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. Winnand Subaru collaboration team

IAU253 Transiting Planets: May 20 2008

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

hide approaching side

→ appear to be receding

hide receding side

→ appear to be approaching

planet planetstar

When a transiting planet hides stellar rotation,

Radial velocity would have anomalous excursion

during transit.

The Rossiter-McLaughlin effect

beta Lyrae ： Rossiter (1924)

Algol: McLaughlin (1924)

This effect was originally reported in eclipsing binary systems.

First RM Detection in Transiting System

Queloz et al. (2000)

The RM effect in HD209458

Vp

(m s

-1)

What can we learn from RM observations?

Gaudi & Winn (2007)

The shape of RM anomaly

depends on the trajectory of the transiting planet.

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?

• Type II migration

– planetary disk and planet interaction

• Planet-Planet interaction

– multiple-planet interaction and scattering

• Kozai migration

– perturbation by a binary companion

λ is connected with planet migration models.

e.g.,

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.

0 30 60 90 120 150 180 deg

Nagasawa, Ida, & Bessho (2008)

Misaligned planets might be common in this case.

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

Queloz et al. (2000)

Vp

(m s

-1)

This detection encouraged us to try other transiting systems.

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

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 pl

anet 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!