Showing papers on "Heliosphere published in 1972"
TL;DR: In this paper, a model was constructed to represent the interaction between the solar wind and the neutral component of the interstellar gas, and it was found that the neutral gas has several important effects on the solar-wind expansion beyond the orbit of the earth.
Abstract: A model is constructed to represent the interaction between the solar wind and the neutral component of the interstellar gas. It is found that the neutral gas has several important effects on the solar-wind expansion beyond the orbit of the earth and that it should be possible to infer the presence of the neutral gas from observations of the solar wind made by a space probe traveling into the outer solar system. The effects include a deceleration and heating of the supersonic solar wind, a cooling of and pressure reduction in the subsonic solar wind, and a tightening of the spiral magnetic field in the supersonic solar wind.
238 citations
01 Jan 1972
TL;DR: In this paper, the expected characteristics of the solar wind, extrapolated from the vicinity of the earth, were described and several models were examined for the interaction of solar wind with the interstellar plasma and magnetic field.
Abstract: The expected characteristics of the solar wind, extrapolated from the vicinity of the earth are described. Several models are examined for the interaction of the solar wind with the interstellar plasma and magnetic field. Various aspects of the penetration of neutral interstellar gas into the solar wind are considered. The dynamic effects of the neutral gas on the solar wind are described. Problems associated with the interaction of cosmic rays with the solar wind are discussed.
220 citations
01 Jan 1972
TL;DR: In this paper, the velocity distribution function of He(+) in the solar wind at 1 AU is calculated with the assumption that the source is photoionization of a cold (T = 100 K), neutral interstellar wind.
Abstract: The velocity distribution function of He(+) in the solar wind at 1 AU is calculated with the assumption that the source is photoionization of a cold (T = 100 K), neutral interstellar wind. If the spiral magnetic field is noise free, the velocity distribution is diffuse and would not produce a peak at 4(E over Q) sub H in an E over Q particle spectrum. If the velocity of the interstellar wind with respect to the sun lies in the ecliptic, a large variation of the He(+) number density with respect to ecliptic longitude is expected.
22 citations
01 Jan 1972
TL;DR: In this article, a detailed model of the scattering of solar Lyman alpha from the spatial distribution of neutral hydrogen in interplanetary space is presented, which is established by solar wind and solar ultraviolet ionization processes along the trajectories of the incoming hydrogen atoms.
Abstract: For a sufficiently rapid relative motion of the solar system and the nearby interstellar gas, neutral atoms may be expected to penetrate the heliosphere before becoming ionized. Recent satellite measurements of the Lyman alpha emission above the geocorona indicate such an interstellar wind of neutral hydrogen emerging from the direction of Sagittarius and reaching to within a few astronomical units of the sun. A detailed model of the scattering of solar Lyman alpha from the spatial distribution of neutral hydrogen in interplanetary space is presented. This asymmetric distribution is established by solar wind and solar ultraviolet ionization processes along the trajectories of the incoming hydrogen atoms. The values of the interstellar density, the relative velocity, and the gas temperature are adjusted to agree with the Lyman alpha measurements. The results may be interpreted in terms of two models, the cold model and the hot model of the interstellar gas, depending on whether galactic Lyman alpha emission is present at its maximum allowable value or negligibly small.
20 citations
TL;DR: In this paper, a model of solar wind expansion beyond the heliosphere is given on the basis of the assumption of a continuous, stationary outflow, and the effect of the relative motion between cool interstellar atomic hydrogen and the solar wind protons in the interstellar space has been included.
9 citations
01 Jan 1972
7 citations
TL;DR: In this article, three requirements for determinations of the mean volume density of the interstellar neutral hydrogen, nH, from Lyman α absorption measurements are presented, and the best candidates for a meaningful measurement are early-type main-sequence stars or horizontal branch stars.
Abstract: WE have listed1 three requirements that have to be fulfilled for determinations of the mean volume density of the interstellar neutral hydrogen, nH, from Lyman α absorption measurements, (a) Stars that are likely to be surrounded by circumstellar envelopes, such as early-type giants and supergiants, have to be excluded, because circumstellar envelopes can give rise to a Lyman α emission sufficient to affect the absorption measurements by a significant amount. The best candidates for a meaningful measurement are therefore early-type main-sequence stars or horizontal branch stars. (b) Good spectral resolution (Δλ ≤ 2 A) is needed to resolve Lyman α from other strong nearby absorption features. (c) Observations of a large number of stars are needed in order to reduce the error in the determination of nH due to the rather large uncertainties in the measured equivalent widths and in the adopted distance to each star.
5 citations
TL;DR: A review of the forces that control the motions of interstellar gas and its variations in density and temperature can be found in this paper, where the observed degree of ionization has led to the cloud-intercloud model of the interstellar gas, which implies that the gas may be in a very dynamic, turbulent state.
Abstract: Our knowledge of interstellar space has been revolutionized by many recent observations. This article reviews some of the forces that we now believe control the motions of interstellar gas, and its variations in density and temperature. The observed degree of ionization has led to the cloud-intercloud model of interstellar gas. It also implies that the gas may be in a very dynamic, turbulent state, so that hydrostatic equations of state for this gas must be used with caution. Cosmic rays contribute an important force to interstellar gas dynamics and are an additional source of heat. They are most effective near cosmic-ray sources and at the edge of the galactic disk. Galactic structure affects gas dynamics, not only through the shock that bounds spiral arms, but also by a large-scale, ordered magnetic field in a way that encourages escape of gas, cosmic rays, and magnetic flux out of the galactic disk. But this field amplffication also depends on local "turbulence." Minuet or Rock? Large-scale order or turbulence? You don't have one without the other! Key words: interstellar clouds - cosmic rays - magnetic dynamo
5 citations
01 Jan 1972
TL;DR: The solar Lyman-alpha radiation pressure affects the orbits and velocities of the interstellar particles entering the solar system and leads to enhanced particle losses in the heliosphere, since particles spend a longer time crossing it as mentioned in this paper.
Abstract: The solar Lyman-alpha radiation pressure affects the orbits and the velocities of the interstellar particles entering the solar system. This leads to enhanced particle losses in the heliosphere, since particles spend a longer time crossing it. This causes a stronger decrease of the density with decreasing distances from the sun than had been calculated without accounting for the radiation pressure. Furthermore, the emission pattern of the solar Lyman-alpha radiation is anisotropic and rotates with the sun in a 27-day period. This causes a temporal change in the location of the intensity extrema. At the same time it produces hydrogen density anisotropies with extrema deviating in their directions from those which had been calculated without consideration of the radiation pressure.
1 citations