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1 th CoRoT Symposium, February 01 - 05, Paris, France, 2009

Determining the mass loss boundary for hot gas giants: What can we learn from transit observations?.

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1 th CoRoT Symposium, February 01 - 05, Paris, France, 2009

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  1. Determining the mass loss boundary for hot gas giants: What can we learn from transit observations? H. Lammer (1), M. L. Khodachenko (1), H. I. M. Lichtenegger (1), Yu. N. Kulikov (2), N. V. Erkaev (3), G. Wuchterl (4), P. Odert (5), M. Leitzinger (5), J. Weingrill (1), A. Hanslmeier (5), T. Penz (6) (1) Space Research Institute, Austrian Academy of Sciences, Graz, Austria (2) Polar Geophysical Institute, Russian Academy of Sciences, Murmansk, Russian Federation (3) Institute for Computational Modelling, Russian Academy of Sciences, and Siberian Federal University, Russian Federation (4) Thüringer Landessternwarte Tautenburg, Tautenburg, Germany (5) Institute for Physics, University of Graz, Graz, Austria (6) On leave from the INAF - Osservatorio Astronomico, Palermo, Italy 1th CoRoT Symposium, February 01 - 05, Paris, France, 2009

  2. Motivation • What is the effect on the mass evolution of close-in gas giants related to thermal and non-thermal atmospheric escape? • Are these loss processes efficient enough to remove the hydrogen inventory of very close gas giants during their life-time? • What is the influence of these loss processes to the mass and size of discovered hot Neptune`s and other lower mass exoplanets? Energy limited approaches → thermal escape modelling - Lammer et al. [ApJ 598, L121, 2003] → evolution studies (Loss overestimation) - Baraffe et al. [A&A 419, L13, 2004] → evolution studies (Loss overestimation) - Lecavalier des Etangs et al. [A&A 418, L1, 2004] (Loss overestimation) - Lecavalier des Etangs [A&A 461, 1185, 2007] → evolution studies (Loss overestimation) - Hubbard et al. [Icarus 187, 358, 2007] - Hubbard et al. [ApJ 685, L59, 2007] - Penz et al. [A&A 477, 309, 2008] → evolution studies Hydrodynamic approaches → thermal escape modelling - Yelle [Icarus 170, 167, 2004] - Tian et al. [ApJ 621, 1049, 2005] - Gracia Muñoz [PSS 55, 1426, 2007] - Penz et al. [PSS 56, 1260, 2008] → evolution studies Stellar plasma – atmosphere erosion → non-thermal escape modelling - Erkaev et al. [ApJS 157, 396, 2005] - Khodachenko et al. [PSS 55, 631, 2007] → evolution studies

  3. Thermal escape of hydrogen from close-in gas giants → non-linear process Energy limited approach incl. Roche lobe effect Hydrodynamic approach Solar proxies- Sun in Time program - G stars → XUV evolution Penz et al. [A&A 477, 309, 2008] Penz et al. [PSS, 56, 1260, 2008] HD209458b at 0.045 AU

  4. Loss enhancement due to the Roche Lobe η K is the potential energy reduction factor due to the stellar tidal forces Erkeav et al. [A&A 472, 329–334 (2007)] HD209458b at 0.02 AU Penz et al. [PSS, 56, 1260, 2008]

  5. Thermal escape of hydrogen from close-in gas giants Based on the hydro-loss model of Penz et al. [A.&A, 477, 309, 2008]; Penz et al. [PSS, 56, 1260, 2008] EGP I: MEGP I = 1 × 1029 g  16.7 MEarth ~ 1 MNeptune EGP II: MEGP II = 1 × 1030 g  167 MEarth ~ 1.75 MSaturn ~ 0.5 MJupiter A Neptune-type body can loose its hydrogen envelope due to thermal escape Thermal escape is not efficient enough to evaporate a Hot Jupiter down to its core size

  6. ♦ White-lightSoHO/LASCO coronagraphs imagesempirical power-law dependence for nCME(d) (Lara, et al., Geofísica Internacional, 43, 75, 2004): nminCME(d) =4.88 (d / d0)-2.3 nmaxCME(d) =7.10 (d / d0)-3.0 withd0 = 1 AU nCME(d) = n0 (d / d0)-3.6 - good approximation within  20 RSun (n0 ~ (5-50)x105 cm-3 ; d0 ~ (3 - 5)RSun) ♦At the larger distances (0.3 – 1) AUnCME and CMEare measured in-situ by spacecraft.Magnetic Clouds (MCs) – the indicator of far CME - approximation at > 0.3 AU (n0MC = 6.47  0.95 cm-3 ; d0 = 1 AU) nMC(d) = n0MC (d / d0)(-2.4  0.3) Stellar wind &CME activity → extreme plasma interaction → non-thermal escape ●Parameters of CMEs:density [Khodachenko et al. PSS, 55, 631, 2007]

  7. Stellar plasma propagation modelling For G-type stars using the Sun as a proxy

  8. Estimation of stellar plasma induced ion erosion from a Jupiter-mass exoplanet Lammer et al., in preparation based on test-particle model explained in Khodachenko et al. [PSS, 55, 631, 2007] In case the planet has no or a very weak intrinsic magnetic field the stellar plasma dynamic pressure will be ballanced by the ionospheric pressure THE QUESTION IS: at which altitude distance can the obstacle form? If the planetary obstacle builds up at a distance of about 1.5 planetary radii above the visual radius of the exoplanet, huge ion erosion can be expected!

  9. Ionosphere profiles of hot Jupiter`s 0.1 AU 0.45 AU 0.01 AU 0.3 Rp/R = 3.3 Rp Yelle [Icarus, 170, 167, 2004]

  10. Ionopause estimation for non- or weakly magnetized hot Jupiter’s Non-magnetic hot Jupiter`s: Can they survive? Closer d → denser stellar plasma → lower plasma velocity Closer d → higher ionoization → higher ion pressure 3Rpl Rip ≥ 3 Rpl→ We do not expect that stellar plasma erosion at close orbital distances is efficient enough to remove the whole hydrogen atmoshere of a hot Jupiter so that the core of these gas giants remain

  11. Conclusions All discovered hot Neptune`s are not remaining remnants of more massive gas giants! They may have lost or loose their hydrogen envelopes but they originated as lower mass planets Roche lobe effect becomes relevant at d ≤ 0.02 AU!

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