A Third Exoplanetary System with Misaligned Orbital and Stellar Spin Axes1

Johnson, John Asher; Winn, Joshua N.; Albrecht, S.; Howard, Andrew W.; Marcy, Geoffrey W.; Gazak, J. Zachary

doi:10.1086/644604

Cited by 110 publications

(86 citation statements)

References 40 publications

(61 reference statements)

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“…When combining the 26 RM effects that have been observed, we now see that eight planets are severely misaligned: XO-3b (Hébrard et al 2008;Winn et al 2009c), HD 80606b Pont et al 2009;Winn et al 2009a), WASP-14b (Johnson et al 2009), Hat-P-7b (Winn et al 2009b;Narita et al 2009), WASP-8b ) and WASP-2b, WASP15b and WASP17b. Of these eight, five have been found to be in retrograde orbits, four from our survey.…”

Section: Discussionmentioning

confidence: 72%

“…At that time, the spin-orbit misalignment of XO-3b (Hébrard et al 2008) comprised the only evidence of the isotropic population. Since then, the misalignment of XO3b has been confirmed by Winn et al (2009c), and significant misalignments have been found for HD 80606b ) and WASP-14b (Johnson et al 2009). Moreover, retrograde orbital motion has been identified in HAT-P-7b (Winn et al 2009b;Narita et al 2009).…”

Section: Introductionmentioning

confidence: 87%

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Spin-orbit angle measurements for six southern transiting planets

Triaud

Cameron

Queloz

et al. 2010

A&A

418

435

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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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Section: Discussionmentioning

confidence: 72%

Section: Introductionmentioning

confidence: 87%

Spin-orbit angle measurements for six southern transiting planets

Triaud

Cameron

Queloz

et al. 2010

A&A

418

435

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“…As suggested by Johnson et al (2009) and Hébrard et al (2010), planetary mass apparently is also a key parameter. The seven retrograde and three polar planets all have masses below 3 M Jup .…”

Section: Discussionmentioning

confidence: 79%

The retrograde orbit of the HAT-P-6b exoplanet

Hébrard

Ehrenreich

Bouchy

et al. 2011

A&A

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We observed the transit of the HAT-P-6b exoplanet across its host star with the SOPHIE spectrograph (OHP, France). The resulting stellar radial velocities display the Rossiter-McLaughlin anomaly and reveal a retrograde orbit: the planetary orbital spin and the stellar rotational spin point in approximately opposite directions. A fit to the anomaly measures a sky-projected angle λ = 166 • ± 10 • between these two spin axes. All seven known retrograde planets are hot Jupiters with masses M p < 3 M Jup . About two thirds of the planets in this mass range, however, are prograde and aligned (λ 0 • ). In contrast, most of the more massive planets (M p > 4 M Jup ) are prograde but misaligned. Different mechanisms may therefore be responsible for planetary obliquities above and below ∼3.5 M Jup .

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“…The XO-3, WASP-14, and HD 80606 systems all have a close-in, massive planet on a very eccentric orbit and with a significant spin-orbit misalignment (e.g., Johnson et al 2009, and references therein) 8 . At first glance, this might imply that the orbital migration history of massive, eccentric exoplanets is somehow different for less massive close-in Jupiters, However, the picture is not likely to be so simple, not only because of the evidence of other transiting systems with massive, eccentric planets (HAT-P-2, HD 17156) showing no signs of spin-orbit misalignment (e.g., Winn et al 2007;Barbieri et al 2009), but also for the recent measurements of the R-M effect in transiting systems with Jupiter-mass planets on circular orbits, such as CoRot-1, HAT-P-7, and WASP-17 (Pont et al 2009, and references therein) that point toward high values of the projected spin-orbit angles.…”

Section: Formation and Orbital Evolution Of Massive Planets And Brownmentioning

confidence: 99%

Hipparcos preliminary astrometric masses for the two close-in companions to HD 131664 and HD 43848

Sozzetti¹,

Desidera

2009

A&A

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Context. Several mechanisms for forming brown dwarfs have been proposed, which today are not believed to be mutually exclusive. Among the fundamental characteristics of brown dwarfs that are intrinsically tied to their origins, multiplicity is particularly relevant. Any successful determination of the actual mass for such objects in any systems is thus worthwhile, as it allows one to improve on the characterization of the multiplicity properties (e.g., frequency, separation, mass-ratio distribution) of sub-stellar companions. Aims. We attempt to place better constraints on the masses of two Doppler-detected substellar companions to the nearby G dwarfs HD 131664 and HD 43848. Methods. We carried out orbital fits to the Hipparcos Intermediate Astrometric Data (IAD) for the two stars, taking advantage of the knowledge of the spectroscopic orbits, and solving for the inclination angle i and the longitude of the ascending node Ω, the two orbital elements that can be determined in principle solely by astrometry, A number of checks were carried out to assess the reliability of the orbital solutions thus obtained.Results. The best-fit solution for HD 131664 yields i = 55 ± 33 deg and Ω = 22 ± 28 deg. The resulting inferred true companion mass is then M c = 23 +26 −5 M J . For HD 43848, we find i = 12 ± 7 deg and Ω = 288 ± 22 deg, and a corresponding M c = 120 +167 −43 M J . Based on the statistical evidence from an F-test, the study of the joint confidence intervals of variation in i and Ω and the comparison of the derived orbital semi-major axes with a distribution of false astrometric orbits obtained for single stars observed by Hipparcos, the astrometric signal of the two companions to HD 131664 and HD 43848 is then considered detected in the Hipparcos IAD, with a level of statistical confidence not exceeding 95%. Conclusions. We constrain the true mass of HD 131664b to that of a brown dwarf to within a somewhat statistically significant degree of confidence (∼2 − σ). For HD 43848b, a true mass in the brown dwarf regime is ruled out at the 1 − σ confidence level. The results are discussed in the context of the properties of the (few) close substellar and massive planetary companions to nearby solar-type stars and their implications for proposed models of formation and structure of massive planets and brown dwarfs.

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A Third Exoplanetary System with Misaligned Orbital and Stellar Spin Axes1

Cited by 110 publications

References 40 publications

Spin-orbit angle measurements for six southern transiting planets

Spin-orbit angle measurements for six southern transiting planets

The retrograde orbit of the HAT-P-6b exoplanet

Hipparcos preliminary astrometric masses for the two close-in companions to HD 131664 and HD 43848

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