scholarly journals Stellar wind effects on the atmospheres of close-in giants: a possible reduction in escape instead of increased erosion

2020 ◽  
Vol 494 (2) ◽  
pp. 2417-2428 ◽  
Author(s):  
A A Vidotto ◽  
A Cleary
Keyword(s):  
Parameter Space ◽  
Stellar Wind ◽  
Planetary Atmospheres ◽  
External Pressure ◽  
Stellar Winds ◽  
Wind Effects ◽  
Atmospheric Escape ◽  
Large Pressure ◽  
Ram Pressure ◽  
Host Stars

ABSTRACT The atmospheres of highly irradiated exoplanets are observed to undergo hydrodynamic escape. However, due to strong pressures, stellar winds can confine planetary atmospheres, reducing their escape. Here, we investigate under which conditions atmospheric escape of close-in giants could be confined by the large pressure of their host star’s winds. For that, we simulate escape in planets at a range of orbital distances ([0.04, 0.14] au), planetary gravities ([36, 87 per cent] of Jupiter’s gravity), and ages ([1, 6.9] Gyr). For each of these simulations, we calculate the ram pressure of these escaping atmospheres and compare them to the expected stellar wind external pressure to determine whether a given atmosphere is confined or not. We show that although younger close-in giants should experience higher levels of atmospheric escape, due to higher stellar irradiation, stellar winds are also stronger at young ages, potentially reducing escape of young exoplanets. Regardless of the age, we also find that there is always a region in our parameter space where atmospheric escape is confined, preferably occurring at higher planetary gravities and orbital distances. We investigate confinement of some known exoplanets and find that the atmosphere of several of them, including π Men c, should be confined by the winds of their host stars, thus potentially preventing escape in highly irradiated planets. Thus, the lack of hydrogen escape recently reported for π Men c could be caused by the stellar wind.

scholarly journals Effects of the stellar wind on the Ly α transit of close-in planets

2020 ◽  
Vol 500 (3) ◽  
pp. 3382-3393
Author(s):  
S Carolan ◽  
A A Vidotto ◽  
C Villarreal D’Angelo ◽  
G Hazra
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Escape Rate ◽  
Stellar Winds ◽  
Solar Mass ◽  
Atmospheric Escape ◽  
Exchange Processes ◽  
Sonic Surface

ABSTRACT We use 3D hydrodynamics simulations followed by synthetic line profile calculations to examine the effect increasing the strength of the stellar wind has on observed Ly α transits of a hot Jupiter (HJ) and a warm Neptune (WN). We find that increasing the stellar wind mass-loss rate from 0 (no wind) to 100 times the solar mass-loss rate value causes reduced atmospheric escape in both planets (a reduction of 65 per cent and 40 per cent for the HJ and WN, respectively, compared to the ‘no wind’ case). For weaker stellar winds (lower ram pressure), the reduction in planetary escape rate is very small. However, as the stellar wind becomes stronger, the interaction happens deeper in the planetary atmosphere, and, once this interaction occurs below the sonic surface of the planetary outflow, further reduction in evaporation rates is seen. We classify these regimes in terms of the geometry of the planetary sonic surface. ‘Closed’ refers to scenarios where the sonic surface is undisturbed, while ‘open’ refers to those where the surface is disrupted. We find that the change in stellar wind strength affects the Ly α transit in a non-linear way (note that here we do not include charge-exchange processes). Although little change is seen in planetary escape rates (≃ 5.5 × 1011 g s−1) in the closed to partially open regimes, the Ly α absorption (sum of the blue [−300, −40 km s−1] and red [40, 300 km s−1] wings) changes from 21 to 6 per cent as the stellar wind mass-loss rate is increased in the HJ set of simulations. For the WN simulations, escape rates of ≃ 6.5 × 1010 g s−1 can cause transit absorptions that vary from 8.8 to 3.7 per cent, depending on the stellar wind strength. We conclude that the same atmospheric escape rate can produce a range of absorptions depending on the stellar wind and that neglecting this in the interpretation of Ly α transits can lead to underestimation of planetary escape rates.

scholarly journals On the effects of stellar winds on exoplanetary magnetospheres

