### The following is a listing of papers coming out of the Heliosphere and Astrosphere Research Group at Dartmouth College. For papers about the heliosphere, we hope to establish a selection soon; in the meantime, this link will provide a long list.

A search engine output for Müller's contibutions: http://adsabs.harvard.edu/abstract_service.html

# Publications in Refereed Journals

## Decades-long changes of the interstellar wind through our solar system

Authors: P.C. Frisch, M. Bzowski, G. Livadiotis, D.J. McComas, E. Moebius, H.-R. Müller, W.R. Pryor, N.A. Schwadron, J.M. Sokol, J.V. Vallerga and J.M. Ajello
Journal-ref: Science Magazine 341, 1080-1082, doi: 10.1126/science.1239925 (2013)
Full text links: doi: 10.1126/science.1239925; journal: Science Article
Comments: 3 pages + Supplement; 4 Figures; 2 Tables.

The journey of the Sun through the dynamically active local interstellar medium creates an evolving heliosphere environment. This motion drives a wind of interstellar material through the heliosphere that has been measured with Earth-orbiting and interplanetary spacecraft for 40 years. Recent results obtained by NASA's Interstellar Boundary Explorer mission during 2009–2010 suggest that neutral interstellar atoms flow into the solar system from a different direction than found previously. These prior measurements represent data collected from Ulysses and other spacecraft during 1992–2002 and a variety of older measurements acquired during 1972–1978. Consideration of all data types and their published results and uncertainties, over the three epochs of observations, indicates that the trend for the interstellar flow ecliptic longitude to increase linearly with time is statistically significant.

## Solar Radiation Pressure and Local Interstellar Medium Flow Parameters from Interstellar Boundary Explorer Low Energy Hydrogen Measurements

Authors: N.A. Schwadron, E. Moebius, H. Kucharek, M.A. Lee, J. French, L. Saul, P. Wurz, M. Bzowski, S. Fuselier, G. Livadiotis, D.J. McComas, P.C. Frisch, M. Gruntman, and H.-R. Müller
Journal-ref: The Astrophysical Journal 760, 46, doi: 10.1088/0004-637X/760/1/46 (2013)
Full text links: doi: 10.1088/0004-637X/775/2/86; journal: ApJ Article (IOP)
Comments: 2.5 MB; 14 pages; 14 Figures; 4 Tables.
Keywords: ISM: abundances; ISM: atoms; solar wind; Sun: heliosphere

Neutral hydrogen atoms that travel into the heliosphere from the local interstellar medium (LISM) experience strong effects due to charge exchange and radiation pressure from resonant absorption and re-emission of Lya. The radiation pressure roughly compensates for the solar gravity. As a result, interstellar hydrogen atoms move along trajectories that are quite different than those of heavier interstellar species such as helium and oxygen, which experience relatively weak radiation pressure. Charge exchange leads to the loss of primary neutrals from the LISM and the addition of new secondary neutrals from the heliosheath. IBEX observations show clear effects of radiation pressure in a large longitudinal shift in the peak of interstellar hydrogen compared with that of interstellar helium. Here, we compare results from the Lee et al. interstellar neutral model with IBEX-Lo hydrogen observations to describe the distribution of hydrogen near 1 AU and provide new estimates of the solar radiation pressure. We find over the period analyzed from 2009 to 2011 that radiation pressure divided by the gravitational force (mu) has increased slightly from mu = 0.94 +- 0.04 in 2009 to mu = 1.01 +- 0.05 in 2011. We have also derived the speed, temperature, source longitude, and latitude of the neutral H atoms and find that these parameters are roughly consistent with those of interstellar He, particularly when considering the filtration effects that act on H in the outer heliosheath. Thus, our analysis shows that over the period from 2009 to 2011, we observe signatures of neutral H consistent with the primary distribution of atoms from the LISM and a radiation pressure that increases in the early rise of solar activity.

## Synthetic four-solar-cycle solar wind at 1 AU generated from the OMNI data set

Authors: L.J. Thatcher and H.-R. Müller
Journal-ref: J. Geophys. Res. 118, 615-627, doi: 10.1002/jgra.50150 (2013)
Full text links: doi: 10.1002/jgra.50150; journal: Wiley
Comments: 976 kB; 13 pages; 8 Figures; 4 Tables.
Keywords: OMNI data; solar wind

Numerical modeling provides key insights into the physics of the outer heliosphere. The solar wind data utilized by these models impact their accuracy and should be as close as possible to the actual solar wind. Because of the time scales involved, such a data set should also span several solar cycles. Yet the bulk of solar wind measurements in such a time frame was obtained near Earth. A method to infer the solar wind at points not directly observed is developed such that a 1 AU ring in the ecliptic plane is filled with four solar cycles of solar wind data. Hourly OMNI data are used as the seed data. The OMNI data are separated into four separate categories, and those categories are first extrapolated, generating a continuous 2-D category map of the solar wind for the full four solar cycles covered by OMNI. The category map is used to determine solar wind characteristics. The solar wind values are determined by local running averages coupled with a random walk technique. The averages provide baseline values and the random walk adds short-duration deviations from this baseline. The statistics from the extrapolated data are compared to the statistics of the original OMNI data set. Category durations, relative coverage, variable distributions, and correlations are similar to those of the OMNI data, although with some discrepancies.

Authors: B.T. Kress, M.K. Hudson, A.Y. Ukhorskiy, and H.-R. Müller
Journal-ref: Geophysical Monograph Series 199, 151-160, doi: 10.1029/2012GM001333 (2012)
Full text links: doi: 10.1029/2012GM001333; publisher: agu.org/books/gm/v199/2012GM001333
Comments: 1453 kB; 10 pages; 6 Figures.

Radial transport in the Earth's radiation belts is frequently modeled with a diffusion equation. In some cases, however, solar wind dynamic pressure fluctuations can cause significant changes in the phase space density radial profile that are not diffusive, e.g., shock-associated injections observed during storm sudden commencements. Three forms of radial transport driven by solar wind dynamic pressure fluctuations are briefly reviewed: (1) radial diffusion, (2) large changes in the phase space density radial profile due to a single or few ULF drift-resonant interactions, and (3) shock-associated injections of radiation belt electrons occurring in less than a single drift period. This is followed by a presentation of numerical results comparing radial diffusion with transport modeled by computing electron-guiding center trajectories in MHD magnetospheric model fields. Initial results suggest that radial transport of MeV electrons in the outer radiation belt due to moderate solar wind fluctuations is not well modeled by a diffusion equation.

## Trajectories and Distribution of Interstellar Dust Grains in the Heliosphere

Authors: J.D. Slavin, P.C. Frisch, H.-R. Müller, J. Heerikhuisen, N.V. Pogorelov, W.T. Reach, and G.P. Zank
Journal-ref: The Astrophysical Journal 760, 46, doi: 10.1088/0004-637X/760/1/46 (2012)
Full text links: doi: 10.1088/0004-637X/760/1/46; journal: ApJ Article [preprint: arXiv:1210.1127]
Keywords: dust, extinction, ISM: abundances, Sun: heliosphere

The solar wind carves a bubble in the surrounding interstellar medium (ISM) known as the heliosphere. Charged interstellar dust grains (ISDG) encountering the heliosphere may be diverted around the heliopause or penetrate it depending on their charge-to-mass ratio. We present new calculations of trajectories of ISDG in the heliosphere, and the dust density distributions that result. We include up-to-date grain charging calculations using a realistic UV radiation field and full three-dimensional magnetohydrodynamic fluid + kinetic models for the heliosphere. Models with two different (constant) polarities for the solar wind magnetic field (SWMF) are used, with the grain trajectory calculations done separately for each polarity. Small grains a_gr <~ 0.01 mu are completely excluded from the inner heliosphere. Large grains, a_gr >~ 1.0 mu, pass into the inner solar system and are concentrated near the Sun by its gravity. Trajectories of intermediate size grains depend strongly on the SWMF polarity. When the field has magnetic north pointing to ecliptic north, the field de-focuses the grains resulting in low densities in the inner heliosphere, while for the opposite polarity the dust is focused near the Sun. The ISDG density outside the heliosphere inferred from applying the model results to in situ dust measurements is inconsistent with local ISM depletion data for both SWMF polarities but is bracketed by them. This result points to the need to include the time variation in the SWMF polarity during grain propagation. Our results provide valuable insights for interpretation of the in situ dust observations from Ulysses.

## Statistical investigation of hourly OMNI solar wind data

Authors: L.J. Thatcher and H.-R. Müller
Journal-ref: J. Geophys. Res. 116, A12107, doi: 10.1029/2011JA017027 (2011)
Full text links: doi: 10.1029/2011JA017027; journal: 2011JA017027
Comments: 260 kB; 10 pages; 8 Figures; 2 Tables.
Keywords: OMNI data; solar wind; solar wind categorization

Hourly OMNI solar wind data are sorted into categories reflecting membership of each data point to either slow or fast solar wind streams, or to either coronal mass ejection or corotating interaction region environments. The categorization is inspired by Yermolaev et al. (2009) and modified from there. Durations and coverage fractions of each category are investigated, together with their dependence on the solar activity cycle. The results are in line with physical expectations for the solar wind at 1 AU. A further analysis, treating hourly solar wind fluctuations as a constrained random walk process, is carried out independently for each solar wind category and discussed. The resulting step size distributions are found to be largely symmetric across zero, resembling a random walk deviation from a long-term average. This constrained random walk can in principle be used to fill gaps in the OMNI data and perform other OMNI data extrapolations.

