lines from the local 60-Hz power system. This observation led to the suggestion that harmonic radiation from the power system enters the magnetosphere and interacts with the triggered emissions. New evidence supporting this suggestion has been found in spectrograms of simultaneous recordings made at Roberval and at Siple Station in Antarctica. It is shown that line radiation, near harmonics of 60 Hz, travels along the earth's magnetic field in the whistler mode and is received in the conjugate hemisphere at Siple Station. Echoing of the line radiation between Siple and Roberval is often observed. The magnetospheric lines are usually shifted in frequency by 20-30 Hz with respect to the adjacent induction line, but their spacings are near 120 Hz. They may trigger and cut off emissions as do signals from VLF transmitters.

Helliwell, R. A.↗
NASA NTRS1975

Resonance-line transfer with partial redistribution. VII Angle-dependent redistribution

A method is presented for treating radiative transfer in resonance lines, allowing for the full angle and frequency dependence of redistribution in the scattering process, as seen in the laboratory frame. The case of an equivalent-two-level-atom source function is considered; the problem to be treated is then linear in the radiation field. We apply this method to the Ca II lines in the solar atmosphere, using a redistribution function which takes into account a mixture of coherence in the atom's frame, with Doppler redistribution in the laboratory frame (for atoms which have not suffered an elastic collision), and of complete redistribution in the laboratory frame (for atoms that are collisionally perturbed during the emission process). Both the angle-averaged approximation and the full angle-dependent solution were obtained, and were compared to assess, differentially, the effects of angular redistribution upon the computed line profile and its center-to-limb behavior. For the Ca II line in a homogeneous solar chromosphere the angle-dependent effects are found to be negligible, indicating that one may use angle-averaged redistribution functions when studying partial redistribution effects in line profiles.

Milkey, R. W.↗
NASA NTRS1975

Ultraviolet observations of cool stars. IV - Intensities of Lyman-alpha and Mg II in epsilon Pegasi and epsilon Eridani, and line width-luminosity correlations

A spectrometer on the Copernicus satellite has been used to confirm the existence of a line width-luminosity relation for the Ly-alpha and Mg II 2800-A chromospheric emission lines in K-type stars by observation of a K2 dwarf (epsilon Eri) and a K2 supergiant (epsilon Peg). Combined with previously reported observations of lines in three K giants (alpha Boo, alpha Tau, and beta Gem), the data are consistent with an identical dependence of line width on absolute visual magnitude for the Ca II K, Ly-alpha, and Mg II 2795-A lines. Surface fluxes of Ly-alpha, Mg II 2800-A, and O V 1218-A (upper limit) for epsilon Eri, and of Mg II 2800-A for epsilon Peg are also compared with values reported previously for the three giant stars.

Mcclintock, W.↗
NASA NTRS1976

Observations of heavy-element recombination lines in the Rho Ophiuchi dark cloud at 13 centimeters wavelength

High-sensitivity observations at the carbon 140-alpha and 141-alpha recombination-line frequencies in the direction of the Rho Oph dust cloud show the presence of recombination lines of carbon and sulfur, but not of other heavy elements. These results require that the elements Si, Fe, and Mg are depleted by factors greater than 15, 10, and 2, respectively, most likely into interstellar grains, whereas sulfur is undepleted. They also require that only approximately one-sixth of the carbon is present in the gas phase in the cloud. From the observed size of the C II region together with the observed carbon depletion, it is inferred that the density in the carbon-line-emitting region is 25,000 per cu cm and that the size of the S II region is significantly larger than that of the C II region. The agreement between the widths of the recombination lines (which arise in a small region of the cloud) and those of the more widely distributed molecular species suggests that the lines in this cloud are broadened by microturbulence on a scale of much less than 0.1 pc.

Knapp, G. R.↗
NASA NTRS1976

A demonstration of a transportable radio interferometric surveying system with 3-cm accuracy on a 307-m base line

A precision geodetic measurement system (Aries, for Astronomical Radio Interferometric Earth Surveying) based on the technique of very long base line interferometry has been designed and implemented through the use of a 9-m transportable antenna and the NASA 64-m antenna of the Deep Space Communications Complex at Goldstone, California. A series of experiments designed to demonstrate the inherent accuracy of a transportable interferometer was performed on a 307-m base line during the period from December 1973 to June 1974. This short base line was chosen in order to obtain a comparison with a conventional survey with a few-centimeter accuracy and to minimize Aries errors due to transmission media effects, source locations, and earth orientation parameters. The base-line vector derived from a weighted average of the measurements, representing approximately 24 h of data, possessed a formal uncertainty of about 3 cm in all components. This average interferometry base-line vector was in good agreement with the conventional survey vector within the statistical range allowed by the combined uncertainties (3-4 cm) of the two techniques.

Ong, K. M.↗
NASA NTRS1976

Experimental investigation of Stark broadening and plasma polarization shift of ionized helium resonance lines

Stark broadening and shift measurements were performed on ionized helium resonance lines from a fully ionized helium plasma in a low-inductance electromagnetic T tube. Both time-integrated photographic and time-resolved photoelectric measurements of the lines were performed with a grazing incidence spectrometer. Electron density and temperature were determined from the widths of the He II 4686-A and the He I 5876-A lines and the He II 4686-A line to continuum ratio, respectively. It was found that all ionized helium resonance lines were emitted optically thick by a homogeneous plasma slab and self-reversed by a thin cooler boundary layer. Marked blue shifts of 0.07 plus or minus 0.05 A which may be due to plasma polarization were noted.

Neiger, M.↗