2013 ◽  
Vol 9 (S302) ◽  
pp. 251-254
Author(s):  
V. See ◽  
M. Jardine ◽  
A. A. Vidotto ◽  
P. Petit ◽  
S. C. Marsden ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Parameter Space ◽  
Liquid Water ◽  
Stellar Wind ◽  
Important Variable ◽  
Planetary Atmosphere ◽  
Stellar Winds ◽  
Habitable Zone ◽  
Wind Model ◽  
The Impact

AbstractThe habitable zone is the range of orbital distances from a host star in which an exoplanet would have a surface temperature suitable for maintaining liquid water. This makes the orbital distance of exoplanets an important variable when searching for extra-solar Earth analogues. However, the orbital distance is not the only important factor determining whether an exoplanet is potentially suitable for life. The ability of an exoplanet to retain an atmosphere is also vital since it helps regulate surface temperatures. One mechanism by which a planetary atmosphere can be lost is erosion due to a strong stellar wind from the host star. The presence of a magnetosphere can help to shield a planetary atmosphere from this process. Using a simple stellar wind model, we present the impact that stellar winds might have on magnetospheric sizes of exoplanets. This is done with the aim of further constraining the parameter space in which we look for extra-solar Earth analogues.

scholarly journals Physical Processes in Nebular Shells and the Interpretation of Nebular Spectra

1983 ◽  
Vol 103 ◽  
pp. 219-227
Author(s):  
J. Patrick Harrington
Keyword(s):  
Charge Transfer ◽  
Simple Model ◽  
Stellar Wind ◽  
High Velocity ◽  
Planetary Nebulae ◽  
Geometrical Parameters ◽  
Stellar Winds ◽  
Physical Processes ◽  
Rapid Cooling ◽  
Particle Distributions

Computed models are now recognized as useful tools for interpretation of the spectra of planetary nebulae. However, even the most detailed models need geometrical parameters such as filling factors which are poorly determined by observations. Some effects may be seen more clearly by modeling the stratification than by just using total fluxes. A simple model for NGC 6720 is presented which reproduces the behavior of (Ne III) λ3869 observed by Hawley and Miller (1977), clearly showing the effects of charge transfer. The behavior of C II λ4267 remains puzzling. Finally, we comment on the interaction of high velocity stellar winds with nebular shells. Non-equilibrium particle distributions at the contact between the shocked stellar wind and the nebula may result in the rapid cooling of the shocked gas.

scholarly journals The particle and magnetic environments surrounding close-in exoplanets

2015 ◽  
Vol 11 (S320) ◽  
pp. 397-402
Author(s):  
A. A. Vidotto ◽  
R. Fares ◽  
M. Jardine ◽  
C. Moutou ◽  
J.-F. Donati
Keyword(s):  
Magnetic Fields ◽  
Radio Emission ◽  
Magnetic Field Intensity ◽  
Three Dimensional ◽  
Stellar Winds ◽  
Local Conditions ◽  
Hot Jupiters ◽  
The Earth ◽  
Weather Events ◽  
Host Stars

AbstractThe proper characterisation of stellar winds is essential for the study of propagation of eruptive events (flares, coronal mass ejections) and the study of space weather events on exoplanets. Here, we quantitatively investigate the nature of the stellar winds surrounding the hot Jupiters HD46375b, HD73256b, HD102195b, HD130322b, HD179949b. We simulate the three-dimensional winds of their host stars, in which we directly incorporate their observed surface magnetic fields. With that, we derive the wind properties at the position of the hot-Jupiters’ orbits (temperature, velocity, magnetic field intensity and pressure). We show that the exoplanets studied here are immersed in a local stellar wind that is much denser than the local conditions encountered around the solar system planets (e.g., 5 orders of magnitude denser than the conditions experienced by the Earth). The environment surrounding these exoplanets also differs in terms of dynamics (slower stellar winds, but higher Keplerian velocities) and ambient magnetic fields (2 to 3 orders of magnitude larger than the interplanetary medium surrounding the Earth). The characterisation of the host star's wind is also crucial for the study of how the wind interacts with exoplanets. For example, we compute the exoplanetary radio emission that is released in the wind-exoplanet interaction. For the hot-Jupiters studied here, we find radio fluxes ranging from 0.02 to 0.13 mJy. These fluxes could become orders of magnitude higher when stellar eruptions impact exoplanets, increasing the potential of detecting exoplanetary radio emission.

scholarly journals Can we detect aurora in exoplanets orbiting M dwarfs?