## Time-variability in the Interstellar Boundary Conditions of the Heliosphere: Effect of the Solar Journey on the Galactic Cosmic Ray Flux at Earth

Authors: P.C. Frisch and H.-R. Müller
Journal-ref: Space Sci. Rev. OnlineFirst (2011)

During the solar journey through galactic space, variations in the physical properties of the surrounding interstellar medium (ISM) modify the heliosphere and modulate the flux of galactic cosmic rays (GCR) at the surface of the Earth, with consequences for the terrestrial record of cosmogenic radionuclides. One phenomenon that needs studying is the effect on cosmogenic isotope production of changing anomalous cosmic ray fluxes at Earth due to variable interstellar ionizations. The possible range of interstellar ram pressures and ionization levels in the low density solar environment generate dramatically different possible heliosphere configurations, with a wide range of particle fluxes of interstellar neutrals, their secondary products, and GCRs arriving at Earth. Simple models of the distribution and densities of ISM in the downwind direction give cloud transition timescales that can be directly compared with cosmogenic radionuclide geologic records. Both the interstellar data and cosmogenic radionuclide data are consistent with two cloud transitions, within the past 10,000 years and a second one 20,000–30,000 years ago, with large and assumption-dependent uncertainties. The geomagnetic timeline derived from cosmic ray fluxes at Earth may require adjustment to account for the disappearance of anomalous cosmic rays when the heliosphere is immersed in ionized interstellar gas.

## Polarization of the Charge-Exchange X-rays Induced in the Heliosphere

Authors: M. Gacesa, H.-R. Müller, R. Cote, and V. Kharchenko
Journal-ref: The Astrophysical Journal Letters 732, L21, doi: 10.1088/2041-8205/732/2/L21 (2011)
Full text links: doi: 10.1088/2041-8205/732/2/L21; journal: ApJL Article [preprint: arXiv:1012.1349]
Keywords: atomic processes - interplanetary medium - X-rays: diffuse background - X-rays: polarization

We report results of a theoretical investigation of polarization of the X-ray emissions induced in charge-exchange collisions of fully stripped solar wind ions C6+ and O8+ with the heliospheric hydrogen atoms. The polarization of X-ray emissions has been computed for line-of-sight observations within the ecliptic plane as a function of solar wind ion velocities, including a range of velocities corresponding to the slow and fast solar wind, and Coronal Mass Ejections. To determine the variability of polarization of heliospheric X-ray emissions, the polarization has been computed for solar minimum conditions with self-consistent parameters of the solar wind plasma and heliospheric gas and compared with the polarization calculated for an averaged solar activity. We predict the polarization of charge-exchange X-rays to be between 3% and 8%, depending on the line-of-sight geometry, solar wind ion velocity, and the selected emission lines.

## Can IBEX Identify Variations in the Galactic Environment of the Sun using Energetic Neutral Atom (ENAs)?

Authors: P.C. Frisch, J. Heerikhuisen, N. V. Pogorelov, B. DeMajistre, G.B. Crew, H.O. Funsten, P. Janzen, D.J. McComas, E. Moebius, H.-R. Müller, D.B. Reisenfeld, E.C. Roelof, N.A. Schwadron, J.D. Slavin, and G.P. Zank
Journal-ref: The Astrophysical Journal 719, 1984-1992
Full text links: doi: 10.1088/0004-637X/719/2/1984; journal: ApJ
Keywords: ISM: clouds; ISM: kinematics and dynamics; ISM: magnetic fields; ISM: structure; plasmas; Sun: heliosphere

The Interstellar Boundary Explorer (IBEX) spacecraft is providing the first all-sky maps of the energetic neutral atoms (ENAs) produced by charge exchange between interstellar neutral Ho atoms and heliospheric solar wind and pickup ions in the heliosphere boundary regions. The "edge" of the interstellar cloud presently surrounding the heliosphere extends less than 0.1 pc in the upwind direction, terminating at an unknown distance, indicating that the outer boundary conditions of the heliosphere could change during the lifetime of the IBEX satellite. Using reasonable values for future outer heliosphere boundary conditions, ENA fluxes are predicted for one possible source of ENAs coming from outside of the heliopause. The ENA-production simulations use three-dimensional MHD plasma models of the heliosphere that include a kinetic description of neutrals and a Lorentzian distribution for ions. Based on this ENA-production model, it is then shown that the sensitivities of the IBEX 1.1 keV skymaps are sufficient to detect the variations in ENA fluxes that are expected to accompany the solar transition into the next upwind cloud. Approximately 20% of the IBEX 1.1 keV pixels appear capable of detecting the predicted model differences at the 3s level, with these pixels concentrated in the Ribbon region. Regardless of the detailed ENA production model, the success of the modeled B · R ~ 0 directions in reproducing the Ribbon locus, together with our results, indicates that the Ribbon phenomenon traces the variations in the heliosphere distortion caused by the relative pressures of the interstellar magnetic and gaseous components.

## Physics of the Solar Wind–Local Interstellar Medium Interaction: Role of Magnetic Fields

Authors: G. P. Zank, N. V. Pogorelov, J. Heerikhuisen, H. Washimi, V. Florinski, S. Borovikov, I. Kryukov and H. R. Müller
Journal-ref: Space Sci. Rev. 146, 295-327 (2009), published online 7 May 2009
Keywords: Interstellar gas - Heliosphere - Instrumentation

The interaction of the solar wind with the local interstellar medium is characterized by the self-consistent coupling of solar wind plasma, both upstream and downstream of the heliospheric termination shock, the interstellar plasma, and the neutral atom component of interstellar and solar wind origin. The complex coupling results in the creation of new plasma components (pickup ions), turbulence, and anomalous cosmic rays, and new populations of neutral atoms and their coupling can lead to energetic neutral atoms that can be detected at 1 AU. In this review, we discuss the interaction and coupling of global sized structures (the heliospheric boundary regions) and kinetic physics (the distributions that are responsible for the creation of energetic neutral atoms) based on models that have been developed by the University of Alabama in Huntsville group.

## Diagnosing the Neutral Interstellar Gas Flow at 1 AU with IBEX-Lo

Authors: E. Möbius, H. Kucharek, G. Clark, M. O’Neill, L. Petersen, M. Bzowski, L. Saul, P. Wurz, S. A. Fuselier, V. V. Izmodenov, D. J. McComas, H. R. Müller and D. B. Alexashov
Journal-ref: Space Sci. Rev. 146, 149-172 (2009), published online 22 April 2009
Keywords: Solar wind boundaries - Interstellar medium - Pickup ions - Energetic neutral atoms

Every year in fall and spring the Interstellar Boundary Explorer (IBEX) will observe directly the interstellar gas flow at 1 AU over periods of several months. The IBEX-Lo sensor employs a powerful triple time-of-flight mass spectrometer. It can distinguish and image the O and He flow distributions in the northern fall and spring, making use of sensor viewing perpendicular to the Sun-pointing spin axis. To effectively image the narrow flow distributions IBEX-Lo has a high angular resolution quadrant in its collimator. This quadrant is employed selectively for the interstellar gas flow viewing in the spring by electrostatically shutting off the remainder of the aperture. The operational scenarios, the expected data, and the necessary modeling to extract the interstellar parameters and the conditions in the heliospheric boundary are described.
The combination of two key interstellar species will facilitate a direct comparison of the pristine interstellar flow, represented by He, which has not been altered in the heliospheric boundary region, with a flow that is processed in the outer heliosheath, represented by O. The O flow distribution consists of a depleted pristine component and decelerated and heated neutrals. Extracting the latter so-called secondary component of interstellar neutrals will provide quantitative constraints for several important parameters of the heliosheath interaction in current global heliospheric models. Finding the fraction and width of the secondary component yields an independent value for the global filtration factor of species, such as O and H. Thus far filtration can only be inferred, barring observations in the local interstellar cloud proper. The direction of the secondary component will provide independent information on the interstellar magnetic field strength and orientation, which has been inferred from SOHO SWAN Ly-a backscattering observations and the two Voyager crossings of the termination shock.

## The Heliosphere in Time

Authors: H.-R. Müller, P. C. Frisch, B. D. Fields, G. P. Zank
Journal-ref: Space Sci. Rev. 143, 415-425 (2009), published online 22 Oct 2008
Keywords: Global heliosphere modeling; time-dependent interstellar conditions

Because of the dynamic nature of the interstellar medium, the Sun should have encountered a variety of different interstellar environments in its lifetime. As the solar wind interacts with the surrounding interstellar medium to form a heliosphere, different heliosphere shapes, sizes, and particle contents result from the different environments. Some of the large possible interstellar parameter space (density, velocity, temperature) is explored here with the help of global heliosphere models, and the features in the resulting heliospheres are compared and discussed. The heliospheric size, expressed as distance of the nose of the heliopause to the Sun, is set by the solar wind - interstellar pressure balance, even for extreme cases. Other heliospheric boundary locations and neutral particle results correlate with the interstellar parameters as well. If the H0 clouds identified in the Millennium Arecibo survey are typical of clouds encountered by the Sun, then the Sun spends ~99.4% of the time in warm low density ISM, where the typical upwind heliosphere radii are up to two orders of magnitude larger than at present.

## Comparing various multi-component global heliosphere models

Authors: H.-R. Müller, V. Florinski, J. Heerikhuisen, V.V. Izmodenov, K. Scherer, D. Alexashov, and H.-J. Fahr
Journal-ref: Astr. Astrophys. 491, 43-51 (2008)
Full text links: doi: 10.1051/0004-6361:20078708 ; journal: A & A; preprint: arXiv:0804.0125
Keywords: heliosphere - interstellar neutral hydrogen - numerical models - kinetic models - multi-fluid models

Modeling of the global heliosphere seeks to investigate the interaction of the solar wind with the partially ionized local interstellar medium. Models that treat neutral hydrogen self-consistently and in great detail, together with the plasma, but that neglect magnetic fields, constitute a sub-category within global heliospheric models. There are several different modeling strategies used for this sub-category in the literature. Differences and commonalities in the modeling results from different strategies are pointed out. Plasma-only models and fully self-consistent models from four research groups, for which the neutral species is modeled with either one, three, or four fluids, or else kinetically, are run with the same boundary parameters and equations. They are compared to each other with respect to the locations of key heliospheric boundary locations and with respect to the neutral hydrogen content throughout the heliosphere. In many respects, the models' predictions are similar. In particular, the locations of the termination shock agree to within 7% in the nose direction and to within 14% in the downwind direction. The nose locations of the heliopause agree to within 5%. The filtration of neutral hydrogen from the interstellar medium into the inner heliosphere, however, is model dependent, as are other neutral results including the hydrogen wall. These differences are closely linked to the strength of the interstellar bow shock. The comparison also underlines that it is critical to include neutral hydrogen into global heliospheric models.

