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A young massive planet in a star-disk system

A young massive planet in a star-disk system. Setiawan, Henning, Launhardt et al. January 2008, Nature Letter 451. ESO Journal Club – January 2008. The target: TW Hya. The disk around TW Hya. Krist et al. 2000 HST/ WFPC R and I-band. Trilling et al. 2001 HST / H-band corono.

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A young massive planet in a star-disk system

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  1. A young massive planet in a star-disk system Setiawan, Henning, Launhardt et al. January 2008, Nature Letter 451 ESO Journal Club – January 2008

  2. The target: TW Hya

  3. The disk around TW Hya Krist et al. 2000 HST/ WFPC R and I-band Trilling et al. 2001 HST / H-band corono. TW Hya is surrounded by a Nearly face-on disk

  4. +- 1 Qi et al. 2004, sub-mm The disk around TW Hya TW Hya is an almost pole-on system

  5. The accretion disk around TW Hya In CCTS: Strong accretion declines with age At 10 Myr: no more accretion (disk lifetime) In TW Hya: Optical spectrum shows strong emission lines related with accretion processes Accretion rate ~ 1e-9 Msun/yr At 10 Myr, the object is still accreting !!

  6. Planets around TW Hya? Lack of IR excess below 10 Microns Gap in the inner disk (0.4 - 5 AU) Calvet et al. 2002 SED modeling: Inner Disk clearing as a consequence of planet formation

  7. Planets around TW Hya? High contrast imaging techniques have not revealed the presence of a planet at separations > 5 AU (e.g., Apai et al. 2004). Setiawan et al. 2008: Hunting planets using RV techniques Advantage: they can study planets in closer orbits Disadvantages: TW Hya is a young and very active star (radial velocity variations due to spots, pulsations…) Moreover, it is an accreting star ???

  8. Planets around young, active stars: the RV technique Setiawan et al. 2007

  9. Planets around young, active stars: the RV technique TW Hya (8-10 Myr) Setiawan et al. 2007

  10. TW Hya: RV observations FEROS observations 2.2 m MPG/ESO telescope 2 data sets from two observing runs: 12 consecutive nights between 28th FEB – 12th MAR 2007 20 consecutive nights between 24th APR – 13th MAY 2007 First run : 33 data points Second run : 33 data points Setiawan et al. 2008, Nature Letter

  11. TW Hya: RV resultsI. RV Variations RV accuracy: 40 m/s RV amplitude: 198 ± 60 m/s Setiawan et al. 2008, Nature Letter

  12. TW Hya: RV resultsII. Periodic RV variations Scargle periodogram FAP (3.56 days)= 1e-14 Three possible periods Setiawan et al. 2008, Nature Letter

  13. TW Hya: RV results Setiawan et al. 2008, Nature Letter

  14. Line Bisector Analysis: Cross-correlation function Velocity span= Vt – Vb _ _ RV variations: Activity or a planet? Bisector of the CCF CCF star Queloz et al. 2001,

  15. RV variations: Activity or a planet? TW Hya Bisector analysis of the CCF: No correlation with the RV Variations The RV variations are not related with stellar activity. then… COMPANION Setiawan et al. 2008, Nature Letter

  16. The planet around TW Hya Setiawan et al. 2008, Nature Letter

  17. The planet around TW Hya Plotoplanetary disk are really protoplanetary… Setiawan et al. 2008, Nature Letter

  18. Timescales of planet formation? Metallicity? Core accretion predicts more efficient planet formation around metal-rich stars [M/H] = -0.11 ± 0.12 (Yang et al. 2005) Mass? Core accretion predicts a deficit of massive planets (Mp > 3 Mjup) at small separations (a < 0.2 AU) 9.8 Mjup at 0.04 AU Santos et al. 2003 The planet around TW Hya:Implications for planet formation theories? Core accretion vs Disk Instability Planet formation and migration must be completed within 10 Myr Setiawan et al. 2008, Nature Letter

  19. Accretion processes in CTTS - Hot spots on the stellar surface (filling factor = 0.1 – 5%) - Accretion shocks: Excess Continuum Emission (veiling) - Emission lines in the accretion columns - Disk winds

  20. Accretion & RV observations • Accretion – RV variation? • Correlation between bisector and RV? • Can veiling affect the RV measurements? • Timescale of accretion processes?

