Neutral gases of interstellar origin in interplanetary space

Blüm, P.; Pfleiderer, J.; Wulf-Mathies, C.

doi:10.1016/0032-0633(75)90070-7

Cited by 33 publications

(7 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Early UV observations (Weller and Meier, 1974, 1979Paresce et al, 1974a,b;Freeman et al, 1976Freeman et al, , 1979Dalaudier et al, 1984;Burgin et al, 1983;Kurt et al, 1984a,b;Chassefière et al, 1986), supported by appropriate modelling (Blum et al, 1975;Fahr et al, 1976Fahr et al, , 1987, led to the conclusion that the interstellar helium at the upwind boundary of the heliosphere had a bulk velocity of about V = 27 km/s and a temperature of about T = 15 000 K, surprisingly different from values derived for the velocity and temperature of neutral hydrogen in the Very Local InterStellar Medium (correspondingly, 20 km/s and 8000 K, see Bertaux et al, 1985). It was soon realized that most probably the velocity vectors and kinetic temperatures of these two elements in the interstellar space were identical but a discrepancy of these quantities at the termination shock of the solar wind should be expected.…”

Section: Introductionmentioning

confidence: 90%

“…The early determinations of helium interstellar parameters were mainly based on measurements of the full width at half maximum of the helium cone glow, which is proportional to the quantity Feldman et al, 1972;Chassefière et al, 1988), as predicted by the modified cold (Blum et al, 1975) or the hot stationary model (Fahr, 1971(Fahr, , 1979Wu and Judge, 1979) of helium distribution. Since, however, the results of such models are valid only for a time-invariant helium ionization rate, they can provide only a qualitative insight into the actual helium density distribution.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Imprints from the solar cycle on the helium atom and helium pickup ion distributions

2003

View full text Add to dashboard Cite

Abstract. Neutral interstellar helium atoms penetrate into the solar system almost unaffected by gas-plasma interactions in the heliospheric interface region, and thus can be considered as carriers of original information on the basic parameters (like density, temperature, bulk velocity) of the Very Local Interstellar Medium (VLISM). Such information can nowadays be derived from analysis of data obtained from different experimental methods: in situ measurements of He atoms (Ulysses), observations of the solar backscattered He 584Å radiation (EUVE), in situ measurements of He + pickup ions (AMPTE, Ulysses, Wind, SOHO, ACE). In view of the current coordinated international ISSI campaign devoted to the study of the helium focusing cone structure and its evolution, we analyze expected variations of neutral He density, of He + pickup fluxes and of their phase space distributions at various phases of the solar activity cycle based on a realistic time-dependent modelling of the neutral helium and He + pickup ion distributions, which reflect solar cycleinduced variations of the photoionization rate. We show that the neutral helium density values are generally anticorrelated with the solar activity phase and in extreme cases (near the downwind axis) the maximum-to-minimum density ratio may even exceed factors of ∼3 at 1 AU. We also demonstrate that in the upwind hemisphere (at 1 AU and beyond) the He + fluxes are correlated with the solar cycle activity, whereas on the downwind side the maximum of the expected flux up to distances of ∼3 AU occurs around solar minimum epoch, and only further away does the correlation with solar activity become positive. Finally, we present the response of the phase space distribution spectra of He + pickup ions (in the solar wind frame) for different epochs of the solar cycle and heliocentric distances from 1 to 5 AU covering the range of Ulysses, Wind and ACE observations.

show abstract

Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Imprints from the solar cycle on the helium atom and helium pickup ion distributions

2003

View full text Add to dashboard Cite

show abstract

“…To calculate the neutral gas distribution neutrals on the upwind side of the heliosphere, we consider a cold model of interstellar gas. As Fahr [1971] and Blum et al [1975] have shown, a finite temperature has a minor influence on the density distribution in the upwind direction, and the cold gas model is accurate enough for most purposes. For this study, we have restricted the ACE SWICS observations to 1 month each year around the upwind direction, which justifies the use of the cold gas approximation.…”

Section: Interstellar Neutral Densitymentioning

confidence: 99%

Observational study of the cooling behavior of interstellar helium pickup ions in the inner heliosphere

et al. 2013

View full text Add to dashboard Cite

[1] The velocity distribution of interstellar pickup ions (PUIs) has typically been described as evolving through fast pitch angle scattering followed by adiabatic cooling while being transported radially outward with the solar wind. In combination, the ionization rate, which controls the radial profile of the interstellar neutrals, and the cooling process determine the slope of the observed PUI distributions. Thus far, a cooling index of 3/2 for the PUI velocity distributions has been used in almost all studies. This value is based on the implicit assumptions of immediate PUI isotropization due to pitch angle scattering and solar wind expansion with the square of the distance from the Sun. Here we determine the observed cooling index in a comparison of He + PUI distributions taken for 1 month in the upwind direction with ACE SWICS from 1999 through 2010 over the past solar cycle with such an isotropic PUI model, treating the cooling index as a free parameter. The ionization rate is obtained simultaneously from independent observations. To separate effects of slow pitch angle scattering of PUIs, the comparison is repeated for times restricted to perpendicular interplanetary magnetic field (IMF). When averaged over the entire data set, the cooling index is very close to 3/2. However, it varies substantially from 1.1 to 1.9 between samples, shows a distinct variation with solar activity, and has a significant correlation with sunspot number when data are restricted to nearly perpendicular IMF (θ Bv SW > 60°) excluding the slow pitch angle scattering in the radial IMF direction. The potential influence of slow pitch angle scattering, solar wind structures, and electron ionization on the cooling index and its variations is discussed.

show abstract

“…A more accurate determination of the density will require better instrumental calibration and time-dependent theoretical models for the penetration of the interstellar gas into interplanetary space (see section 3). [Thomas, 1972], and various others fAxford, 1972; Wulf-Mathies and Blum, 1975].…”

Section: Interplanetary Contribution the Ly A Observations From Ogo mentioning

confidence: 99%

Neutral hydrogen in interplanetary space

Holzer¹

1977

Reviews of Geophysics

160

117

View full text Add to dashboard Cite

The theory and observations relevant to the problem of neutral hydrogen in interplanetary space are reviewed. Emphasis is placed on those theoretical problems whose treatment in the existing literature is not entirely satisfactory, but discussion of all significant observational and theoretical aspects of the interplanetary H problem is provided. Attention is also given to other neutral constituents (particularly He) that are relatively abundant in interplanetary space and in the local interstellar medium, which is the primary source of the interplanetary neutral gas. Some consequences of the passage of the solar system through an interstellar cloud are also briefly considered.

show abstract

Neutral gases of interstellar origin in interplanetary space

Cited by 33 publications

References 7 publications

Imprints from the solar cycle on the helium atom and helium pickup ion distributions

Imprints from the solar cycle on the helium atom and helium pickup ion distributions

Observational study of the cooling behavior of interstellar helium pickup ions in the inner heliosphere

Neutral hydrogen in interplanetary space

Contact Info

Product

Resources

About