## Relationship of the Van Allen radiation belts to solar wind drivers

Authors: M. K. Hudson, B. T. Kress, H.-R. Müller, J. A. Zastrow, and J. B. Blake
Journal-ref: JASTP 70/5, 708-729 (2008)
Keywords: Radiation belts; Trapped energetic particles; Magnetic storms; Coronal mass ejections; High-speed solar wind streams; Plasmapause

Discovery of the Van Allen radiation belts by instrumentation flown on Explorer 1 in 1958 was the first major discovery of the Space Age. A view of the belts as distinct inner and outer zones of energetic particles with different sources was modified by observations made during the Cycle 22 maximum in solar activity in 1989–1991, the first approaching the activity level of the International Geophysical Year of 1957–1958. The dynamic variability of outer zone electrons was measured by the NASA–Air Force Combined Radiation Release and Effects Satellite launched in July 1990. This variability is caused by distinct types of heliospheric structure which vary with the solar cycle. The largest fluxes averaged over a solar rotation occur during the declining phase from solar maximum, when high-speed streams and co-rotating interaction regions (CIRs) dominate the inner heliosphere, leading to recurrent storms. Intense episodic events driven by high-speed interplanetary shocks launched by coronal mass ejections (CMEs) prevail around solar maximum when CMEs occur most frequently. Only about half of moderate storms, defined by intensity of the ring current, lead to an overall flux increase, emphasizing the need to quantify loss as well as source processes; both increase when the magnetosphere is strongly driven. Three distinct types of acceleration are described in this review: prompt and diffusive radial transport, which increases energy while conserving the first invariant, and local acceleration by waves, which change the first invariant. The latter also produce pitch angle diffusion and loss, as does outward radial transport, especially when the magnetosphere is compressed. The effect of a dynamic magnetosphere boundary on radiation belt electrons is described in the context of MHD-test particle simulations driven by measured solar wind input.

## Three-dimensional simulation of the dynamical heliosphere

Authors: L.A. Labun and H.-R. Müller
Journal-ref: J. Geophys. Res. 112, A09105, doi:10.1029/2007JA012256 (2007)
Full text links: doi: 10.1029/2007JA012256; journal: 2007JA012256
Keywords: heliosphere; solar cycle; solar wind heliolatitude variation; three-dimensional solar wind; global heliosphere simulation; interstellar neutrals

The structure of the global heliosphere is driven not only by the properties of the respective interstellar plasma and neutral populations but also by the temporal and spatial variation of the solar wind plasma itself. Often assumptions of symmetry or stationarity are made for modeling the global heliosphere that greatly reduce the problem space. Here, an adaptation of a two-fluid code to a fully realized three-dimensional model of the heliosphere is presented. The boundary functions for the solar wind are derived from recently presented detailed observations and models of solar output by Whang et al. (2005). Neutrals are included as a single separate fluid interacting with the plasma through charge exchange. We first examine temporal and spatial variation of the solar wind separately and finally study a model containing both together. The asymmetric solar wind creates a heliosphere that is slightly elongated over the solar polar directions. Solar maximum conditions act as a pulse of dense material in the outer heliosphere, with fast responses of termination shock and heliopause locations. The pulse propagation in the heliosheath creates a dynamic environment, additionally triggering heliopause instabilities.

## The wind-ISM interaction of alpha Tau

Authors: B.E. Wood, G.M. Harper, Hans-Reinhard Müller, J. Heerikhuisen and G.P. Zank
Journal-ref: Astrophys. J. 655, 946–957 (2007)
Full text links: doi: 10.1086/510404; journal: ApJ510404
Keywords: circumstellar matter — stars: individual (alpha Tau) - stars: winds, outflows — ultraviolet: stars

Ultraviolet spectra of alpha Tau (K5 III) obtained by the Hubble Space Telescope (HST) show many emission lines affected by broad absorption from the strong wind of this red giant star. For the Mg II h & k lines there is also a narrow absorption feature in the midst of the wind absorption that has been interpreted as being from alpha Tau's wind-ISM interaction region (i.e., its "astrosphere"). We try to reproduce this absorption using hydrodynamic models of the alpha Tau astrosphere, which show that stellar wind material heated, compressed, and decelerated at the wind's termination shock (TS) can produce significant absorption at about the right velocity. By experimenting with different model input parameters, we find that the parameter that the absorption is most sensitive to is the ISM pressure, which determines the location and therefore the density at the TS. However, the models underestimate both the amount of deceleration at the TS and the amount of absorption for realistic input parameters. We demonstrate that these problems can in principle be resolved by modeling the TS as a radiative shock. However, a cooling timescale short enough to affect the post-shock is only attainable if alpha Tau's wind speed is increased from the 27 - 30 km/s values derived from fits to wind absorption, to at least 35 km/s. The models also seem to require a very high ISM pressure of P/k = 30,000 cm^3 K to induce densities at the TS high enough to yield sufficient radiative cooling. This pressure is at least a factor of 2 higher than other estimates of ISM thermal pressure within the Local Bubble.

## Heliospheric response to different possible interstellar environments

Authors: Hans-Reinhard Müller, P.C. Frisch, V. Florinski and G.P. Zank
Journal-ref: Astrophys. J. 647, 1491-1505 (2006)
Report-no:
Keywords:cosmic rays - hydrodynamics - interplanetary medium - ISM: clouds - ISM: structure - stars: winds, outflows

At present, the heliosphere is embedded in a warm low density interstellar cloud that belongs to a cloud system flowing through the local standard of rest with a velocity near ~18 km/s. The velocity structure of the nearest interstellar material (ISM), combined with theoretical models of the local interstellar cloud (LIC), suggest that the Sun passes through cloudlets on timescales of < <103-104 yr, so the heliosphere has been, and will be, exposed to different interstellar environments over time. By means of a multi-fluid model that treats plasma and neutral hydrogen self-consistently, the interaction of the solar wind with a variety of partially ionized ISM is investigated, with the focus on low density cloudlets such as are currently near the Sun. Under the assumption that the basic solar wind parameters remain/were as they are today, a range of ISM parameters (from cold neutral to hot ionized, with various densities and velocities) is considered. In response to different interstellar boundary conditions, the heliospheric size and structure change, as does the abundance of interstellar and secondary neutrals in the inner heliosphere, and the cosmic ray level in the vicinity of Earth. Some empirical relations between interstellar parameters and heliospheric boundary locations, as well as neutral densities, are extracted from the models.

## New mass loss measurements from astrospheric Lya absorption

Authors: B.E. Wood, Hans-Reinhard Müller, G.P. Zank, J.L. Linsky, and S. Redfield
Journal-ref: Astrophys. J. Letters 628, L143-L146 (2005)
Report-no:
Keywords: circumstellar matter—stars: winds, outflows—ultraviolet: stars

Measurements of stellar mass-loss rates are used to assess how wind strength varies with coronal activity and age for solar-like stars. Mass loss generally increases with activity, but we find evidence that winds suddenly weaken at a certain activity threshold. Very active stars are often observed to have polar starspots, and we speculate that the magnetic field geometry associated with these spots may be inhibiting the winds. Our inferred mass-loss/age relation represents an empirical estimate of the history of the solar wind. This result is important for planetary studies as well as solar/stellar astronomy, since solar wind erosion may have played an important role in the evolution of planetary atmospheres.

## Stellar Lyman-a emission lines in the Hubble Space Telescope Archive: Intrinsic Line Fluxes and Absorption from the Heliosphere and Astrospheres

Authors: B.E. Wood, S. Redfield, J.L. Linsky, Hans-Reinhard Müller, and G.P. Zank
Journal-ref: Astrophys. J. Supplement, 159, 118-140 (2005)
Report-no:
Keywords: circumstellar matter—ISM: structure—stars: chromospheres—stars: winds, outflows—ultraviolet: ISM—ultraviolet: stars

We search the Hubble Space Telescope (HST) archive for previously unanalyzed observations of stellar H I Lya emission lines, our primary purpose being to look for new detections of Lya absorption from the outer heliosphere and to also search for analogous absorption from the astrospheres surrounding the observed stars. The astrospheric absorption is of particular interest because it can be used to study solar-like stellar winds that are otherwise undetectable. We find and analyze 33 HST Lya spectra in the archive. All the spectra were taken with the E140M grating of the Space Telescope Imaging Spectrograph (STIS) instrument on board HST. The HST STIS spectra yield four new detections of heliospheric absorption (70 Oph, ? Boo, 61 Vir, and HD 165185) and seven new detections of astrospheric absorption (EV Lac, 70 Oph, ? Boo, 61 Vir, d Eri, HD 128987, and DK UMa), doubling the previous number of heliospheric and astrospheric detections. When combined with previous results, 10 of 17 lines of sight within 10 pc yield detections of astrospheric absorption. This high detection fraction implies that most of the ISM within 10 pc must be at least partially neutral, since the presence of H I within the ISM surrounding the observed star is necessary for an astrospheric detection. In contrast, the detection percentage is only 9.7% (3 out of 31) for stars beyond 10 pc. Our Lya analyses provide measurements of ISM H I and D I column densities for all 33 lines of sight, and we discuss some implications of these results. Finally, we measure chromospheric Lya fluxes from the observed stars. We use these fluxes to determine how Lya flux correlates with coronal X-ray and chromospheric Mg II emission, and we also study how Lya emission depends on stellar rotation.

