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Results for “Helioseismology”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

A co-ordinated and synergistic analysis strategy for future ground-based and space helioseismology

The variety of helioseismology observational programs planned for the mid-1990s represents an unprecedented opportunity to improve understanding of the solar interior. This review discusses the coordination of the GONG, IRIS, Birmingham and other ground-based observational programs with the space experiments on the SOHO mission: GOLF, VIRGO, and MDI. The integration and coordination of the different data streams in terms of the spatial and temporal coverage as well as the implications of the different spectral resolution and stability characteristics of each experiment are discussed. The study of the effect of active regions on various helioseismology signals is presented as an example of how ground-based and space experiments can be coordinated.

Ulrich, Roger K.↗
NASA NTRS1988

Inversion of helioseismology data

The paper presents an algorithm for performing an inversion of helioseismology data. The method is characterized by high speed, stability, and versatility. The existence of a method for producing an analog of the Backus-Gilbert optimal kernals is demonstrated. The method performs well, even when a moderate amount of observational noise is included.

Jeffrey, W.↗
NASA NTRS1988

The SOHO project - Helioseismology investigations

The helioseismology instruments on the payload of the planned Solar and Heliospheric Observatory (SOHO) mission are discussed. The SOHO mission and the experiments planned for the mission are described. The plans include the global oscillations at low frequencies experiment to perform uninterrupted velocity oscillations measurements of the full solar disk, the variability of irradiance and gravity oscillations experiment to study solar irradiance variability and oscillations, and the Michelson Doppler imager, a flight version of the Fourier Tachometer. The possible use of data from these studies to examine the radial stratification and longitudinal variation of the physical characteristics of the sun is discussed.

Domingo, V.↗
NASA NTRS1984

Immediate and long-term prospects for helioseismology

Recent extensive measurements of frequencies of free oscillation of the sun have permitted a first direct estimate of the variation of sound speed and angular velocity throughout the sun. The results hint that the answers to some tantalizing questions concerning the sun's interior structure and its history are almost within grasp. Optimists like myself believe that in a few years a worldwide network of ground-based observing stations will give us imortant clues. However, it may be necessary to make observations from space before we can be sure of the answers.

Gough, D. O.↗
NASA NTRS1986

Laser heterodyne spectrometer for helioseismology

The technique of laser heterodyne spectroscopy has been applied to the measurement of solar oscillations. Coherent mixing of solar radiation with the output of a frequency-stabilized CO2 laser permits the measurement of fully resolved profiles of solar absorption lines with high spectral purity and excellent frequency stability. This technique has been used to measure OH pure rotation lines in the infrared solar spectrum. Power spectra of these line frequency measurements show the well-known 5-min oscillations as well as significant velocity power at shorter periods.

Glenar, D. A.↗
NASA NTRS1986

Infrared helioseismology - Detection of the chromospheric mode

Time-series observations of an infrared solar OH absorption line profile have been obtained on two consecutive days using a laser heterodyne spectrometer to view a 2 arcsec portion of the quiet sun at disk center. A power spectrum of the line center velocity shows the well-known photospheric p-mode oscillations very prominently, but also shows a second feature near 4.3 mHz. A power spectrum of the line intensity shows only the 4.3 mHz feature, which is identified as the fundamental p-mode resonance of the solar chromosphere. The frequency of the mode is observed to be in substantial agreement with the eigenfrequency of current chromospheric models. A time series of two beam difference measurements shows that the mode is present only for horizontal wavelengths greater than 19 Mm. The period of a chromospheric p-mode resonance is directly related to the sound travel time across the chromosphere, which depends on the chromospheric temperature and geometric height. Thus, detection of this resonance will provide an important new constraint on chromospheric models.

Deming, D.↗
NASA NTRS1988

Solar models, neutrino experiments, and helioseismology

The event rates and their recognized uncertainties are calculated for 11 solar neutrino experiments using accurate solar models. These models are also used to evaluate the frequency spectrum of the p and g oscillations modes of the sun. It is shown that the discrepancy between the predicted and observed event rates in the Cl-37 and Kamiokande II experiments cannot be explained by a 'likely' fluctuation in input parameters with the best estimates and uncertainties given in the present study. It is suggested that, whatever the correct solution to the solar neutrino problem, it is unlikely to be a 'trival' error.

