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Stellar winds contain enough energy to easily disrupt the parent cloud surrounding a nascent star cluster, and for this reason have been considered candidates for regulating star formation. However, direct observations suggest most wind power is lost, and Lancaster21a,b recently proposed that this is due to efficient mixing and cooling processes. Here, we simulate star formation with wind feedback in turbulent, self-gravitating clouds, extending our previous work. Our simulations cover clouds with initial surface density $10^2-10^4$ $M_{\odot} \, {\rm pc}^{-2}$, and show that star formation and residual gas dispersal is complete within 2 - 8 initial cloud free-fall times. The "Efficiently Cooled" model for stellar wind bubble evolution predicts enough energy is lost for the bubbles to become momentum-driven, we find this is satisfied in our simulations. We also find that wind energy losses from turbulent, radiative mixing layers dominate losses by "cloud leakage" over the timescales relevant for star formation. We show that the net star formation efficiency (SFE) in our simulations can be explained by theories that apply wind momentum to disperse cloud gas, allowing for highly inhomogeneous internal cloud structure. For very dense clouds, the SFE is similar to those observed in extreme star-forming environments. Finally, we find that, while self-pollution by wind material is insignificant in cloud conditions with moderate density (only $\lesssim 10^{-4}$ of the stellar mass originated in winds), our simulations with conditions more typical of a super star cluster have star particles that form with as much as 1\% of their mass in wind material., 20 pages, 5 figures, submitted to ApJL, comments welcome

Stellar winds are one of several ways that massive stars can affect the star formation process on local and galactic scales. In this paper we investigate the numerical resolution needed to inflate an energy-driven stellar wind bubble in an external medium. We find that the radius of the wind injection region, $r_{\rm inj}$, must be below a maximum value, $r_{\rm inj,max}$, in order for a bubble to be produced, but must be significantly below this value if the bubble properties are to closely agree with analytical predictions. The final bubble momentum is within 25 per cent of the value from a higher resolution reference model if $\chi = r_{\rm inj}/r_{\rm inj,max}$ = 0.1. Our work has significance for the amount of radial momentum that a wind-blown bubble can impart to the ambient medium in simulations, and thus on the relative importance of stellar wind feedback., Comment: 9 pages, 6 figures. Accepted by MNRAS

We investigate the interaction between the magnetized stellar wind plasma and the partially ionized hydrodynamic hydrogen outflow from the escaping upper atmosphere of non- or weakly magnetized hot Jupiters. We use the well-studied hot Jupiter HD 209458b as an example for similar exoplanets, assuming a negligible intrinsic magnetic moment. For this planet, the stellar wind plasma interaction forms an obstacle in the planet's upper atmosphere, in which the position of the magnetopause is determined by the condition of pressure balance between the stellar wind and the expanded atmosphere, heated by the stellar extreme ultraviolet (EUV) radiation. We show that the neutral atmospheric atoms penetrate into the region dominated by the stellar wind, where they are ionized by photo-ionization and charge exchange, and then mixed with the stellar wind flow. Using a 3D magnetohydrodynamic (MHD) model, we show that an induced magnetic field forms in front of the planetary obstacle, which appears to be much stronger compared to those produced by the solar wind interaction with Venus and Mars. Depending on the stellar wind parameters, because of the induced magnetic field, the planetary obstacle can move up to ~0.5-1 planetary radii closer to the planet. Finally, we discuss how estimations of the intrinsic magnetic moment of hot Jupiters can be inferred by coupling hydrodynamic upper planetary atmosphere and MHD stellar wind interaction models together with UV observations. In particular, we find that HD 209458b should likely have an intrinsic magnetic moment of 10-20% that of Jupiter., 8 pages, 6 figures, 2 tables, accepted to MNRAS

We report the results of spectroscopic observations and numerical modelling of the H II region IRAS 18153-1651. Our study was motivated by the discovery of an optical arc and two main-sequence stars of spectral type B1 and B3 near the centre of IRAS 18153-1651. We interpret the arc as the edge of the wind bubble (blown by the B1 star), whose brightness is enhanced by the interaction with a photoevaporation flow from a nearby molecular cloud. This interpretation implies that we deal with a unique case of a young massive star (the most massive member of a recently formed low-mass star cluster) caught just tens of thousands of years after its stellar wind has begun to blow a bubble into the surrounding dense medium. Our two-dimensional, radiation-hydrodynamics simulations of the wind bubble and the H II region around the B1 star provide a reasonable match to observations, both in terms of morphology and absolute brightness of the optical and mid-infrared emission, and verify the young age of IRAS 18153-1651. Taken together our results strongly suggest that we have revealed the first example of a wind bubble blown by a main-sequence B star., Comment: 12 pages, 10 figures, accepted for publication in MNRAS

We study the impact of stellar winds and supernovae on the multi-phase interstellar medium using three-dimensional hydrodynamical simulations carried out with FLASH. The selected galactic disc region has a size of (500 pc)$^2$ x $\pm$ 5 kpc and a gas surface density of 10 M$_{\odot}$/pc$^2$. The simulations include an external stellar potential and gas self-gravity, radiative cooling and diffuse heating, sink particles representing star clusters, stellar winds from these clusters which combine the winds from indi- vidual massive stars by following their evolution tracks, and subsequent supernova explosions. Dust and gas (self-)shielding is followed to compute the chemical state of the gas with a chemical network. We find that stellar winds can regulate star (cluster) formation. Since the winds suppress the accretion of fresh gas soon after the cluster has formed, they lead to clusters which have lower average masses (10$^2$ - 10$^{4.3}$ M$_{\odot}$) and form on shorter timescales (10$^{-3}$ - 10 Myr). In particular we find an anti-correlation of cluster mass and accretion time scale. Without winds the star clusters easily grow to larger masses for ~5 Myr until the first supernova explodes. Overall the most massive stars provide the most wind energy input, while objects beginning their evolution as B-type stars contribute most of the supernova energy input. A significant outflow from the disk (mass loading $\gtrsim$ 1 at 1 kpc) can be launched by thermal gas pressure if more than 50% of the volume near the disc mid-plane can be heated to T > 3x10$^5$ K. Stellar winds alone cannot create a hot volume-filling phase. The models which are in best agreement with observed star formation rates drive either no outflows or weak outflows., 23 pages; submitted to MNRAS

