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Motivated by the possible existence of other universes, with possible variations in the laws of physics, this paper explores the parameter space of fundamental constants that allows for the existence of stars. To make this problem…

Aims: We study the evolution of stellar rotation and wind properties for low-mass main-sequence stars. Our aim is to use rotational evolution models to constrain the mass loss rates in stellar winds and to predict how their properties…

What kind of environment may exist on terrestrial planets around other stars? In spite of the lack of direct observations, it may not be premature to speculate on exoplanetary climates, for instance to optimize future telescopic…

During these last decades, our knowledge of evolutionary and structural properties of stars of different mass and chemical composition is significantly improved. This result has been achieved as a consequence of our improved capability in…

In recent years, exciting developments have taken place in the identification of the role of cosmic rays in star-forming environments. Observations from radio to infrared wavelengths and theoretical modelling have shown that low-energy…

In the present universe, the gas is a minor component of giant galaxies, and its dominant phase is atomic (HI). During galaxy evolution in cosmic times, models predict that gas fractions were much higher in galaxies, and gas phases could be…

The brightness of the Sun varies on all time scales on which it has been observed, and there is increasing evidence that it has an influence on climate. The amplitudes of such variations depend on the wavelength and possibly on the time…

X-ray emission is ubiquitous among massive stars. In the last decade, X-ray observations revolutionized our perception of stellar winds but opened a Pandora's box of urgent problems. X-rays penetrating stellar winds suffer mainly continuum…

While it may seem counterintuitive that X-ray astronomy should give any insights into low-temperature planetary systems, planets orbit stars whose magnetized surfaces divert a small fraction of the stellar energy into high energy products:…

The major questions relevant to star and planet formation are: What controls the rate, efficiency, spatial clustering, multiplicity, and initial mass function of star formation, now and in the past? What are the major feedback mechanisms…

Mercury, due to its close location to the Sun, is surrounded by an environment whose conditions may be considered as "extreme" in the entire Solar System. Both solar wind and radiation are stronger with respect to other Solar System bodies,…

This paper considers how planetesimal impacts affect planetary atmospheres. Atmosphere evolution depends on the ratio of gain from volatiles to loss from atmosphere stripping f_v; for constant bombardment, atmospheres with f_v<1 are…

During this last decade our knowledge of the evolutionary properties of stars has significantly improved. This result has been achieved thanks to our improved understanding of the physical behavior of stellar matter in the thermal regimes…

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…

We present a new model atmosphere analysis of nine central stars of planetary nebulae. This study is based on a new generation of realistic stellar model atmospheres for hot stars; state-of-the-art, hydrodynamically consistent, spherically…

Planet Planet scattering is a leading dynamical mechanism invoked to explain the present orbital distribution of exoplanets. Many stars belong to binary systems, therefore it is important to understand how this mechanism works in presence…

Thousands of confirmed and candidate exoplanets have been identified in recent years. Consequently, theoretical research on the formation and dynamical evolution of planetary systems has seen a boost, and the processes of planet-planet…

The rotation rate of a star has important implications for the detectability, characterisation and stability of any planets that may be orbiting it. This chapter gives a brief overview of stellar rotation before describing the methods used…

Stellar evolution, a fundamental bedrock of modern astrophysics, is driven by the physical processes in stellar interiors. While we understand these processes in general terms, we lack some important ingredients. Seemingly small…

The young star clusters we observe today are the building blocks of a new generation of stars and planets in our Galaxy and beyond. Despite their fundamental role we still lack knowledge about the conditions under which star clusters form…