Towards a Unified View of Inhomogeneous Stellar Winds in Isolated Supergiant Stars and Supergiant High Mass X-Ray Binaries

Massive stars, at least \(\sim10\) times more massive than the Sun, have two key properties that make them the main drivers of evolution of star clusters, galaxies, and the Universe as a whole. On the one hand, the outer layers of massive stars are so hot that they produce most of the ionizing ultraviolet radiation of galaxies; in fact, the first massive stars helped to re-ionize the Universe after its Dark Ages. Another important property of massive stars are the strong stellar winds and outflows they produce. This mass loss, and finally the explosion of a massive star as a supernova or a gamma-ray burst, provide a significant input of mechanical and radiative energy into the interstellar space. These two properties together make massive stars one of the most important cosmic engines: they trigger the star formation and enrich the interstellar medium with heavy elements, that ultimately leads to formation of Earth-like rocky planets and the development of complex life. The study of massive star winds is thus a truly multidisciplinary field and has a wide impact on different areas of astronomy.In recent years observational and theoretical evidences have been growing that these winds are not smooth and homogeneous as previously assumed, but rather populated by dense “clumps”. The presence of these structures dramatically affects the mass loss rates derived from the study of stellar winds. Clump properties in isolated stars are nowadays inferred mostly through indirect methods (i.e., spectroscopic observations of line profiles in various wavelength regimes, and their analysis based on tailored, inhomogeneous wind models). The limited characterization of the clump physical properties (mass, size) obtained so far have led to large uncertainties in the mass loss rates from massive stars. Such uncertainties limit our understanding of the role of massive star winds in galactic and cosmic evolution.Supergiant high mass X-ray binaries (SgXBs) are among the brightest X-ray sources in the sky. A large number of them consist of a neutron star accreting from the wind of a massive companion and producing a powerful X-ray source. The characteristics of the stellar wind together with the complex interactions between the compact object and the donor star determine the observed X-ray output from all these systems. Consequently, the use of SgXBs for studies of massive stars is only possible when the physics of the stellar winds, the compact objects, and accretion mechanisms are combined together and confronted with observations.This detailed review summarises the current knowledge on the theory and observations of winds from massive stars, as well as on observations and accretion processes in wind-fed high mass X-ray binaries. The aim is to combine in the near future all available theoretical diagnostics and observational measurements to achieve a unified picture of massive star winds in isolated objects and in binary systems.     

The evolution of massive stars

The evolution of stars with masses between 15 M ₀ and 100M ₀ is considered. Stars in this mass range lose a considerable fraction of their matter during their evolution.The treatment of convection, semi-convection and the influence of mass loss by stellar winds at different evolutionary phases are analysed as well as the adopted opacities.Evolutionary sequences computed by various groups are examined and compared with observations, and the advanced evolution of a 15M ₀ and a 25M ₀ star from zero-age main sequence (ZAMS) through iron collapse is discussed.The effect of centrifugal forces on stellar wind mass loss and the influence of rotation on evolutionary models is examined. As a consequence of the outflow of matter deeper layers show up and when the mass loss rates are large enough layers with changed composition, due to interior nuclear reactions, appear on the surface.The evolution of massive close binaries as well during the phase of mass loss by stellar wind as during the mass exchange and mass loss phase due to Roche lobe overflow is treated in detail, and the value of the parameters governing mass and angular momentum losses are discussed.The problem of the Wolf-Rayet stars, their origin and the possibilities of their production either as single stars or as massive binaries is examined.Finally, the origin of X-ray binaries is discussed and the scenario for the formation of these objects (starting from massive ZAMS close binaries, through Wolf-Rayet binaries leading to OB-stars with a compact companion after a supernova explosion) is reviewed and completed, including stellar wind mass loss.     

