Dust in and Around the Heliosphere and Astrospheres

Space Science Reviews - The ESA Swarm mission, launched on 22 November 2013, consists of three spacecraft each equipped with a Micro Advanced Stellar Compass ( $\mu $ ASC) from the Technical...     

The Solar Wind Charge-eXchange Contribution to the Local Soft X-ray Background

The major sources of the Soft X-ray Background (SXRB), besides distinct structures as supernovae and superbubbles (e.g. Loop I), are: (i) an absorbed extragalactic emission following a power law, (ii) an absorbed thermal component (～2×10⁶ K) from the galactic disk and halo, (iii) an unabsorbed thermal component, supposedly at 10⁶ K, attributed to the Local Bubble and (iv) the very recently identified unabsorbed Solar Wind Charge-eXchange (SWCX) emission from the heliosphere and the geocorona. We study the SWCX heliospheric component and its contribution to observed data. In a first part, we apply a SWCX heliospheric simulation to model the oxygen lines (3/4 keV) local intensities during shadowing observations of the MBM 12 molecular cloud and a dense filament in the south galactic hemisphere with Chandra, XMM-Newton, and Suzaku telescopes. In a second part, we present a preliminary comparison of SWCX model results with ROSAT and Wisconsin surveys data in the 1/4 keV band. We conclude that, in the 3/4 keV band, the total local intensity is entirely heliospheric, while in the 1/4 keV band, the heliospheric component seems to contribute significantly to the local SXRB intensity and has potentially a strong influence on the interpretation of the ROSAT and Wisconsin surveys data in terms of Local Bubble hot gas temperature.     

Correction to: Backscattered Solar Lyman- $\alpha$ Emission as a Tool for the Heliospheric Boundary Exploration

Space Science Reviews - The Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) is a robotic arm-mounted instrument onboard NASA’s Perseverance...     

Interplanetary Lyman α Observations: Intensities from Voyagers and Line Profiles from HST/STIS

We present an analysis of Voyager UVS data obtained between 1993 and mid-2007. These data are used to study the interplanetary background and the hydrogen number density in the outer heliosphere. Two types of observations are studied, first the heliospheric scans performed until 2003 and then the fixed line of sight observations, close to the upwind direction, which are still performed at the end of 2007. We make comparisons with models including multiple scattering and hydrogen distributions derived from self-consistent modeling of the interface region. It is found that there is a remaining discrepancy between models and data. The origin of this difference is unknown but it may be linked to a possible tilting of the heliospheric interface due to the presence of an interstellar magnetic field. We should also estimate alternate sources of emission which are not backscattering of solar photons like collisional excitation of hydrogen in the heliosheath and emission after charge transfer or recombination of proton and electron in HII regions. Line profiles from HST/STIS are also presented.     

The Local Interstellar Medium: Peculiar or Not?

The local Interstellar Medium (ISM) at the 500 pc scale is by many respects a typical place in our Galaxy made of hot and tenuous gas cavities blown by stellar winds and supernovae, that includes the 100 pc wide “Local Hot Bubble (LHB)”, dense and cold clouds forming the cavity “walls”, and finally diffuse and warm clouds embedded within the hot gas, such as the Local Interstellar Cloud (LIC) presently surrounding the Sun. A number of measurements however, including abundance data, have contradicted this “normality” of our interstellar environment. Some contradictions have been explained, some not. I review recent observations at different spatial scales and discuss those peculiarities. At all scales Johannes Geiss has played a major role. At the scale of the first hundred parsecs, there are at least three “anomalies”: (i) the peculiar Gould Belt (GB), (ii) the recently measured peculiar Deuterium abundance pattern, (iii) the low value of the local O, N and ³He gas phase abundances. I discuss here the possibility of a historical link between these three observations: the large scale phenomenon which has generated the Belt, a giant cloud impact or an explosive event could be the common origin. At the 50–100 parsec scale, some of the unexplained or contradictory measurements of the Local Bubble hot gas, including its EUV/soft X ray emissions, ion column-densities and gas pressure may at least partially be elucidated in the light of the newly discovered X-ray emission mechanism following charge transfer between solar wind high ions and solar system neutrals. The Local Bubble hot gas pressure and temperature may be lower than previously inferred. Finally, at the smaller scale of the local diffuse cloudlets (a few parsecs), the knowledge of their structures and physical states has constantly progressed by means of nearby star absorption spectroscopy. On the other hand, thanks to anomalous cosmic rays and pickup ions measurements, local abundances of ISM neutral species are now precisely derived and may be compared with the absorption data. Interestingly these comparisons are now accurate enough to reveal other (noninterstellar) sources of pickup ions. However the actual physical state of the ISM 10–20,000 A.U. ahead along the Sun trajectory, which will be the ambient interstellar medium in a few thousands years, remains unknown. Local Bubble hot gas or warm LIC-type gas? More EUV/UV spectroscopic data are needed to answer this question.     

Swan Observations of the Solar Wind Latitude Distribution and its Evolution Since Launch

SWAN is the first space instrument dedicated to the monitoring of the latitude distribution of the solar wind by the Lyman alpha method. The distribution of interstellar H atoms in the solar system is determined by their destruction during ionization charge-exchange with solar wind protons. Maps of sky Ly-α emission have been recorded regularly since launch. The upwind maximum emission region deviates strongly from the pattern that would be expected from a solar wind that is constant with latitude. It is divided in two lobes by a depression aligned with the solar equatorial plane, called the Lyman-alpha groove, due to enhanced ionization along the neutral sheet where the slow and dense solar wind is concentrated. The groove (or the anisotropy) is more pronounced in 1997 than in 1996, but it then decreases between 1997 and 1998. This revised version was published online in June 2006 with corrections to the Cover Date.