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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 Spec. Type Distance (pc) Mass (M)סּ Radius (R)סּ Teff (K) L (L)סּ Age (Myr) v.sin i (km/s) K7 V 56 ± 7 0.7 ± 0.1 0.9 ± 0.1 4000 ± 150 0.20 ± 0.05 8-10 5-7 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 The disk around TW Hya +- 1 Qi et al. 2004, sub-mm TW Hya is an almost pole-on system 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 !! 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 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 ??? Planets around young, active stars: the RV technique Setiawan et al. 2007 Planets around young, active stars: the RV technique TW Hya (8-10 Myr) Setiawan et al. 2007 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 : Second run : 33 data points 33 data points Setiawan et al. 2008, Nature Letter TW Hya: RV results I. RV Variations RV accuracy: 40 m/s RV amplitude: 198 ± 60 m/s Setiawan et al. 2008, Nature Letter TW Hya: RV results II. Periodic RV variations Scargle periodogram FAP (3.56 days)= 1e-14 Three possible periods Setiawan et al. 2008, Nature Letter TW Hya: RV results Setiawan et al. 2008, Nature Letter RV variations: Activity or a planet? Bisector of the CCF CCF star Line Bisector Analysis: Cross-correlation function _ _ Velocity span= Vt – Vb Queloz et al. 2001, 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 The planet around TW Hya Setiawan et al. 2008, Nature Letter The planet around TW Hya Plotoplanetary disk are really protoplanetary… Setiawan et al. 2008, Nature Letter 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 Timescales of planet formation? Santos et al. 2003 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 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 Accretion & RV observations • Accretion – RV variation? • Correlation between bisector and RV? • Can veiling affect the RV measurements? • Timescale of accretion processes? TW Hya: Photometric Variability 2 weeks of monitoring What is the origin of the brightness modulation? Hot spots on the surface Lawson & Crause 2005 TW Hya: Photometric Variability B-band observations Batalha et al. 2002 TW Hya: Accretion signatures veiling lines lines veiling Line emission and Continuum variability not in phase Batalha et al. 2002 Alencar & Batalha 2002 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) 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? RV & Veiling TW Hya Photosphere Batalha et al. 2002 Alencar & Batalha 2002 Veiling: change in continuum level and, therefore, in the absorption depth of spectral lines It is wavelength dependent RV & Veiling And the bisector? Veiling: Variable CCF Hot spots: RV correlated with the bisector? RU Lup: Activity, accretion or a companion? RU Lup Error = 0.2 Km/s 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 RV variations RV amplitude = 2.2 Km/s Period = 3.7 days Activity, accretion, companion? Stempels et al. 2007 RU Lup: Activity, Accretion or planet? The RV variations are related with stellar activity. Stempels et al. 2007 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 RU Lup: Activity, Accretion or planet? Model R spot = 35 deg T spot = 3400 K The RV variations can be modelled with a big dark spot To create such spots, they estimate B ~ 3 kG) Stempels et al. 2007 RU Lup vs TW Hya RV variation vs the spot properties (Size,temperature) 5 degrees 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 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