The search for exoplanetary radio emission has resulted in zero conclusive detections to date. Various explanations for this have been proposed, from the observed frequency range, telescope sensitivity, to beaming of the emission. In a recent paper, we illustrated that exoplanets can orbit through the radio photosphere of the wind of the host star, a region that is optically thick at a specific frequency, for a large fraction of their orbits. As a result, radio emission originating from the planet could be absorbed or `eclipsed' by the wind of the host star. Here we investigate how the properties of the stellar wind and orbital parameters affect the fraction of the orbit where the planet is eclipsed by the stellar wind. We show that planets orbiting stars with low density winds are more favourable for detection in the radio. In terms of the orbital parameters, emission from transiting planets can escape the stellar wind easiest. We apply our model to the $τ$~Boo planetary system, and show that observing the fraction of the planet's orbit where it is eclipsed by the wind of the host star could be used to constrain the properties of the stellar wind. However, our model developed would need to be used in conjunction with a separate method to disentangle the mass-loss rate and temperature of the stellar wind.
The atmospheres of exoplanets are commonly studied by observing the transit of the planet passing in front of its parent star. The obscuration of part of the stellar disk during a transit will reveal aspects of its surface structure resulting from general centre-to-limb variations (CLVs). These become apparent when forming the ratio between the stellar light in and out of transit. These phenomena can be seen particularly clearly during the progress of a penumbral lunar eclipse, where the Earth transits the solar disk and masks different regions of the solar disk as the eclipse progresses. When…
Photometric survey data from the Kepler mission have been used to discover and characterize thousands of transiting exoplanet and eclipsing binary (EB) systems. These discoveries have enabled empirical studies of occurrence rates which reveal that exoplanets are ubiquitous and found in a wide variety of system architectures and physical compositions. Because the detection strategy of these missions is most sensitive to short orbital periods, the vast majority of these objects reside within 1 AU of their host star. Although other detection techniques have successfully identified exoplanets at w…
We investigate in this paper the astrophysical false-positive configuration in exoplanet-transit surveys that involves eclipsing binaries and giant planets which present only a secondary eclipse, as seen from the Earth. To test how an eclipsing binary configuration can mimic a planetary transit, we generate synthetic light curve of three examples of secondary-only eclipsing binary systems that we fit with a circular planetary model. Then, to evaluate its occurrence we model a population of binaries in double and triple system based on binary statistics and occurrence. We find that 0.061% +/- 0…
It has been posited that lunar eclipse observations may help predict the in-transit signature of Earth-like extrasolar planets. However, a comparative analysis of the two phenomena addressing in detail the transport of stellar light through the planet's atmosphere has not yet been presented. Here, we proceed with the investigation of both phenomena by making use of a common formulation. Our starting point is a set of previously unpublished near-infrared spectra collected at various phases during the August 2008 lunar eclipse. We then take the formulation to the limit of an infinitely distant o…
The methods for determination of the characteristics of the extrema are discussed with an application to irregularly spaced data, which are characteristic for photometrical observations of variable stars. We introduce new special functions, which were named as the "Wall-Supported Polynomial" (WSP) of different orders. It is a parabola (WSP), constant line (WSL) or an "asymptotic" parabola (WSAP) with "walls" corresponding to more inclined descending and ascending branches of the light curve. As the interval is split generally into 3 parts, the approximations may be classified as a "non-polynom…
Secondary eclipses are a powerful tool to measure directly the thermal emission from extrasolar planets, and to constrain their type and physical parameters. We started a project to obtain reliable broad-band measurements of the thermal emission of transiting exoplanets. Ground-based high-cadence near-infrared relative photometry was used to obtain sub-millimagnitude precision light curve of a secondary eclipse of WASP-4b -- a 1.12 M_J hot Jupiter on a 1.34 day orbit around G7V star. The data show a clear ~10-σdetection of the planet's thermal emission at 2.2 μm. The calculated thermal emissio…
Er et al. (2021) recently proposed a two-planet solution to account for eclipse timing variations (ETVs) observed from the sdB binary NY Virginis. We tested the proposed planetary system for orbit stability using both numerical simulations and chaotic behavior analysis. The best-fit orbits, as well as those with parameters varying by the published uncertainty range in each parameter, were unstable on a timescale much less than the presumed lifetime of the PCEB phase ($\sim$100 Myr). suggesting that the proposed circumbinary companions fail to provide a complete explanation for the observed ETV…
Surface magnetism is believed to be the main driver of coronal heating and stellar wind acceleration. Coronae are believed to be formed by plasma confined in closed magnetic coronal loops of the stars, with winds mainly originating in open magnetic field line regions. In this Chapter, we review some basic properties of stellar coronae and winds and present some existing models. In the last part of this Chapter, we discuss the effects of coronal winds on exoplanets.