## Prediction of the timing of the 2-3 kHz radio emission within the solar cycle

Authors: J.J. Mitchell, I.H. Cairns, Hans-Reinhard Müller and G.P. Zank
Journal-ref: Geophysical Research Letters 32, L07101, doi: 10.1029/2004GL021472 (2005)
Report-no:
Keywords: 7536 Solar Physics, Astrophysics, and Astronomy: Solar activity cycle (2162); 7847 Space Plasma Physics: Radiation processes.

High power radio emissions near 2–3 kHz originating in the outer heliosphere have been observed by the Voyager spacecraft. Recent theories for these emissions combine acceleration of nonthermal electrons at global merged interaction region shocks with formation of a superthermal electron tail by lower-hybrid drive associated with pick-up ions, beyond the heliopause. This paper examines the efficiency of this process during the solar cycle, based on variations of the availability of pick-up ions in the source region associated with periodic solar cycle variations in the solar wind ram pressure. It is predicted that high levels of pick-up ions are present in the source region approximately 2–3 years after solar maximum, leading to strong emissions, in close agreement with the observed timing of events: the 1983–84, 1992–93 and 2003 events were preceded by solar maxima in 1980, 1990 and 2000, respectively. These results provide further evidence for the proposed model.

## Heliospheric filtration of interstellar heavy atoms: Sensitivity to hydrogen background

Authors: Hans-Reinhard Müller and G.P. Zank
Journal-ref: J. Geophys. Res. 109, A07104, doi: 10.1029/2003JA010269 (2004)
Report-no:
Comments: 12 pages, 8 figures [JGR html]; [JGR pdf (2.5 Mb)]; [preprint (pdf, 3.0 Mb)] .
Subj-class: Heliospheric modeling; heavy interstellar atoms

Heavy elements including He, C, N, O, Ne, and Ar are present in the interstellar medium surrounding the heliosphere. They form the most important source for heavy pickup ions and anomalous cosmic rays in the heliosphere. Kinetic numerical models are used to study the entrance and the heliospheric distribution of neutrals and singly charged ions of these six heavy element species as they interact through charge exchange with the neutral and ionized hydrogen of the heliosphere. Since the interstellar hydrogen parameters are not known precisely, three different representative hydrogen heliospheric models are used to study the heavy element distribution, and the sensitivity of key results, including filtration ratios of heavy elements and increased heavy neutral densities (walls), to the different hydrogen backgrounds is established. The key neutral heavy element results are largely insensitive to the specifics of the hydrogen background. The location and extent of neutral element features depends sensitively on the hydrogen background, as do all the heavy ion results.

## The heliospheric hydrogen wall and astrospheres

Authors: B.E. Wood, Hans-Reinhard Müller, G.P. Zank, V.V. Izmodenov, and J.L. Linsky
Journal-ref: Adv. Space Res. 34, 66 - 73, doi: 10.1016/j.asr.2003.01.035 (2004)
Report-no:
Comments: 8 pages, 3 eps figures, [html].
Keywords: Heliosphere; Heliospheric hydrogen wall; Charge exchange; H I Ly alpha emission

Charge exchange processes in the outer heliosphere produce a population of hot hydrogen gas within the heliosphere, creating a "hydrogen wall" between the heliopause and bow shock. The heliospheric hydrogen wall scatters Ly photons passing through it, producing a detectable absorption signature in observations of H I Ly emission from nearby stars. This heliospheric absorption has been observed using observations from the Hubble Space Telescope (HST), and these observations have also yielded detections of analogous "astrospheric" absorption from material surrounding the observed stars. The astrospheric detections dramatize the importance of understanding the heliospheric interaction, since similar interactions exist around other stars and can now be studied with HST. We review comparisons that have been made between the observed heliospheric absorption and the predictions of various models. The astrospheric absorption provides a way to empirically estimate the mass loss rates of solar-like stars, leading to the first empirical estimates of how solar-like winds vary with stellar age and activity. Thus, we also review these astrospheric results and discuss their ramifications for solar, stellar, and planetary science.

## A search for Lyman-a emission from the astrosphere of 40 Eridani A

Authors: B.E. Wood, J.L. Linsky, Hans-Reinhard Müller, G.P. Zank
Journal-ref: Astrophys. J. 591, 1210 - 1219 (2003)
Report-no: astro-ph/03xxxxx
Keywords:

We report the results of Hubble Space Telescope (HST) observations of the nearby (d = 5.0 pc) K1 V star 40 Eri A, which we use to search for scattered Ly-alpha emission surrounding the star indicative of the interaction between the stellar wind and the ISM. Absorption from circumstellar hot H I has previously been detected around many solar-like stars in HST observations of their Ly-alpha lines, so there is potential for circumstellar Ly-alpha emission to be detectable as well. There was previously a tentative detection of absorption for 40 Eri A, but unfortunately we do not detect any circumstellar emission around 40 Eri A in our new observations. We use hydrodynamic models of the stellar "astrosphere" (i.e., the stellar wind-ISM interaction region) and radiative transfer calculations to demonstrate that emission should have been detected for assumed mass loss rates of M dot <= 2 M dot sol, assuming that the star is surrounded by warm, partially neutral ISM material like that which surrounds the Sun. In contrast, when the models are compared with the absorption data, we find consistency with the data only for M dot >= 2 M dot sol. We believe that the most likely explanation for these apparently contradictory results is that the previous tentative detection of astrospheric absorption towards 40 Eri A is erroneous, and that 40 Eri A probably lies within the hot ionized phase of the ISM. Thus, there is no interstellar HI within the astrosphere for us to detect either in absorption or emission, and no meaningful constraints on the mass loss rate of 40 Eri A can be derived from the HST data.

## The dynamical heliosphere

Authors: G.P. Zank and Hans-Reinhard Müller
Journal-ref: J. Geophys. Res. 108 (A6), 1240, doi: 10.1029/2002JA009689 (2003)
Report-no:
Comments: 15 pages, 17 figures [html]; [pdf] .
Subj-class: Heliospheric modeling; Heliopause and solar wind termination; Solar cycle variations; Interplanetary shocks

The solar cycle induces substantial changes in the solar wind, which can have an important effect on the structure of the global heliosphere. In the ecliptic, the ram pressure can vary from one cycle to the other, being greater during periods of minimum activity. We investigate the response of the heliosphere to a temporally varying solar wind. Since neutral hydrogen is a key component in determining the large-scale structure of the heliosphere, we employ a multi-fluid model in which the charge-exchange interaction between neutral hydrogen and protons is included self-consistently. The variability of the termination shock location is described and the response of the hydrogen wall to the temporal solar wind is discussed. Both two-shock and one-shock models are considered. The propagation of global shock waves analogous to those driven by global merged interactions (GMIR) is considered too for both one- and two-shock models. The global response of the heliosphere to a single GMIR disturbance can last for nearly a solar cycle (~ 9.5 years). As a result of both a variable solar cycle ram pressure and the presence of disturbances of global extent, such as GMIRs, the large-scale heliosphere is most likely highly time-dependent and dynamical.

## Measured mass-loss rates of solar-like stars as a function of age and activity

Authors: B.E. Wood, Hans-Reinhard Müller, G.P. Zank, and J.L. Linsky
Journal-ref: Astrophys. J. 574, 412 - 425 (July 20, 2002)
Report-no: BA-01-52; astro-ph/0203437
Keywords:

Collisions between the winds of solar-like stars and the local ISM result in a population of hot hydrogen gas surrounding these stars. Absorption from this hot H I can be detected in high resolution Ly alpha spectra of these stars from the Hubble Space Telescope. The amount of absorption can be used as a diagnostic for the stellar mass loss rate. We present new mass loss rate measurements derived in this fashion for four stars (epsilon Eri, 61 Cyg A, 36 Oph AB, and 40 Eri A). Combining these measurements with others, we study how mass loss varies with stellar activity. We find that for the solar-like GK dwarfs, the mass loss per unit surface area is correlated with X-ray surface flux. Fitting a power law to this relation yields \dot{M}\propto F_{x}^{1.15\pm 0.20}. The active M dwarf Proxima Cen and the very active RS CVn system lambda And appear to be inconsistent with this relation. Since activity is known to decrease with age, the above power law relation for solar-like stars suggests that mass loss decreases with time. We infer a power law relation of \dot{M}\propto t^{-2.00\pm 0.52}. This suggests that the solar wind may have been as much as 1000 times more massive in the distant past, which may have had important ramifications for the history of planetary atmospheres in our solar system, that of Mars in particular.

## Modeling the heliosphere: Influence of the magnetic fields in the presence of LISM neutral hydrogen

Authors: R. Ratkiewicz, A. Barnes, Hans-Reinhard Müller, G.P. Zank, and G.M. Webb
Journal-ref:Adv. Space Res. 29, 433-438 (2002)
Report-no:
Keywords:

Abstract pending

## The Interaction of the Solar Wind and Stellar Winds with the Partially Ionized Interstellar Medium

Authors: G.P. Zank, Hans-Reinhard Müller, and Brian E. Wood
Journal-ref: Physics of Plasmas 8, 2385 (2001)
Report-no: BA-00-XX
Comments: 21 pages, 7 figures, Word
Subj-class: Space Plasma Physics

Plasmas in the laboratory and interstellar and interplanetary space are frequently partially ionized. Thus, the solar wind and stellar winds often interact with an interplanetary medium that is an admixture of protons, electrons, other charged ions, and neutral atoms. For example, the very local interstellar medium surrounding our heliosphere may be less than 50% ionized, with the dominant constituent being neutral hydrogen (H). As a result, the composition of the solar wind in the outer heliosphere beyond some 10 - 15 AU is dominated by neutral interstellar H. Our understanding of the complex physics describing the interaction of the solar wind with the partially ionized local interstellar medium has advanced significantly in the last 5 years with the development of very sophisticated models which treat the coupling of neutral atoms and plasma self-consistently. A number of major predictions have emerged from these models, such as the existence of a large wall of heated neutral hydrogen upstream of the heliosphere. Remarkably, in the ensuing years, this prediction has been confirmed by high resolution Hubble Space Telescope Lyman-alpha spectroscopic data. Subsequent models now consider the interaction of various stellar winds with the ISM, and Hubble observations provide supporting data. An introductory review of the basic physics, and associated observations, of the interaction of the solar wind and stellar winds with the interstellar medium is presented for this exciting and rapidly developing field.

