scholarly journals Magnetohydrodynamic modelling of star–planet interaction and associated auroral radio emission

2020 ◽  
Vol 494 (4) ◽  
pp. 5044-5055
Author(s):  
Sam Turnpenney ◽  
J D Nichols ◽  
G A Wynn ◽  
X Jia
Keyword(s):  
Radio Emission ◽  
Stellar Wind ◽  
Derived Relations ◽  
Hot Jupiters ◽  
Cyclotron Maser ◽  
Consistent Picture ◽  
Energy Dissipated ◽  
Analytic Models ◽  
Radio Power ◽  
Hot Jupiter

ABSTRACT We present calculations of auroral radio powers of magnetized hot Jupiters orbiting Sun-like stars, computed using global magnetohydrodynamic (MHD) modelling of the magnetospheric and ionospheric convection arising from the interaction between the magnetosphere and the stellar wind. Exoplanetary auroral radio powers are traditionally estimated using empirical or analytically derived relations, such as the radiometric Bode’s law (RBL), which relates radio power to the magnetic or kinetic energy dissipated in the stellar wind–planet interaction. Such methods risk an oversimplification of the magnetospheric electrodynamics giving rise to radio emission. As the next step towards a self-consistent picture, we model the stellar wind–magnetosphere–ionosphere coupling currents using a 3D MHD model. We compute electron-cyclotron maser instability-driven emission from the calculated ionospheric field-aligned current density. We show that the auroral radio power is highly sensitive to interplanetary magnetic field (IMF) strength, and that the emission is saturated for plausible hot Jupiter Pedersen conductances, indicating that radio power may be largely independent of ionospheric conductance. We estimate peak radio powers of 1014 W from a planet exposed to an IMF strength of 103 nT, implying flux densities at a distance of 15 pc from Earth potentially detectable with current and future radio telescopes. We also find a relation between radio power and planetary orbital distance that is broadly consistent with results from previous analytic models of magnetosphere–ionosphere coupling at hot Jupiters, and indicates that the RBL likely overestimates the radio powers by up to two orders of magnitude in the hot Jupiter regime.

Influence of the magnetic field of stellar wind on hot jupiter’s envelopes

2019 ◽  
Vol 15 (S354) ◽  
pp. 268-279
Author(s):  
Dmitry V. Bisikalo ◽  
Andrey G. Zhilkin
Keyword(s):  
Magnetic Field ◽  
Plasma Flow ◽  
Coronal Mass Ejections ◽  
Stellar Wind ◽  
Roche Lobe ◽  
Bow Shock ◽  
Hot Jupiters ◽  
The Magnetic Field ◽  
Alfven Velocity ◽  
Hot Jupiter

AbstractHot Jupiters have extended gaseous (ionospheric) envelopes, which extend far beyond the Roche lobe. The envelopes are loosely bound to the planet and, therefore, are strongly influenced by fluctuations of the stellar wind. We show that, since hot Jupiters are close to the parent stars, magnetic field of the stellar wind is an important factor defining the structure of their magnetospheres. For a typical hot Jupiter, velocity of the stellar wind plasma flow around the atmosphere is close to the Alfvén velocity. As a result stellar wind fluctuations, such as coronal mass ejections, can affect the conditions for the formation of a bow shock around a hot Jupiter. This effect can affect observational manifestations of hot Jupiters.

scholarly journals Multi-Component MHD Model of Hot Jupiter Envelopes

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 422
Author(s):  
Andrey Zhilkin ◽  
Dmitri Bisikalo
Keyword(s):  
Magnetic Field ◽  
Shock Wave ◽  
Numerical Model ◽  
Stellar Wind ◽  
Bow Shock ◽  
Model Description ◽  
Hot Jupiters ◽  
Bow Shock Wave ◽  
Field Lines ◽  
Hot Jupiter

