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The Magnificent Seven have all been discovered by their exceptional soft X-ray spectra and high ratios of X-ray to optical flux. They all are considered to be nearby sources. Searching for similar objects with larger distances, one expects larger interstellar absorption resulting in harder X-ray counterparts. Current interstellar absorption treatment depends on chosen abundances and scattering cross-sections of the elements as well as on the 3D distribution of the interstellar medium. After a discussion of these factors we use the comprehensive 3D measurements of the Local Bubble by Lallement et al. (2003, Astron. Astrophys. 411, 447) to construct two simple models of the 3D distribution of the hydrogen column density. We test these models by using a set of soft X-ray sources with known distances. Finally, we discuss possible applications for distance estimations and population synthesis studies.

The galactic environment of the Sun varies over short timescales as the Sun and interstellar clouds travel through space. Small variations in the dynamics, ionization, density, and magnetic field strength of the interstellar medium (ISM) surrounding the Sun yield pronounced changes in the heliosphere. We discuss essential information required to understand short-term variations in the galactic environment of the Sun, including the distribution and radiative transfer properties of nearby ISM, and variations in the boundary conditions of the heliosphere as the Sun traverses clouds. The most predictable transitions are when the Sun emerged from the Local Bubble interior and entered the cluster of local interstellar clouds flowing past the Sun, within the past 140,000 years, and again when the Sun entered the local interstellar cloud now surrounding and inside of the solar system, sometime during the past 44,000 years.

We have performed high resolution 3D simulations with adaptive mesh refinement, following the ISM evolution in a star forming galaxy both on small ( 10 kpc) scales, enabling us to track structures in cooling shock compressed regions as well as the entire Galactic fountain flow. It is shown in an MHD run that the latter one is not inhibited by a large scale disk parallel magnetic field. The fountain plays a vital role in limiting the volume filling factor of the hot gas. Contrary to classical models most of the gas between 100K and 8000 K is found to be thermally unstable. On scales of superbubbles we find that the internal temperature structure is rather inhomogeneous for an old object like our Local Bubble, leading to low OVI column densities, consistent with observations.

Thermal plasma emission in the soft X-ray band (0.1 – 2.0 keV) is believed to be responsible for the bulk of the X-ray intensity seen from the Local Bubble, a low-density cavity extending over ∼ 70 – 200 pc around the Sun. The state of the hot plasma is still a matter of discussion as previous instrumentation like aboard ROSAT was not able to unambiguously distinguish between equilibrium and non-equilibrium emission models and thus to pin-point the origin of the Local Bubble. Recent missions like DXS, XQC, and XMM-Newton have shed more light on this subject and observations indicate that collisional ionization equilibrium with solar abundances cannot explain the data: lines appear at positions and with intensities in contradiction to standard models. Analysis of EPIC-pn data of X-ray shadowing observations (MBM 12, Ophiuchus molecular cloud) suggest a component with higher temperature (kT ∼ 0.14 keV) besides the standard kT ∼ 0.09 keV plasma.

An accurate value of the D/H ratio in the local interstellar medium (LISM) and a better understanding of the D/H variations with position in the Galactic disk and halo are vitally important questions as they provide information on the primordial D/H ratio in the Galaxy at the time of the protosolar nebula, and the amount of astration and mixing in the Galaxy over time. Recent measurements have been obtained with UV spectrographs on FUSE, HST, and IMAPS using hot white dwarfs, OB stars, and late-type stars as background light sources against which to measure absorption by D and H in the interstellar medium along the lines of sight. Recent analyses of FUSE observations of seven white dwarfs and subdwarfs provide a weighted mean value of DIR = (1.52 ± 0.08) x 10—5(15.2 ± 0.8 ppm), consistent with the value of (1.50 ± 0.10) x 10-5(15.0 + 1.0 ppm) obtained from analysis of lines of sight toward nearby late-type stars. Both numbers refer to the ISM within about 100 pc of the Sun, which samples warm clouds located within the Local Bubble. Outside of the Local Bubble at distances of 200 to 500 pc, analyses of far-UV spectra obtained with the IMAPS instrument indicate a much wider range of D/H ratios between 0.8 to 2.2 ppm. This portion of the Galactic disk provides information on inhomogeneous astration in the Galaxy.

Data obtained with a high resolution, high sensitivity spectrometer flown on the Spanish MINIS AT 01 satellite were used to test the Sciama model of radiatively decaying massive neutrinos. The observed emission is far less intense than that expected in the Sciama model.