The Supermassive Black Hole—Galaxy Connection

The observed scaling relations imply that supermassive black holes (SMBH) and their host galaxies evolve together. Near-Eddington winds from the SMBH accretion discs explain many aspects of this connection. The wind Eddington factor \(\dot{m}\) should be in the range ～1–30. A factor \(\dot{m}\sim 1\) give black hole winds with velocities v～0.1c, observable in X-rays, just as seen in the most extreme ultrafast outflows (UFOs). Higher Eddington factors predict slower and less ionized winds, observable in the UV, as in BAL QSOs. In all cases the wind must shock against the host interstellar gas and it is plausible that these shocks should cool efficiently. There is detailed observational evidence for this in some UFOs. The wind sweeps up the interstellar gas into a thin shell and propels it outwards. For SMBH masses below a certain critical (M–σ) value, all these outflows eventually stall and fall back, as the Eddington thrust of the wind is too weak to drive the gas to large radii. But once the SMBH mass reaches the critical M–σ value the global character of the outflow changes completely. The wind shock is no longer efficiently cooled, and the resulting thermal expansion drives the interstellar gas far from the black hole, which is unlikely to grow significantly further. Simple estimates of the maximum stellar bulge mass M _b allowed by self-limited star formation show that the SMBH mass is typically about 10^?3 M _b at this point, in line with observation. The expansion-driven outflow reaches speeds v _out?1200 km?s^?1 and drives rates \(\dot{M}_{\mathrm{out}}\sim 4000~\mathrm {M}_{\odot }\,\mathrm{yr}^{-1}\) in cool (molecular) gas, giving a typical outflow mechanical energy L _mech?0.05L _Edd, where L _Edd is the Eddington luminosity of the central SMBH. This is again in line with observation. These massive outflows may be what makes galaxies become red and dead, and can have several other potentially observable effects. In particular they have the right properties to enrich the intergalactic gas with metals. Our current picture of SMBH-galaxy coevolution is still incomplete, as there is no predictive theory of how the hole accretes gas from its surroundings. Recent progress in understanding how large-scale discs of gas can partially cancel angular momentum and promote dynamical infall offers a possible way forward.     

A Self-Consistent Determination of the Temperature Profile and The Magnetic Field Geometry in Winds of Late-Type Stars

Cool giant and supergiant stars generally present low velocity winds with high mass-loss rates. Several models have been proposed to explain the acceleration process of these winds. Although dust is known to be present in these objects, the radiation pressure on these particles is uneffective in reproducing the observed physical parameters of the wind. The most promising acceleration mechanism cited in the literature is the transference of momentum and energy from Alfvén waves to the gas. Usually, these models consider the wind to be isothermal. We present a stellar wind model in which the Alfvén waves are used as the main acceleration mechanism, and determine the temperature profile by solving the energy equation taking into account both the radiative losses and the wave heating. We also determine, self-consistently, the magnetic field geometry as the result of the competition between the magnetic field and the thermal pressure gradient. As the main result, we show that the magnetic geometry presents a super-radial index in the region where the gas pressure is increasing. However, this super-radial index is greater than that observed for the solar corona.     

In-Situ CHAMP Observation of Ionosphere-Thermosphere Coupling

The coupling between the ionised plasma and the neutral thermospheric particles plays an important role for the dynamics of the upper atmosphere. Significant progress in understanding the related processes has been achieved thanks to the availability of continuous accurate measurements of thermospheric parameters like mass density and wind by high resolution accelerometers on board the satellites CHAMP and GRACE. Here we present some examples of ionosphere-thermosphere coupling where CHAMP observations contributed considerably to their interpretation. We start with the derived properties of the thermosphere at altitudes around 400 km. A new aspect is the significant control of the geomagnetic field geometry on thermospheric features. Phenomena discussed in some depths are the equatorial mass density anomaly, the cusp-related mass density enhancement and the thermospheric response to magnetospheric substorms. Here we consider both the effect on the density and on the wind. A?long predicted process is the wind-driven ionospheric F region dynamo. The high-resolution magnetic field measurements of CHAMP enabled for the first time a systematic study of that phenomenon considering longitudinal, local time, seasonal and solar flux dependences. Some open issues that require further investigations are mentioned at the end.     

