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How has the solar wind evolved to reach what it is today? In this review, I discuss the long-term evolution of the solar wind, including the evolution of observed properties that are intimately linked to the solar wind: rotation, magnetism and activity. Given that we cannot access data from the solar wind 4 billion years ago, this review relies on stellar data, in an effort to better place the Sun and the solar wind in a stellar context. I overview some clever detection methods of winds of solar-like stars, and derive from these an observed evolutionary sequence of solar wind mass-loss rates. I then link these observational properties (including, rotation, magnetism and activity) with stellar wind models. I conclude this review then by discussing implications of the evolution of the solar wind on the evolving Earth and other solar system planets. I argue that studying exoplanetary systems could open up new avenues for progress to be made in our understanding of the evolution of the solar wind.

The presence of an atmosphere over sufficiently long timescales is widely perceived as one of the most prominent criteria associated with planetary surface habitability. We address the crucial question of whether the seven Earth-sized planets transiting the recently discovered ultracool dwarf star TRAPPIST-1 are capable of retaining their atmospheres. To this effect, we carry out numerical simulations to characterize the stellar wind of TRAPPIST-1 and the atmospheric ion escape rates for all of the seven planets. We also estimate the escape rates analytically and demonstrate that they are in good agreement with the numerical results. We conclude that the outer planets of the TRAPPIST-1 system are capable of retaining their atmospheres over billion-year timescales. The consequences arising from our results are also explored in the context of abiogenesis, biodiversity, and searches for future exoplanets. In light of the many unknowns and assumptions involved, we recommend that these conclusions must be interpreted with due caution.

FEEDBACK is a SOFIA (Stratospheric Observatory for Infrared Astronomy) legacy program dedicated to study the interaction of massive stars with their environment. It performs a survey of 11 galactic high mass star-forming regions in the 158 m (1.9 THz) line of [C ii] and the 63 m (4.7 THz) line of [O i]. We employ the 14 pixel Low Frequency Array and 7 pixel High Frequency Array upGREAT heterodyne instrument to spectrally resolve (0.24 MHz) these far-infrared fine structure lines. With a total observing time of 96h, we will cover ∼6700 arcmin2 at 14 1) angular resolution for the [C ii] line and 6 3 for the [O i] line. The observations started in spring 2019 (Cycle 7). Our aim is to understand the dynamics in regions dominated by different feedback processes from massive stars such as stellar winds, thermal expansion, and radiation pressure, and to quantify the mechanical energy injection and radiative heating efficiency. This is an important science topic because feedback of massive stars on their environment regulates the physical conditions and sets the emission characteristics in the interstellar medium (ISM), influences the star formation activity through molecular cloud dissolution and compression processes, and drives the evolution of the ISM in galaxies. The [C ii] line provides the kinematics of the gas and is one of the dominant cooling lines of gas for low to moderate densities and UV fields. The [O i] line traces warm and high-density gas, excited in photodissociations regions with a strong UV field or by shocks. The source sample spans a broad range in stellar characteristics from single OB stars, to small groups of O stars, to rich young stellar clusters, to ministarburst complexes. It contains well-known targets such as Aquila, the Cygnus X region, M16, M17, NGC7538, NGC6334, Vela, and W43 as well as a selection of H ii region bubbles, namely RCW49, RCW79, and RCW120. These [C ii] maps, together with the less explored [O i] 63 m line, provide an outstanding database for the community. They will be made publically available and will trigger further studies and follow-up observations.

Magnetic activity of stars like the Sun evolves in time because of spin-down owing to angular momentum removal by a magnetized stellar wind. These magnetic fields are generated by an internal dynamo driven by convection and differential rotation. Spin-down therefore converges at an age of about 700 Myr for solar-mass stars to values uniquely determined by the stellar mass and age. Before that time, however, rotation periods and their evolution depend on the initial rotation period of a star after it has lost its protostellar/protoplanetary disk. This non-unique rotational evolution implies similar non-unique evolutions for stellar winds and for the stellar high-energy output. I present a summary of evolutionary trends for stellar rotation, stellar wind mass loss and stellar high-energy output based on observations and models.

A thin, spherical shell with a clumpy structure around the red giant star R Sculptoris is shown to contain a spiral structure, implying that the star is a binary system that underwent a thermal pulse 1,800 years ago, ejecting three times more mass than expected A closer look at a late stage of stellar evolution New images of the asymptotic-giant-branch star R Sculptoris — early data from the ultra-high-resolution Atacama Large Millimeter/submillimeter Array radio telescope in Chile — have sufficient resolution to reveal a previously unrecognized spiral structure in the thin shell of dust and gas surrounding the star. The shell is thought to have been created when a thermal pulse caused increased mass loss. Similar spiral structures have been observed in association with circumstellar envelopes before, and are thought to be characteristic of binary systems. Combining the observational data with hydrodynamic simulations, the authors conclude that R Sculptoris is a binary that underwent a thermal pulse about 1,800 years ago. The pulse probably lasted for about 200 years and mass loss was approximately three times greater than previously thought. The asymptotic-giant-branch star R Sculptoris is surrounded by a detached shell of dust and gas 1 , 2 . The shell originates from a thermal pulse during which the star underwent a brief period of increased mass loss 3 , 4 . It has hitherto been impossible to constrain observationally the timescales and mass-loss properties during and after a thermal pulse—parameters that determine the lifetime of the asymptotic giant branch and the amount of elements returned by the star. Here we report observations of CO emission from the circumstellar envelope and shell around R Sculptoris with an angular resolution of 1.3″. What was previously thought to be only a thin, spherical shell with a clumpy structure is revealed to also contain a spiral structure. Spiral structures associated with circumstellar envelopes have been previously seen, leading to the conclusion that the systems must be binaries 5 , 6 , 7 , 8 . Combining the observational data with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse about 1,800 years ago, lasting approximately 200 years. About 3 × 10 −3 solar masses of material were ejected at a velocity of 14.3 km s −1 and at a rate around 30 times higher than the pre-pulse mass-loss rate. This shows that about three times more mass was returned to the interstellar medium during and immediately after the pulse than previously thought.