After three year of observations, EURD (Espectrografo Ultravioleta extremo de Radiation Difusa) continues gathering new data of extreme and far ultraviolet diffuse radiation. We present here the results obtained on interstellar medium, atmospheric airglow, decaying neutrinos, Moon and early type stars.

The state of our observational and theoretical knowledge of the local interstellar medium (LISM) is reviewed. The LISM stretches out from the local Cloud, surrounding the solar system to the boundary of the Local Bubble, which is a region of distinct anticorrelation between HI (N H < 1020 cm−2) and 1/4 keV diffuse soft X-rays. After discussing some key observations in soft X-rays, obtained by ROSAT and DXS, and in the EUV by the EUVE satellite and the EURD instrument onboard Minisat, I will critically review models of the LISM. Since we cannot determine the plasma state (temperature, density, etc.) directly, the best plasma diagnostic tool is high resolution spectroscopy. The interpretation of the data then has to rely heavily on plasma emission models. I will point out several caveats in the standard procedure. Preference is given to dynamical models of the Local Bubble in general and to non-equilibrium plasma emission models in particular, which have to be calculated self-consistently. Such a model can explain (i) the deficiency of EUV lines as observed by EUVE, (ii) the dispersion measure and scintillation properties of a nearby pulsar, (iii) the existence of local neutral HI clouds, and (iv) OVI absorption line widths. New model spectra of the LISM will be presented and briefly compared with DXS, EUVE and preliminary EURD results.

Results from new observations of pulsars using the Ooty Radio Telescope (ORT) are used for investigating the structure of the Local Interstellar Medium (LISM) and the nature of the plasma turbulence spectrum in the Interstellar Medium (ISM). The observations show anomalous scintillation towards several nearby pulsars, and these are modelled in terms of large-scale spatial inhomogeneities in the distribution of plasma density fluctuations in the LISM. A 3-component model, where the Solar neighborhood is surrounded by a shell of enhanced plasma turbulence, is proposed for the LISM. The inferred scattering structure is strikingly similar to the Local Bubble. The nature of the plasma turbulence spectrum is found to be Kolmogorov-like in the spatial scale range ∼ 106 m to ∼ 1011 m, and there is evidence for excess power at larger spatial scales.

Pulsar scintillation measurements from the Ooty Radio Telescope (ORT) are used toinvestigate the distribution of scattering in the Local Interstellar Medium (LISM; region of ≲ 1 kpcof the Sun), specifically the region in and around the Local Bubble. A 3-component model, wherethe Solar neighborhood is surrounded by a shell of enhanced plasma turbulence, is proposed forthe LISM. Further, the Ooty data, along with those from Parkes and other telescopes are used forinvestigating the distribution of scattering towards the nearby Loop I Superbubble.

High resolution observations of interstellar Na I absorptions in the spectra of early-type stars in the second Galactic quadrant have been used to derive the spatial distribution of the nearby interstellar gas in the Galactic anticentre hemisphere. The data show the presence, within the region explored and within the nearest 150 pc, of eight diffuse interstellar clouds with LSR velocities in the range 15–55 km s−1. Molecular gas previously identified close to the Sun by (1995) and (1996) is embedded in one of the clouds. The motion of these clouds does not reflect any motion of the gas away from the Scorpio-Centaurus association, showing that the kinematics observed in the neighbourhood of the Sun by (1992) is restricted, in the second Galactic quadrant, to the nearest ∼ 50 pc.

In this paper I will use recent results about the heliosphere and the so-called ‘H walls’ around nearby star ‘asteropauses’ (the equivalent of the heliopause for other stars) to show new connections between heliospheric physics and other fields in space physics.

We analyse Hubble Space Telescope GHRS observations of the interstellar medium in the direction to e CMa, the strongest EUV source in the sky located 200 pc away in a region deficient in neutral gas. We show that the neutral gas density is the lowest yet measured in a galactic sight-line. The line of sight contains three main components among which the Local Cloud, and we derive their column densities, their velocity their temperature and their turbulence velocity. We discuss the ionization of the Local Cloud and we show that we detect the conductive interface between diffuse local cloud and the hot local bubble.

This paper summarizes some of the discussions of working group 8–9 during the ISSI Conference on “The Heliosphere in the Local Interstellar Medium”. Because the subject of these working groups has become significantly broader during the last ten years, we have selected three topics for which recent observations have modified and improved our knowledge of the heliosphere and the surrounding interstellar medium. These topics are the number densities and ISM ionization states of hydrogen and helium, the newly discovered hot gas from the “H wall” seen in absorption, and the comparison between ISM and heliospheric minor element abundances. Papers from this volume in which more details on these topics can be found are quoted throughout the report.