A numerical model description of a hot Jupiter extended envelope based on the approximation of multi-component magnetic hydrodynamics is presented. The main attention is focused on the problem of implementing the completed MHD stellar wind model. As a result, the numerical model becomes applicable for calculating the structure of the extended envelope of hot Jupiters not only in the super-Alfvén and sub-Alfvén regimes of the stellar wind flow around and in the trans-Alfvén regime. The multi-component MHD approximation allows the consideration of changes in the chemical composition of hydrogen–helium envelopes of hot Jupiters. The results of calculations show that, in the case of a super-Alfvén flow regime, all the previously discovered types of extended gas-dynamic envelopes are realized in the new numerical model. With an increase in magnitude of the wind magnetic field, the extended envelope tends to become more closed. Under the influence of a strong magnetic field of the stellar wind, the envelope matter does not move along the ballistic trajectory but along the magnetic field lines of the wind toward the host star. This corresponds to an additional (sub-Alfvénic) envelope type of hot Jupiters, which has specific observational features. In the transient (trans-Alfvén) mode, a bow shock wave has a fragmentary nature. In the fully sub-Alfvén regime, the bow shock wave is not formed, and the flow structure is shock-less.

scholarly journals How expanded ionospheres of Hot Jupiters can prevent escape of radio emission generated by the cyclotron maser instability

2017 ◽  
Vol 469 (3) ◽  
pp. 3505-3517 ◽  
Author(s):  
C. Weber ◽  
H. Lammer ◽  
I. F. Shaikhislamov ◽  
J. M. Chadney ◽  
M. L. Khodachenko ◽  
...  
Keyword(s):  
Radio Emission ◽  
Hot Jupiters ◽  
Cyclotron Maser

scholarly journals Tuning in to the radio environment of HD189733b

2019 ◽  
Vol 15 (S354) ◽  
pp. 305-309
Author(s):  
R. D. Kavanagh ◽  
A. A. Vidotto ◽  
D. Ó Fionnagáin ◽  
V. Bourrier ◽  
R. Fares ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Flux Density ◽  
Stellar Wind ◽  
Planetary Orbit ◽  
Close Proximity ◽  
Peak Flux ◽  
Detection Capabilities ◽  
Reconstructed Surface ◽  
Hot Jupiter

AbstractThe hot Jupiter HD189733b is expected to be a source of strong radio emission, due to its close proximity to its magnetically active host star. Here, we model the stellar wind of its host star, based on reconstructed surface stellar magnetic field maps. We use the local stellar wind properties at the planetary orbit obtained from our models to compute the expected radio emission from the planet. Our findings show that the planet emits with a peak flux density within the detection capabilities of LOFAR. However, due to absorption by the stellar wind itself, this emission may be attenuated significantly. We show that the best time to observe the system is when the planet is near primary transit of the host star, as the attenuation from the stellar wind is lowest in this region.

scholarly journals Optical hydrogen absorption consistent with a bow shock around the hot Jupiter HD 189733 b

2015 ◽  
Vol 11 (S320) ◽  
pp. 376-381 ◽  
Author(s):  
P. Wilson Cauley ◽  
Seth Redfield ◽  
Adam G. Jensen ◽  
Travis Barman ◽  
Michael Endl ◽  
...  
Keyword(s):  
Stellar Wind ◽  
Bow Shock ◽  
Transmission Spectra ◽  
Shock Model ◽  
Hot Jupiters ◽  
Balmer Lines ◽  
Planetary Magnetic Field ◽  
Host Stars ◽  
Hot Jupiter

AbstractHot Jupiters, i.e., Jupiter-mass planets with orbital semi major axes of <10 stellar radii, can interact strongly with their host stars. If the planet is moving supersonically through the stellar wind, a bow shock will form ahead of the planet where the planetary magnetosphere slams into the the stellar wind or where the planetary outflow and stellar wind meet. Here we present high resolution spectra of the hydrogen Balmer lines for a single transit of the hot Jupiter HD 189733 b. Transmission spectra of the Balmer lines show strong absorption ~70 minutes before the predicted optical transit, implying a significant column density of excited hydrogen orbiting ahead of the planet. We show that a simple geometric bow shock model is able to reproduce the important features of the absorption time series while simultaneously matching the line profile morphology. Our model suggests a large planetary magnetic field strength of ~28 G. Follow-up observations are needed to confirm the pre-transit signal and investigate any variability in the measurement.