The activity of stars such as the Sun varies over timescales ranging from the very short to the very long—stellar and planetary evolutionary timescales. Experience from our solar system indicates that short-term, transient events such as stellar flares and coronal mass ejections create hazardous space environmental conditions that impact Earth-orbiting satellites and planetary atmospheres. Extreme events such as stellar superflares may play a role in atmospheric mass loss and create conditions unsuitable for life. Slower, long-term evolutions of the activity of Sun-like stars over millennia to billions of years result in variations in stellar wind properties, radiation flux, cosmic ray flux, and frequency of magnetic storms. This coupled evolution of star-planet systems eventually determines planetary and exoplanetary habitability. The Solar Evolution and Extrema (SEE) initiative of the Variability of the Sun and Its Terrestrial Impact (VarSITI) program of the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) aimed to facilitate and build capacity in this interdisciplinary subject of broad interest in astronomy and astrophysics. In this review, we highlight progress in the major themes that were the focus of this interdisciplinary program, namely, reconstructing and understanding past solar activity including grand minima and maxima, facilitating physical dynamo-model-based predictions of future solar activity, understanding the evolution of solar activity over Earth’s history including the faint young Sun paradox, and exploring solar-stellar connections with the goal of illuminating the extreme range of activity that our parent star—the Sun—may have displayed in the past, or may be capable of unleashing in the future.

There have been many research works involving mass transfer in stellar binaries, all of which are limited to certain systems with specific binary parameters. In this work, we use three-dimensional smoothed particle (3D-SPH) simulations to explore the impact of binary mass ratio and wind speed on the fraction of mass transferred to the accreting companion and the structure of accretion discs. We examine all possible cases of binary mass ratios as well as different conditions of wind speed in the vicinity of the accretor. We adhere to thermally driven winds, with sound speed being the main parameter, in which transonic stellar winds expand in the binary medium. We find that mass accretion fraction is close to unity for slow winds. However, fast winds lead to mass accretion fraction of thousandths which agree very well with the Bondi–Hoyle estimates. Mass accretion fraction is found to be the largest when the mass ratio is unity. Our results show that an increase in either sound speed or binary mass ratio leads to decrease in accretion disc size. In most cases, the disc shifts from being circular. These results would allow us to estimate the rate of mass accretion and the structure of accretion discs in any type of stellar binaries.

Depending on the distance of the exoplanet from the central star and the properties of this star, different regimes of stellar wind flow around it arise. If the exoplanet is located at a distance up to the Alfvén radius, where the wind speed is equal to the Alfvén speed, or the Alfvén Mach number , the exoplanet generates Alfvén wings. If it is situated beyond the Alfvén radius, a comet-like magnetosphere appears, similar to that of the planets of the Solar System. The paper examines how the transition from one flow regime to another can be described on the base of a paraboloid model of the magnetospheric magnetic field using the example of exoplanet HD 209458b.

We present the results of our study of the influence of stellar activity on the efficiency of the plasma radio emission generation mechanism and the properties of this emission in the atmospheres of exoplanets with a weak magnetic field. The plasma generation mechanism can be efficiently realized in the case where the Langmuir frequency exceeds the electron gyrofrequency, and the electron cyclotron maser is inefficient. This mechanism, which depends significantly on plasma parameters, suggests the generation of plasma (quasi-static) waves by energetic electrons followed by their conversion into electromagnetic radiation. The stellar wind, depending on its intensity, can modify significantly the plasmasphere of an exoplanet and change its parameters. Using the interaction of the exoplanet HD 189733b with a stellar wind of various intensities from the central star as an example, we show that the plasma mechanism can be realized at any stellar wind intensity, only the requirements for the parameters of the plasma mechanism change. In particular, the plasma wave energy density needed to generate a radio flux accessible to detection by modern radio-astronomical means changes, and its frequency range changes. The latter will allow the detected radio emission to be used as an indicator of the activity of the parent star.

We discuss possible existence of a magnetodisk around the exoplanet HAT–P–11b. We used available observations to determine properties of the exoplanet and the stellar wind passing by it and obtained a rough estimate of the size of the planet’s magnetosphere. Comparing our estimate to published results of computations in a 3D electromagnetic relativistic and collisionless particle-in-cell model of the magnetosphere, we found a discrepancy in the magnetosphere size estimated using these two techniques. A possible interpretation of the discrepancy is suggested.