## Modeling the ISM - Stellar Wind Interactions of lambda Andromedae and epsilon Indi

Authors: Hans-Reinhard Müller, G.P. Zank, and B.E. Wood
Journal-ref: Astrophys. J. 551, 495-506 (2001)
Report-no: BA-00-33
Subj-class: hydrodynamics - stars: individual (epsilon Ind, lambda And) - stars: winds, outflows - ultraviolet: ISM

A numerical study is presented of the interaction between the partially ionized interstellar medium and the stellar wind of the very active RS CVn-type binary star lambda And (G8 IV - III+?). Similar to results found for the heliosphere/ISM interaction, a termination shock, a tangential discontinuity (the astropause''), and a bow shock are found in the model. More importantly, a hydrogen wall forms in the model, and its neutral density, temperature, and velocity are investigated. As an application, the additional absorption of the Lyman-alpha line of lambda And due to the hydrogen wall is calculated and compared to high-resolution UV spectra obtained by HST. Variation of stellar wind parameters results in different astrospheres and hydrogen walls, with distinct Ly-alpha absorption. Though not studied here, variation of interstellar parameters will alter the astrospheres as well, just like in the heliospheric case. Thus, establishing a good model fit to the HST data is a tool to constrain the combination of parameters of stellar wind and ambient interstellar medium. A second numerical study is undertaken for the nearby star epsilon Ind (K5 V). Again, a hydrogen wall is encountered, and the correction to interstellar Ly-alpha absorption demonstrated. While epsilon Ind is interesting in that it has a high relative velocity with respect to the ISM, lambda And is interesting in that it is a large, extremely active star that we therefore model with a higher mass loss rate than the Sun. The numerous assumptions that are made in the models preclude a definitive measurement of mass loss rates for these stars at this point, but our models suggest that for epsilon Ind the observed Ly-alpha absorption can be reproduced adequately by a wind with roughly the solar mass loss rate. For lambda And, a mass loss rate of roughly 10 times solar is suggested, which is actually lower than one might have expected since the star has about 55 times the surface area of the Sun.

## Observational Estimates for the Mass-Loss Rates of alpha Centauri and Proxima Centauri Using HST Ly-alpha Spectra

Authors: B.E. Wood, J.L. Linsky, Hans-Reinhard Müller, and G.P. Zank
Journal-ref: Astrophys. J. 547, L49-L52 (2001)
Report-no: BA-00-45; astro-ph/0011153
Comments: 6 pages, 3 eps figures, AASTeX 5.0 + mkfig [src (72kb), ps]; full article; references; citations.
Keywords:

We study H I Lyman-alpha absorption observed by the Hubble Space Telescope toward the nearby binary system Alpha Cen (G2 V+K0 V) and its distant companion star Proxima Cen (M5.5 Ve). Absorption from heliospheric H I heated by the solar wind/ISM interaction is observed toward both Alpha Cen and Proxima Cen. Absorption from analogous "astrospheric" material surrounding the stars is detected toward Alpha Cen, but not Proxima Cen. The nondetection of astrospheric absorption toward Proxima Cen suggests that the stellar wind of Proxima Cen must be significantly weaker than that of the Alpha Cen system. We use hydrodynamic models of the astrospheres computed assuming different mass-loss rates to predict astrospheric Lyman-alpha absorption for comparison with the observations. The model that best matches the Alpha Cen data has a mass-loss rate of twice the solar rate, and the models suggest an upper limit of 0.2 solar for Proxima Cen. Finally, we note that the heliospheric absorption observed toward Proxima Cen in 2000 May is identical to the heliospheric absorption observed toward Alpha Cen in 1995 May, implying that the structure of the outer heliosphere does not change significantly during the solar activity cycle.

## Self-consistent hybrid simulations of the interaction of the heliosphere with the local interstellar medium

Authors: Hans-Reinhard Müller, G.P. Zank, and A.S. Lipatov
Journal-ref: J. Geophys. Res. 105, 27,419 - 27,438 (2000)
Report-no: BA-99-67
Comments: 20 pages, 5 figures, 4 color plates, jgrsty [pdf]; .
Subj-class: Heliospheric modeling

A new method for investigating the interaction of the solar wind with the partially ionized local interstellar medium (LISM) is presented. The solar wind and the interstellar plasma are modeled using a two-dimensional (2-D) hydrodynamic numerical code. The plasma is coupled to the neutral hydrogen (of both interstellar and solar wind origin) via resonant charge exchange. To model the neutral H distribution, we use a nonstationary 2.5-D particle mesh method to solve the Boltzmann equation, which is coupled self-consistently to the interstellar and solar wind plasma. Numerical self-consistency is achieved by iterating the plasma and neutral H distributions between the two numerical schemes until a steady state is achieved. Results from three test applications are presented and discussed, including the first one-shock kinetic simulation. The simulations are able to reproduce the main features of the heliosphere such as shock structure, hydrogen wall, and heating, deceleration and filtration of neutral hydrogen. In addition, they enable the study and interpretation of the non-Maxwellian hydrogen distribution function. Traces of fast neutrals originating inside the termination shock and the heliosheath/heliotail region can be found far upstream of the outer heliosphere. The influence of different interstellar plasma boundary values on the heliosphere is highlighted in the comparison of two supersonic simulations and one subsonic simulation. In particular, by comparing the simulated energetic neutral atom (ENA) fluxes at 1 AU of the supersonic and subsonic models, it is found that the subsonic flux is significantly underabundant in the energy range 10 - 60 eV compared to the supersonic case. This may offer an important diagnostic for determining whether the heliosphere possesses a bow shock or not.

## Hydrogen Lyman-alpha Absorption Predictions by Boltzmann Models of the Heliosphere

Authors: B.E. Wood, Hans-Reinhard Müller, and G.P. Zank
Journal-ref: Astrophys. J. 542, 493-503 (2000)
Report-no: BA-00-22; astro-ph/0007171
Comments: 24 pages, 9 eps figures, AASTeX5.0 [Full Text, TeX src (243kb), ps (282kb)]; references; citations.
Keywords: hydrodynamics - stars: individual (epsilon Ind, lambda And) - stars: winds, outflows - ultraviolet: ISM

We use self-consistent kinetic/hydrodynamic models of the heliosphere to predict H I Lyman-alpha absorption profiles for various lines of sight through the heliosphere. These results are compared with Lyman-alpha absorption lines of six nearby stars observed by the Hubble Space Telescope. The directions of these lines of sight range from nearly upwind (36 Oph) to nearly downwind (epsilon Eri). Only three of the Lyman-alpha spectra (36 Oph, alpha Cen, and Sirius) actually show evidence for the presence of heliospheric absorption, which is blended with the ubiquitous interstellar absorption, but the other three spectra still provide useful upper limits for the amount of heliospheric absorption for those lines of sight. Most of our models use a Boltzmann particle code for the neutrals, allowing us to estimate neutral velocity distributions throughout the heliosphere, from which we compute model Lyman-alpha absorption profiles. In comparing these models with the data, we find they predict too much absorption in sidewind and downwind directions, especially when higher Mach numbers are assumed for the interstellar wind. Models created assuming different values of the interstellar temperature and proton density fail to improve the agreement. Somewhat surprisingly, a model that uses a multi-fluid treatment of the neutrals rather than the Boltzmann particle code is more consistent with the data, and we speculate as to why this may be the case.

## How to count Kinks: From the Continuum to the Lattice and Back

Authors: Marcelo Gleiser, Hans-Reinhard Müller (Dartmouth College)
Journal-ref: Phys. Lett. B 422, 69-75 (1998)
Report-no: DART-HEP-97/04; hep-lat/9704005
Comments: 6 pages, 5 eps figures, RevTeX [src (128kb), ps]; references; citations.
Subj-class: High Energy Physics - Lattice; Statistical Mechanics

We investigate the matching between (1+1)-dimensional nonlinear field theories coupled to an external stochastic environment and their lattice simulations. In particular, we focus on how to obtain numerical results which are lattice-spacing independent, and on how to extract the correct effective potential which emerges from the simulations. As an application, we study the thermal production of kink-antikink pairs, obtaining a number density of pairs which is lattice-spacing independent and the effective barrier for pair production, i.e., the effective kink mass.

## Oscillons: Resonant Configurations During Bubble Collapse

Authors: E.J. Copeland, M. Gleiser, and H.-R. Müller
Comments: 31 pages Revtex, 20 uufiles-encoded figures.
Report-no: SUSX-TH-95/3-3, Fermilab-Pub-95/021-A, DART-HEP-95/01
Journal-ref:Phys. Rev. D 52 (1995), 1920-1933

Oscillons are localized, non-singular, time-dependent, spherically-symmetric solutions of nonlinear scalar field theories which, although unstable, are extremely long-lived. We show that they naturally appear during the collapse of subcritical bubbles in models with symmetric and asymmetric double-well potentials. By a combination of analytical and numerical work we explain several of their properties, including the conditions for their existence, their longevity, and their final demise. We discuss several contexts in which we expect oscillons to be relevant. In particular, their nucleation during cosmological phase transitions may have wide-ranging consequences.