scholarly journals Tidally induced stellar oscillations: converting modelled oscillations excited by hot Jupiters into observables

2020 ◽  
Vol 500 (2) ◽  
pp. 2711-2731
Author(s):  
Andrew Bunting ◽  
Caroline Terquem
Keyword(s):  
Radial Velocity ◽  
Orbital Period ◽  
Planetary Systems ◽  
Velocity Signal ◽  
Convective Flux ◽  
Hot Jupiters ◽  
Stellar Oscillations ◽  
Orbital Periods ◽  
Hot Jupiter

ABSTRACT We calculate the conversion from non-adiabatic, non-radial oscillations tidally induced by a hot Jupiter on a star to observable spectroscopic and photometric signals. Models with both frozen convection and an approximation for a perturbation to the convective flux are discussed. Observables are calculated for some real planetary systems to give specific predictions. The photometric signal is predicted to be proportional to the inverse square of the orbital period, P−2, as in the equilibrium tide approximation. However, the radial velocity signal is predicted to be proportional to P−1, and is therefore much larger at long orbital periods than the signal corresponding to the equilibrium tide approximation, which is proportional to P−3. The prospects for detecting these oscillations and the implications for the detection and characterization of planets are discussed.

scholarly journals TOI-150b and TOI-163b: two transiting hot Jupiters, one eccentric and one inflated, revealed by TESS near and at the edge of the JWST CVZ

2019 ◽  
Vol 490 (1) ◽  
pp. 1094-1110 ◽  
Author(s):  
Diana Kossakowski ◽  
Néstor Espinoza ◽  
Rafael Brahm ◽  
Andrés Jordán ◽  
Thomas Henning ◽  
...  
Keyword(s):  
High Resolution ◽  
Time Scale ◽  
High Resolution Spectroscopy ◽  
Spin Orbit ◽  
Eccentric Orbit ◽  
Hot Jupiters ◽  
Eclipse Observations ◽  
James Webb Space Telescope ◽  
Hot Jupiter

Abstract We present the discovery of TYC9191-519-1b (TOI-150b, TIC 271893367) and HD271181b (TOI-163b, TIC 179317684), two hot Jupiters initially detected using 30-min cadence Transiting Exoplanet Survey Satellite (TESS) photometry from Sector 1 and thoroughly characterized through follow-up photometry (CHAT, Hazelwood, LCO/CTIO, El Sauce, TRAPPIST-S), high-resolution spectroscopy (FEROS, CORALIE), and speckle imaging (Gemini/DSSI), confirming the planetary nature of the two signals. A simultaneous joint fit of photometry and radial velocity using a new fitting package juliet reveals that TOI-150b is a $1.254\pm 0.016\ \rm {R}_ \rm{J}$, massive ($2.61^{+0.19}_{-0.12}\ \rm {M}_ \rm{J}$) hot Jupiter in a 5.857-d orbit, while TOI-163b is an inflated ($R_ \rm{P}$ = $1.478^{+0.022}_{-0.029} \,\mathrm{ R}_ \rm{J}$, $M_ \rm{P}$ = $1.219\pm 0.11 \, \rm{M}_ \rm{J}$) hot Jupiter on a P = 4.231-d orbit; both planets orbit F-type stars. A particularly interesting result is that TOI-150b shows an eccentric orbit ($e=0.262^{+0.045}_{-0.037}$), which is quite uncommon among hot Jupiters. We estimate that this is consistent, however, with the circularization time-scale, which is slightly larger than the age of the system. These two hot Jupiters are both prime candidates for further characterization – in particular, both are excellent candidates for determining spin-orbit alignments via the Rossiter–McLaughlin (RM) effect and for characterizing atmospheric thermal structures using secondary eclipse observations considering they are both located closely to the James Webb Space Telescope (JWST) Continuous Viewing Zone (CVZ).

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 (&lt;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 $\dot{M} u_{\rm sw}^{3} \gtrsim 1.8\times 10^{-4} \, {\rm M}_\odot \,{\rm yr}^{-1}\, ({\rm km\,s^{-1}})^{3}$.

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