X-Ray Observations of Powerful AGN Outflows

Highly ionised winds with velocities ～0.1–0.2c were first detected in X-ray spectra of non-BAL AGN a decade ago. Subsequent observations and archival searches have shown such winds to be a common feature of luminous AGN, increasing the belief that powerful ionised winds have a wider importance in galaxy feedback models. Paradoxically, for the best-quantified high velocity outflow (the luminous Seyfert PG1211+143) the wind appears too powerful to be compatible with the observed stellar bulge and black hole masses, suggesting the energy coupling of wind to bulge gas must be inefficient. A recent XMM-Newton observation of the narrow line Seyfert NGC 4051 offers an explanation of this apparent paradox, finding evidence for the fast ionised wind to lose most of its kinetic energy after shocking against the ISM. Importantly, the wind momentum is maintained through such a shock, supporting the view that a momentum-driven flow provides the critical link between black hole and stellar bulge growth implied by the observed M–σ relationship.     

The third solar wind conference: A summary

The Third Solar Wind Conference was convened from March 25 to 29,1974 at the Asilomar Conference Grounds, Pacific Grove, California. The conference consisted of nine sessions dealing with solar abundances; the history and evolution of the solar wind; the structure and dynamics of the solar wind; the structure and dynamics of the solar corona; macroscopic and microscopic properties of the solar wind; cosmic rays as a probe of the solar wind; spatial gradients; stellar winds; and interactions with objects in the solar wind. This paper summarizes the invited and contributed talks presented at the conference.Institute of Geophysics and Planetary Physics Publication Number 1354-51.     

Galactic Wind: Mass Fractionation and Cosmic Ray Acceleration

The dynamical and chemical effects of the Galactic Wind are discussed. This wind is primarily driven by the pressure gradient of the Cosmic Rays. Assuming the latter to be accelerated in the Supernova Remnants of the disk which at the same time produce the Hot Interstellar Medium, it is argued that the gas removed by the wind is enriched in the nucleosynthesis products of Supernova explosions. Therefore the moderate mass loss through this wind should still be able to remove a substantial amount of metals, opening the way for stars to produce more metals than observed in the disk, by e.g. assuming a Salpeter-type stellar initial mass function beyond a few Solar masses. The wind also allows a global, physically appealing interpretation of Cosmic Ray propagation and escape from the Galaxy. In addition the spiral structure of the disk induces periodic pressure waves in the expanding wind that become a sawtooth shock wave train at large distances which can re-accelerate “knee” particles coming from the disk sources. This new Galactic Cosmic Ray component can reach energies of a few×10¹⁸ eV and may contribute to the juncture between the particles of Galactic and extragalactic origin in the observed overall Cosmic Ray spectrum.     

A gentle process for the formation of Algols

This work is concerned with binary systems that we call ‘moderately close’. These are systems in which the primary (by which we mean the initially more massive star) fills its Roche lobe when it is on the giant branch with a deep convective envelope but before helium ignition (late case B). We find that if the mass ratio q(= M ₁/M ₂) < q _crit = 0.7 when the primary fills its Roche lobe positive feedback will lead to a rapid hydrodynamic phase of mass transfer which will probably lead to common envelope evolution and thence to either coalescence or possibly to a close binary in a planetary nebula. Although most Algols have probably filled their Roche lobes before evolving off the main-sequence we find that some could not have and are therefore ‘moderately close’. Since rapid overflow is unlikely to lead to an Algol-like system there must be some way of avoiding it. The most likely possibility is that the primary can lose sufficient mass to reduce q below q _crit before overflow begins. Ordinary mass loss rates are insufficient but evidence that enhanced mass loss does take place is provided by RS CVn systems that have inverted mass ratios but have not yet begun mass transfer. We postulate that the cause of enhanced mass loss lies in the heating of the corona by by magnetic fields maintained by an α — ω dynamo which is enhanced by tidal effects associated with corotation. In order to model the the effects of enhanced mass loss we ignore the details and adopt an empirical approach calibrating a simple formula with the RS CVn system Z Her. Using further empirical relations (deduced from detailed stellar models) that describe the evolution of red giants we have investigated the effect on a large number of systems of various initial mass ratios and periods. These are notable in that some systems can now enter a much gentler Algol-like overflow phase and others are prevented from transferring mass altogether. We have also investigated the effects of enhanced angular momentum loss induced by corotation of the wind in the strong magnetic fields and consider this in relation to observed period changes. We find that a typical ‘moderately close’ Algol-like system evolves through an RS CVn like system and then possibly a symbiotic state before becoming an Algol and then goes on through a red giant-white dwarf state which may become symbiotic before ending up as a double white dwarf system in either a close or wide orbit depending on how much mass is lost before the secondary fills its Roche lobe.     

