1. IAU253 Transiting Planets: May 20 2008
The Rossiter-McLaughlin Effect and a Possible Spin-Orbit Misalignment in HD17156b
Norio Narita
(National Astronomical Observatory of Japan)
in collaboration with
Bun’ei Sato, Osamu Ohshima, Joshua N. Winn
and Subaru collaboration team

2. Outline Introduction of the RM effect
Link to planetary migration models
Previous observations of the RM effect
The case for HD17156b

3. Radial velocity anomaly during transit
When a transiting planet hides stellar rotation,
hide approaching side
→ appear to be receding
hide receding side
→ appear to be approaching
planet
star
Radial velocity would have anomalous excursion
during transit.

4. The Rossiter-McLaughlin effect
This effect was originally reported in eclipsing binary systems.
beta Lyrae： Rossiter (1924)
Algol: McLaughlin (1924)

5. First RM Detection in Transiting System
The RM effect in HD209458
Vp (m s-1)
Queloz et al. (2000)

6. What can we learn from RM observations?
The shape of RM anomaly
depends on the trajectory of the transiting planet.
Gaudi & Winn (2007)

7. Observable parameter λ： sky-projected angle between
the stellar spin axis and the planetary orbital axis
(e.g., Ohta et al. 2005, Gimentz 2006, Gaudi & Winn 2007)

8. Why is the RM effect interesting?
λ is connected with planet migration models.
Type II migration
planetary disk and planet interaction
Planet-Planet interaction
multiple-planet interaction and scattering
Kozai migration
perturbation by a binary companion
e.g.,
to explain current orbital distribution of planets

9. Comparison of resultant planets
Type II migration
small eccentricity and inclination
can roughly explain semi-major axis distribution (Ida & Lin 2004)
but cannot explain eccentric planets
Planet-Planet interaction / Kozai migration
possible large eccentricity and inclination
would explain eccentricity distribution when combined with Type II migration models

10. Simulation Result by Nagasawa et al.
Misaligned planets might be common in this case. 30 60 90
120
150
180 deg
Nagasawa, Ida, & Bessho (2008)

11. Motivation of RM observations
λ is an important and basic parameter to characterize planetary systems.
We can test those planet migration models via the RM effect.
Anyway, it is interesting if any misaligned or retrograde planet could be found.
The RM study is unique for transiting systems!

12. First RM Observation in Transiting System
This detection encouraged us to try other transiting systems.
Vp (m s-1)
Queloz et al. (2000)

13. RM observations in literature
HD Queloz et al. 2000, Winn et al. 2005
HD Winn et al. 2006
TrES Narita et al. 2007
HAT-P Winn et al. 2007, Loeillet et al. 2008
HD Wolf et al. 2007
HD Narita et al. 2008
TrES Winn et al. 2008
CoRoT-Exo-2 Bouchy et al. 2008
HAT-P Johnson et al. 2008
XO Hebrard et al. 2008
red: eccentric
blue: binary

14. HD17156b Reported by Fischer et al. (May 2007)
Transit was detected by Barbieri et al. (Oct. 2007)
magnitude: V ~ 8.2 (bright!)
planet mass: Mp ~ 3.1 MJup (massive!)
eccentricity: e ~ (eccentric!)
period: P ~ 21.2 days (long!)
We arranged simultaneous spectroscopic/photometric obs.
Okayama Astrophysical Observatory (OAO) 188cm telescope
Japanese Transit Observation Network (amateur astronomers)
Observations were conducted on Nov in Japan

15. Our data Upper panel Rc band photometry 251 samples ~4 mmag accuracy
Lower panel
OAO radial velocity
25 samples (incl. other nights)
10 ~ 20 m/s accuracy

16. Analysis Combined with published RV dataset
Subaru 9, Keck 24 samples (Fischer et al. 2007)
Simultaneous fitting with analytic formulae
Ohta, Taruya, & Suto (2005, 2006)
Fitting statistics
constraint on VsinIs to match SME analysis in Fischer et al. (2007)

17. Radial velocity fitting
error of RV offset is 3.9 m/s
red circle: OAO, triangle: Subaru, square: Keck

18. Around transit phase

19. Discussion Our data show a possible spin-orbit misalignment
but statistically marginal
need confirmation with larger telescopes
If the misalignment could be true, the result would support recent planet-planet interaction models.
If not, any damping mechanism for spin-orbit alignment may be needed.
note: another eccentric planet HAT-P-2b did not show misalignment (Winn et al. 2007, Loeillet et al. 2008)

20. Summary
The RM effect provide us opportunities to test planet migration models.
transiting planets with eccentricity or in binary system would be important RM targets in the future
See also,
Poster No. 5 (Barbieri et al.) and No. 20 (Triaud et al.) for another HD17156 results!
Poster No. 44 (Hebrard et al.) for XO-3’s new result!