Bahcall, John N.↗
NASA NTRS1988

Helioseismology from the South Pole: Comparison of 1987 and 1981 Results

Full disk images with 10 arc sec pixels and filtered to a 7 A pass band centered on the Ca II K line were obtained from the geographic South Pole in 1981 and 1987. In 1981, 50hr of essentially uninterrupted data were obtained. In 1987, three such runs were obtained over a period of 325 hours for a duty cycle of 47 percent. The 1987 observations are characterized by a much lower level of solar activity than 1981, a much improved CCD camera, considerably better image stability and a varying amount of instrumental scatter. The 1987 data have a substantially better signal-to-noise ratio than the 1981 data so that oscillations with degrees from 0 to 150 and frequencies from 2 to 7 mHz are well observed. The observations were reduced to spectra in l, m, and v. A comparison of p-mode frequencies measured in 1981 and 1987, and coefficients of Legendre polynomial expansions of frequency shifts caused by solar rotation are presented. The time behavior of systematic frequency shifts which depend upon m but which do not arise from rotation is described.

Jefferies, S. M.↗
NASA NTRS1991

Helioseismology with the ACRIM instrument on the Solar Maximum Mission

The Active Cavity Radiometer Irradiance Monitor (ACRIM) instrument on board SMM pioneered high-precision solar photometry from space, and provided the first detection of solar p-mode oscillations at low degree by this technique. The observations extended from February, 1980, until December, 1989, with a hiatus of low sampling rate in 1981-1984. During summer 1989, the instrument operated in a 'no-shutter' mode with continuous viewing between the orbital gaps. This resulted in a fourfold increase of the duty cycle, and an effective increase in the Nyquist frequency from 3.815 mHz to some tens of mHz. This review discusses the initial results from this campaign along with a general review of the analyses to date of the entire ACRIM data set.

Hudson, Hugh S.↗
NASA NTRS1984

Solar Inverse Theory

Helioseismological inversion, as with the inversion of any other data, is divided into three phases. The first is the solution of the so-called forward problem: namely, the calculation of the eigenfrequencies of a theoretical equilibrium state. The second is an attempt to understand the results, either empirically by determining how those frequencies vary as chosen parameters defining the equilibrium model are varied, or analytically from asymptotic expansions in limiting cases of high order or degree. The third phase is to pose and solve an inverse problem, which seeks to find a plausible equilibrium model of the Sun whose eigenfrequencies are consistent with observation. The three phases are briefly discussed in this review, and the third, which is not yet widely used in helioseismology, is illustrated with some selected inversions of artificial solar data.

Gough, D.↗
NASA NTRS1985

The future of solar physics

Outstanding problems for the future of solar physics and stellar physics are examined. The physics of stellar interiors has been called into serious question by the very low measured neutrino flux from the sun. The Ga-71 neutrino detection experiment is the next step in unravelling this mystery. The new methods of helioseismology, for probing the interior of the sun, have already found the primordial rapid rotation of the central core. The forthcoming worldwide helioseismology observing network will permit fuller exploitation of the method, promising to provide the first direct sounding of the interior of a star, hitherto known to us only through theoretical inference and the discrepant neutrino emission. An essential step in developing the physics of stellar activity will be the Solar Optical Telescope (presently planned by NASA to be launched early in the next decade) to permit a 'microscopic' examination of the surface of the sun to study the source of the action. The activity and X-ray emission of other stars depend on much the same effects, so that the study of the sun is essential to determining the significance of the X-ray emission from other stars.

Parker, E. N.↗
DOE OSTI2025

Does the Sun have a dark disk?

The Sun is not quite a perfect sphere, and its oblateness, thought to be induced through its rotation, has been measured using optical observations of its radius. Its gravitational quadrupole moment can then be deduced using solar models, or through helioseismology, and it can also be determined from measurements of its gravitational effects on Mercury’s orbit. The various assessments do not appear to agree, with the most complete and precise orbital assessments being in slight excess of other determinations. This may speak to the existence of a nonluminous disk or ring, where we also note evidence for a circumsolar dust ring within Mercury’s orbit from the Solar TErrestrial RElations Observatory (STEREO) mission. Historically, too, a protoplanetary disk may have been key to reconciling the Sun’s metallicity with its neutrino yield. The distribution of the nonluminous mass within Mercury’s orbit can modify the relative size of the optical and orbital quadrupole moments in different ways. We develop how we can use these findings to limit the mass of a dark disk, ring, or halo in the immediate vicinity of the Sun, and we note how future observational studies of the inner Solar System can not only refine these constraints but can also help to identify and to assess the mass of its dark-matter component. Published by the American Physical Society 2025

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1985

Comments on techniques for spectral deconvolution

Current observational questions in asteroseismology require high spectral resolution that can be only be obtained with observations spanning many days or months. The primary constraint in the full utilization of single mid-latitude observing sites is the presence of diurnal data gaps. Several methods for removing the effect of these gaps in the spectral obtained from velocity observations have been suggested. In the case of data coverage of less than 50%, none of the methods considered has been successful at unambiguously recovering the true spectrum from test spectra with realistic complexity. The limitations of these methods and their applicability to the helioseismology problem is discussed.

