Kepler-65: Three well-aligned super-Earths

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Kepler-65: Three well-aligned super-Earths

Post by Sirius_Alpha on 17th February 2013, 9:24 pm

Asteroseismic determination of obliquities of the exoplanet systems Kepler-50 and Kepler-65
http://arxiv.org/abs/1302.3728

Results on the obliquity of exoplanet host stars -- the angle between the stellar spin axis and the planetary orbital axis -- provide important diagnostic information for theories describing planetary formation. Here we present the first application of asteroseismology to the problem of stellar obliquity determination in systems with transiting planets and Sun-like host stars. We consider two systems observed by the NASA Kepler Mission which have multiple transiting small (super-Earth sized) planets: the previously reported Kepler-50 and a new system, Kepler-65, whose planets we validate in this paper. Both stars show rich spectra of solar-like oscillations. From the asteroseismic analysis we find that each host has its rotation axis nearly perpendicular to the line of sight with the sines of the angles constrained at the 1-sigma level to lie above 0.97 and 0.91, respectively. We use statistical arguments to show that coplanar orbits are favoured in both systems, and that the orientations of the planetary orbits and the stellar rotation axis are correlated.

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Re: Kepler-65: Three well-aligned super-Earths

Post by Lazarus on 20th February 2013, 4:46 pm

Similar result for KOI-94 and Kepler-25:

Low stellar obliquities in compact multiplanet systems
http://arxiv.org/abs/1302.4443

So five multiplanet systems so far appear to be well-aligned (Kepler-25, Kepler-30, Kepler-50, Kepler-65, KOI-94) - looks like the way these planets ended up close to the star is not the same way that the hot Jupiters did.

On the other hand Dynamics of Cats mentions:
One, still unpublished discovery, from Josh Carter et al, for a KOI-not-to-be-named, used transit geometry from two planets and measurements of the stellar spin from astroseismology to show that the stellar spin was misaligned to the plane of the transiting planets, but that the two planets were very close to coplanar.
This is somewhat puzzling, because the disk the planets form from carries a lot of angular momentum and should also accrete onto the star and align its spin, but there is a hint of a third planet in the system, which may be misaligned with the other two. If it is aligned with the stellar spin axis, things will get very interesting.
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