Energetic particles, such as stellar cosmic rays, produced at a heightened rate by active stars (like the young Sun) may have been important for the origin of life on Earth and other exoplanets. Here we compare, as a function of stellar rotation rate ($Ω$), contributions from two distinct populations of energetic particles: stellar cosmic rays accelerated by impulsive flare events and Galactic cosmic rays. We use a 1.5D stellar wind model combined with a spatially 1D cosmic ray transport model. We formulate the evolution of the stellar cosmic ray spectrum as a function of stellar rotation. The maximum stellar cosmic ray energy increases with increasing rotation i.e., towards more active/younger stars. We find that stellar cosmic rays dominate over Galactic cosmic rays in the habitable zone at the pion threshold energy for all stellar ages considered ($t_*=0.6-2.9\,$Gyr). However, even at the youngest age, $t_*=0.6\,$Gyr, we estimate that $\gtrsim\,80$MeV stellar cosmic ray fluxes may still be transient in time. At $\sim1\,$Gyr when life is thought to have emerged on Earth, we demonstrate that stellar cosmic rays dominate over Galactic cosmic rays up to $\sim$4$\,$GeV energies during flare events. Our results for $t_*=0.6\,$Gyr ($Ω= 4Ω_\odot$) indicate that $\lesssim$GeV stellar cosmic rays are advected from the star to 1$\,$au and are impacted by adiabatic losses in this region. The properties of the inner solar wind, currently being investigated by the Parker Solar Probe and Solar Orbiter, are thus important for accurate calculations of stellar cosmic rays around young Sun-like stars.
Faint young Sun paradox (FYSP) is one of the unsolved problem in solar physics. The present study aims to get a possible solution for the FYSP through sun-like G stars and their exoplanetary systems. Using physical properties of exoplanetary data, an empirical relationship between the rate of mass loss ($\frac{dM}{dt}$) with stellar mass (M$_{\star}$) and age ({\em t}) is obtained. We found mass loss rate varies with stellar mass as $\propto$ $(M_{\star}/M_\odot)^{-3.788}$ and proportional to the age as $\propto$ t$^{-1.25}$, which indicates rate of mass loss is higher during early evolutionar…
The Earth's magnetosphere extension is controlled by the solar activity level via solar wind properties. Understanding such a relation in the Solar System is important for predicting also the condition of exoplanetary magnetospheres near Sun-like stars. We use measurements of a chromospheric proxy, the Ca II K index, and solar wind OMNI parameters to connect the solar activity variations, on the decennial time scales, to the solar wind properties. The data span over the time interval 1965-2021, which almost entirely covers the last 5 solar cycles. Using both cross-correlation and mutual inform…
Energetic particles may have been important for the origin of life on Earth by driving the formation of prebiotic molecules. We calculate the intensity of energetic particles, in the form of stellar and Galactic cosmic rays, that reach Earth at the time when life is thought to have begun ($\sim$3.8Gyr ago), using a combined 1.5D stellar wind model and 1D cosmic ray model. We formulate the evolution of a stellar cosmic ray spectrum with stellar age, based on the Hillas criterion. We find that stellar cosmic ray fluxes are larger than Galactic cosmic ray fluxes up to $\sim$4 GeV cosmic ray energ…
Stellar high-energy radiation (X-ray and extreme ultraviolet, XUV) drives atmospheric escape in close-in exoplanets. Given that stellar irradiation depends on the stellar magnetism and that stars have magnetic cycles, we investigate how cycles affect the evolution of exoplanetary atmospheric escape. Firstly, we consider a hypothetical HD209458b-like planet orbiting the Sun. For that, we implement the observed solar XUV radiation available over one and a half solar cycles in a 1D hydrodynamic escape model of HD209458b. We find that atmospheric escape rates show a cyclic variation (from 7.6 to 1…
We are studying the influence of stellar multiplicity on exoplanet systems, in particular systems that have been detected via radial-velocity searches. We are in particular interested in the closest companions as they would have a strong influence on the evolution of the original planet forming disks. In this study we present new companions detected during our ongoing survey of exoplanet hosts with VLT/SPHERE. We are using the extreme adaptive optics imager SPHERE at the ESO/VLT to search for faint (sub)stellar companions. We utilized the classical coronagraphic imaging mode to perform a snaps…
Stellar variability due to magnetic activity and flows at different spatial scales strongly impacts radial velocities. This variability is seen as oscillations, granulation, supergranulation, and meridional flows. The effect of this latter process is poorly known but could affect exoplanet detectability. We aim to quantify its amplitude when integrated over the disc and its temporal variability, first for the Sun, seen with different inclinations, and then for other solar-type stars. We used long time series of solar latitudinal meridional circulation to reconstruct its integrated contribution…
