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Macqueen, R. M.

Publications and source records attributed to Macqueen, R. M..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

The three-dimensional structure of 'loop-like' coronal mass ejections

Measurements of the brightness and latitudinal extent of the depleted (cavity) region behind the leading edge of three coronal mass ejection (CME) events from the Skylab epoch are reported. The preevent coronal brightness was matched by a model corona, assuming both a background contribution and a contribution from a range of hypothetical streamer models, distinguished by differing longitudinal extent. Under the assumption that the cavities are voided regions in which the local electron density is negligible, their minimum line-of-sight extent is estimated and found to be comparable to, or greater than, their measured latitudinal extent. This is suggested to unambiguously demonstrate the 3D nature of these events.

Macqueen, R. M.↗
NASA NTRS1991

Sungrazing comets observed by the Solar Maximum Mission coronagraph

The 10 sun-grazing comets (all members of the Kreutz group) detected by the white-light coronagraph of the SMM satellite during its 6-year operational lifetime are described. Numerical data are summarized in tables, and images are provided. Consideration is given to the question of detectability, apparent motions and orbits, coma brightness variations, tail behavior, and occurrence rates. The data are shown to confirm the episodic nature of sun-grazing events, as suggested by Marsden (1967).

Macqueen, R. M.↗
NASA NTRS1988

Measurement of the 3-dimensional positions of type III bursts in the solar corona

The three-dimensional positions of type III sources in the corona are calculated on the basis of ground and spacecraft data. Simultaneous observations of the corona in visible light from Skylab make it possible to relate the apparent radio-source positions to slowly evolving coronal structures. It is found that open magnetic field lines connecting the low coronal levels to the interplanetary medium only exist in a relatively narrow region, and diverge rapidly upwards.

Poquerusse, M.↗
NASA NTRS1988

The solar coronal mass ejection of 20-21 November, 1973

An analysis of the polarization signal of the nonloop-like coronal transient event of November 20-21 is presented. It is found that the event can be described as an axisymmetric-cylindrical or conical volume, the boundaries of which remain constant over its lifetime. The results are used to place bounds on the variation of transient spatial density with height and on the variation of density with time.

Macqueen, R. M.↗
NASA NTRS1985

Broadening of looplike solar coronal transients

The broadening of the tops of nine outwardly expanding looplike coronal mass-ejection transients observed during 1973-1974 and 1980 has been examined. Five of the nine transients exhibit increased breadth with time (height); although the rates vary widely, no event shows an increase which can be fitted by a power-law form with a greater-than-linear increase with height. The breadth of four events decreases with height. When all nine events are considered together, the transient breadth with height is fitted with an expression h varies as R exp 0.48 with large scatter. In addition, measurements of the total observed loop length of the nine transients show that this length L varies as R exp 1.30. Both of these results are contrary to the predictions of one model of loop expulsion as a result of an assumed azimuthal magnetic field gradient. Finally, when combined with the facts that looplike mass ejections are usually associated with the occurrence of eruptive prominences, and that such mass ejections are generally accelerated through the corona, it is found that the observed variation of transient breadth with height contradicts some characteristics of self-similar fluid flow which have been ascribed to mass-ejection transients.

Macqueen, R. M.↗
NASA NTRS1984

Density distribution in looplike coronal transients - A comparison of observations and a theoretical model

Skylab coronagraph observations of intensity changes in the five outer coronal 'loop-like' transients indicate trends toward the greatest concentration of material at the flanks of the bright loops characterizing such transients, together with the presence of a large depleted density region within the loops and the development of bright legs which contain most of the material in the transient and display minimal lateral motion as the top of the bright loop moves radially outward through the corona. Theoretical models for these phenomena predict a maximum enhancement at the top of the loop, rather than at the flanks, and legs that move laterally with a significant fraction of the propagation speed of the loop top, in contrast with observation. Agreement cannot be achieved without the use of a geometry that conflicts with that used for the model calculations.

Sime, D. G.↗
NASA NTRS1983

The excitation of type II radio bursts in the corona

Simultaneous radioheliograph and orbital coronagraph observation of coronal transient activity shows metric type II radio emission originating early in the event, well below the visible white light transient. It is suggested that the shock which excites the type II emission is independent of the transient, in the sense that it is initiated in the low corona (probably in association with a flare) and travels through the already-existing transient disturbance with a propagation speed significantly greater than that of the front edge of the transient itself. Radio emission then results when the flare shock overtakes, first, the region of principal density pile-up along the sides of the expanding transient and only later the top of the transient.

Wagner, W. J.↗
NASA NTRS1983

The properties of coronal voids

Skylab coronagraph observations of the outer solar corona have revealed dark, ray-like structures whose identification as a true coronal phenomenon rather than a subtle photographic effect is presently undertaken. Photometric analysis indicates that these features represent a reduction of 5% in coronal radiance, and the use of a previously developed model of the coronal electron component allows the specification of void electron densities over a 2.5-4.5 solar radius range. Projection of the phenomena onto synoptic surface maps indicates a close relationship with filaments and neutral lines, and a potentially significant temporal correlation between void formation and the formation of the underlying prominence is noted.

Macqueen, R. M.↗
NASA NTRS1981

The evolution of a coronal streamer and the photospheric magnetic field

A large equatorial coronal streamer observed in the outer corona grew in brightness and size during successive limb passages between October 6, 1973 and January 10, 1974 (solar rotations 1606-1611). Unlike previous studies of streamers and their photospheric associations, no definite surface feature could be identified in the present case. This suggests that the streamer is associated with the large scale photospheric magnetic field. Comparison of the streamer growth with observed underlying photospheric magnetic flux changes indicated that as the streamer increased in brightness, areal extent, and density, the photospheric magnetic flux decreased. Three possible explanations for the streamer's growth are presented, the conceptually simplest being that the decrease in photospheric field results in an opening of the flux tubes under the streamer, which permits an increase mass flux through the streamer.