Stellar winds govern the angular momentum evolution of solar-like stars throughout their main-sequence lifetime. The efficiency of this process depends on the geometry of the star's magnetic field. There has been a rapid increase recently in the number of stars for which this geometry can be determined through spectropolarimetry. We present a computationally efficient method to determine the 3D geometry of the stellar wind and to estimate the mass loss rate and angular momentum loss rate based on these observations. Using solar magnetograms as examples, we quantify the extent to which the values obtained are affected by the limited spatial resolution of stellar observations. We find that for a typical stellar surface resolution of 20$^{\rm o}$-30$^{\rm o}$, predicted wind speeds are within 5$\%$ of the value at full resolution. Mass loss rates and angular momentum loss rates are within 5-20$\%$. In contrast, the predicted X-ray emission measures can be under-estimated by 1-2 orders of magnitude, and their rotational modulations by 10-20$\%$., Comment: 6 pages, 6 figures

Solar-like stars influence their environments through their coronal emis- sion and winds. These processes are linked through the physics of the stellar magnetic field, whose strength and geometry has now been explored for a large number of stars through spectropolarimetric observations. We have now detected trends with mass and rotation rate in the distribution of magnetic energies in different geometries and on also different length scales. This has implications both for the dynamo processes that generate the fields and also for the dynamics and evolution of the coronae and winds. Modelling of the surface driving processes on stars of various masses and rotation rates has revealed tantalising clues about the dynamics of stellar coronae and their ejecta. These new observations have also prompted a resurgence in the modelling of stellar winds, which is now uncovering the range of different interplanetary conditions that exoplanets might experience as they evolve.

While the source of the fast solar wind is known to be coronal holes, the source of the slow solar wind has remained a mystery. Long time scale trends in the composition and charge states show strong correlations between solar wind velocity and plasma parameters, yet these correlations have proved ineffective in determining the slow wind source. We take advantage of new high time resolution (12 min) measurements of solar wind composition and charge state abundances at L1 and previously identified 90 min quasiperiodic structures to probe the fundamental timescales of slow wind variability. The combination of new high temporal resolution composition measurements and the clearly identified boundaries of the periodic structures allows us to utilize these distinct solar wind parcels as tracers of slow wind origin and acceleration. We find that each 90 min (2000 Mm) parcel of slow wind has near-constant speed yet exhibits repeatable, systematic charge state and composition variations that span the entire range of statistically determined slow solar wind values. The classic composition-velocity correlations do not hold on short, approximately hourlong, time scales. Furthermore, the data demonstrate that these structures were created by magnetic reconnection. Our results impose severe new constraints on slow solar wind origin and provide new, compelling evidence that the slow wind results from the sporadic release of closed field plasma via magnetic reconnection at the boundary between open and closed flux in the Sun's atmosphere.

Observed hot Jupiter (HJ) systems exhibit a wide range of stellar spin-orbit misalignment angles. The origin of these HJs remains unclear. This paper investigates the inward migration of giant planets due to Lidov-Kozai (LK) oscillations induced by a distant (100-1000 AU) stellar companion. We conduct a large population synthesis study, including the octupole gravitational potential from the stellar companion, mutual precession of the host stellar spin axis and planet orbital axis, tidal dissipation in the planet, and stellar spin-down in the host star due to magnetic braking. We consider a range of planet masses ($0.3-5\,M_J$) and initial semi-major axes ($1-5$AU), different properties for the host star, and varying tidal dissipation strengths. The fraction of systems that result in HJs depends on planet mass and stellar type, with $f_{\rm HJ} = 1-4\%$ (depending on tidal dissipation strength) for $M_p=1\,M_J$, and larger (up to $8\%$) for more massive planets. The production efficiency of "hot Saturns" ($M_p=0.3M_J$) is much lower, because most migrating planets are tidally disrupted. We find that the fraction of systems that result in either HJ formation or tidal disruption, $f_{\rm mig} \simeq 11-14\%$ is roughly constant, having little variation with planet mass, stellar type and tidal dissipation strength. This "universal" migration fraction can be understood qualitatively from analytical migration criteria based on the properties of octupole LK oscillations. The distribution of final HJ stellar obliquities exhibits a complex dependence on the planet mass and stellar type. For $M_p = (1-3)M_J$, the distribution is always bimodal, with peaks around $30^{\circ}$ and $130^{\circ}$. The distribution for $5M_J$ planets depends on host stellar type, with a preference for low obliquities for solar-type stars, and higher obliquities for more massive ($1.4M_{\odot}$) stars., Comment: 35 pages, 26 figures, 3 tables, published in MNRAS

The interaction of the heliosphere with the local interstellar medium (LISM) results in a complicated series of boundary regions. The Voyager 1 and 2 spacecraft are exploring these distant boundaries in situ, as is the Interstellar Boundary Explorer from 1 AU, which measures energetic neutral atoms created in the distant reaches of the heliosphere and LISM. Lyman-α absorption and backscatter measurements also probe the structure and physics of the interface of the heliosphere and LISM. We survey the suite of observations, the underlying theory, and the resulting models that describe the boundary regions of the solar wind and LISM.

The interaction between the solar wind and the interstellar medium represents a collision between two plasma flows, resulting in a heliosphere with an extended tail. While the solar wind is mostly ionized material from the corona, the interstellar medium is only partially ionized. The ion and neutral populations are coupled through charge-exchange collisions that operate on length scales of tens to hundreds of astronomical units. About half the interstellar hydrogen flows into the heliosphere where it may charge-exchange with solar wind protons. This process gives rise to a nonthermal proton, known as a pickup ion, which joins the plasma. In this paper we investigate the effects of approximating the total ion distribution of the subsonic solar wind as a generalized Lorentzian, or κ distribution, using an MHD neutral code. We illustrate the effect different values of the κ parameter have on both the structure of the heliosphere and the energetic neutral atom flux at 1 AU. We find that using a κ distribution in our simulations yields levels of energetic neutral atom flux that are within a factor of about 2 or 3 over the IBEX-Hi range of energies from 0.5 to 6 keV. While the presence of a suprathermal tail in the proton distribution leads to the production of high-energy neutrals, the sharp decline in the charge-exchange cross section around 10 keV mitigates the enhanced transfer of energy from the ions to the neutrals that might otherwise be expected.