  21. TW Hya: Photometric Variability 2 weeks of monitoring What is the origin of the brightness modulation? Hot spots on the surface Lawson & Crause 2005

  22. TW Hya: Photometric Variability B-band observations Batalha et al. 2002

  23. veiling lines lines veiling TW Hya: Accretion signatures Line emission and Continuum variability not in phase Batalha et al. 2002 Alencar & Batalha 2002

  24. TW Hya: Timescale of Accretion Events ‘The accretion is a highly time dependent process on timescales ranging from hours to months, maybe even years…’ ( Bouvier et al.2004) The fact that Setiawan et al. are able to reproduce the same periodicity in 2 independent datasets strengthens the planet interpretation In the case of TW Hya… The orbital period is ‘close’ to the ones found in TW Hya Accretion events. TW Hya: Up to know variable periodicities (due to accretion) within years, not months… And the target is one of the oldest CTTS (accretion rate ~2 orders of magnitude smaller than younger CTTS)

  25. TW Hya: RV & Accretion • What is important in the case of RV studies? • Accretion shocks • 1. Hot continuum excess (veiling) • - It varies the depth of the absorption lines, it can affect the RV calculation and produce variable CCF • - It does not affect the line profile • 2. Hot spots: stellar surface inhomogeneity • What is the expected RV variation? Size, Temperature • Do they change the line profile? • Is the bisector correlated with the RV variation?

  26. RV & Veiling TW Hya Photosphere Alencar & Batalha 2002 Batalha et al. 2002 Veiling: change in continuum level and, therefore, in the absorption depth of spectral lines It is wavelength dependent

  27. RV & Veiling And the bisector? Veiling: Variable CCF Hot spots: RV correlated with the bisector?

  28. RU Lup: Activity, accretion or a companion? RU Lup CTTS K7 Teff = 4000 K Dist ~ 200 pc Age ~ 2-5 Myr Ṁ = 10e-7 Mסּ/yr v.sin i = 9 km/s Inclination ~ 24 deg Activity and accretion Error = 0.2 Km/s RV variations RV amplitude = 2.2 Km/s Period = 3.7 days Activity, accretion, companion? Stempels et al. 2007

  29. RU Lup: Activity, Accretion or planet? The RV variations are related with stellar activity. Stempels et al. 2007

  30. RV: Activity, Accretion or planet? RV variation vs the spot properties (Size,temperature) Cold Spot Model Hot spots: They cover 0.1 – 5 % of the stellar surface of CTTS They need a 40 deg hot spot with 7000 K to get 2.2 Km/s Stempels et al. 2007

  31. Model R spot = 35 deg T spot = 3400 K RU Lup: Activity, Accretion or planet? The RV variations can be modelled with a big dark spot To create such spots, they estimate B ~ 3 kG) Stempels et al. 2007

  32. 5 degrees RU Lup vs TW Hya RV variation vs the spot properties (Size,temperature) Hot spots: They cover 0.1 – 5 % of the stellar surface of CTTS TW Hya: f~ 0.3-1.6%, Tspot ~8000K B = 2.61 ±0.23 kG --- Cold spots must be present.… Stempels et al. 2007

  33. Some final remarks… If the planet is real: The detection of the planet confirms that protoplanetary disks are certainly protoplanetary… Comparison with planet formation theories will provide new clues about the planetary formation process The theories should try to reproduce the formation of this planet My personal conclusions: (I think) Some work on RV and Accretion is needed for these stars

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