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

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

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.

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

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

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

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)

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

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

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)

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!

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

RM observations in literature HD209458 Queloz et al. 2000, Winn et al. 2005 HD189733 Winn et al. 2006 TrES-1 Narita et al. 2007 HAT-P-2 Winn et al. 2007, Loeillet et al. 2008 HD149026 Wolf et al. 2007 HD17156 Narita et al. 2008 TrES-2 Winn et al. 2008 CoRoT-Exo-2 Bouchy et al. 2008 HAT-P-1 Johnson et al. 2008 XO-3 Hebrard et al. 2008 red: eccentric blue: binary

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 ~ 0.67 (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. 12 2007 in Japan

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

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)

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

Around transit phase

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)

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!