Winds of cool dwarfs are difficult to observe, with only a few M dwarfs presenting observationally-derived mass-loss rates (Mdot), which span several orders of magnitude. Close-in exoplanets are conveniently positioned in the inner regions of stellar winds and can, thus, be used to probe the otherwise-unobservable local properties of their host-stars' winds. Here, we use local stellar wind characteristics observationally-derived in the studies of atmospheric evaporation of the warm-neptune GJ436 b to derive the global characteristics of the wind of its M-dwarf host. Using an isothermal wind model, we constrain the stellar wind temperature to be in the range [0.36,0.43] MK, with Mdot=[0.5,2.5] x 10^{-15} Msyn/yr. By computing the pressure balance between the stellar wind and the interstellar medium, we derive the size of the astrophere of GJ436 to be around 25 au, significantly more compact than the heliosphere. We demonstrate in this paper that transmission spectroscopy, coupled to planetary atmospheric evaporation and stellar wind models, can be a useful tool for constraining the large-scale wind structure of planet-hosting stars. Extending our approach to future planetary systems discoveries will open new perspectives for the combined characterisation of planetary exospheres and winds of cool dwarf stars., Comment: MNRAS in press

We follow the evolution of compact binaries under the coupled effect of tides and stellar winds until the onset of Roche-lobe overflow. These binaries contain a compact object (either a black-hole, a neutron-star, or a planet) and a stellar component. We integrate the full set of tidal equations, which are based on Hut's model for tidal evolution, and we couple them with the angular momentum loss in a stellar wind. Our aim is twofold. Firstly, we wish to highlight some interesting evolutionary outcomes of the coupling. When tides are coupled with a non-massive stellar wind, one interesting outcome is that in certain types of binaries, the stellar spin tends to reach a quasi-equilibrium state, where the effect of tides and wind are counteracting each other. When tides are coupled with a massive wind, we parametrize the evolution in terms of the decoupling radius, at which the wind decouples from the star. Even for small decoupling radii this \emph{wind braking} can drive systems on the main sequence to Roche-lobe overflow that otherwise would fail to do so. Our second aim is to inspect whether simple timescale considerations are a good description of the evolution of the systems. We find that simple timescale considerations, which rely on neglecting the coupling between tides and stellar winds, do not accurately represent the true evolution of compact binaries. The outcome of the coupled evolution of the rotational and orbital elements can strongly differ from simple timescale considerations, as already pointed out by Barker & Ogilvie 2009 in the case of short-period planetary systems., 16 pages, 20 figures, accepted for publication in MNRAS

As per the recent study by the MiMeS collaboration, only about 10% of massive stars possess organized global magnetic fields, typically dipolar in nature. The competition between such magnetic fields and highly non-linear radiative forces that drive the stellar winds leads to a highly complex interaction. Such an interplay can lead to a number of observable phenomena, e.g. X-ray, wind confinement, rapid stellar spindown. However, due to its complexity, such an interaction cannot usually be modeled analytically, instead numerical modeling becomes a necessary tool. In this talk, I will discuss how numerical magnetohydrodynamic (MHD) simulations are employed to understand the nature of such magnetized massive star winds.

The well-established Type Ia remnant of Tycho's supernova (SN 1572) reveals discrepant ambient medium density estimates based on either the measured dynamics or on the X-ray emission properties. This discrepancy can potentially be solved by assuming that the supernova remnant (SNR) shock initially moved through a stellar wind bubble, but is currently evolving in the uniform interstellar medium with a relatively low density. We investigate this scenario by combining hydrodynamical simulations of the wind-loss phase and the supernova remnant evolution with a coupled X-ray emission model, which includes non-equilibrium ionization. For the explosion models we use the well-known W7 deflagration model and the delayed detonation model that was previously shown to provide good fits to the X-ray emission of Tycho's SNR. Our simulations confirm that a uniform ambient density cannot simultaneously reproduce the dynamical and X-ray emission properties of Tycho. In contrast, models that considered that the remnant was evolving in a dense, but small, wind bubble reproduce reasonably well both the measured X-ray emission spectrum and the expansion parameter of Tycho's SNR. Finally, we discuss possible mass loss scenarios in the context of single- and double-degenerate models which possible could form such a small dense wind bubble., Comment: 12 pages, 7 figures, accepted for publication in MNRAS

The structures of the protoplanetary disk have been examined under various conditions of the stellar wind and the mass distribution of the disk, by assuming that the disk is steady and geometrically thick. T Tauri stars are commonly accompanied by disks as well as the stellar wind. Therefore, the disk around a T Tauri star should be influenced by the stellar wind. The height of the geometrical surface of the disk is suppressed by the dynamical pressure of the wind but depends very weakly on the wind strength. The surface becomes slightly higher when the wind strength becomes weaker. Furthermore, the dependency on the mass distribution of the disk is also weak. As a natural result, the temperature distribution in the disk is insensitive to the wind strength and also the mass distribution of the disk. Thus, we can conclude that the temperature and the geometrical surface height of the disk under the stellar wind does not depend on either the wind properties or the mass distribution of the disk.

The dynamical processes of the interaction of slow wind beyond Red Giant phase with fast wind of central star of nebula are evaluated. The mechanism of interaction stellar wind model (ISW) is found to be responsible for producing a relatively dense shell of gas which increases in mass and radius at a constant rate. Both slow wind and superwind are assumed to be time independent and radial density is calculated at initial time to ~ 60 yrs with the fast wind velocity (v ≈ 1000 km/s). The results showed that, at the outer rim of super wind region, a small density hump appears due to the relative velocity between slow winds and central star winds, in a good agreement with the previous models. The dynamical requirements of the observed expansion of planetary nebulae can be satisfied by the mechanism of interacting stellar wind model with reasonable mass loss rate from central star.

