Star-planet interaction and planetary characterization methods

Transcription

1 Star-planet interaction and planetary characterization methods K. G. Kislyakova (1), H. Lammer (1), M. Holmström (2), C.P. Johnstone (3) P. Odert (4), N.V. Erkaev (5,6) (1) Space Research Institute (IWF), Austrian Academy of Sciences, Graz, Austria (2) Swedish Institute of Space Physics, Kiruna, Sweden (3) University of Vienna, Department of Astrophysics, Wien, Austria (4) Institute of Physics, University of Graz, Graz, Austria (5) Institute of Computational Modelling, Siberian Division of Russian Academy of Sciences, Krasnoyarsk, Russia (6) Siberian Federal University, Krasnoyarsk, Russia K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

2 Aims & processes Characterization of the stellar plasma environment around exoplanets Estimation of the pickup ion escape Estimation of the planetary magnetic moment Included processes for an exospheric atom: Charge-exchange with stellar H + Ionization (photoionization, electron impact ionization) Scattering of an UV photon (radiation pressure, velocity dependent) Elastic collision with another hydrogen atom Gravitational effects (besides gravity - tidal, coriolis, centrifugal forces) Self-shielding (optical thickness in Lyα). K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

3 Planetary densities and populations [Rauer et al., ExA, 2014] K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

4 XUV/EUV stellar evolution Sun-type star, 1 AU, normalized to the present solar values of [5.27,1.69] erg cm 2 s 1 Comparison to an M dwarf (Gliese 436) [Lammer et al., MNRAS, 2014] [Kislyakova et al., Astrobiology, 2013] K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

5 Evolution of captured envelopes All processes are calculated for planets orbiting a Sun-type star at 1 AU [Lammer et al., MNRAS, 2014] K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

6 Simulation domain geometry The assumed magnetospheric obstacle ( X = R s 1 x 2 + y 2 ) where R s and R t define the location of the substellar point and the obstacle width, respectively. R 2 t K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

7 Energetic neutral atoms (ENAs) H + sw + H pl H ENA sw H + sw + N pl H ENA sw H + sw + O pl H ENA sw H + sw + C pl H ENA sw + H + pl + N + pl + O + pl + C + pl Chassefière, 1996, JGR ENAs or energetic neutral atoms were observed everywhere around the Solar system planets where the corresponding equipment was available K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

8 Estimated XUV and Lyα emission XUV fluxes enhancement factors (at Kepler-11b f orbital locations: I XUV =60; 45; 20; 13; 8) are used to calculate the photoionization rate τ pi UV absorption rate (shown left) is defined as β abs = σ(λ)φ(λ)dλ, where σ(λ) is the absorption cross-section and Φ(λ) is the stellar Lyα spectrum. The absorption cross-section is σ(λ) = ψ(v)σ N (λ )dv, where ψ(v) is the normalized atomic velocity distribution and σ N (λ ) is the natural absorption cross-section of an atom traveling with velocity v, for which λ = λ(1 v/c) Estimated by P. Odert K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

9 Atmospheric expansion Based on following equation system (Penz, T., Erkaev, N.V., Kulikov, Yu.N., et al.: Planet. Space Sci. 56, 1260, 2008): n t + 1 nvr 2 r 2 n n t r = 0 v + nv r + 1 p m r = nf grav ) = ( r r 2 χ T ) r nm ( E t + v E r q p 1 r 2 r 2 v r + 1 r 2 [Erkaev et al., Astrobiology, 2013, number 11] where p = nkt, E = 1 p γ 1 nm - the set of the hydrodynamic fluid equations for mass, momentum and energy conservation in spherical coordinate system K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

10 Stellar wind plasma properties Stellar wind parameters were obtained using the publicly available code NIRVANA. The code is used to estimate stellar wind density n sw, velocity v sw and temperature T sw at the planetary orbital locations taking into account that Kepler-11 is a Sun-type star (6-10 Gyr). (simulations performed by C. P. Johnstone) K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

11 Paraboloid magnetic model (PMM) [Khodachenko et al., ApJ, 2012, 744] K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

12 Nonthermal escape study: HZ of GJ436 [Kislyakova et al., Astrobiology, 2013] K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

13 Parameters of the Kepler-11 system Table : Planetary and stellar parameters for the Kepler-11 system (Lissauer et al., 2011, Exoplanet/star Kepler-11 Kepler-11b Kepler-11c Kepler-11d Kepler-11e Kepler-11f d [AU] 613 [pc] K.G. Kislyakova (IWF) i, [deg] Rpl [RL ] 1.1±0.1 [RJ ] 1.97± ± ± ± ±0.25 Rpl [m] Star-planet interaction... Mpl [ML ] 0.95±0.1 [MJ ] Mpl [kg] December 04, / 20

14 Modeling results, η=15% [Kislyakova et al., A&A, 2014, 562] K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

15 Ion pickup VS thermal escape Ion production rates and thermal escape rates in [g s 1 ]. Thermal escape rates are taken from Table 3 of Lammer et al., MNSRAS, η=15% η=40% Exoplanet L ion L th L ion L th Kepler-11b Kepler-11c Kepler-11d Kepler-11e Kepler-11f We assume that an ion is lost from the planet if its gyro radius does not exceed R 0. The biggest gyro radius estimated for the simulations is r g = m Hv qb = [m] Magnetic field is the one of the star. The particle is assumed to be accelerated up to the stellar wind velocity. K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

16 Geometry and modelling, HD b ( ) 8π M = 2 Rs 6 ρ swvrel 2 1/2 µ 0 f0 2 [Kislyakova et al., Science, 2014, 346] K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

17 Modelling results, HD b Estimated magnetic moment: M pl A m M Jup [Kislyakova et al., Science, 2014, 346] K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

18 The detection range of PLATO 2.0 [Rauer et al., ExA, 2014] K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

19 Main conclusions High radiation pressure and intense charge-exchange reshape the hydrogen cloud around the planet leading to strong asymmetry. Ion pickup loss rates for the hydrogen-dominated exoplanets are approximately one magnitude smaller than the thermal losses. DSMC modelling combined with Lyα transit observations can be used to determine the magnetic moment of an exoplanet Taking HD b as an example, the method predicts the magnetic moment of 10% M Jup. The PLATO mission will grant new perspective targets. K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20

20 Main publications: Erkaev et al., Astrobiology, 2013 Kislyakova et al., Astrobiology, 2013 Lammer et al., MNRAS, 2013 Lammer et al., MNRAS, 2014 Kislyakova et al., A&A, 2014 Kislyakova et al., Science, 2014 K.G. Kislyakova (IWF) Star-planet interaction... December 04, / 20