a young massive planet in a star-disk system
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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 K7 VDistance (pc) 56 ± 7Mass (Mּס) 0.7 ± 0.1Radius (Rּס) 0.9 ± 0.1Teff (K) 4000 ± 150L (Lּס) 0.20 ± 0.05Age (Myr) 8-10v.sin i (km/s) 5 - 7
The disk around TW HyaKrist 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
Qi et al. 2004, sub-mm
+- 1
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?
Calvet et al. 2002
SED modeling: Inner Disk clearing as a consequence of planet formation
Lack of IR excess below 10 Microns
Gap in the inner disk (0.4 - 5 AU)
Planets around TW Hya?
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 ???
High contrast imaging techniques have not revealed the presence of a planet at separations > 5 AU (e.g., Apai et al. 2004).
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 observationsFEROS observations 2.2 m MPG/ESO telescope
2 data sets from two observing runs:
12 consecutive nights between 28th FEB – 12th MAR 200720 consecutive nights between 24th APR – 13th MAY 2007
First run : 33 data pointsSecond run : 33 data points
Setiawan et al. 2008, Nature Letter
TW Hya: RV resultsI. RV Variations
Setiawan et al. 2008, Nature Letter
RV amplitude:
198 ± 60 m/s
RV accuracy:
40 m/s
TW Hya: RV resultsII. Periodic RV variations
Setiawan et al. 2008, Nature Letter
FAP (3.56 days)= 1e-14
Three possible periods
Scargle periodogram
TW Hya: RV results
Setiawan et al. 2008, Nature Letter
RV variations: Activity or a planet?
Queloz et al. 2001,
Line Bisector Analysis:
Cross-correlation function
Velocity span= Vt – Vb_ _
CCF starBisector of the CCF
RV variations: Activity or a planet?
Setiawan et al. 2008, Nature Letter
TW Hya
Bisector analysis of the CCF:
No correlation with the RV Variations
The RV variations are not related with stellar activity.
then…
COMPANION
The planet around TW Hya
Setiawan et al. 2008, Nature Letter
The planet around TW Hya
Setiawan et al. 2008, Nature Letter
Plotoplanetary disk are really protoplanetary…
The planet around TW Hya:Implications for planet formation theories?
Setiawan et al. 2008, Nature Letter
Core accretion vs Disk Instability
Planet formation and migration must be completed within 10 Myr
Santos et al. 2003
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
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
What is the origin of the brightness modulation?
Lawson & Crause 2005
Hot spots on the surface
2 weeks of monitoring
TW Hya: Photometric Variability
Batalha et al. 2002
B-band observations
TW Hya: Accretion signatures
Batalha et al. 2002Alencar & Batalha 2002
lines
veiling
veilinglines
Line emission and Continuum variability not in phase
TW Hya: Timescale of Accretion Events
( Bouvier et al.2004)
‘The accretion is a highly time dependent process on timescalesranging from hours to months, maybe even years…’
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 & AccretionWhat 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
Veiling: change in continuum level and, therefore, in the absorption depth of spectral lines
It is wavelength dependent
Alencar & Batalha 2002Batalha et al. 2002
TW Hya Photosphere
RV & VeilingAnd the bisector?
Veiling: Variable CCF Hot spots: RV correlated with the bisector?
RU Lup: Activity, accretion or a companion?
Stempels et al. 2007
RU LupCTTSK7 Teff = 4000 K
Dist ~ 200 pcAge ~ 2-5 MyrṀ = 10e-7 Mּס/yrv.sin i = 9 km/sInclination ~ 24 deg
Activity and accretion
RV variations
RV amplitude = 2.2 Km/sPeriod = 3.7 days
Error = 0.2 Km/s
Activity, accretion, companion?
RU Lup: Activity, Accretion or planet?
Stempels et al. 2007
The RV variations are related with stellar activity.
RV: Activity, Accretion or planet?
Stempels et al. 2007
RV variation vs the spot properties (Size,temperature)
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
Cold Spot Model
RU Lup: Activity, Accretion or planet?
Stempels et al. 2007
The RV variations can be modelled with a big dark spotTo create such spots, they estimate B ~ 3 kG)
ModelR spot = 35 degT spot = 3400 K
RU Lup vs TW Hya
Stempels et al. 2007
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.…
Some final remarks…If the planet is real:
The detection of the planet confirms that protoplanetary disks arecertainly protoplanetary…
Comparison with planet formation theories will provide new cluesabout 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