We present new wind models for {\tau} Bo\"otis ({\tau} Boo), a hot-Jupiter-host-star whose observable magnetic cycles makes it a uniquely useful target for our goal of monitoring the temporal variability of stellar winds and their exoplanetary impacts. Using spectropolarimetric observations from May 2009 to January 2015, the most extensive information of this type yet available, to reconstruct the stellar magnetic field, we produce multiple 3D magnetohydrodynamic stellar wind models. Our results show that characteristic changes in the large-scale magnetic field as the star undergoes magnetic cycles produce changes in the wind properties, both globally and locally at the position of the orbiting planet. Whilst the mass loss rate of the star varies by only a minimal amount ($\sim$ 4 percent), the rates of angular momentum loss and associated spin-down timescales are seen to vary widely (up to $\sim$ 140 percent), findings consistent with and extending previous research. In addition, we find that temporal variation in the global wind is governed mainly by changes in total magnetic flux rather than changes in wind plasma properties. The magnetic pressure varies with time and location and dominates the stellar wind pressure at the planetary orbit. By assuming a Jovian planetary magnetic field for {\tau} Boo b, we nevertheless conclude that the planetary magnetosphere can remain stable in size for all observed stellar cycle epochs, despite significant changes in the stellar field and the resulting local space weather environment., Comment: 10 pages, 3 figures, Accepted for publication in MNRAS

Nearly all types of massive stars with radiatively driven stellar winds are X-ray sources that can be observed by the presently operating powerful X-ray telescopes. In this review I briefly address recent advances in our understanding of stellar winds obtained from X-ray observations. The winds of OB dwarfs with subtypes later than O9V may be predominantly in a hot phase, and X-ray observations offer the best window for their studies. The X-ray properties of OB supergiants are largely determined by the effects of radiative transfer in their clumped stellar winds. The recently suggested method to directly measure mass-loss rates of O stars by fitting the shapes of X-ray emission lines is considered but its validity cannot be confirmed. To obtain robust quantitative information on stellar wind parameters from X-ray spectroscopy, a multiwavelength analysis by means of stellar atmosphere models is required. Independent groups are now performing such analyses with encouraging results. Joint analyses of optical, UV, and X-ray spectra of OB supergiants yield consistent mass-loss rates. Depending on the adopted clumping parameters, the empirically derived mass-loss rates are comparable (within a factor of a few) to those predicted by standard recipes (Vink et al. 2001). All sufficiently studied O stars display variable X-ray emission that might be related to corotating interaction regions in their winds. In the latest stages of stellar evolution, single red supergiants and luminous blue variable stars do not emit observable amounts of X-rays. On the other hand, nearly all types of Wolf-Rayet (WR) stars are X-ray sources. X-ray spectroscopy allows a sensitive probe of WR wind abundances and opacities., Comment: review, to appear in the special issue of Advances in Space Research "X-ray emission from hot stars"

Along with the considerations of the effect of constraint of gravitation on the matter loss of stellar wind and the disturbances of the radiation pressure and turbulent pressure on it, by introducing the mechanism of compressible flow, the effect of promotion of the convective region in stellar outer shell on the matter loss of stellar wind is investigated. Hence a new formula of matter loss of stellar wind is established. After this and via the computation of the rate of mass loss of stellar wind in the theoretical model of 3∼5Mө stars, the following is revealed. From the main sequence up to the stage of termination of central helium-core burning, the rate of mass loss of stellar wind calculated with the new formula agrees almost completely with that given by the classical formula. But in the TP-AGB stage the stellar model calculated with the new formula of mass loss of stellar wind is not affected by luminosity and gives rise to the persistent and large matter loss of stellar wind. This rather well agrees with the results of actual observations.

The expansion of stellar wind bubbles inside evolving H ii regions is studied in spherical symmetry, with stellar wind parameters and ionizing photon rate appropriate to θ1Ori C, the main exciting source of the Orion nebula. The effects of mass loading due to embedded proplyds and thermal conduction at the edge of the hot, shocked stellar wind bubble on the expansion are investigated. The predicted X-ray luminosities and spectra of these models are calculated and compared to published observations. The models all have excess emission at higher energies compared to the observations. This emission comes from hot gas behind the stellar wind shock and its temperature depends solely on the stellar wind velocity, which for θ1Ori C is well established. Possible mechanisms for lowering the temperature of this gas are discussed.

We explore the imprints of the solar wind interaction with the local interstellar medium on spectral properties of backscattered solar Ly- α radiation. We employ a newly developed effective model for the interstellar H atom velocity distribution function in the heliosphere ( Katushkina and Izmodenov, 2011 ). The model takes into account both global effects of H atom perturbations at the heliospheric boundaries and local (i.e. within 10–20 AU from the Sun) effects of the solar ionization, charge exchange, solar gravitation and radiation pressure. Backscattered solar Ly- α profiles, intensities, line-shifts and line-widths were computed at 1 AU for the anti-solar lines-of-sight. Then the intensities, line-shifts and line-widths are compared with those calculated by using more simplified one-component and two-component hot models. The largest differences between the new model and hot models are seen in the line-width of the backscattered Ly- α profiles. The line-width is very sensitive to the kinetic properties of the H atom distribution function after passing the interaction region between the solar wind and the interstellar medium.

