Transcript 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
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