2019 ◽  
Vol 488 (1) ◽  
pp. 633-644 ◽  
Author(s):  
A A Vidotto ◽  
N Feeney ◽  
J H Groh
Keyword(s):  
Solar System ◽  
Radio Emission ◽  
Stellar Wind ◽  
Engineering Calculation ◽  
M Dwarfs ◽  
Radio Detection ◽  
Dwarf Planets ◽  
M Dwarf ◽  
Host Stars ◽  
New Instruments

ABSTRACT New instruments and telescopes, such as SPIRou, CARMENES, and Transiting Exoplanet Survey Satellite (TESS), will increase manyfold the number of known planets orbiting M dwarfs. To guide future radio observations, we estimate radio emission from known M dwarf planets using the empirical radiometric prescription derived in the Solar system, in which radio emission is powered by the wind of the host star. Using solar-like wind models, we find that the most promising exoplanets for radio detections are GJ 674 b and Proxima b, followed by YZ Cet b, GJ 1214 b, GJ 436 b. These are the systems that are the closest to us (<10 pc). However, we also show that our radio fluxes are very sensitive to the unknown properties of winds of M dwarfs. So, which types of winds would generate detectable radio emission? In a ‘reverse engineering’ calculation, we show that winds with mass-loss rates $\dot{M} \gtrsim \kappa _{\rm sw} /u_{\rm sw}^3$ would drive planetary radio emission detectable with present-day instruments, where usw is the local stellar wind velocity and κsw is a constant that depends on the size of the planet, distance, and orbital radius. Using observationally constrained properties of the quiescent winds of GJ 436 and Proxima Cen, we conclude that it is unlikely that GJ 436 b and Proxima b would be detectable with present-day radio instruments, unless the host stars generate episodic coronal mass ejections. GJ 674 b, GJ 876 b, and YZ Cet b could present good prospects for radio detection, provided that their host stars’ winds have $\dot{M} u_{\rm sw}^{3} \gtrsim 1.8\times 10^{-4} \, {\rm M}_\odot \,{\rm yr}^{-1}\, ({\rm km\,s^{-1}})^{3}$.

scholarly journals Coupling thermal evolution of planets and hydrodynamic atmospheric escape in mesa

2020 ◽  
Vol 499 (1) ◽  
pp. 77-88 ◽  
Author(s):  
Daria Kubyshkina ◽  
Aline A Vidotto ◽  
Luca Fossati ◽  
Eoin Farrell
Keyword(s):  
Mass Fraction ◽  
Thermal State ◽  
Thermal Evolution ◽  
Detailed Comparison ◽  
Planetary Atmospheres ◽  
Gravitational Energy ◽  
Atmospheric Escape ◽  
Mass Fractions ◽  
The Stability ◽  
Atmospheric Mass

ABSTRACT The long-term evolution of hydrogen-dominated atmospheres of sub-Neptune-like planets is mostly controlled to by two factors: a slow dissipation of the gravitational energy acquired at the formation (known as thermal evolution) and atmospheric mass-loss. Here, we use mesa to self-consistently couple the thermal evolution model of lower atmospheres with a realistic hydrodynamical atmospheric evaporation prescription. To outline the main features of such coupling, we simulate planets with a range of core masses (5–20 M⊕) and initial atmospheric mass fractions (0.5–30 per cent), orbiting a solar-like star at 0.1 au. In addition to our computed evolutionary tracks, we also study the stability of planetary atmospheres, showing that the atmospheres of light planets can be completely removed within 1 Gyr and that compact atmospheres have a better survival rate. From a detailed comparison between our results and the output of the previous-generation models, we show that coupling between thermal evolution and atmospheric evaporation considerably affects the thermal state of atmospheres for low-mass planets and, consequently, changes the relationship between atmospheric mass fraction and planetary parameters. We, therefore, conclude that self-consistent consideration of the thermal evolution and atmospheric evaporation is of crucial importance for evolutionary modelling and a better characterization of planetary atmospheres. From our simulations, we derive an analytical expression between planetary radius and atmospheric mass fraction at different ages. In particular, we find that, for a given observed planetary radius, the predicted atmospheric mass fraction changes as age0.11.