Venus-like interactions between stellar wind and planets can be expected to change radically when the interplanetary magnetic field (IMF) is quasiparallel to the stellar wind velocity in the frame of a planet. There should exist close-in orbits in which planets are ideally exposed to such (quasi)parallel stellar winds. The abundance of close-in exoplanets make it likely that exoplanets in such orbits exist. We study how the Venus-like interaction between a supersonic stellar wind and a terrestrial exoplanet with atmosphere but no intrinsic magnetic field orbiting a Sun-like star at 0.2 AU, depends on the IMF-stellar wind angle. We extend an earlier study by adding simulations for the very lowest IMF-stellar wind angles. For this we use a hybrid simulation code, A.I.K.E.F., that models ions as macroparticles and electrons as a massless, charge-neutralizing adiabatic fluid. We find that as the IMF becomes closer and closer to parallel to the stellar wind, the lack of shielding stellar wind-induced magnetic fields leads to the collapse of the magnetosheath and dayside bow shock and stellar wind impacting the atmosphere in bulk, opening up for extensive direct interaction between stellar wind and atmosphere, e.g. ENA production, energy deposition and atmospheric erosion. Combined with an observed order-of-magnitude decrease in the rate of ionospheric ions being lost to the stellar wind, the result may prove relevant for atmospheric evolution. Model shortcomings potentially weaken the conclusions that can be drawn from the most extreme case, the perfectly parallel interaction (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Interaction of the solar wind with the interstellar medium leads to the formation of the heliosphere and termination shock. This article addresses three aspects of the plasma and magnetic field on two sides of the heliopause: (1) The interstellar magnetic field surrounding the heliopause. In the limit of very low plasma β-ratio an analytical solution is obtained for the 3D interstellar magnetic field by means of a line dipole method. The undisturbed magnetic field in the upstream is allowed to have an arbitrary inclination angle. The solution describes the heliosphere as having a blunt-nosed geometry on the upwind side and approaching a cylindrical geometry on the downwind side. The distortion of the magnetic field can penetrate very deep into the interstellar space. (2) Interaction of the interstellar neutral hydrogen with the global solar wind. The ionization process leads to removal of interstellar neutral hydrogen in the heliosphere: on the upwind side, 90% of hydrogen depletion occurs inside 60 AU, the hydrogen density changes rapidly inside 10 AU. A hydrogen cavity forms inside ∼4 AU; the cavity extends on the downwind side to form a long cavity wake. Outside the cavity and cavity wake, pickup protons are produced, they cause deceleration and heating of the solar wind. The wind speed and temperature also increase steadily with heliolatitude caused by the latitudinal increase in wind speed at the inner boundary. (3) The global geometry of the termination shock. The termination shock has been treated as having a closed geometry in previous heliosphere models. This study presents a new perspective that the global termination shock may have a bow-shaped open geometry. The termination shock forms on the upwind side because the forward motion of the supersonic solar wind is blocked at the blunt-nosed heliopause. However, the heliopause likely to be open on the downwind side; the motion of the supersonic solar wind is unobstructed for shock formation. Thus, the global termination shock likely has an open geometry. On the upwind side the shock flares out and weakens from the nose to its flanks. Eventually, the shock asymptotically reduces to a Mach wave. The supersonic solar wind remains shock free in the heliotail.

Determining the source at the Sun of the slow solar wind is one of the major unsolved problems in solar and heliospheric physics. First, we review the existing theories for the slow wind and argue that they have difficulty accounting for both the observed composition of the wind and its large angular extent. A new theory in which the slow wind originates from the continuous opening and closing of narrow open field corridors, the S-Web model, is described. Support for the S-Web model is derived from MHD solutions for the quasisteady corona and wind during the time of the August 1, 2008 eclipse. Additionally, we perform fully dynamic numerical simulations of the corona and heliosphere in order to test the S-Web model as well as the interchange model proposed by Fisk and co-workers. We discuss the implications of our simulations for the competing theories and for understanding the corona - heliosphere connection, in general.

We analyse the behaviour of the stellar winds of evolved stars and the outcome of Type Ia supernova (SN) explosions in a relativistic bubble driven by active galactic nuclei (AGNs). We find that the expansion of wind shells is efficiently decelerated by the relativistic pressure; however, their bulk motion is preserved, so they cross the bubble together with the parent star. The wind material occupies a small fraction of the bubble volume and does not substantially affect the expansion of SN remnants. The estimated maximal radius of a SN remnant in the bubble is 30–40 pc, if the envelope keeps its integrity and remains spherical. A fragmentation of the SN shell as a result of Rayleigh–Taylor instability can alleviate the propagation of the SN material so the ejecta fragments are able to cross the relativistic bubble. Outside the bubble, wind shells and SN fragments are decelerated in the intracluster medium at close range off the bubble boundary. The deposited SNe Ia material can enrich the intracluster gas with metals in a thin layer at the boundary of the relativistic bubble. This process may lead to a rim of enhanced line emission. In contrast, when the fragmentation of the SN remnant is moderate or absent, the SNe Ia matter is advected by the relativistic plasma and may leave the central region of the bright cluster galaxy together with buoyantly moving bubbles.

Alfven waves have been invoked as an important mechanism of particle acceleration in stellar winds of cool stars. After their identification in the solar wind they started to be studied in winds of stars located in different regions of the HR diagram. We discuss here some characteristics of these waves and we present a direct application in the acceleration of late-type stellar winds., Comment: Accepted for publication in Advances in Space Research. Presented at the World Space Environment Forum 2007, Egypt. 9 pages, 2 figures

The Wolf–Rayet (WR) stars are hot luminous objects which are suffering an extreme mass loss via a continuous stellar wind. The high values of mass loss rates and high terminal velocities of the WR stellar winds constitute a challenge to the theories of radiation driven winds. Several authors incorporated magnetic forces to the line driven mechanism in order to explain these characteristics of the wind. Observations indicate that the WR stellar winds may reach, at the photosphere, velocities of the order of the terminal values, which means that an important part of the wind acceleration occurs at the optically thick region. The aim of this study is to analyze a model in which the wind in a WR star begins to be accelerated in the optically thick part of the wind. We used as initial conditions stellar parameters taken from the literature and solved the energy, mass and momentum equations. We demonstrate that the acceleration only by radiative forces is prevented by the general behavior of the opacities. Combining radiative forces plus a flux of Alfven waves, we found in the simulations a fast drop in the wind density profile which strongly reduces the extension of the optically thick region and the wind becomes optically thin too close its base. The understanding how the WR wind initiate is still an open issue.

