Spin-orbit alignment of Hot Jupiters - Many misaligned planets

To avoid clotting the SuperWASP Results thread with marginally relevant information, I've started a new thread here about this.

From SuperWASP

Quote :

The discovery of several new transiting exoplanets is announced today at the RAS National Astronomy Meeting (NAM 2010) in Glasgow. When these new results were combined with earlier observations of transiting exoplanets astronomers were surprised to find that six out of a larger sample of 27 were found to be orbiting in the opposite direction to the rotation of their host star — the exact reverse of what is seen in our own Solar System. The new discoveries provide an unexpected and serious challenge to current theories of planet formation. They also suggest that systems with exoplanets of the type known as hot Jupiters are unlikely to contain Earth-like planets.

From Centauri-Dreams.
From UniverseToday.

A very interesting post about the issue from Oklo.org, where Greg Laughlin turns to his favourite planet, HD 80606 b, for clues about what's going on here.
(animation of Kozai oscillations here, can anyone get it to load?)

Lazarus wrote:

WHAT HAVE YOU DONE, CICERON???

(from here)

Interesting how our perspectives have changed since not too long ago.

Greg Laughlin's post illustrates an important point: the Rossiter-McLaughlin effect only deals with sky-projected angles. This is important when you consider the transformation to the real inclination distribution: what is the inclination distribution of the transiting planet host stars?

What's really needed now is some reliable determination of stellar inclinations... interesting how extrasolar planet science seems to be driving quite a bit of stellar science as it goes along.

Since some may not be able to play the animation of the Kozai mechanism, I've uploaded it to YouTube.

https://www.youtube.com/watch?v=xVFRYkux0bQ

Hot Stars with Hot Jupiters Have High Obliquities
http://arxiv.org/abs/1006.4161

Abstract wrote:

We show that stars with transiting planets for which the stellar obliquity is large are preferentially hot (T_eff > 6250 K). This could explain why small obliquities were observed in the earliest measurements, which focused on relatively cool stars drawn from Doppler surveys, as opposed to hotter stars that emerged later from transit surveys. The observed trend could be due to differences in planet formation and migration around stars of varying mass. Alternatively, we speculate that hot-Jupiter systems begin with a wide range of obliquities, but the photospheres of cool stars realign with the orbits due to tidal dissipation in their convective zones, while hot stars cannot realign because of their thinner convective zones. This in turn would suggest that hot Jupiters originate from few-body gravitational dynamics, and that disk migration plays at most a supporting role.

There's a nice table in the back showing RM effect measurements for 28 systems.

So the probability of alignment depends on the depth of the convective zone of the star? Interesting.

Wonder how the scattering mechanism explains the 3-day pileup.

This paper suggests stars may reorient themselves via interaction with the disk, driving high stellar obliquities without the need for planet-planet scattering or Kozai effects to explain the observed misalignments.

But observations of disk inclinations and derrived stellar rotation axes do not seem to support the idea.
http://arxiv.org/abs/1009.4132

The Time Dependence of hot Jupiters' Orbital Inclinations
http://arxiv.org/abs/1109.5813

Quote :

Via the Rossiter-McLaughlin effect, it is possible to measure the sky-projected angle between the stellar spin and a planet's orbital spin. Observed orbital inclinations have been found to range over all possible angles. A tentative detection of a correlation between the dispersion in spin/orbit angle and the youth of the system is revealed, using spin/orbit measurements for hot Jupiters around stars with masses larger than 1.2 Solar Masses for which age estimates are more accurately determined. The chance of this pattern arising by chance has been computed to 7%. This appears in accordance with tidal dissipation where non-coplanar hot Jupiters' orbits tidally realign. The results show they would do so within about 2.5 Gyr. For the considered sample, the results give support to hot Jupiters being placed on non coplanar orbits early in their history rather than this happening late. Such events could involve strong planet-planet scattering.

Calibration of Equilibrium Tide Theory for Extrasolar Planet Systems II
http://arxiv.org/abs/1204.3903

Quote :

We present a new empirical calibration of equilibrium tidal theory for extrasolar planet systems, extending a prior study by incorporating detailed physical models for the internal structure of planets and host stars. The resulting strength of the stellar tide produces a coupling that is strong enough to reorient the spins of some host stars without causing catastrophic orbital evolution, thereby potentially explaining the observed trend in alignment between stellar spin and planetary orbital angular momentum. By isolating the sample whose spins should not have been altered in this model, we also show evidence for two different processes that contribute to the population of planets with short orbital periods.
We apply our results to estimate the remaining lifetimes for short period planets, examine the survival of planets around evolving stars, and determine the limits for circularisation of planets with highly eccentric orbits. Our analysis suggests that the survival of circularised planets is strongly affected by the amount of heat dissipated, which is often large enough to lead to runaway orbital inflation and Roche lobe overflow.

Tidal realignment of cooler systems doesn't seem to fit the observations. Primordially misaligned hot Jupiter systems should realign to prograde, retrograde or 90 degrees. This is not the observed distribution of spin-orbit alignment angles for cooler stars.

On the Tidal Dissipation of Obliquity
http://arxiv.org/abs/1304.4148