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## Contribution of Peculiar Shear Motions to Large-Scale Structure

Authors: H.-R. Müller and R. A. Treumann
Journal-ref: ApJ 427 (1994), L5-L8
Comments: 10 pages Revtex, 2 uufiles-encoded figures. [ps (100K)]; references; citations.

Self-gravitating shear flow instability simulations in a cold-dark-matter-dominated expanding Einstein-de Sitter Universe have been performed. When the shear flow speed exceeds a certain threshold, self-gravitating Kelvin-Helmholtz instability occurs forming density voids and excesses along the shear flow layer which serve as seeds for large-scale structure formation. A possible mechanism for generating shear peculiar motions are velocity fluctuations induced by the density perturbations of the post-inflation era. In this scenario, short scales grow earlier than large scales. A model of this kind may contribute to the cellular structure of the luminous mass distribution in the Universe.

# Publications in Refereed Proceedings

## Interstellar helium in the heliosphere

Authors: H.-R. Müller, M. Bzowski, E. Möbius, and G.P. Zank,
Reference: Solar Wind 13,
G.P. Zank et al. (Eds.), AIP Conference Proceedings 1539, 348-351, doi: 10.1063/1.4811058 (2013)
Keywords: interstellar matter, solar composition, solar wind

Several years of neutral measurements by NASA/IBEX-Lo have yielded detailed observations of direct interstellar neutral helium (primary particles). Prior to IBEX, interstellar helium had been observed through UV backscattering, pickup ions, and directly by Ulysses-GAS. The IBEX measurements now also provide strong indications for the presence of secondary neutral helium that is thought to originate in the outer heliosheath from charge exchange. In order to model both primary and secondary particle populations and characterize them throughout the heliosphere, a detailed calculation method based on Keplerian orbits is used, and some sample results are presented. The helium velocity distribution functions throughout the heliosphere are characterized. In the inner heliosphere they exhibit an intricate structure, in particular downwind of the Sun where the helium focusing cone resides as well.

## Direct modeling of neutral helium in the heliosphere

Author: H.-R. Müller
Reference: Proceedings of the 6th International Conference of Numerical Modeling of Space Plasma Flows (Astronum 2011),
N.V. Pogorelov, J.A. Font,E. Audit, and G.P. Zank (Eds.), ASP Conference Series 459, 228-233 (2012)
Full text links: Article [pdf]; preprint: arXiv:1205.1555
Keywords: interstellar helium, heliosphere

Several years of neutral particle measurements by the NASA/IBEX mission have yielded direct observations of interstellar neutral helium and oxygen. The data indicate the presence of secondary neutral helium and oxygen, which are created within the heliosphere by charge exchange involving helium or oxygen ions. This contribution describes a detailed conserving calculation method based on Keplerian orbits that has been developed to characterize helium distribution functions throughout the heliosphere, in particular in the innermost heliosphere, while accounting for loss and production of neutral particles along their path. Coupled with global heliosphere models of plasma distributions, this code is useful for predicting the fluxes of heavy neutral atoms at spacecraft detectors, so enabling inferences on the characteristics of the interstellar medium.

## Primary neutral helium in the heliosphere

Authors: H.-R. Müller and J.H. Cohen
Reference: Physics of the Heliosphere: A 10-year Retrospective,
J. Heerikhuisen, G. Li, N. Pogorelov, and G. Zank (Eds.), AIP Conference Proceedings 1436, 233-238 (2012)
Full text links: doi: 10.1063/1.4723613; preprint: arXiv:1205.0967
Keywords: interstellar helium, heliosphere

Two years of neutral measurements by IBEX-Lo have yielded several direct observations of interstellar neutral helium and oxygen during preferred viewing seasons. Besides the interstellar signal, there are indications of the presence of secondary neutral helium and oxygen created in the heliosphere. Detailed modeling of these particle species is necessary to connect the measured fluxes to the pristine local interstellar medium while accounting for loss and production of neutral particles during their path through the heliosphere. In this contribution, global heliosphere models are coupled to analytic calculations of neutral trajectories to obtain detailed estimates of the neutral distribution function of primary interstellar helium atoms in the heliosphere, in particular in the inner heliosphere.

## Exclusion of tiny interstellar dust grains from the heliosphere

Authors: J.D. Slavin, P.C. Frisch, J. Heerikhuisen, N.V. Pogorelov, H.-R. Müller, W.T. Reach, G.P. Zank, B. Dasgupta, and K. Avinash,
Reference: Proceedings of the SW 12 conference,
M. Maksimovic et al. (Eds.), AIP Conference Proceedings 1216, 497 (2010)
Full text links: doi: 10.1063/1.3396301; preprint: arXiv:0911.1492
Keywords: interstellar matter, interstellar magnetic fields, magnetohydrodynamics, shock waves

The distribution of interstellar dust grains (ISDG) observed in the Solar System depends on the nature of the interstellar medium-solar wind interaction. The charge of the grains couples them to the interstellar magnetic field (ISMF) resulting in some fraction of grains being excluded from the heliosphere while grains on the larger end of the size distribution, with gyroradii comparable to the size of the heliosphere, penetrate the termination shock. This results in a skewing the size distribution detected in the Solar System.

We present new calculations of grain trajectories and the resultant grain density distribution for small ISDGs propagating through the heliosphere. We make use of detailed heliosphere model results, using three-dimensional (3-D) magnetohydrodynamic/kinetic models designed to match data on the shape of the termination shock and the relative deflection of interstellar H0 and He0 flowing into the heliosphere. We find that the necessary inclination of the ISMF relative to the inflow direction results in an asymmetry in the distribution of the larger grains (0.1 mu) that penetrate the heliopause. Smaller grains (0.01 mu) are completely excluded from the Solar System at the heliopause.

## Heliospheric termination shock strength from a multi-fluid model

Authors: Hans-Reinhard Müller, L. M. Woodman, G.P. Zank,
Reference: Proceedings of the IGPP 2008 conference on Particle Acceleration and Transport in the heliosphere and beyond, G. Li et al (Eds.),
AIP conference series 1039, 384-389 (2008)
Full text links: doi: 10.1063/1.2982475; publisher (AIP) (pdf, 677k)
Comments: 6 pages, 2 figures, LaTeX.
Subj-class:

A suite of 64 global heliospheric models, for which the interstellar densities and temperatures are varied within reasonable bounds, is analyzed with respect to the location of the termination shock on and off the stagnation axis, its temperature, and its compression ratio. The empirical relations regarding the termination shock, the heliopause and the interstellar bow shock, are discussed, as are the physical reasons behind these relations.

## Modeling of heavy ions and atoms in the heliosphere

Authors: Hans-Reinhard Müller, and G.P. Zank
Reference: Proceedings of the CalSpace-IGPP 2006 conference on Numerical modeling of space plasma flows, N. Pogorelov and G. Zank (Eds.), proceedings of the Astronomical Society of the Pacific, 359, 276-281 (2006)
Comments: 6 pages, 1 figure, LaTeX [Full Text (pdf, 169k)].
Subj-class:

Interstellar hydrogen and heavier neutral atoms have access to the inner heliosphere, and they, together with secondary products after charge exchange interactions, are important messengers of the local interstellar medium and of remote heliospheric regions. This forms part of the motivation for the IBEX mission. The neutral atom populations are out of equilibrium, which warrants a kinetic modeling approach. Some of the issues of this type of modeling are detailed, including particle injection at the boundaries and improvements of particle statistics.

## Effects of variable interstellar environments on the heliosphere

Authors: Hans-Reinhard Müller, G.P. Zank, P. Faurot-Pigeon, V. Jiwariyavej, R. Mutiso, and F. Shafi
Reference: Proceedings of the IGPP-UCR 2006 conference on The physics of the inner heliosheath, AIP conference series 858, 33-38 (2006)
Comments: 6 pages, 2 figures, LaTeX [Full Text (pdf, 147k)].
Subj-class:

A suite of global heliospheric models, for which the interstellar densities and temperatures are varied within reasonable bounds, is analyzed with respect to the heliospheric morphology and the locations of heliospheric boundaries, to arrive at empirical relations and to assess the sensitivity of the heliosphere to the interstellar conditions. Additionally, the differences between the termination shock at the Voyager 1 location and on the stagnation axis are discussed.

## Interaction of Heavy Interstellar Atoms with the Heliosphere

Authors: Hans-Reinhard Müller and G.P. Zank
Reference: Proceedings of the IGPP-UCR 2004 conference on the Physics of the Outer Heliosphere, AIP conference series 719, 99 - 104 (2004)NN, NN (2004)
Comments: 6 pages, 1 figure, LaTeX [Full Text (pdf, 4.6M)].
Subj-class:

Heavy elements including He, C, N, O, Ne, and Ar are present in the interstellar medium surrounding the heliosphere. They form the most important source for heavy pickup ions and anomalous cosmic rays in the heliosphere. Kinetic numerical models are used to study the entrance and the heliospheric distribution of neutrals and singly charged ions of helium and oxygen as they interact through charge exchange with the neutral and ionized hydrogen of the heliosphere. A representative hydrogen heliospheric model is used to study the heavy element distribution, and key results such as filtration ratios and increased heavy neutral densities (walls) are discussed.

## Influence of the Interstellar Medium on the Shaping of Planetary Nebulae

Authors: Hans-Reinhard Müller, Florian Kerber, Thomas Rauch, Eva-Maria Pauli
Comments: 4 pages, 3 figures; to appear in "Asymmetric Planetary Nebulae III", M. Meixner, J. Kastner, N. Soker, B. Balick (Eds.), ASP Conf. Series 313, 292 (2004)
The interaction of the ISM with the evolution of PNe is studied for cases where there is a large relative velocity between ISM and central star, for example for high-proper motion PNe. In such cases the ISM wind already interacts strongly with the AGB wind, and extensive PN asymmetries result.