A summary of the lively discussions in working group 2 (WG2) on the origin and evolution of the LB is given below. The debate focussed mainly on the problem of how to pin down the physical properties of the LB. As a first step, we had to critically assess the observational constraints that are put on any model, predominantly from the SXR and EUV data. Next we were discussing models on the origin and evolution of the LB, which are able to explain the observations and which would allow to infer basic LB properties. A simple model, emphasizing the self-consistent dynamical and thermal evolution of a non-equilibrium plasma is presented. We also found, that picturing the LB as an isolated phenomenon is not supported by the data. Instead, the LB environment and its influence on the evolution of the LB have to be taken into consideration. Two different views are presented here. Either the LB and the Loop I superbubble are two physically separate phenomena, which are currently interacting, or star formation epochs in the Scorpius-Centaurus Association interacting with the molecular gas in the Aquila Rift and the interarm region around the Sun may have sculpted the configuration of interstellar matter within 200 parsecs, including the Local Bubble. However, so far observational constraints are insufficient to establish a canonical model of the evolution and the origin of the LB.

We are finally on the threshold of obtaining a coherent morphological and physical picture for the local interstellar medium (LISM), especially the region within 300 pc of the Sun. The EUVE is playing a special role in revealing this picture. This instrument can provide direct measurements of the the radiation field that photoionizes both hydrogen and helium. It also can yield direct measurements of the column densities of hydrogen, but especially He I and He II toward nearby white dwarfs. These observations suggest that the ionization in the Local Cloud, the cloud in which the Sun is embedded, is not in equilibrium, but in a recombination phase. Heuristic calculations imply that the the present ionization is due to the passage of shocks, at times greater than 3 × 106 years ago. the origin of these shocks are probably linked to the supernova which was responsible for the expanding nebular complex of clouds know as the Loop I supernova remnant, of which the Local Cloud is a part. extreme-UV radiation field, that which ionizes both hydrogen and helium in the LISM. Of the ISM within 300 pc, the volume appears to be predominantly filled by hot (106 K) coronal gas. This gas is laced with six largescale shell structures with diameters ∼100–150 pc including the long-recognized radio loops, Loop I-IV, as well as the Orion-Eridanus and Gum Nebulae are identified. An idea that has evolved in the literature for over two decades is that the kinematically-linked OB associations representing Gould’s Belt, plus the gas and dust of Lindblad’s Ring, require that previous supernova activity and stellar winds carved out a 400–600 pc diameter cavity some 3 to 6 × 107 yr ago. this activity produced a pre-existing low density region, into which the present young loop structures have expanded. The outer boundaries of the identified expanding loop structures, inside this preexisting cavity, delineate the periphery of the the mis-named “local interstellar bubble.” Thus, this picture naturally explains some of the problems often associated with the presence of this low density region exterior to Loop I.

In the context of a review of work on the global structure of the interstellar medium, supernova remnant evolution, flows in multiphase media, cosmic ray moderation of flows, theories of the Galactic halo gas, and the nature of the local superbubble are considered. Speculations about the nature of a one parameter fully self-consistent model of the interstellar medium-supernova-radiation and cosmic ray background system are offered.

Effects of poor gas distribution, liquid mixing, and rates of interphase mass transfer continue to be important issues in the design and scaleup of gas-liquid, gas-liquid-solid, slurry catalyzed gas-liquid, and biologicalgrowth reactors. Most studies of mass transfer rates, which directly affect reaction rates and yield, have been done on a volume-averaged basis, although some measurements of bubble size and bubble surface area have been done to determine local variations. Preliminary work is reported in this paper on measurements and simulation of local bubble dynamics and effects on liquid hydrodynamics (flow patterns). Laser-Doppler anemometry (LDA) was used to measure liquid velocities with and without sparged gas. It was necessary to maintain low relative gas rates and high impeller rates in order to maintain a regime where LDA gave useful results. Air was sparged into tap water giving bubble sizes which were estimated to be 1 to 5mm. Simulations done with the code FLUENT gave results with close similarity to the experimental measurements and showed aspects of bubble dynamics that are very difficult to see visually. Importantly, most of the gas, even under highly dispersed conditions, channels upward along the upstream sides of the baffles. Also the higher the gas loading at a given impeller rotation rate, the greater is the channelling tendency and the poorer is gas distribution. Preliminary mass transfer rate computations gave promising results and will lead to more studies.

This article reviews the last 20 years of the struggle to understand the diffuse ISM, highlighting recent changes of fundamental aspects. It then provides a pictorial description consistent with those developments. Various caveats are discussed and a number of areas for future investigation identified. It ends with a hopeful glance toward understanding ISM phase segregation.