Retrieval of a wind profile from the Galileo Probe telemetry signal

Ultrastable oscillators onboard the Galileo Probe and Orbiter will permit very accurate determinations of the frequency of the Probe's telemetry signal as the Probe descends from a pressure level of several hundred mb to a level of about 20 bars. Analysis of the time-varying frequency can provide, in principle, a unique and important definition of the vertical profile of the zonal wind speed in the Jovian atmosphere. In this paper, we develop a protocol for retrieving the zonal wind profile from the Doppler shift of the measured frequency; assess the impact of a wide range of error sources on the accuracy of the retrieved wind profile; and perform a number of simulations to illustrate our technique and to assess the likely accuracy of the retrieval.Because of unavoidably large uncertainties in the absolute frequencies of the oscillators, we use time-differenced frequencies in our analysis. Nevertheless, it is possible to recover absolute wind speeds as well as wind shears, since the Orbiter/Probe geometry changes significantly during the Probe relay link. We begin with the full relativistic Doppler shift equation. Through the use of power series expansions and a basis function representation of the wind profiles, we reduce the basic equation to a set of linear equations that can be solved with standard linear least-squares techniques.There are a very large number of instrumental and environmental factors that can introduce errors into the measured signal or to the recovery of zonal winds from the data. We provide estimates of the magnitudes of all these error sources and consider the degree to which they may be reduced by a posteriori information as well as the results of calibration tests. The most important error source is the a posteriori uncertainty in the Probe's entry longitude. The accuracy of the retrieved winds is also limited by errors in the Probe's descent velocity, as obtained from atmospheric parameters measured by several Probe experiments, and in the a posteriori knowledge of secular drifts in the oscillators' frequencies during the relay link, due, for example, to aging and radiation damage.Our simulations indicate that zonal winds may be retrieved from the Doppler data to an accuracy of several m s^-1. Therefore, it may be possible to discriminate among alternative models for the basic drive of the zonal winds, since they differ significantly in the implied zonal wind profile.     

Ion Energization and Escape on Mars and Venus

Mars and Venus do not have a global magnetic field and as a result solar wind interacts directly with their ionospheres and upper atmospheres. Neutral atoms ionized by solar UV, charge exchange and electron impact, are extracted and scavenged by solar wind providing a significant loss of planetary volatiles. There are different channels and routes through which the ionized planetary matter escapes from the planets. Processes of ion energization driven by direct solar wind forcing and their escape are intimately related. Forces responsible for ion energization in different channels are different and, correspondingly, the effectiveness of escape is also different. Classification of the energization processes and escape channels on Mars and Venus and also their variability with solar wind parameters is the main topic of our review. We will distinguish between classical pickup and ??mass-loaded?? pickup processes, energization in boundary layer and plasma sheet, polar winds on unmagnetized planets with magnetized ionospheres and enhanced escape flows from localized auroral regions in the regions filled by strong crustal magnetic fields.     