Poland, A. I.↗
NASA NTRS1981

The Pinhole/Occulter Facility

A large occulting system in space can be used for high resolution X-ray observations and for large aperture coronagraphic observations in visible and UV light. The X-ray observations can combine high angular resolution in hand (10 keV) X-radiation with the high sensitivity of a multiple pinhole camera, and can permit sensitive observations of bremsstrahlung from nonthermal particles in the corona. The large aperture coronagraphs have two major advantages: high angular resolution and good photon collection. This will permit observations of small scale structures in the corona for the first time and will give sufficient counting rates above the coronal background rates for sensitive diagnostic analysis of intensities and line profiles for coronal structures in the solar wind acceleration region. The technical basis for performing observations with a large occulting system in these three wavelength ranges is described as well as a pinhole/occulter facility presently being considered for Spacelab. Some indications about future developments are included.

Hudson, H. S.↗
NASA NTRS1981

The Spacelab Lyman alpha and white light coronagraphs program

The Harvard-Smithsonian Center for Astrophysics and the High Altitude Observatory have defined a joint coronagraphs experiment for a future Spacelab mission. The instrumentation package would include an ultraviolet light coronagraph to measure the intensity and profiles of spectral lines formed between 1.2 and 8 solar radii from sun center and a white light coronagraph to measure the intensity and polarization of visible light. The overall goals of the joint program are to use new coronal plasma diagnostic techniques to understand the physical processes and mechanisms operating in the solar corona, to understand the acceleration of high-speed and low-speed solar wind streams and to extrapolate this knowledge to other stars in order to help understand the physics of stellar coronae and stellar mass loss.

Kohl, J. L.↗
NASA NTRS1980

Measurements of coronal kinetic temperatures from 1.5 to 3 solar radii

A rocket-borne Lyman-alpha coronagraph has been used to make the first measurements of the spectral line profile of resonantly scattered hydrogen Lyman-alpha coronal radiation between 1.5 and 3 solar radii. These data provide, for the first time, direct measurements of coronal temperatures above 1.5 solar radii. Data were obtained in a coronal hole, quiet region, and streamer. The widths of the profiles from the quiet region decrease with height and correspond to a steady decrease in hydrogen kinetic temperature, with increasing radius, from about 2.5 million K at r = 2 solar radii to about 1 million K at r = 9 solar radii. In the coronal hole the measured line widths indicate a kinetic temperature of 1.8 million K at r = 2.5 solar radii.

Kohl, J. L.↗
NASA NTRS1980

The High Altitude Observatory Coronagraph/Polarimeter on the Solar Maximum Mission

The paper examines the High Altitude Observatory Coronagraph/Polarimeter designed to produce images of the solar corona in 7 wavelength bands in the visible spectral range, and to be flown on the NASA Solar Maximum Mission satellite. The spectral bands were chosen to exclude or include 'chromospheric' spectral lines, so as to allow discrimination between ejecta at coronal and chromospheric temperatures. The major goals of the instrument include: (1) observation of the corona in the flare process and of the ejecta from the flare site and the overlying corona, and (2) examination of the evolution of the solar corona near the period of solar maximum activity.

Macqueen, R. M.↗
NASA NTRS1979

The association of coronal mass ejection transients with other forms of solar activity

Coronal mass-ejection transients observed with the white-light coronagraph on Skylab are found to be associated with several other forms of solar activity. There is a strong correlation between such mass-ejection transients and chromospheric H-alpha activity, with three-quarters of the transients apparently originating in or near active regions. It is inferred that 40% of transients are associated with flares, 50% are associated with eruptive prominences solely (without flares), and more than 70% are associated with eruptive prominences or filament disappearances (with or without flares). Nine of ten flares that displayed apparent mass ejections of H-alpha-emitting material from the flare site could be associated with coronal transients. Within each class of activity, the more energetic events are more likely to be associated with an observable mass ejection.

Munro, R. H.↗
NASA NTRS1978

Multicolor imaging and photopolarimetry: Disk features, K and F coronas, zodiacal light

The unique vantage points and viewing geometries afforded by a close-in solar probe are briefly examined with regard to line and continuum measurements of features on the solar disk, the K and F coronas, and the zodiacal light. Common instrument and observing requirements are identified, suggesting that a single instrument could provide much of the necessary observational data on these phenomena.

Weinberg, J. L.↗
NASA NTRS1977

Temporal evolution of the equatorial K-corona

Variation of the equatorial K-corona radiance at 2.5 solar radii from the sun center was studied on a daily basis during the Skylab mission (May 1973 to February 1974). The radiance data may be divided into three periods, the first characterized by a smooth variation in time, the second by a signal that is neither persistent in the short term nor recurrent from one limb passage to the next, and the third (and longest period) by a signal exhibiting an orderly, periodically increasing intensity. The data may be interpreted as indicating a general simplification of the coronal magnetic field; harmonic analysis of the surface field provides additional information on the evolution of the equatorial K-corona structures.

Macqueen, R. M.↗
NASA NTRS1977

Radiance calibration of the High Altitude Observatory white-light coronagraph on Skylab

The processing of over 35,000 photographs of the solar corona obtained by the white-light coronograph on Skylab is described. Calibration of the vast amount of data was complicated by temporal effects of radiation fog and latent image loss. These effects were compensated by imaging a calibration step wedge on each data frame. Absolute calibration of the wedge was accomplished through comparison with a set of previously calibrated glass opal filters. Analysis employed average characteristic curves derived from measurements of step wedges from many frames within a given camera half-load. The net absolute accuracy of a given radiance measurement is estimated to be 20%.

Poland, A. I.↗