KOI-1474 - Eccentric giant planets with low mutual inclination

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KOI-1474 - Eccentric giant planets with low mutual inclination

Post by Sirius_Alpha on 21st May 2014, 10:25 pm

Large eccentricity, low mutual inclination: the three-dimensional architecture of a hierarchical system of giant planets
http://arxiv.org/abs/1405.5229

We establish the three-dimensional architecture of the KOI-1474 system to be eccentric yet with a low mutual inclination. KOI-1474b is a warm Jupiter at semi-major axis a = 0.370 +0.007/-0.006 AU with a large eccentricity (e=0.85 +0.08/-0.07) measured via the "photoeccentric effect." It exhibits transit timing variations induced by the non-transiting KOI-1474c, which we uniquely constrain to be a moderately eccentric (e=0.184 +/- 0.002), hierarchically-separated (a=1.68 +/- 0.03 AU) giant planet (7.3 +/- 0.4 MJup). We combine sixteen quarters of Kepler photometry, radial-velocity (RV) measurements from the HIgh Resolution Echelle Spectrometer (HIRES) on Keck, and improved stellar parameters that we derive from spectroscopy and asteroseismology. From the RVs, we measure the mass of inner planet to be 2.6 +/- 0.3 MJup and confirm its photometrically-measured eccentricity, refining the value to e=0.83 +/- 0.01. The RV acceleration is consistent with the properties of the outer planet derived from TTVs. We find that, despite their sizable eccentricities, the planets are coplanar to within 10 +8/-6 degrees, and therefore the inner planet's large eccentricity and close-in orbit are unlikely to be the result of Kozai migration. Moreover, even over many secular cycles, the inner planet's periapse is most likely never small enough for tidal circularization. Finally, we present and measure a transit time and impact parameter from four simultaneous ground-based light curves from 1m-class telescopes, demonstrating the feasibility of ground-based follow-up of Kepler giant planets exhibiting large TTVs.

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Re: KOI-1474 - Eccentric giant planets with low mutual inclination

Post by Stalker on 22nd May 2014, 2:42 am

KOI-1474 b is the "proto-hot jupiter" from an older studie:

THE PHOTOECCENTRIC EFFECT AND PROTO-HOT JUPITERS. II. KOI-1474.01, A CANDIDATE ECCENTRIC PLANET PERTURBED BY AN UNSEEN COMPANION
The exoplanets known as hot Jupiters—Jupiter-sized planets with periods of less than 10 days—likely are relics of dynamical processes that shape all planetary system architectures. Socrates et al. argued that high eccentricity migration (HEM) mechanisms proposed for situating these close-in planets should produce an observable population of highly eccentric proto-hot Jupiters that have not yet tidally circularized. HEM should also create failed-hot Jupiters, with periapses just beyond the influence of fast circularization. Using the technique we previously presented for measuring eccentricities from photometry (the "photoeccentric effect"), we are distilling a collection of eccentric proto- and failed-hot Jupiters from the Kepler Objects of Interest (KOI). Here, we present the first, KOI-1474.01, which has a long orbital period (69.7340 days) and a large eccentricity e = 0.81+0.10 –0.07, skirting the proto-hot Jupiter boundary. Combining Kepler photometry, ground-based spectroscopy, and stellar evolution models, we characterize host KOI-1474 as a rapidly rotating F star. Statistical arguments reveal that the transiting candidate has a low false-positive probability of 3.1%. KOI-1474.01 also exhibits transit-timing variations of the order of an hour. We explore characteristics of the third-body perturber, which is possibly the "smoking-gun" cause of KOI-1474.01's large eccentricity. We use the host star's period, radius, and projected rotational velocity to measure the inclination of the stellar spin. Comparing KOI 1474.01's inclination, we find that its orbit is marginally consistent with being aligned with the stellar spin axis, although a reanalysis is warranted with future additional data. Finally, we discuss how the number and existence of proto-hot Jupiters will not only demonstrate that hot Jupiters migrate via HEM, but also shed light on the typical timescale for the mechanism.

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Re: KOI-1474 - Eccentric giant planets with low mutual inclination

Post by Lazarus on 25th May 2014, 4:55 pm

Interesting result, makes the system rather harder to explain and makes the "proto-hot Jupiter" classification rather less likely.
Key point:
Although KOI-1474 itself is just one data point, if other eccentric, hierarchical systems are found to have low mutual inclinations, this may call into question the interpretation that the extreme spin-orbit misalignments observed for hot Jupiters are the result of the planet’s orbit being tilted out of the plane it formed in by scattering, Kozai, or secular chaos.
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Re: KOI-1474 - Eccentric giant planets with low mutual inclination

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