Scherrer, P. H.↗
NASA NTRS1986

Comments on techniques for spectral deconvolution

Current observational questions in asteroseismology require high spectral resolution that can only be obtained with observations spanning many days or months. The primary constraint in the full utilization of single mid-latitude observing sites is the presence of diurnal data gaps. Several methods for removing the effect of these gaps in the spectral obtained from velocity observations have been suggested. In the case of data coverage of less than 50 percent, none of the methods considered has been successful at unambiguously recovering the true spectrum from test spectra with realistic complexity. The limitations of these methods and their applicability to the helioseismology problem is discussed.

Scherrer, Philip H.↗
NASA NTRS1986

On strategies for inverting remote sensing data

Attention is given to a number of methods for inverting remote sensing data obtained in a variety of astronomical applications. Applications include image restoration, inversion of helioseismological data to obtain the internal rotation rate of stars such as the sun, fitting of spectra (especially thermal line spectra) to grating or other dispersed observed spectra, differential emission measure analysis, and reconstruction of images derived from interferometric observations. The results consider the tradeoff between resolution and variance and the stability properties for each method and propose an inversion stragegy using the available techniques.

Jeffrey, W.↗
NASA NTRS1987

Solar variability and oscillations

Within this decade, observations of total solar irradiance have become good enough to make it possible to study directly the solar luminosity variations on a wide range of time scales, up to several years. At the same time, there has been considerable improvement in understanding the classical indicators of solar activity, such as UV and visible chromospheric lines, soft X-rays, and radio fluxes. The observed variations include the effects of sunspots and plage solar-cycle effects, and signatures of global oscillations and convection. In addition, new characteristic time-scales (154 days and possibly 320 days) have been discovered. This review covers these developments and comments briefly on the subject of helioseismology.

Hudson, Hugh S.↗
NASA NTRS1988

The efficiency of convective energy transport in the sun

Mixing length theory (MLT) utilizes adiabatic expansion (as well as radiative transport) to diminish the energy content of rising convective elements. Thus in MLT, the rising elements lose their energy to the environment most efficiently and consequently transport heat with the least efficiency. On the other hand Malkus proposed that convection would maximize the efficiency of energy transport. A new stellar envelope code is developed to first examine this other extreme, wherein rising turbulent elements transport heat with the greatest possible efficiency. This other extreme model differs from MLT by providing a small reduction in the upper convection zone temperatures but greatly diminished turbulent velocities below the top few hundred kilometers. Using the findings of deep atmospheric models with the Navier-Stokes equation allows the calculation of an intermediate solar envelope model. Consideration is given to solar observations, including recent helioseismology, to examine the position of the solar envelope compared with the envelope models.

Schatten, Kenneth H.↗
NASA NTRS1988

Initial high-degree p-mode frequency splittings from the 1988 Mt. Wilson 60-foot Tower Solar Oscillation Program

The initial frequency splitting results of solar p-mode oscillations obtained from the 1988 helioseismology program at the Mt. Wilson Observatory are presented. The frequency splittings correspond to the rotational splittings of sectoral harmonics which range in degree between 10 and 598. They were obtained from a cross-correlation analysis of the prograde and retrograde portions of a two-dimensional (t - v) power spectrum. This power spectrum was computed from an eight-hour sequence of full-disk Dopplergrams obtained on July 2, 1988, at the 60-foot tower telescope with a Na magneto-optical filter and a 1024x1024 pixel CCD camera. These frequency splittings have an inherently larger scatter than did the splittings obtained from earlier 16-day power spectra. These splittings are consistent with an internal solar rotational velocity which is independent of radius along the equatorial plane. The normalized frequency splittings averaged 449 + or - 3 nHz, a value which is very close to the observed equatorial rotation rate of the photospheric gas of 451.7 nHz.

Rhodes, Edward J., Jr.↗