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## Interaction of planetary nebulae with the interstellar medium: A progress report

Authors: Hans-Reinhard Müller, Florian Kerber, Thomas Rauch, Eva-Maria Pauli
Comments: to appear in "Asymmetric Planetary Nebulae III", M. Meixner, J. Kastner, N. Soker, B. Balick (Eds.), ASP Conf. Series 313, 272 (2004)
Abstract Pending...

## Investigating a Possible Spectral Signature of the Wind-ISM Interaction Region of Alpha Tau

Authors: B.E. Wood, J.L. Linsky, Hans-Reinhard Müller, G.P. Zank
Journal-ref:Modelling of stellar atmospheres, IAU Symposium 210 Uppsala 2002, N.E. Piskunov, W.W. Weiss, and D.F. Gray (eds.), Volume 210, F6 (2003)
Report-no: astro-ph/0209086
Comments: 6 pages, 3 eps figures, AASTeX 5.0 [src (72kb), ps]; references; citations.
Keywords:

Ultraviolet spectra from the GHRS instrument on board the Hubble Space Telescope reveal the presence of a mysterious absorption feature in the Mg II h & k lines of the nearby (d=20.0 pc) K5 III star Alpha Tau. The narrow absorption looks like an interstellar absorption feature but it is in the wrong location based on our knowledge of the local ISM flow vector. Since the absorption is close to the rest frame of the star, it has been interpreted as being from the interaction region between Alpha Tau's massive, cool wind and the interstellar medium, i.e., Alpha Tau's "astrosphere". We compute hydrodynamic models of the Alpha Tau astrosphere in order to see if the models can reproduce the Mg II absorption feature. These models do predict that stellar wind material heated, decelerated, and compressed after passing through a termination shock a few thousand AU from the star should produce a Mg II absorption feature with about the right width at roughly the right velocity. However, our first models underestimate the Mg II column density by an order of magnitude. A much larger parameter search is necessary to see whether the observed Mg II absorption can be reproduced by acceptable changes to the adopted stellar wind and ISM properties.

## Galactic Environment of the Sun and Stars: Interstellar and Interplanetary Material

Authors: P.C. Frisch, Hans-Reinhard Müller, G. Zank and C. Lopate

Journal-ref: Phys. Lett. B 422, 69-75 (1998)
Report-no: astro-ph/0208556
Comments: 6 pages, 3 eps figures, AASTeX 5.0 [src (72kb), ps]; references; citations.
Subj-class:

Interstellar material surrounding an extrasolar planetary system interacts with the stellar wind to form the stellar astrosphere, and regulates the properties of the interplanetary medium and cosmic ray fluxes throughout the system. Advanced life and civilization developed on Earth during the time interval when the Sun was immersed in the vacuum of the Local Bubble and the heliosphere was large, and probably devoid of most anomalous and galactic cosmic rays. The Sun entered an outflow of diffuse cloud material from the Sco-Cen Association within the past several thousand years. By analogy with the Sun and solar system, the Galactic environment of an extrasolar planetary system must be a key component in understanding the distribution of systems with stable interplanetary environments, and inner planets which are shielded by stellar winds from interstellar matter (ISM), such as might be expected for stable planetary climates.

## Winds of late-type dwarf stars - observational constraints

Authors: J.L. Linsky, B.E. Wood, Hans-Reinhard Müller, and G.P. Zank
Comments: in Modelling of stellar atmospheres, N.E. Piskunov, W.W. Weiss, and D.F. Gray (eds.), IAU Volume 210, F14 (2003)

Abstract Pending ...

## Modeling heavy ions and atoms throughout the heliosphere

Authors: Hans-Reinhard Müller and G.P. Zank
Comments: Solar Wind 10, M. Velli et al. (Eds.), AIP Conference Proceedings 679, 89-92 (2003)

Abstract pending...

## Winds of late-type dwarf stars - observational constraints

Authors: J.L. Linsky, B.E. Wood, Hans-Reinhard Müller, and G.P. Zank
Comments: in Modelling of stellar atmospheres, N.E. Piskunov, W.W. Weiss, and D.F. Gray (eds.), IAU Volume 210, F14 (2003)

Abstract Pending ...

## Influence of the time-dependent heliosphere on global structure

Authors: G.P. Zank and Hans-Reinhard Müller
Comments: Solar Wind 10, M. Velli et al. (Eds.), AIP Conference Proceedings 679, 762-765 (2003)

Abstract pending...

## Mass loss rates for solar-like stars measured from Ly-a absorption

Authors: B.E. Wood, Hans-Reinhard Müller, G.P. Zank, and J.L. Linsky
Comments: Proceedings of the Twelfth Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Boulder Colo. (2001)

Abstract pending...

## Relating Models of the Heliosphere to Lyman-alpha Absorption Observed in Hubble Spectra

Authors: Hans-Reinhard Müller and B.E. Wood
Reference: Proceedings of the COSPAR Potsdam 2000 meeting, 11, 13 (2001)
Comments: 10 pages, 5 figures, LaTeX [Full Text (pdf, 322K)].
Subj-class: hydrodynamics - stars: winds, outflows - ultraviolet: ISM

We model the interaction of the solar wind with the partially ionized local ISM using a self-consistent hybrid model in which the Boltzmann equation for neutral hydrogen is solved with a kinetic particle code. The degree of external contribution to the ISM plasma pressure (e.g. due to cosmic rays or to magnetic pressure) is varied as a model parameter, resulting in a family of heliospheric models ranging from two-shock models to one-shock heliospheres (subsonic ISM). We give an overview of the neutral hydrogen distributions in these models.
The column density and temperature of the heliospheric neutral hydrogen have been observed to be large enough to produce detectable absorption signatures in Lyman-alpha spectra of nearby stars. The heliospheric models can be used to predict the amount of absorption for various lines of sight, and we compare these predictions with Lyman-alpha observations of six nearby stars obtained by the Hubble Space Telescope, sampling lines of sight ranging from nearly upwind to nearly downwind. We find that the Boltzmann models tend to predict too much absorption in sidewind and downwind directions, especially when we assume high Mach numbers for the interstellar wind.

## Modeling stellar wind interaction with the ISM: Exploring astrospheres and their Lyman-a absorption

Authors: H.-R. Müller, G.P. Zank, and B.E. Wood
Comments: The Outer Heliosphere, K. Scherer et al. (Eds.), Cospar Conference Proceedings 11, 53 (2001)

Abstract pending...

## Effect of possible interstellar environments on the heliosphere: A numerical study

Authors: Hans-Reinhard Müller, G.P. Zank, and P.C. Frisch
Comments: The Outer Heliosphere, K. Scherer et al. (Eds.), Cospar Conference Proceedings, 11, 329 (2001)

Abstract pending...

## Physics of the solar wind interaction with the local interstellar medium

Authors: G.P. Zank and Hans-Reinhard Müller
Comments: The Outer Heliosphere, K. Scherer et al. (Eds.), Cospar Conference Proceedings, 11, 3 (2001)

Abstract pending...

## The injection problem for anomalous cosmic rays

Authors: G.P. Zank, W.K.M. Rice, J.A. le Roux, J.Y. Lu, and Hans-Reinhard Müller
Comments: Acceleration and transport of energetic particles observed in the heliosphere (ACE-2000 symposium), R.A. Mewaldt, J.R. Jokipii, M.A. Lee, E. Möbius, and T.H. Zurbuchen (Eds.), AIP Conference Proceedings 528, 317-324 (2000)

Abstract pending...

## Self-consistent hybrid simulations of the interaction of the heliosphere with the local interstellar medium

Authors: H.-R. Müller and G.P. Zank
Full text links: doi: 10.1063/1.58662; journal: AIP conf. proceedings
Comments: Solar Wind Nine, S.R. Habbal, R. Esser, J.V. Hollweg, and P.A. Isenberg (Eds.), AIP Conference Proceedings 471, 819 (1999)

A hydrodynamic plasma simulation of the ionized component of the global heliosphere has been coupled to a nonstationary Boltzmann particle-mesh method which describes the neutral hydrogen present in the same region. This coupling is a numerical model of the physical charge-exchange process through which the two particle species interact. Numerical self-consistency is achieved by iterating the distributions of the two particle species between the two numerical schemes until a steady state is achieved. This approach will contribute to the understanding of the solar wind—LISM interaction.

## The interaction of heavy interstellar atoms with the heliosphere

Authors: G.P. Zank, A.S. Lipatov, and Hans-Reinhard Müller
Full text links: doi: 10.1063/1.58661; journal: AIP conf. proceedings
Comments: Solar Wind Nine, S.R. Habbal, R. Esser, J.V. Hollweg, and P.A. Isenberg (Eds.), AIP Conference Proceedings 471, 811 (1999)

It is now reasonably well understood that the interaction of neutral interstellar hydrogen (H) with the heliosphere is highly nonlinear. In particular, neutral H does not stream unimpeded into the heliosphere, experiencing instead considerable "filtration" in the region upstream of the heliopause. This leads to the formation of a hydrogen wall. A recently developed 2D Boltzmann code is used to investigate the entrance of neutral helium, oxygen, carbon, and other heavy species into the heliosphere. The role of filtration for heavy interstellar neutral atoms is described and distribution functions throughout the heliosphere are presented.