冲击风作用下大跨屋盖多模态随机风致响应研究

雷暴冲击风是一种近地面短时产生的瞬态强风,它与传统的边界层风场特征具有明显的差别,冲击风将会引起屋盖的强烈振动,甚至发生破坏.本文根据混合随机模型,详细研究了冲击风风场的数值模拟方法.应用Wood竖直风剖面方程与Holmes经验模型模拟平均风场,使用稳态高斯随机过程模拟脉动风场,模拟的风场与实际的雷暴冲击风较为一致.结合多阶模态加速度法和等效风荷载原理,详细推导了大跨屋盖随机风致响应的计算方法.结合边界层风洞试验,比较冲击风产生的表面风压特性,计算得到屋盖冲击风致动力响应时程,并研究了冲击风作用下大跨屋盖荷载风效应系数和位移风效应系数的分布特点.研究结果可作为评估大跨屋盖冲击风致响应的一种参考.     

Self-consistent Simulations of Alfv��n Wave Driven Winds from the Sun and Stars

We review our recent results of Alfvén wave-driven winds. First, we present the result of self-consistent 1D MHD simulations for solar winds from the photosphere to interplanetary region. Here, we emphasize the importance of the reflection of Alfvén waves in the density stratified corona and solar winds. We also introduce the recent Hinode observation that might detect the reflection signature of transverse (Alfvénic) waves by Fujimura and Tsuneta (Astrophys. J. 702:1443, 2009). Then, we show the results of Alfvén wave-driven winds from red giant stars. As a star evolves to the red giant branch, the properties of stellar winds drastically change from steady coronal winds to intermittent chromospheric winds. We also discuss how the stellar evolution affects the wave reflection in the stellar atmosphere and similarities and differences of accretion disk winds by MHD turbulence.     

The nonthermal energy content and gamma ray emission of starburst galaxies and clusters of galaxies

The nonthermal particle production in contemporary starburst galaxies and in galaxy clusters is estimated from the Supernova rate, the iron content, and an evaluation of the dynamical processes which characterize these objects. The primary energy derives from SN explosions of massive stars. The nonthermal energy is transformed by various secondary processes, like acceleration of particles by Supernova Remnants as well as diffusion and/or convection in galactic winds. If convection dominates, the energy spectrum of nonthermal particles will remain hard. At greater distances from the galaxy almost the entire enthalpy of thermal gas and Cosmic Rays will be converted into wind kinetic energy, implying a fatal adiabatic energy loss for the nonthermal component. If this wind is strong enough then it will end in a strong termination shock, producing a new generation of nonthermal particles which are subsequently released without significant adiabatic losses into the external medium. In clusters of galaxies this should only be the case for early type galaxies, in agreement with observations. Clusters should also accumulate their nonthermal component over their entire history and energize it by gravitational contraction. The pion decay -ray fluxes of nearby contemporary starburst galaxies is quite small. However rich clusters should be extended sources of very high energy -rays, detectable by the next generation of systems of air Cherenkov telescopes. Such observations will provide an independent empirical method to investigate these objects and their cosmological history.     

Cosima – High Resolution Time-of-Flight Secondary Ion Mass Spectrometer for the Analysis of Cometary Dust Particles onboard Rosetta

