12 research outputs found
Hydrogen wall and heliosheath Lyman-alpha absorption toward nearby stars: possible constraints on the heliospheric interface plasma flow
In this paper, we study heliospheric Ly- absorption toward nearby
stars in different lines of sight. We use the Baranov-Malama model of the solar
wind interaction with a two-component (charged component and H atoms)
interstellar medium. Interstellar atoms are described kinetically in the model.
The code allows us to separate the heliospheric absorption into two components,
produced by H atoms originating in the hydrogen wall and heliosheath regions,
respectively. We study the sensitivity of the heliospheric absorption to the
assumed interstellar proton and H atom number densities. These theoretical
results are compared with interstellar absorption toward six nearby stars
observed by the Hubble Space Telescope.Comment: 10 pages, accepted for publication in JGR-Space Physic
Effects of interstellar and solar wind ionized helium on the interaction of the solar wind with the local interstellar medium
The Sun is moving through a warm (6500 K) and partly ionized local
interstellar cloud (LIC) with a velocity of 26 km/s. Recent measurements
of the ionization of the LIC (Wolff et al., 1999) suggest that interstellar
helium in the vicinity of the Sun is 30-40 % ionized, while interstellar
hydrogen is less ionized. Consequently, interstellar helium ions contribute up
to 50% of the total dynamic pressure of the ionized interstellar component. Up
to now interstellar helium ions have been ignored in existing models of the
heliospheric interface. In this paper we present results of a new model of the
solar wind interaction with the interstellar medium, which takes into account
interstellar helium ions. Using results of this model we find that the
heliopause, termination and bow shocks are closer to the Sun when compared to
the model results that ignore ions. The influence of interstellar helium
ions is partially compensated by solar wind alpha particles, which are taken
into account in our new model as well. Finally, we apply our new model to place
constraints on the plausible location of the termination shock.Comment: accepted for publication in Astrophys. J. Letter
Velocity distribution of interstellar H atoms in the heliospheric interface
Abstract. In this paper we present first results of a numerical computation of the velocity distribution function of interstellar H atoms in the heliospheric interface, the region of the solar and interstellar wind interaction. The velocity distribution is a key tool to evaluate uncertainties introduced by various simplified models of the interface. We numerically solve the kinetic equation for gas of H-atoms self-consistently with the hydrodynamic equations for plasma. Neutral and plasma components are efficiently coupled by charge exchange. The interaction disturbs the atom velocity distribution, which is assumed to be Maxwellian in the circumsolar local interstellar medium. It is shown that besides "original" interstellar atoms, there are three other important atom populations originating in the heliospheric interface. Velocity distribution functions of these populations at the heliopause are presented and discussed
Hydrogen atoms in the inner heliosphere: SWAN-SOHO and MASCS-MESSENGER observations
International audienceWe present here a study made by two instruments, MASCS on MESSENGER and SWAN on SOHO that observed the interplanetary background in 2010. The combination of these two data sets allows us to perform the first study of the distribution of hydrogen atoms inside the Earth's orbit. Triangulation of the position of the Maximum Emissivity Region (MER) was performed for the data of the UVVS channel of the MASCS-MESSENGER instrument. We find that the ecliptic longitude of the MER is 253.2° ±2.0°. This is the same value that was found from the analysis of the SWAN-SOHO H cell data obtained in 1996. This strongly suggests that the direction of the interstellar hydrogen wind has not changed between 1996 and 2010. We have also determined the distance of the MER to the Sun. We find that the volume emission rate peaks at 2.37âAU ±0.2âAU from the Sun. This value is a good test for the solar parameters for total H ionization and radiation pressure used in models. Comparison between the two datasets obtained by the UVVS-MASCS channel and SWAN on SOHO allow to derive the intensity between the two spacecraft at peak emission. Based on the SWAN-SOHO calibration, we find an intensity of 80 R ±36 R. This corresponds to a column density of 1540âmâ3 AUx2.3âĂâ1014âmâ3 . When divided by the distance between the two spacecraft, we find an average number density of 2300âmâ3
Voyager Measurements of Hydrogen Lyman-α Diffuse Emission from the Milky Way
International audienceDoppler-shifted hydrogen Lyman-alpha (Lyα) emission from galaxies is currently measured and used in cosmology as an indicator of star formation. Until now, the Milky Way emission has not been detected, owing to far brighter local sources, including the H Glow--i.e., solar Lyα radiation backscattered by interstellar atoms that flow within the solar system. Because observations from the Voyager spacecraft, now leaving the heliosphere, are decreasingly affected by the H glow, the Ultraviolet Spectrographs are detecting Lyα diffuse emission from our galaxy. The surface brightness toward nearby star-forming regions is about 3 to 4 Rayleigh. The escape fraction of the radiation from the brightest H II regions is on the order of 3% and is highly spatially variable. These results will help constraining models of Lyα radiation transfer in distant galaxies
Using Lyman-α to probe the interior and edges of the heliosphere
International audienceUnderstanding the role of neutral atoms in the heliospheric interface (between the bow shock and heliopause) is critical to identifying dynamics within our local bubble. This article recommends building upon existing measurements with new, high-spectral resolution observations of H Lyman-α, from a heliospheric mapping mission, to resolve the momentum exchange in reactions between the solar wind and energetic neutral atoms that are key to identifying the most important heliospheric processes