This paper studies the global solar wind between 1 AU and the termination shock, taking into account the highly latitude dependent solar wind at the 1 AU boundary and the ionization of interstellar neutral hydrogen. A system of two-fluid magnetohydrodynamics equations governs the flow of solar wind plasma; the conditions of the solar wind at 1 AU are generated from Ulysses data for the relatively stable state of the wind during the declining phase and solar minimum of the solar cycle. A one-fluid model is used to describe the flow of neutral hydrogen and its condition in the far-field boundary outside the termination shock. Simultaneous solutions are obtained using a high-resolution computational code for the two equation systems coupled by the ionization of neutral hydrogen. The ionization process leads to removal of neutral hydrogen in the heliosphere: a hydrogen cavity forms inside ~4 AU; the cavity extends on the downwind side to form a long cavity wake. Solutions show how the ionization process and the wind condition at 1 AU boundary affect the spatial variation of the wind speed, temperature, pickup proton, fast Mach number, and plasma β-ratio. The wind properties inside 4 AU are axisymmetrical about the solar rotation axis; this axi-symmetry totally disappears in the outer heliosphere. All wind properties are substantially modified at an increasing heliocentric distance on the upwind side to generate an upwind-downwind asymmetry dictated by the direction of the relative motion between the Sun and the interstellar medium.

Conventionally, long GRBs are thought to be caused by the core collapses of massive stars. During the lifetime of a massive star, a stellar wind bubble environment should be produced. Furthermore, the microphysics shock parameters may vary along with the evolution of the fireball. Here we investigate the variation of the microphysics shock parameters under the condition of wind bubble environment, and allow the microphysics shock parameters to be discontinuous at shocks in the ambient medium. It is found that our model can acceptably reproduce the rebrightenings observed in GRB afterglows, at least in some cases. The effects of various model parameters on rebrightenings are investigated. The rebrightenings observed in both the R-band and X-ray afterglow light curves of GRB 060206, GRB 070311 and GRB 071010A are reproduced in this model.

We present the prompt BAT and afterglow XRT data of Swift-discovered GRB081109A up to ~ 5\times 10^5 sec after the trigger, and the early ground-based optical follow-ups. The temporal and spectral indices of the X-ray afterglow emission change remarkably. We interpret this as the GRB jet first traversing the freely expanding supersonic stellar wind of the progenitor with density varying as $\rho \propto r^{-2}$. Then after approximately 300 sec the jet traverses into a region of apparent constant density similar to that expected in the stalled-wind region of a stellar wind bubble or the interstellar medium (ISM). The optical afterglow data are generally consistent with such a scenario. Our best numerical model has a wind density parameter {$A_{*} \sim 0.02$, a density of the stalled wind $n\sim 0.12 {\rm cm}^{-3}$, and a transition radius $ \sim 4.5 \times 10^{17}$ cm}. Such a transition radius is smaller than that predicted by numerical simulations of the stellar wind bubbles and may be due to a rapidly evolving wind of the progenitor close to the time of its core-collapse.

The solar system galactic frontier—the region where the expanding solar wind meets the surrounding galactic medium—remains poorly explored. The sheer size of the essentially asymmetric heliosphere calls for remote techniques to probe the properties of its global time-varying three-dimensional boundary. The Interstellar Boundary Explorer (IBEX) mission (launch in 2008) will image the region between the termination shock and the heliopause, the heliospheric sheath, in fluxes of energetic neutral atoms. Global imaging in extreme ultraviolet (EUV) will likely be the next logical step in remote exploration of the galactic frontier from 1 AU. Imaging in EUV will establish directional and spectral properties of (1) the glow of singly charged helium ( He + ) ions in the interstellar and solar wind plasmas; (2) emissions of hot plasma in the Local Bubble; and (3) characteristic emissions of the solar wind. Global imaging with ultrahigh sensitivity and ultrahigh spectral resolution will map the heliopause and reveal the three-dimensional flow pattern of the solar wind, including the flow over the Sun's poles. This article presents the emerging concept of the experiment and space mission for heliosphere global imaging in EUV.

Context. The ionized solar wind interacts directly with the interstellar neutrals which flow into the heliosphere. These neutrals are ionized, mainly by charge exchange, then accelerated to the solar wind speed with the momentum and energy removed from the bulk flow of the solar wind. Thus, by measuring the solar wind slowdown, one can estimate the interstellar neutral density. Aims. In July 2005, Ulysses at 5 AU and Voyager 2 near 80 AU were at the same heliolatitude. We use this alignment to determine the solar wind speed decrease between these two spacecraft. Methods. Ulysses data are used as input to a 1-D MHD model which includes the effects of pickup ions. We removed a section of data contaminated by an ICME directed toward Voyager 2. Results. Comparison of the Voyager 2 speeds with the model results shows that the solar wind speed decreased by 67 km s −1 between Ulysses and Voyager 2, consistent with an interstellar neutral density at the termination shock of 0.09 cm −3 .

Massive stars with strong stellar winds are expected to have a huge impact on their interstellar surroundings, an effect which, in a surprisingly large number of cases, is not observed. This work is part of a concerted effort to obtain a better and more homogeneous observational data base with which to test the predictions of theoretical models. Analysis of the interstellar medium around the Of star HD 229196 shows that it coincides (in projection) with a region of lower radio continuum emission. This suggests that the star has shaped the surrounding interstellar medium via its ionizing flux and stellar wind. However, we find no clear evidence of the star's action in atomic hydrogen images. The radio continuum morphology and absence of a clear expanding H i shell are consistent with the possibility that the star, which is travelling supersonically at ∼30 km s-1 with respect to its local interstellar medium, is creating a weak bow shock. We cannot however rule out the possibility that the observed asymmetry is due to an inhomogeneous interstellar density distribution. We use data from the Canadian Galactic Plane Survey to carry out this study., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

We present solutions for the structure and evolution of bubbles created by slow stellar winds, during their fully and partially radiative phases. Exact limiting forms are derived for the partially radiative case, and the transition between the two phases is analysed under the assumption of steady spherical flow. We compute the factor by which the bubble's radial momentum is amplified relative to that of the wind, and provide accurate formulae for its expansion across the fully-to-partially radiative transition. Our results will be useful in the study of protostellar outflow cocoons and bubbles driven by mass-loaded winds from star clusters.