The ESA mission Rosetta, launched on March 2nd, 2004, carries an instrument suite to the comet 67P/Churyumov-Gerasimenko. The COmetary Secondary Ion Mass Anaylzer – COSIMA – is one of three cometary dust analyzing instruments onboard Rosetta. COSIMA is based on the analytic measurement method of secondary ion mass spectrometry (SIMS). The experiment’s goal is in-situ analysis of the elemental composition (and isotopic composition of key elements) of cometary grains. The chemical characterization will include the main organic components, present homologous and functional groups, as well as the mineralogical and petrographical classification of the inorganic phases. All this analysis is closely related to the chemistry and history of the early solar system. COSIMA covers a mass range from 1 to 3500 amu with a mass resolution m/Δm @ 50% of 2000 at mass 100 amu. Cometary dust is collected on special, metal covered, targets, which are handled by a target manipulation unit. Once exposed to the cometary dust environment, the collected dust grains are located on the target by a microscopic camera. A pulsed primary indium ion beam (among other entities) releases secondary ions from the dust grains. These ions, either positive or negative, are selected and accelerated by electrical fields and travel a well-defined distance through a drift tube and an ion reflector. A microsphere plate with dedicated amplifier is used to detect the ions. The arrival times of the ions are digitized, and the mass spectra of the secondary ions are calculated from these time-of-flight spectra. Through the instrument commissioning, COSIMA took the very first SIMS spectra of the targets in space. COSIMA will be the first instrument applying the SIMS technique in-situ to cometary grain analysis as Rosetta approaches the comet 67P/Churyumov-Gerasimenko, after a long journey of 10 years, in 2014.     

Effect of areal expansion and coronal heating on the solar wind

Empirical studies have shown that the solar wind speed at Earth is inversely correlated with the areal expansion rate of magnetic flux tubes near the Sun. Recent model calculations that include a self-consistent determination of the coronal temperature allow one to understand the physical basis of this relationship; they also suggest why the solar wind mass flux is relatively constant.     

Chemical and photometric evolution of elliptical galaxies

In this paper we present the new chemical-spectro-photometric models of population synthesis by Bressan, Chiosi & Fagotto (1993). The models are specifically designed for elliptical galaxies. They include the presence of dark matter and galactic winds triggered by the energy deposit from supernovae and winds of massive stars. The models are aimed at studying the UV-excess and its dependence on the metallicity, the color-magnitude relation, and the color evolution as a function of the redshift. It is shown that in order to explain the color-magnitude relation as a result of galactic winds, the energy input from massive stars is required. Supernovae alone cannot provide sufficient energy to start galactic wind before the metallicity and hence colors have got saturated. We show that the main source of the UV-excess are the old, hot HB and AGB manque stars of high metallicity present in varying percentages in the stellar content of a galaxy. Since in our model the mean and maximum metallicity are ultimately driven by the mass of the galaxy, this provides a natural explanation for the observed correlation between UV-excess and metallicity. Finally, looking at the color evolution as function of the redshift, we suggest that a sudden change occurring in the color (1550-V) at the onset of the old, hot HB and AGB manque stars of high metallicity, is a good age indicator. The detection of this feature at a certain redshift would impose firm constraints on the underlying cosmological model of the universe.     

The ARTEMIS Mission

The Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon??s Interaction with the Sun (ARTEMIS) mission is a spin-off from NASA??s Medium-class Explorer (MIDEX) mission THEMIS, a five identical micro-satellite (hereafter termed ??probe??) constellation in high altitude Earth-orbit since 17 February 2007. By repositioning two of the five THEMIS probes (P1 and P2) in coordinated, lunar equatorial orbits, at distances of ??55?C65 R _E geocentric (??1.1?C12 R _L selenocentric), ARTEMIS will perform the first systematic, two-point observations of the distant magnetotail, the solar wind, and the lunar space and planetary environment. The primary heliophysics science objectives of the mission are to study from such unprecedented vantage points and inter-probe separations how particles are accelerated at reconnection sites and shocks, and how turbulence develops and evolves in Earth??s magnetotail and in the solar wind. Additionally, the mission will determine the structure, formation, refilling, and downstream evolution of the lunar wake and explore particle acceleration processes within it. ARTEMIS??s orbits and instrumentation will also address key lunar planetary science objectives: the evolution of lunar exospheric and sputtered ions, the origin of electric fields contributing to dust charging and circulation, the structure of the lunar interior as inferred by electromagnetic sounding, and the lunar surface properties as revealed by studies of crustal magnetism. ARTEMIS is synergistic with concurrent NASA missions LRO and LADEE and the anticipated deployment of the International Lunar Network. It is expected to be a key element in the NASA Heliophysics Great Observatory and to play an important role in international plans for lunar exploration.