scholarly journals Influence of decoupling effect on stellar wind variability

2010 ◽  
Vol 6 (S272) ◽  
pp. 218-219
Author(s):  
Viktor Votruba ◽  
Klára Šejnová ◽  
Pavel Koubský ◽  
Daniela Korčáková
Keyword(s):  
Momentum Transfer ◽  
Stellar Wind ◽  
Stellar Winds ◽  
Spectral Changes ◽  
Wind Variability ◽  
Decoupling Effect ◽  
Hydrodynamic Code

AbstractA detailed investigation of momentum transfer in radiatively driven stellar winds shows that for the thin wind case ion decoupling may occur. The decoupling of absorbing ions significantly affects dynamics of the wind. We analysed such effects using our hydrodynamic code and predicted spectral changes with the help of the SHELLSPEC code.

scholarly journals Erosion of an exoplanetary atmosphere caused by stellar winds

2019 ◽  
Vol 630 ◽  
pp. A52 ◽  
Author(s):  
J. M. Rodríguez-Mozos ◽  
A. Moya
Keyword(s):  
Stellar Wind ◽  
Extreme Environment ◽  
Stellar Winds ◽  
Habitable Zone ◽  
Low Mass Stars ◽  
Zone Versus ◽  
Low Mass ◽  
The Difference ◽  
Interaction Regions ◽  
The Impact

Aims. 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 M⊙. 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. Methods. Using different formulations in the literature in addition to stellar and exoplanet physical characteristics, we estimated the stellar magnetic induction, the main characteristics of the stellar wind, and the different star-planet interaction regions (sub- and super-Alfvénic, sub- and supersonic). With this information, we can estimate the radius of the exoplanet magnetopause and thus the exoplanet unprotected surface. Results. We have conducted a study of the auroral aperture angles for Earth-like exoplanets orbiting the habitable zone of its star, and found different behaviors depending on whether the star is in rotational saturated or unsaturated regimes, with angles of aperture of the auroral ring above or below 36°, respectively, and with different slopes for the linear relation between the auroral aperture angle at the inner edge of the habitable zone versus the difference between auroral aperture angles at the two boundaries of the habitable zone. When the planet is tidally locked, the unprotected angle increases dramatically to values higher than 40° with a low likelihood of keeping its atmosphere. When the impact of stellar wind is produced in the sub-Alfvénic regime, the likelihood of keeping the atmosphere is almost zero for exoplanets orbiting very close to their star, regardless of whether they are saturated or not.

CFD Analysis of Wind Effects on High-Rise Buildings Complex "Panorama City in Bratislava"

2016 ◽  
Vol 837 ◽  
pp. 1-4
Author(s):  
Roland Antal ◽  
Norbert Jendzelovsky
Keyword(s):  
Pressure Coefficient ◽  
External Pressure ◽  
Wind Tunnels ◽  
Wind Flow ◽  
3D Analysis ◽  
Cfd Analysis ◽  
Wind Effects ◽  
High Rise ◽  
Modeling Software ◽  
Volume Method

Analysis of wind flow upon high-rise buildings is very common topic. Nowadays, there are no general or analytical ways how to analyze wind effects on irregular shaped high-rise buildings complexes. Scaled experiments tested in wind tunnels are best for precise solutions, however they are time consuming and expensive too. Therefore we use computational modeling software based on finite volume method to analyze these effects and then, thanks to these analysis we can design structures and optimize them. Paper deals with simplified 3D analysis of wind effects on high-rise buildings complex "Panorama City" located in Bratislava-Slovakia. Through this analysis we obtain results for wind speed near objects and external pressure coefficient as well. Both of them will be helpful to gain insight for future constructions or verification of already constructed ones.

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