K2 News and Results

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Re: K2 News and Results

Post by Stalker on 3rd August 2018, 6:23 am

HD 89345: a bright oscillating star hosting a transiting warm Saturn-sized planet observed by K2
https://arxiv.org/abs/1805.01860

We report the discovery and characterization of HD 89345b (K2-234b; EPIC 248777106b), a Saturn-sized planet orbiting a slightly evolved star. HD 89345 is a bright star (V=9.3 mag) observed by the K2 mission with one-minute time sampling. It exhibits solar-like oscillations. We conducted asteroseismology to determine the parameters of the star, finding the mass and radius to be 1.12+0.04−0.01 M⊙ and 1.657+0.020−0.004 R⊙, respectively. The star appears to have recently left the main sequence, based on the inferred age, 9.4+0.4−1.3 Gyr, and the non-detection of mixed modes. The star hosts a "warm Saturn" (P=11.8~days, Rp=6.86±0.14 R⊕). Radial-velocity follow-up observations performed with the FIES, HARPS, and HARPS-N spectrographs show that the planet has a mass of 35.7±3.3 M⊕. The data also show that the planet's orbit is eccentric (e≈0.2). An investigation of the rotational splitting of the oscillation frequencies of the star yields no conclusive evidence on the stellar inclination angle. We further obtained Rossiter-McLaughlin observations, which result in a broad posterior of the stellar obliquity. The planet seems to conform to the same patterns that have been observed for other sub-Saturns regarding planet mass and multiplicity, orbital eccentricity, and stellar metallicity.

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Re: K2 News and Results

Post by Stalker on 3rd August 2018, 6:28 am

EPIC229426032 b and EPIC246067459 b: discovery and characterization of two new transiting hot Jupiters from K2
https://arxiv.org/abs/1801.07959
We report the discovery of two hot Jupiters orbiting the stars EPIC229426032 and EPIC246067459. We used photometric data from Campaign 11 and 12 of the Kepler K2 Mission and radial velocity data obtained using the HARPS, FEROS, and CORALIE spectrographs. EPIC229426032 b and EPIC246067459 b have masses of 1.60+0.11−0.11 and 0.86+0.13−0.12MJup, radii of 1.65+0.07−0.08 and 1.30+0.15−0.14RJup, and are orbiting their host stars in 2.18 and 3.20-day orbits, respectively. The large radius of EPIC229426032 b leads us to conclude that this candidate corresponds to a highly inflated hot Jupiter. EPIC2460674559 b has a radius consistent with theoretical models, considering the high incident flux falling on the planet. We consider EPIC229426032 b to be a excellent system for follow-up studies, since not only is it very inflated, but it also orbits a relatively bright star (V=11.6).

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Re: K2 News and Results

Post by Sirius_Alpha on 3rd August 2018, 7:02 am

Those two papers were covered here and here.

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Re: K2 News and Results

Post by Edasich on 3rd August 2018, 10:59 am

Hasn't this one been noticed? A new 4-planets system from K2:

Detection and Doppler monitoring of EPIC 246471491, a system of four transiting planets smaller than Neptune

The Kepler extended mission, also known as K2, has provided the community with a wealth of planetary candidates that orbit stars typically much brighter than the targets of the original mission. These planet candidates are suitable for further spectroscopic follow-up and precise mass determinations, leading ultimately to the construction of empirical mass-radius diagrams. Particularly interesting is to constrain the properties of planets between the Earth and Neptune in size, the most abundant type of planets orbiting Sun-like stars with periods less than a few years. Among many other K2 candidates, we discovered a multi-planetary system around EPIC246471491, with four planets ranging in size from twice the size of Earth, to nearly the size of Neptune. We measure the mass of the planets of the EPIC246471491 system by means of precise radial velocity measurements using the CARMENES spectrograph and the HARPS-N spectrograph. With our data we are able to determine the mass of the two inner planets of the system with a precision better than 15%, and place upper limits on the masses of the two outer planets. We find that EPIC246471491b has a mass of 9.68 Me, and a radius of 2.59 Re, yielding a mean density of 3.07 g/cm3, while EPIC246471491c has a mass of 15.68 Me, radius of 3.53 Re, and a mean density of 19.5 g/cm3. For EPIC246471491d (R=2.48Re) and EPIC246471491e (R=1.95Re) the upper limits for the masses are 6.5 and 10.7 Me, respectively. The system is thus composed of a nearly Neptune-twin planet (in mass and radius), two sub-Neptunes with very different densities and presumably bulk composition, and a fourth planet in the outermost orbit that resides right in the middle of the super-Earth/sub-Neptune radius gap. Future comparative planetology studies of this system can provide useful insights into planetary formation, and also a good test of atmospheric escape and evolution theories.
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Re: K2 News and Results

Post by Sirius_Alpha on 3rd August 2018, 12:21 pm

Yes, here.

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Re: K2 News and Results

Post by Edasich on 3rd August 2018, 4:29 pm

Sirius_Alpha wrote:Yes, here.

Ouch! I hadn't spotted that! Embarassed

Better merging the posts... Wink
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Re: K2 News and Results

Post by Lazarus on 14th August 2018, 1:08 pm

Rodríguez Martínez et al. "Characterization of Low Mass K2 Planet Hosts Using Near-Infrared Spectroscopy"
https://arxiv.org/abs/1808.03652

Some exoplanet candidates around cool stars.
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Re: K2 News and Results

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