Authors: B.E. Wood, G.M. Harper, Hans Reinhard-Müller, J. Heerikhuisen and G.P. Zank
Journal-ref: Astrophys.
J.
6xx, in press (2006)
Report-no:
Comments:
[journal link ApJ65854 (subscription);
preprint link astro-ph/0610401]
Keywords: circumstellar matter — stars: individua (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.
Authors: Hans Reinhard-Müller, P.C. Frisch, V. Florinski and G.P. Zank
Journal-ref: Astrophys.
J.
647, 1491 (2006)
Report-no:
Comments: 24 pages, 9 figures, 2 tables
[journal link ApJ63185 (subscription);
preprint link astro-ph/0607600]
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.
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:
Comments: 4 pages, 3 figures, 1 table
[journal link ApJL19561 (subscription);
preprint link astro-ph/0506401]
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.
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:
Comments: 23 pages, 15 figures, 4 tables
[journal link ApJS61522 (subscription);
preprint link astro-ph/0503372]
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.
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:
Comments:
[journal link (subscription)]
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.
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.
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.
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
Comments: 20 pages, 3 eps figures, AASTeX 5.0 [src
(72kb), ps];
full
article;
references;
citations.
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.
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.
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
Comments: 6 pages, 3 eps figures, AASTeX 5.0 [src
(72kb), ps];
full
article;
references;
citations.
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.
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:
Comments:
Keywords:
Abstract pending
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.
Authors:
Hans-Reinhard
Müller,
G.P.
Zank, and
B.E.
Wood
Journal-ref: Astrophys.
J.
551, 495-506 (2001)
Report-no: BA-00-33
Comments: 24 pages, 9 eps figures, AASTeX5.0
full
article;
.
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.
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.
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.
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.
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.
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.
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.
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 et al. (Eds.),
proceedings of the Astronomical Society of the Pacific, in press NN, NN (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.
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.
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.
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.
References and citations for this submission:
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HEP (refers to
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cited by, arXiv
reformatted);
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Abstract Pending...
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.
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.
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 ...
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...
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 ...
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...
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...
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.
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...
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...
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...
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...
Authors: H.-R. Müller and G.P. Zank
Comments: Solar Wind Nine, S.R. Habbal, R. Esser, J.V. Hollweg, and P.A. Isenberg (Eds.), AIP Conference Proceedings 471, 819 (1999)
Abstract pending...
Authors: G.P. Zank, A.S. Lipatov, and Hans Reinhard-Müller
Comments: Solar Wind Nine, S.R. Habbal, R. Esser, J.V. Hollweg, and P.A. Isenberg (Eds.), AIP Conference Proceedings 471, 811 (1999)
Abstract pending...
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.
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.
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.
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.
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.
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.
Authors: Heerikhuisen, Jacob; Zank, G.P.; Florinski, V.; Mueller, H.-R.
Abstract pending...
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...
Authors: Moebius, Eberhard; Bzowski, M.; Mueller, H.-R.; P., Wurz
Abstract pending...
Authors: Wood, Brian; Mueller, H. -R.; Linsky, J. L.; Zank, G. P.
Abstract pending...
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...
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...
Author: Hans-Reinhard-Müller
Comments: Ph.D. thesis, 100pp, Dartmouth College, Hanover NH (May 1997)
Abstract pending...
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...
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...
Author: Hans-Reinhard-Müller
Comments: Ludwig-Maximilians-Universität München, Germany (April 1992)
Abstract pending...
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