A solar wind parcel evolves as it moves outward, interacting with the solar wind plasma ahead of and behind it and with the interstellar neutrals. This structure varies over a solar cycle as the latitudinal speed profile and current sheet tilt change. We model the evolution of the solar wind with distance, using inner heliosphere data to predict plasma parameters at Voyager. The shocks which pass Voyager 2 often have different structure than expected; changes in the plasma and/or magnetic field do not always occur simultaneously. We use the recent latitudinal alignment of Ulysses and Voyager 2 to determine the solar wind slowdown due to interstellar neutrals at 80 AU and estimate the interstellar neutral density. We use Voyager data to predict the termination shock motion and location as a function of time.

An overview is presented of magnetic-field-related effects in the solar wind (SW) interaction with the local interstellar medium (LISM) and the different theoretical approaches used in their investigation. We discuss the possibility that the interstellar magnetic field (ISMF) introduces north–south and east–west asymmetries of the heliosphere, which might explain observational data obtained by the Voyager 1 and Voyager 2 spacecraft. The SW–LISM interaction parameters that are responsible for the deflection of the interstellar neutral hydrogen flow from the direction of propagation of neutral helium in the inner heliosheath are outlined. The possibility of a strong ISMF, which increases the heliospheric asymmetry and the H–He flow deflection, is discussed. The effect of the combination of a slow-fast solar wind during solar minimum over the Sun’s 11-year activity cycle is illustrated. The consequences of a tilt between the Sun’s magnetic and rotational axes are analyzed. Band-like areas of an increased magnetic field distribution in the outer heliosheath are sought in order to discover regions of possible 2–3 kHz radio emission.

We show that energetic ions, appearing in plasmas due to injection of charge-exchange-induced new ions into the magnetized plasma background, flow due to their freely convertible energy drive turbulences of Alfvenic and magneto-acoustic types. This becomes important especially under conditions of strongly charge-exchanging fluids with supersonic differential bulk velocities, as is the condition in the inner heliosphere. These ion-driven waves lead to strongly enhanced fluctuation amplitudes. As a consequence, both low- and high-energy ion populations can partly reabsorb these wave energies, and thereby experience non-thermal heatings. As a quantitative example, we calculate the non-adiabatic behaviours of solar wind ions and pick-up ions expanding with the solar wind towards large solar distances. While pick-up ions behave nearly isothermal, normal solar wind ions behave pseudo-polytropically with negative effective polytropic indices that describe temperature increases at diverging plasma flows....

A model for a nebula exposed to the radiation and stellar wind from the central star has been examined. T Tauri stars commonly have disks and stellar wind, though we have no theoretical model on nebular thermal structure under the wind. The aims of this paper are to propose a theoretical nebula model, and to perform mathematical analysis on the geometrical structure and temperature distribution of a passive nebula. Its geometrical surface is determined by the dynamical pressure of the stellar wind. The nebular surface is assumed to be a black body surface, heated by the incident stellar photon flux. We obtain temperature from the equation of energy balance between the stellar radiation upon this nebular surface and the black body radiation from it. The temperature distribution in passive disks is insensitive to the wind strength and is almost identical even if the wind strength changes by five orders of magnitude. The nebula temperature is not expressed by a simple power law function of the distance from the central star. This is an important difference between our results and those of previous works. Since the nebula surrounding a T Tauri star is influenced by stellar wind, our model may be more appropriate than any other simple single power law temperature for passive protoplanetary nebulae.

International audience; Radio emission from extrasolar giant planets in close orbits around their host star is an active field of research, including both observational efforts and theoretical work aiming at reasonable predictions for different target planets. So far, most theoretical work assumed a distance-independent, constant stellar wind velocity. This approach is improved and expanded in two respects: first, from stellar wind models, it is known that at close distances the stellar wind is still slow and has not yet reached the velocity it has at larger distances. For this reason, less energy is available for the generation of planetary radio emission than predicted by simplified models. This correspondingly reduces the intensity of stellar wind-driven planetary radio emission, which is calculated taking into account the stellar age. Second, it can be shown that under certain conditions the steady stellar wind has to be replaced by stellar coronal mass ejections. In those cases, the planetary radio flux is strongly increased. The different flux levels expected for planets subject to different stellar wind conditions are analyzed and compared. In addition, different uncertainties in this radio flux estimation are calculated and discussed.

Fast (>700 km s−1) and slow (~400 km s−1) winds stream from the Sun, permeate the heliosphere and influence the near-Earth environment. While the fast wind is known to emanate primarily from polar coronal holes, the source of the slow wind remains unknown. Here we identify possible sites of origin using a slow solar wind source map of the entire Sun, which we construct from specially designed, full-disk observations from the Hinode satellite, and a magnetic field model. Our map provides a full-Sun observation that combines three key ingredients for identifying the sources: velocity, plasma composition and magnetic topology and shows them as solar wind composition plasma outflowing on open magnetic field lines. The area coverage of the identified sources is large enough that the sum of their mass contributions can explain a significant fraction of the mass loss rate of the solar wind., Both fast and slow solar winds emanate from our Sun, although the source of the slow component remains elusive. Towards identifying this, Brooks et al. present full-Sun spectral images from Hinode, combined with magnetic modelling, to produce a solar wind source map.

Exposure to the solar wind can have significant long term consequences for planetary atmospheres, especially for planets such as Mars that are not protected by global magnetospheres. Estimating the effects of solar wind exposure requires knowledge of the history of the solar wind. Much of what we know about the Sun’s past behavior is based on inferences from observations of young solar-like stars. Stellar analogs of the weak solar wind cannot be detected directly, but the interaction regions between these winds and the interstellar medium have been detected and used to estimate wind properties. I here review these observations, with emphasis on what they suggest about the history of the solar wind.

The ionization of hydrogen atoms that penetrate into the heliosphere from the interstellar medium gives rise to a peculiar population of energetic protons (interstellar pickup protons) in the solar wind. The short-wavelength Alfvenic turbulence in the outer heliosphere is entirely attributable to the source associated with the instability of the initial anisotropic pickup proton velocity distribution. The bulk of the generated turbulent energy is subsequently absorbed by the pickup protons themselves through the cyclotron-resonance particle-wave interaction, and only an insignificant fraction of this energy can be transferred to the solar wind protons and heat them up.

