Measurement of Spin‐Orbit Alignment in an Extrasolar Planetary System

Winn, Joshua N.; Noyes, R. W.; Holman, Matthew J.; Charbonneau, David; Ohta, Yuichi; Taruya, Atsushi; Suto, Yasushi; Narita, Norio; Turner, Edwin L.; Johnson, John Asher; Marcy, Geoffrey W.; Butler, R. Paul; Vogt, Steven S.

doi:10.1086/432571

Cited by 336 publications

(366 citation statements)

References 36 publications

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“…Therefore, our general result provides further evidence for planet formation in a circumstellar disk, and suggests that the evolution of planetary systems might not lead to excitation of extreme inclinations for planetary orbits relative to the original plane of the disk. Additional evidence from observations of exoplanetary systems for planet formation in a disk and little inclination from the original plane includes the coplanarity of an exoplanet's orbit with a debris disk and the stellar spin -planet orbit alignment of a number of transiting planet systems (Winn et al 2005(Winn et al , 2006Wolf et al 2007;Winn et al 2007;Narita et al 2007;Bouchy et al 2008;Winn et al 2008;Loeillet et al 2008;Johnson et al 2008;Cochran et al 2008), although see Hébrard et al (2008) for one possible exception to this trend.…”

Section: Discussionmentioning

confidence: 99%

The architecture of the GJ 876 planetary system

Bean¹,

Seifahrt²

2009

A&A

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We present a combined analysis of previously published high-precision radial velocities and astrometry for the GJ 876 planetary system using a self-consistent model that accounts for the planet-planet interactions. Assuming the three planets so far identified in the system are coplanar, we find that including the astrometry in the analysis does not result in a best-fit inclination significantly different than that found by Rivera and collaborators from analyzing the radial velocities alone. In this unique case, the planet-planet interactions are of such significance that the radial velocity data set is more sensitive to the inclination of the system through the dependence of the interactions on the true masses of the two gas giant planets in the system (planets b and c). The astrometry does allow determination of the absolute orbital inclination (i.e. distinguishing between i and 180 − i) and longitude of the ascending node for planet b, which allows us to quantify the mutual inclination angle between its orbit and planet c's orbit when combined with the dynamical considerations. We find that the planets have a mutual inclination Φ bc = 5.0 • +3.9 • −2.3 • . This result constitutes the first determination of the degree of coplanarity in an exoplanetary system around a normal star. That we find the two planets' orbits are nearly coplanar, like the orbits of the Solar System planets, indicates that the planets likely formed in a circumstellar disk, and that their subsequent dynamical evolution into a 2:1 mean motion resonance only led to excitation of a small mutual inclination. This investigation demonstrates how the degree of coplanarity for other exoplanetary systems could also be established using data obtained from existing facilities.

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Section: Discussionmentioning

confidence: 99%

The architecture of the GJ 876 planetary system

Bean¹,

Seifahrt²

2009

A&A

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“…In Schlesinger's observations, the less luminous companion occulted varying parts of the rapidly rotating primary, allowing measurement of variations in apparent radial velocity. This 'Rossiter-McLaughlin' effect (Rossiter 1924;McLaughlin 1924) is now a phenomenon commonly observed with transiting extrasolar planets, and is a useful tool for probing the alignment of the orbital plane relative to the stellar rotation axis (see, e.g., Winn et al 2005).…”

Section: Spectroscopic Underpinningsmentioning

confidence: 99%

Interferometric observations of rapidly rotating stars

Belle

2012

Astron Astrophys Rev

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Optical interferometry provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Through direct observation of rotationally distorted photospheres at sub-milliarcsecond scales, we are now able to characterize latitude dependencies of stellar radius, temperature structure, and even energy transport. These detailed new views of stars are leading to revised thinking in a broad array of associated topics, such as spectroscopy, stellar evolution, and exoplanet detection. As newly advanced techniques and instrumentation mature, this topic in astronomy is poised to greatly expand in depth and influence.

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“…This parameter is potentially a sensitive tracer of past migration history. Dynamical studies indicate that the obliquity (the real spin-orbit angle ψ) of an orbit evolves only slowly and is not as strongly affected by the proximity of the star as the eccentricity (Hut 1981;Winn et al 2005;Barker & Ogilvie 2009). Disc migration is expected to leave planets orbiting close to the stellar equatorial plane.…”

Section: Introductionmentioning

confidence: 99%

Spin-orbit angle measurements for six southern transiting planets

Triaud

Cameron

Queloz

et al. 2010

A&A

430

440

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Context. Several competing scenarios for planetary-system formation and evolution seek to explain how hot Jupiters came to be so close to their parent stars. Most planetary parameters evolve with time, making it hard to distinguish between models. The obliquity of an orbit with respect to the stellar rotation axis is thought to be more stable than other parameters such as eccentricity. Most planets, to date, appear aligned with the stellar rotation axis; the few misaligned planets so far detected are massive (>2 M J ). Aims. Our goal is to measure the degree of alignment between planetary orbits and stellar spin axes, to search for potential correlations with eccentricity or other planetary parameters and to measure long term radial velocity variability indicating the presence of other bodies in the system. Methods. For transiting planets, the Rossiter-McLaughlin effect allows the measurement of the sky-projected angle β between the stellar rotation axis and a planet's orbital axis. Using the HARPS spectrograph, we observed the Rossiter-McLaughlin effect for six transiting hot Jupiters found by the WASP consortium. We combine these with long term radial velocity measurements obtained with CORALIE. We used a combined analysis of photometry and radial velocities, fitting model parameters with the Markov Chain Monte Carlo method. After obtaining β we attempt to statistically determine the distribution of the real spin-orbit angle ψ. Results. We found that three of our targets have β above 90 • : WASP-2b: β = 153 • +11 −15 , WASP-15b: β = 139.6 • +5.2 −4.3 and WASP17b: β = 148.5 • +5.1 −4.2 ; the other three (WASP-4b, WASP-5b and WASP-18b) have angles compatible with 0 • . We find no dependence between the misaligned angle and planet mass nor with any other planetary parameter. All six orbits are close to circular, with only one firm detection of eccentricity e = 0.00848 +0.00085 −0.00095 in WASP-18b. No long-term radial acceleration was detected for any of the targets. Combining all previous 20 measurements of β and our six and transforming them into a distribution of ψ we find that between about 45 and 85% of hot Jupiters have ψ > 30 • . Conclusions. Most hot Jupiters are misaligned, with a large variety of spin-orbit angles. We find observations and predictions using the Kozai mechanism match well. If these observational facts are confirmed in the future, we may then conclude that most hot Jupiters are formed from a dynamical and tidal origin without the necessity to use type I or II migration. At present, standard disc migration cannot explain the observations without invoking at least another additional process.

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Measurement of Spin‐Orbit Alignment in an Extrasolar Planetary System

Cited by 336 publications

References 36 publications

The architecture of the GJ 876 planetary system

The architecture of the GJ 876 planetary system

Interferometric observations of rapidly rotating stars

Spin-orbit angle measurements for six southern transiting planets

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