The great majority of exoplanets discovered so far are orbiting cool, low-mass stars whose properties are relatively similar to the Sun. However, the stellar magnetism of these stars can be significantly different from the solar one, both in topology and intensity. In addition, due to the present-day technology used in exoplanetary searches, most of the currently known exoplanets are found orbiting at extremely close distances to their host stars ($< 0.1$ au). The dramatic differences in stellar magnetism and orbital radius can make the interplanetary medium of exoplanetary systems remarkably …
We investigate directly imaging exoplanets around eclipsing binaries, using the eclipse as a natural tool for dimming the binary and thus increasing the planet to star brightness contrast. At eclipse, the binary becomes point-like, making coronagraphy possible. We select binaries where the planet-star contrast would be boosted by $>10\times$ during eclipse, making it possible to detect a planet that is $\gtrsim10\times$ fainter or in a star system that is $\sim2$-$3\times$ more massive than otherwise. Our approach will yield insights into planet occurrence rates around binaries versus individu…
A 2014 study of the eclipsing binary star 1SWASPJ011351.29+314909.7 (J0113+31) reported an unexpectedly high effective temperature for the M-dwarf companion to the 0.95-M$_{\odot}$ primary star. The effective temperature inferred from the secondary eclipse depth was $\sim$600 K higher than the value predicted from stellar models. Such an anomalous result questions our understanding of low-mass stars and might indicate a significant uncertainty when inferring properties of exoplanets orbiting them. We seek to measure the effective temperature of the M-dwarf companion using the light curve of J0…
The cumulative effect of the magnetized stellar winds on exoplanets dominates over other forms of star-planet interactions. When combined with photoevaporation, these winds will lead to atmospheric erosion. This is directly connected with the concept of Habitable Zone (HZ) planets around late-type stars. Our knowledge of these magnetized winds is limited, making numerical models useful tools to explore them. In this preliminary study, we focus on solar-like stars exploring how different stellar wind properties scale with one another. We used one of the most detailed physics-based models, the 3…
By analogy with the solar system, it is believed that stellar winds will form bow shocks around exoplanets. For hot Jupiters the bow shock will not form directly between the planet and the star, causing an asymmetric distribution of mass around the exoplanet and hence an asymmetric transit. As the planet orbits thorough varying wind conditions, the strength and geometry of its bow shock will change, thus producing transits of varying shape. We model this process using magnetic maps of HD 189733 taken one year apart, coupled with a 3D stellar wind model, to determine the local stellar wind cond…
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…
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 mo…
Of the 342 planets discovered so far orbiting other stars, 58 "transit" the stellar disk, meaning that they can be detected by a periodic decrease in the starlight flux. The light from the star passes through the atmosphere of the planet, and in a few cases the basic atmospheric composition of the planet can be estimated. As we get closer to finding analogues of Earth, an important consideration toward the characterization of exoplanetary atmospheres is what the transmission spectrum of our planet looks like. Here we report the optical and near-infrared transmission spectrum of the Earth, obta…
Recent work investigating the impact of winds and outflows from active galactic nuclei (AGN) on the habitability of exoplanets suggests that such activity could be deleterious for the long-term survival of planetary atmospheres and the habitability of planets subject to such winds. Here, we discuss the relative importance of the effect of AGN winds compared to stellar winds and the effect of the planet's magnetosphere and stellar irradiation and conclude that AGN winds are not likely to play a significant role in the evolution of atmospheric conditions in planets under conditions otherwise fav…
Program SHELLSPEC is designed to calculate light-curves, spectra and images of interacting binaries and extrasolar planets immersed in a moving circumstellar environment which is optically thin. It solves simple radiative transfer along the line of sight in moving media. The assumptions include LTE and optional known state quantities and velocity fields in 3D. Optional (non)transparent objects such as a spot, disc, stream, jet, ufo, shell or stars may be defined (embedded) in 3D and their composite synthetic spectrum calculated. Roche model can be used as a boundary condition for the radiative…
Atmospheric escape from close-in exoplanets is thought to be crucial in shaping observed planetary populations. Recently, significant progress has been made in observing this process in action through excess absorption in transit spectra and narrowband light curves. We model the escape of initially-homogeneous planetary winds interacting with a stellar wind. The ram pressure balance of the two winds governs this interaction. When the impingement of the stellar wind on the planetary outflow is mild or moderate, the planetary outflow expands nearly spherically through its sonic surface before fo…