## Physics of the Solar Wind Interaction with the Local Interstellar Medium

Authors: G.P. Zank and Hans-Reinhard Müller
Journal-ref: N.N. NN, NN (2001)
Report-no:
Comments: 6 pages, 5 eps figures, Word [src (128kb), ps]; references; citations.
Subj-class: Space Plasma Physics

Plasmas in interstellar and interplanetary space are frequently partially ionized. Thus, the solar wind and stellar winds often interact with an interplanetary medium that is an admixture of protons, electrons, other charged ions, and neutral atoms. For example, the very local interstellar medium surrounding our heliosphere may be less than 50% ionized, with the dominant constituent being neutral hydrogen (H). As a result, the composition of the solar wind in the outer heliosphere beyond some 10 - 15 AU is dominated by neutral interstellar H. Our understanding of the complex physics describing the interaction of the solar wind with the partially ionized local interstellar medium has advanced significantly in the last 5 years with the development of very sophisticated models which treat the coupling of neutral atoms and plasma self-consistently. A number of major predictions have emerged from these models, such as the existence of a large wall of heated neutral hydrogen upstream of the heliosphere. Remarkably, in the ensuing years, this prediction has been confirmed by high resolution Hubble Space Telescope Lyman-alpha spectroscopic data. An introductory review of the physics, and associated observations, of the interaction of the solar wind with the interstellar medium is presented for this exciting, rapidly developing field.

## Towards Numerical and Analytical Studies of First Order Phase Transitions

Author: Hans-Reinhard Mueller
Comments: 4 pages, 4 eps figures, latex, uses sprocl.sty; to be published in Proceedings of the 1996 Texas Symposium on Relativistic Astrophysics, A. Olinto, J. Frieman and D. Schramm (eds.), World Scientific, Singapore
Report-no: DART-HEP-97/03 [src (120kb), ps] refers to, cited by
Subj-class: High Energy Physics - Lattice; Statistical Mechanics

Discrete lattice simulations of an one-dimensional phi^4 theory coupled to an external heat bath are being carried out. Great care is taken to remove the effects of lattice discreteness and finite size and to establish the correct correspondence between simulations and the desired, finite-temperature continuum limit.

# Book Chapters

## Heliospheric Variation in Response to Changing Interstellar Environments

Authors: G.P. Zank, Hans-Reinhard Müller, V. Florinski, and P.C. Frisch
Comments: "Solar Journey: The Significance of our Galactic Environment for the Heliosphere and Earth", P.C. Frisch (Ed.), pp 23-51, Springer Academic publishers, New York (2006)
Keywords: Interstellar medium; heliosphere; structure; partially ionized plasma

While unchanging on human timescales, the interstellar environment has been and will be very different from current conditions. Historically, the heliosphere and solar system have been in regions of the galaxy that were much hotter, or contained higher concentrations of neutral hydrogen, or with interstellar clouds with higher or lower speeds, than is the case today. In this chapter, we describe the response of the heliosphere to different interstellar environments, taking into account the basic physics of the coupled neutral hydrogen and plasma self-consistently.

## Effects in the inner heliosphere caused by changing conditions in the galactic environment

Authors: E. Möbius, M. Bzowski, Hans-Reinhard Müller, and P. Wurz
Comments: "Solar Journey: The Significance of our Galactic Environment for the Heliosphere and Earth", P.C. Frisch (Ed.), pp 209-258, Springer Academic publishers, New York (2006)
Keywords: neutral particles; pickup ions; energetic neutral atoms; energetic particles; heliosphere-ISM interaction; Interstellar cloud variations

Interstellar neutral gas flows through the inner heliosphere because of the Sun’s relative motion with respect to the surrounding local interstellar medium. For contemporary medium conditions, interstellar He constitutes the largest neutral gas contributor in interplanetary space at Earth’s orbit. This neutral gas is the source of a small, but noticeable population of pickup ions in the solar wind, which subsequently is injected into ion acceleration processes much more efficiently than solar wind ions. In fact, He+ has been found to be the third most abundant energetic ion species at 1 AU after H+ and He2+. During its history, the solar system must have encountered a variety of interstellar environments, including hot and dilute bubbles and much denser clouds, and will continue to do so in the future. We have studied the neutral gas and its secondary products in the in-ner heliosphere, such as pickup ions and energetic particles, for conditions that range from that of a hot bubble to dense clouds with densities up to 100 times the current value, allowing for variation in temperature and bulk flow velocity. We have used multi-fluid models of the global heliosphere and kinetic models of the He flow, to derive the spatial distribution of interstellar neutral H and He in the inner heliosphere. With this limitation the termination shock is at >8 AU, and the Earth remains in the supersonic solar wind. Except for the case when the Sun is immersed in a hot bubble with no neutral gas, interstellar He maintains its dominant role in the inner heliosphere. However, even for the highest densities, the interstellar gas generally does not yet affect the solar wind dynamically at 1 AU, except for the region of the He focusing cone on the downwind side of the interstellar flow. Because dense clouds usually are also cold, a rather narrow cone with a drastically increased density develops, which acts like a huge and stationary comet in the sense that the solar wind would be decelerated to approximately the interstellar flow speed at 1 AU. Under such conditions energetic particles generated from interstellar pickup ions would dominate the energetic particle population at least during solar minimum.

# Non-Refereed Publications

## Heliospheric response to changes in the galactic environment

Authors: Mueller, Hans; Frisch, P.C.; Florinski, V.; Zank, G.P.
Keywords: local interstellar medium, heliosphere variability

On time scales as short as several thousand years, the heliosphere is exposed to different interstellar environments, as suggested by the observation of interstellar cloud types within several hundred pc of the Sun which vary in their density, temperature, degree of ionization, and galactic velocity. In particular, the Sun was once located in the hot, ionized, low-density plasma interior of the Local Bubble, and may occasionally be battered by high-velocity interstellar shock fronts.

By means of numerical modeling, the interaction of the solar wind with a variety of partially ionized interstellar media is investigated. A range of ISM densities, relative velocities, and temperatures is considered. The resulting changed heliospheric structures and particle distributions are discussed.

## Solar cycle effects on heliospheric neutrals

Authors: Mueller, Hans; Kharchenko, V.; Zank, G.P.
Keywords: solar wind activity cycle; solar wind charge exchange X-ray emission

The numerical modeling of the self-consistent interaction of the partially ionized local interstellar medium with the solar wind yields detailed estimates of the distribution of neutral particles throughout the heliosphere. The solar wind undergoes long-term variability on the time scale of the periodic 11 year solar sunspot cycle. We study the consequences of this variability on the neutrals in the heliosphere through a time-dependent global heliospheric model, assuming an idealized 11 year solar wind variation. Charge exchange between neutral hydrogen of interstellar origin (and secondary neutrals) and solar wind heavy ions produces characteristic X-ray emission. We evaluate the time-dependent X-ray (volume) emission and present line-of-sight integrated X-ray intensity predictions. The integration will mix features from different phases in the solar cycle.

## Interaction of the Solar Wind with Interstellar Neutral Gas: a Comparison of Self-consistent Monte-Carlo and Multi-fluid Approaches

Authors: Heerikhuisen, Jacob; Zank, G.P.; Florinski, V.; Mueller, H.-R.

Abstract pending...

## Consolidation of the Physical Interstellar Medium Parameters and Neutral Gas Filtration - Coordinated Effort at ISSI

Authors: Moebius, Eberhard; Bzowski, M.; Fahr, H.-J.; Frisch, P. C.; Gangopadhyay, P.; Gloeckler, G.; Izmodenov, V.; Lallement, R.; Mueller, H.-R.; Pryor, W.; Raymond, J.; Richardson, J.; Scherer, K.; Slavin, J.; Witte, M.

Abstract pending...

## Impact of Dense Interstellar Gas Clouds on the Neutral Gas and Secondary Particle Environment in the Inner Heliosphere

Authors: Moebius, Eberhard; Bzowski, M.; Mueller, H.-R.; P., Wurz

Abstract pending...

## Inferences about the History of the Solar Wind from Stellar Wind Measurements

Authors: Wood, Brian; Mueller, H. -R.; Linsky, J. L.; Zank, G. P.

Abstract pending...

## The winds of solar-like main sequence stars

Authors: B.E. Wood, S. Redfield, J.L. Linsky, H.-R. Müller, and G.P. Zank
Comments: Proc. 13th Cool Stars workshop 5-9 July 2004, F. Favata et al. (eds) ESA Special Publications series, in press (2005)

Abstract pending...

## HST observations of heliospheric and astrospheric Ly-a absorption toward the a Cen system

Authors: B.E. Wood, J.L. Linsky, Hans-Reinhard Müller, G.P. Zank, and J.A. Valenti
Comments: IAU General Assembly, Birmingham UK, p. , (2001)

Abstract pending...

## Analytical and numerical studies of coherent field configurations

Author: Hans-Reinhard Müller
Comments: Ph.D. thesis, 100pp, Dartmouth College, Hanover NH (May 1997)

Abstract pending...

## Towards numerical and analytical studies of first order phase transitions

Author: Hans-Reinhard Müller
Comments: Proceedings of the 18th Texas Symposium on Relativistic Astrophysics, A. Olinto, J. Frieman, and D. Schramm (eds), World Scientific, Singapore (1997)

Abstract pending...

## Numerische Untersuchung zur Kelvin-Helmholtz-Instabilität mit Selbstgravitation und kosmologischer Expansion: Ein Beitrag zur Entstehung von Struktur im Universum (Numerical investigation of the Kelvin-Helmholtz instability with selfgravity and cosmological expansion: A contribution to structure formation in the universe)

Author: Hans-Reinhard Müller
Comments: (In German), 130pp, Max-Planck Institute for Extraterrestrial Physics, Garching, Germany, MPE Report no. 238, ISSN 0178-0719 (July 1992)

Abstract pending...

## Diplomarbeit (Masters Thesis)

Author: Hans-Reinhard Müller
Comments: Ludwig-Maximilians-Universität München, Germany (April 1992)

Abstract pending...