The Young Suns Exoplanet Survey (YSES) consists of a homogeneous sample of 70 young, solar-mass stars located in the Lower Centaurus-Crux subgroup of the Scorpius-Centaurus association with an average age of $15\pm3\,$Myr. We report the detection of a co-moving companion around the K3IV star TYC 8998-760-1 (2MASSJ13251211-6456207) that is located at a distance of $94.6\pm0.3\,$pc using SPHERE/IRDIS on the VLT. Spectroscopic observations with VLT/X-SHOOTER constrain the mass of the star to $1.00\pm0.02\,M_{\odot}$ and an age of $16.7\pm1.4\,$Myr. The companion TYC 8998-760-1 b is detected at a …
Rayleigh scattering in a hydrogen-dominated exoplanet atmosphere can be detected from ground or space based telescopes, however, stellar activity in the form of spots can mimic Rayleigh scattering in the observed transmission spectrum. Quantifying this phenomena is key to our correct interpretation of exoplanet atmospheric properties. We obtained long-slit optical spectroscopy of two transits of HAT-P-11b with the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at Gran Telescopio Canarias (GTC) on August 30 2016 and September 25 2017. We integrated t…
A Helicity-Based Method to Infer the CME Magnetic Field Magnitude in Sun and Geospace: Generalization and Extension to Sun-Like and M-Dwarf Stars and Implications for Exoplanet Habitability
Patsourakos等人（Astrophys. J. 817，14，2016）和Patsourakos和Georgoulis（Astron. Astrophys. 595，A121，2016）介绍了一种方法来推断在太阳日冕和更远的行星际介质中的通量绳日冕物质抛射（CME）中的轴向磁场。该方法基于磁螺旋度守恒原理，使用太阳源区的相对磁螺旋度作为输入估计，以及相应的CME通量绳的半径和长度。该方法最初应用于圆柱形的力免费磁通绳，令人鼓舞的结果。我们在此将我们的框架沿着两条不同的路线延伸。首先，我们将我们的形式主义推广到几种可能的磁通绳配置（线性和非线性的力自由，非力自由，spheromak，和环面）调查的依赖性所产生的CME轴向磁场的输入参数和所采用的磁通绳配置。其次，我们将我们的框架推广到类太阳和活跃的M-矮星的超级耀斑。在定性意义上，我们发现地球可能不会经历严重的大气侵蚀磁层压缩，即使是爆发的太阳超级耀斑，其能量比目前观测到的最大的地球静止运行环境卫星（GOES）X级耀斑高约10^4倍。此外，最近发现的两颗与地球相似性指数最高的系外行星开普勒438 b和比邻星b似乎位于行星际日冕物质抛射（ICME）造成的大气侵蚀的禁止区域，除非它们拥有比地球高得多的行星磁场。
Kepler Space Telescope and Transiting Exoplanet Survey Satellite unveiled that Sun-like stars frequently host exoplanets. These exoplanets are subject to fluxes of ionizing radiation in the form of X-ray and extreme-ultraviolet (EUV) radiation that may cause changes in their atmospheric dynamics and chemistry. While X-ray fluxes can be observed directly, EUV fluxes cannot be observed because of severe interstellar medium absorption. Here, we present a new empirical method to estimate the whole stellar XUV (X-ray plus EUV) and FUV spectra as a function of total unsigned magnetic fluxes of stars…
Context: The stellar wind and the interplanetary magnetic field modify the topology of planetary magnetospheres. Consequently, the hazardous effect of the direct exposition to the stellar wind, for example regarding the integrity of satellites orbiting the Earth or the habitability of exoplanets, depend upon the space weather conditions. Aims: The aim of the study is to analyze the response of an Earth-like magnetosphere for various space weather conditions and interplanetary coronal mass ejections. The magnetopause stand off distance, open-close field line boundary and plasma flows towards th…
Large ground- and space-based telescopes will be able to observe Earth-like planets in the near future. We explore how different planetary surfaces can strongly influence the climate, atmospheric composition, and remotely detectable spectra of terrestrial rocky exoplanets in the habitable zone depending on the host star's incident irradiation spectrum for a range of Sun-like host stars from F0V to K7V. We update a well-tested 1D climate-photochemistry model to explore the changes of a planetary environment for different surfaces for different host stars. Our results show that using a wavelengt…
Surfaces of the Sun and other cool stars are filled with magnetic fields, which are either seen as dark compact spots or more diffuse bright structures like faculae. Both hamper detection and characterisation of exoplanets, affecting stellar brightness and spectra, as well as transmission spectra. However, the expected facular and spot signals in stellar data are quite different, for instance they have distinct temporal and spectral profiles. Consequently, corrections of stellar data for magnetic activity can greatly benefit from the insight on whether the stellar signal is dominated by spots …
Cyclic activity on the Sun and stars is primarily explained by generation of the magnetic field by a dynamo mechanism, which converts the energy of the poloidal field into the energy of the toroidal component due to differential rotation. There is, however, an alternative point of view, which explains the field generation by gravitational influence of the planetary system and, first of all, Jupiter. This hypothesis can be verified by comparing the characteristics of exoplanets with the activity variations on their associated stars. We have performed such a comparison and have drawn a negative …