Small-scale Alfvturbulence in the outer helio- sphere is mainly determined by a source which is connected with the instability of the initially highly anisotropic velocity distribution of interstellar pick-up protons. The main portion of the generated turbulent energy is subsequently absorbed by the pick-up protons themselves due to the cyclotron- resonant interaction between waves and particles. A small fraction of this energy can be transferred to solar wind pro- tons resulting in their heating. The heating is more efficient in the high-speed solar wind.

We report the discovery of two new second-quadrant supernova remnants, G96.0+2.0 and G113.0+0.2, in the data of the Canadian Galactic Plane Survey. The two SNRs are residents of the Perseus spiral arm at distances of 4.0 kpc and 3.1 kpc, respectively. The distances were determined kinematically by associating the objects with neutral hydrogen and molecular material. G96.0+2.0 is most likely located at the edge of a large stellar wind bubble with a systemic velocity of about −44 km s −1 . It consists of a relatively bright shell where the shock is encountering the wall of H i and slowly fades away towards the interior of the stellar wind bubble. The visible part of the remnant has a diameter of about 30 pc and a radio spectral index of α ≈− 0.66 (S ∼ ν α ), indicating that it is a shell-type remnant in an early stage of development. The SNR is most likely the remnant of a type Ib/c supernova explosion. G113.0+0.2 is located in an area of confusing thermal emission not far from the radio-bright supernova remnant Cassiopeia A. It has an unusual elongated structure consisting of a long polarized filament and a more complex head structure that is interacting with a small molecular cloud; it resides in a butterfly-shaped H i cavity, probably a stellar wind bubble. It is about 36 pc long and 15 pc wide at a position angle of 70 ◦ with the Galactic Plane. A pulsar with a relatively low period derivative, giving it a characteristic age of 10 million years, is located close to the centre of the radio continuum emission at a Perseus arm distance. Whether the pulsar is the result of the same supernova explosion that created G113.0+0.2 or if it was left behind by an earlier supernova that also shaped the stellar wind bubble remains uncertain.

Magnetized giant exoplanets in close orbits around their host star are expected to be strong nonthermal radio emitters. The anticipated radio flux is strong enough to allow its detection on Earth using the next generation of instruments. However, the measured quantity will not be the planetary radio flux but the sum of planetary and stellar emission. We compare the expected stellar and planetary radio signal for stellar systems of different ages. Solar-like stellar wind parameters as well as conditions corresponding to the young solar system (i.e. with increased stellar wind density and velocity) are considered. For young stellar systems, conditions appear to be more favorable than for older stellar systems. It is shown that configurations exist where the separation of the planetary signal from the stellar emission seems feasible.

Close-in extrasolar planets of Sun-like stars are exposed to stellar wind conditions that differ considerably from those for planets in the solar system. Unfortunately, these stellar winds belong to the still unknown parameters of these planetary systems. On the other hand, they play a crucial role in a number of star-planet interaction processes that may lead to observable radiation events. In order to lay a foundation for the investigation of such interaction processes, we estimate stellar wind parameters on the basis of the solar wind model by Weber & Davis and study the implications of the stellar magnetic fields. Our results suggest that in contrast to the solar system planets, some close-in extrasolar planets may be obstacles in a sub- Alfvenic stellar wind flow. In this case, the stellar wind magnetic pressure is comparable to or even larger than the dynamic flow pressure. We discuss possible consequences of these findings for the wind-exoplanet interactions. Further, we derive upper limit estimates for the energies such stellar winds can deposit in the exoplanetary magnetospheres. We finally discuss the implications the sub-Alfvenic environment may have on the star-planet interaction.

The solar wind is a high Reynolds’ number plasma flow of solar origin that permeates the whole heliosphere. It is also the only accessible medium in which to study collisionless magnetohydrodynamic turbulence performing direct measurements. This represents a topic of fundamental importance to both plasma physics and astrophysics. During the past decades, in situ observations on the ecliptic and at high heliographic latitudes have been very valuable to shed some light on the intricate nature of space plasma turbulence. In this brief review, we will mainly describe the evolution experienced by the turbulence as the solar wind expands into the interplanetary space. We will also address implications due to different processes of local generation of turbulence which might be at work on the ecliptic and at high latitude. Moreover, the fact that solar wind fluctuations are not isotropic and poorly single scale-invariant, two of the fundamental hypotheses at the basis of Kolmogorov’s theory (K41), will give us the possibility to discuss also the relevance of intermittency in the study of space plasma turbulence.

We present results of a new time-dependent kinetic model of the H atom penetration through the solar wind - interstellar medium interaction region. A kinetic 6D (time, two dimensions in space, and three dimensions in velocity-space) equation for interstellar H atoms was solved self-consistently with time-dependent Euler equations for the solar wind and interstellar charged components. We study the response of the interaction region to 11-year solar cycle variations of the solar wind dynamic pressure. It is shown that the termination shock location varies within ±7 AU, the heliopause variation is ∼ 4A U, and the bow shock variation is negligible. At large heliocentric distances, the solar cycle induces 10-12% fluctuations in the number density of both primary and secondary interstellar H atoms and atoms created in the inner heliosheath. We underline the kinetic behavior of the fluctuations of the H atom populations. Closer to the Sun the fluctuations increase up to 30-35% at 5 AU due to solar cycle variation of the charge exchange rate. Solar cycle variations of interstellar H atoms in the heliospheric interface and within the heliosphere may have major importance for the interpretation of H atom observations inside the heliosphere.

A number of features are detected outside the nebula NGC 6888, within 1.2° (30 pc) of the star WR 136, which can be explained in a two-phase stellar-wind model. These include regions with fine filamentary gas structure that do not contain sources of stellar wind, extended radial “streams,” ultra-compact HII regions with high-velocity gas motions, and high-velocity gas motions outside the envelope of NGC 6888. The two-phase wind consists of a rarefied component and dense compact condensations, or “bullets.” The bullets generate cylindrical shocks in the interstellar gas, resulting in the presence of high-velocity gas up 20–30 pc from the star, outside the cavity formed by the rarified component of the wind.