The transit method of exoplanet discovery and characterization has enabled numerous breakthroughs in exoplanetary science. These include measurements of planetary radii, mass-radius relationships, stellar obliquities, bulk density constraints on interior models, and transmission spectroscopy as a means to study planetary atmospheres. The Transiting Exoplanet Survey Satellite (TESS) has added to the exoplanet inventory by observing a significant fraction of the celestial sphere, including many stars already known to host exoplanets. Here we describe the science extraction from TESS observations…
Here, I review some recent works on magnetism of cool, main-sequence stars, their winds and potential impact on surrounding exoplanets. The winds of these stars are very tenuous and persist during their lifetime. Although carrying just a small fraction of the stellar mass, these magnetic winds carry away angular momentum, thus regulating the rotation of the star. Since cool stars are likely to be surrounded by planets, understanding the host star winds and magnetism is a key step towards characterisation of exoplanetary environments. As rotation and activity are intimately related, the spin do…
The search for extrasolar rocky planets has already found the first transiting rocky super-Earth, Corot 7b, with a surface temperature that allows for magma oceans. Here we ask if we could distinguish rocky planets with recent major volcanism by remote observation. We develop a model for volcanic eruptions on an Earth-like exoplanet based on the present day Earth, derive the observable features in emergent and transmission spectra for multiple scenarios of gas distribution and cloudcover. We calculate the observation time needed to detect explosive volcanism on exoplanets in primary as well as…
This Letter capitalizes on a unique set of total solar eclipse observations, acquired between 2006 and 2020, in white light, Fe XI 789.2 nm ($\rm T_{fexi}$ = $1.2 \pm 0.1$ MK) and Fe XIV 530.3 nm ($\rm T_{fexiv}$ = $ 1.8 \pm 0.1$ MK) emission, complemented by in situ Fe charge state and proton speed measurements from ACE/SWEPAM-SWICS, to identify the source regions of different solar wind streams. The eclipse observations reveal the ubiquity of open structures, invariably associated with Fe XI emission from $\rm Fe^{10+}$, hence a constant electron temperature, $\rm T_{c}$ = $\rm T_{fexi}$, in…
Kinematically Resolving the Fe K Complex in Her X-1: The Accretion Disk and Ionized Wind Across X-ray Eclipses
Kyoto University（京都大学）；RIKEN Center for Advanced Photonics（理化学研究所先进光子学中心）；Center for Astrophysics — Harvard & Smithsonian（哈佛与史密森尼天体物理中心）；RIKEN Tamagawa High Energy Astrophysics Laboratory（理化学所玉川高能天体物理学实验室）；Universität Tübingen（蒂宾根大学）；University of Michigan（密歇根大学）
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…
Stellar wind and photon radiation interactions with a planet can cause atmospheric depletion, which may have a potentially catastrophic impact on a planet's habitability. While the implications of photoevaporation on atmospheric erosion have been researched to some degree, studies of the influence of the stellar wind on atmospheric loss are in their infancy. Here, we use three-dimensional magnetohydrodynamic simulations to model the effect of the stellar wind on the magnetosphere and outflow of a hypothetical planet, modeled to have an H-rich evaporating envelope with a pre-defined mass loss r…
The architecture of exoplanetary systems is often different from the solar system, with some exoplanets being in close orbits around their host stars and having orbital periods of only a few days. In analogy to interactions between stars in close binary systems, one may expect interactions between the star and the exoplanet as well. From theoretical considerations, effects on the host star through tidal and magnetic interaction with the exoplanet are possible; for the exoplanet, some interesting implications are the evaporation of the planetary atmosphere and potential effects on the planetary…
Context: The principle definition of habitability for exoplanets is whether they can sustain liquid water on their surfaces, i.e. that they orbit within the habitable zone. However, the planet's magnetosphere should also be considered, since without it, an exoplanet's atmosphere may be eroded away by stellar winds. Aims: The aim of this paper is to investigate magnetospheric protection of a planet from the effects of stellar winds from solar-mass stars. Methods: We study hypothetical Earth-like exoplanets orbiting in the host star's habitable zone for a sample of 124 solar-mass stars. These ar…
Using time-series photometry from the Kilodegree Extremely Little Telescope (KELT) exoplanet survey, we are looking for eclipses of stars by their protoplanetary disks, specifically in young stellar associations. To date, we have discovered two previously unknown, large dimming events around the young stars RW Aurigae and V409 Tau. We attribute the dimming of RW Aurigae to an occultation by its tidally disrupted disk, with the disruption perhaps resulting from a recent flyby of its binary companion. Even with the dynamical environment of RW Aurigae, the distorted disk material remains very com…
Vela X-1 is the prototype of the class of wind-fed accreting pulsars in high mass X-ray binaries hosting a supergiant donor. We have analyzed in a systematic way ten years of INTEGRAL data of Vela X-1 (22-50 keV) and we found that when outside the X-ray eclipse, the source undergoes several luminosity drops where the hard X-rays luminosity goes below 3x10^35 erg/s, becoming undetected by INTEGRAL. These drops in the X-ray flux are usually referred to as "off-states" in the literature. We have investigated the distribution of these off-states along the Vela X-1 ~8.9 d orbit, finding that their …