Recently, many Earth-sized planets have been discovered around stars other than the Sun that might possess appropriate conditions for life. The development of theoretical methods for assessing the putative habitability of these worlds is of paramount importance, since it serves the dual purpose of identifying and quantifying what types of biosignatures may exist and determining the selection of optimal target stars and planets for subsequent observations. This Colloquium discusses how a multitude of physical factors act in tandem to regulate the propensity of worlds for hosting detectable bios…
The solar gravitational lens (SGL) offers unique capabilities for high-resolution imaging of faint, distant objects, such as exoplanets. In the near future, a spacecraft carrying a meter-class telescope with a solar coronagraph would be placed in the focal region of the SGL. That region begins at ~547 astronomical units from the Sun and occupies the vicinity of the target-specific primary optical axis - the line that connects the center of the target and that of the Sun. This axis undergoes complex motion as the exoplanet orbits its host star, as that star moves with respect to the Sun, and ev…
Study Analysis Group 21 (SAG21) of NASA's Exoplanet Exploration Program Analysis Group (ExoPAG) was organized to study the effect of stellar contamination on space-based transmission spectroscopy, a method for studying exoplanetary atmospheres by measuring the wavelength-dependent radius of a planet as it transits its star. Transmission spectroscopy relies on a precise understanding of the spectrum of the star being occulted. However, stars are not homogeneous, constant light sources but have temporally evolving photospheres and chromospheres with inhomogeneities like spots, faculae, plages, g…
In antiquity, all of the enduring celestial bodies that were seen to move relative to the background sky of stars were considered planets. During the Copernican revolution, this definition was altered to objects orbiting around the Sun, removing the Sun and Moon but adding the Earth to the list of known planets. The concept of planet is thus not simply a question of nature, origin, composition, mass or size, but historically a concept related to the motion of one body around the other, in a hierarchical configuration. After discussion within the IAU Commission F2 "Exoplanets and the Solar Syst…
This topical collection summarizes recent advances in observing and modeling irradiance variations of the Sun and Sun-like stars, emphasizing the links between surface magnetic fields and the resulting solar and stellar variability. In particular, the articles composing this collection summarize recent progress in i) solar-irradiance measurements; ii) modeling of solar- and stellar-irradiance variability; and iii) understanding of the effects of such variability on Earth's climate and exoplanet environments. This topical-collection overview article gives background and more details on these as…
Transits of exoplanets across cool stars contain blended information about structures on the stellar surface and about the planetary body and atmosphere. To advance understanding of how this information is entangled, a surface-flux transport code, based on observed properties of the Sun's magnetic field, is used to simulate the appearance of hypothetical stellar photospheres from the visible near 4000 Angstrom to the near-IR at 1.6 micron, by mapping intensities characteristic of faculae and spots onto stellar disks. Stellar appearances are computed for a Sun-like star of solar activity up to …
Investigating the High-energy Radiation Environment of Planets in Sun-like Binary Systems
University of Colorado, Boulder（科罗拉多大学博尔德分校）；Laboratory for Atmospheric and Space Physics（大气与空间物理实验室）；Vanderbilt University（范德堡大学）；Leiden University（莱顿大学）
A breakthrough in exoplanet detections is foreseen with the unprecedented astrometric measurement capabilities offered by instrumentation aboard Gaia space observatory. Besides, astrometric discoveries of exoplanets are expected from the planned space mission, Small-JASMINE. In this setting, the present series of papers focuses on estimating the effect of magnetic activity of G2V-type host stars on the astrometric signal. This effect interferes with the astrometric detections of Earth-mass planets. While the first two papers considered stars rotating at the solar rotation rate, this paper focu…
Energetic flares and associated coronal mass ejections (CMEs) from young magnetically active solar-like stars can play a critical role in setting conditions for atmospheric escape as well aspenetration of accelerated particles into their atmospheres that promotes formation of biologically relevant molecules. We have used the observationally reconstructed magnetic field of the 0.7 Gyr-young Suns twin, k1 Ceti, to study the effects of CME deflections in the magnetic corona of the young Sun and their effects on the impact frequency on the early Venus, Earth and Mars. We find that the coronal magn…
Transit observations in the helium triplet around 10830 Angstrom are a successful tool to study exoplanetary atmospheres and their mass loss. Forming those lines requires ionisation and recombination of helium in the exoplanetary atmosphere. This ionisation is caused by stellar photons at extreme ultra-violet (EUV) wavelengths; however, no currently active telescopes can observe this part of the stellar spectrum. The relevant part of the stellar EUV spectrum consists of individual emission lines, many of them being formed by iron at coronal temperatures. The stellar iron abundance in the coron…
The majority of potentially habitable exoplanets detected orbit stars cooler than the Sun, and therefore are irradiated by a stellar spectrum peaking at longer wavelengths than that incident on Earth. Here, we present results from a set of simulations of tidally-locked terrestrial planets orbiting three different host stars to isolate the effect of the stellar spectra on the simulated climate. Specifically, we perform simulations based on TRAPPIST-1e, adopting an Earth-like atmosphere and using the UK Met Office Unified Model in an idealised 'aqua-planet' configuration. Whilst holding the plan…
We present the latest results of an ongoing multiplicity survey of exoplanet hosts, which was initiated at the Astrophysical Institute and University Observatory Jena, using data from the second data release of the ESA-Gaia mission. In this study the multiplicity of 289 targets was investigated, all located within a distance of about 500 pc from the Sun. In total, 41 binary, and 5 hierarchical triple star systems with exoplanets were detected in the course of this project, yielding a multiplicity rate of the exoplanet hosts of about 16 %. A total of 61 companions (47 stars, a white dwarf, and …
The advent of Gaia, capable of measuring stellar wobbles caused by orbiting planets, raised an interest to the astrometric detection of exoplanets. Another source of such wobbles (often also called jitter) is stellar magnetic activity. A quantitative assessment of the stellar astrometric jitter is important for a more reliable astrometric detection and characterisation of exoplanets. We calculate the displacement of the solar photocentre due to the magnetic activity for an almost 16-year period (February 2, 1999 - August 1, 2014). We also investigate how the displacement depends on the spectra…
We present a formalism for a first-order estimation of the magnetosphere radius of exoplanets orbiting stars in the range from 0.08 to 1.3 Mo. With this radius, we estimate the atmospheric surface that is not protected from stellar winds. We have analyzed this unprotected surface for the most extreme environment for exoplanets: GKM-type and very low-mass stars at the two limits of the habitable zone. The estimated unprotected surface makes it possible to define a likelihood for an exoplanet to retain its atmosphere. This function can be incorporated into the new habitability index SEPHI. Using…
Galactic chemical evolution (GCE), solar analogues or twins, and peculiarities of the solar composition with respect to the twins are inextricably related. We examine GCE parameters from the literature and present newly derived values using a quadratic fit that gives zero for a Solar age (i.e., 4.6 Gyr). We show how the GCE parameters may be used not only to "correct" abundances to the solar age, but to predict relative elemental abundances as a function of age. We address the question of whether the solar abundances are depleted in refractories and enhanced in volatiles and find that the answ…
Since the first observations of solar oscillations in 1962, helioseismology has probably been one of the most successful fields of astrophysics. Besides the improvement of observational data, solar seismologists developed sophisticated techniques to infer the internal structure of the Sun. Back in 1990s these comparisons showed a very high agreement between solar models and the Sun. However, the downward revision of the CNO surface abundances in the Sun in 2005, confirmed in 2009, induced a drastic reduction of this agreement leading to the so-called solar modelling problem. More than ten year…
Our knowledge of the population of young (age <=750 Myr) stars that lie within ~120 pc of the Sun is rapidly accelerating. The vast majority of these nearby, young stars can be placed in kinematically coherent groups (nearby, young moving groups; NYMGs). NYMGs and their member stars afford unmatched opportunities to explore a wide variety of aspects of the early evolution of stars and exoplanet systems, including stellar initial mass functions and age determination methods; the magnetic activities and high-energy radiation environments of young, late-type stars; the dynamics of young binary an…
