K2 News and Results

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Re: K2 News and Results

Post by Lazarus on 16th March 2018, 3:26 pm

Led_Zep wrote:Sad

https://www.nasa.gov/feature/ames/nasa-s-kepler-spacecraft-nearing-the-end-as-fuel-runs-low

NASA’s Kepler Spacecraft Nearing the End as Fuel Runs Low
All good things...

Still, it's had a pretty good run, no?
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Re: K2 News and Results

Post by Lazarus on 22nd March 2018, 6:29 pm

A sub-Neptune in the 3-billion-year-old open cluster Ruprecht 147.

Curtis et al., "K2-231 b: A sub-Neptune exoplanet transiting a solar twin in Ruprecht 147"
https://arxiv.org/abs/1803.07430
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Re: K2 News and Results

Post by Sirius_Alpha on 26th March 2018, 5:13 pm

K2-229b is a very dense planet in a multiple planet system.

An Earth-sized exoplanet with a Mercury-like composition
https://www.nature.com/articles/s41550-018-0420-5

This tweet thread has more graphics and information.
https://twitter.com/exohugh/status/978308332976066560

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Re: K2 News and Results

Post by Lazarus on 27th March 2018, 4:57 pm

News release about K2-229: http://spaceref.com/extrasolar-planets/newly-discovered-planet-is-hot-metallic-and-dense-as-mercury.html

On a non-exoplanet-related topic, K2 also has been useful for studying Fast-Evolving Luminous Transients, which are identified as supernovae exploding within dust shells: http://spaceref.com/astronomy/kepler-solves-mystery-of-fast-and-furious-explosions.html
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Re: K2 News and Results

Post by Sirius_Alpha on 28th March 2018, 9:23 pm

Sirius_Alpha wrote:EPIC247098361b: a transiting warm Saturn on an eccentric P=11.2 days orbit around a V=9.9 star
https://arxiv.org/abs/1802.08865

Star has received the designation K2-232.

K2-232 b: a transiting warm Saturn on an eccentric P = 11.2 days orbit around a V = 9.9 star
https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/sty795/4955565?redirectedFrom=fulltext

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Re: K2 News and Results

Post by Edasich on 17th April 2018, 4:58 am

Updates for K2-55 b: A high-density Hot Neptune.

Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars III: A High Mass & Low Envelope Fraction for the Warm Neptune K2-55b

K2-55b is a Neptune-sized planet orbiting a K7 dwarf with a radius of 0.715+0.043−0.040R⊙, a mass of 0.688±0.069M⊙, and an effective temperature of 4300+107−100 K. Having characterized the host star using near-infrared spectra obtained at IRTF/SpeX, we observed a transit of K2-55b with Spitzer/IRAC and confirmed the accuracy of the original K2 ephemeris for future follow-up transit observations. Performing a joint fit to the Spitzer/IRAC and K2 photometry, we found a planet radius of 4.43+0.29−0.32R⊕, an orbital period of 2.8492725+7×10−6−6.6×10−6 days, and an equilibrium temperature of roughly 900K. We then measured the planet mass by acquiring twelve radial velocity (RV) measurements of the system using HIRES on the 10-m Keck I Telescope. Our RV data set precisely constrains the mass of K2-55b to 44.0±5.3M⊕, indicating that K2-55b has a bulk density of 2.8+0.7−0.6 g cm−3 and can be modeled as a rocky planet capped by a modest H/He envelope (Menvelope=12±3%Mp). K2-55b is denser than most similarly sized planets, raising the question of whether the high planetary bulk density of K2-55b could be attributed to the high metallicity of K2-55. The absence of a substantial volatile envelope despite the large mass of K2-55b poses a challenge to current theories of gas giant formation. We posit that K2-55b may have escaped runaway accretion by migration, late formation, or inefficient core accretion or that K2-55b was stripped of its envelope by a late giant impact.
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Re: K2 News and Results

Post by Lazarus on 3rd May 2018, 1:18 am

Sirius_Alpha wrote:Characterization of the K2-18 multi-planetary system with HARPS: A habitable zone super-Earth and discovery of a second, warm super-Earth on a non-coplanar orbit
https://arxiv.org/abs/1707.04292
CARMENES observations cast doubt on the planetary interpretation of the 9-day signal...

Paula et al. "The CARMENES search for exoplanets around M dwarfs: A low-mass planet in the temperate zone of the nearby K2-18"
https://arxiv.org/abs/1805.00830
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Re: K2 News and Results

Post by Sirius_Alpha on 6th May 2018, 8:30 pm

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 Led_Zep on 9th May 2018, 6:50 pm

The last harvest ?

Twitter :

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Re: K2 News and Results

Post by Sirius_Alpha on 9th May 2018, 9:03 pm

Evidence of a Sub-Saturn around EPIC~211945201
https://arxiv.org/abs/1805.03466

We report here strong evidence for a sub-Saturn around EPIC~211945201 and confirm its planetary nature. EPIC~211945201b was found to be a planetary candidate from {\it K2} photometry in Campaigns 5 \& 16, transiting a bright star (Vmag=10.15, G0 spectral type) in a 19.492 day orbit. However, the photometric data combined with false positive probability calculations using VESPA was not sufficient to confirm the planetary scenario. Here we present high-resolution spectroscopic follow-up of the target using the PARAS spectrograph (19 radial velocity observations) over a time-baseline of 420 days. We conclusively rule out the possibility of an eclipsing binary system and confirm the 2-σ detection of a sub-Saturn planet. The confirmed planet has a radius of 6.12±0.1 R⊕, and a mass of 27+14−12.6~M⊕. We also place an upper limit on the mass (within the 3-σ confidence interval) at 42~M⊕ above the nominal value. This results in the Saturn-like density of 0.65+0.34−0.30 g~cm−3. Based on the mass and radius, we provide a preliminary model-dependent estimate that the heavy element content is 60-70 \% of the total mass. This detection is important as it adds to a sparse catalog of confirmed exoplanets with masses between 10-70 M⊕ and radii between 4-8 R⊕, whose masses and radii are measured to a precision of 50\% or better (only 23 including this work).

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Re: K2 News and Results

Post by Sirius_Alpha on 14th May 2018, 8:43 pm

An 8 Mearth super-Earth in a 2.2 day orbit around the K5V star K2-216
https://arxiv.org/abs/1805.04774

The KESPRINT consortium identified K2-216 as a planetary candidate host star in the K2 space mission Campaign 8 field with a transiting super-Earth. The planet was also recently validated by Mayo et al. 2018. Our aim was to confirm the detection and to derive the main physical characteristics of K2-216b, including the mass. We performed a series of follow-up observations: high resolution imaging with the FastCam camera at the TCS, the Infrared Camera and Spectrograph at Subaru, and high resolution spectroscopy with HARPS (ESO, La Silla), HARPS-N (TNG) and FIES (NOT). The stellar spectra were analysed with the SpecMatch-Emp and SME codes to derive the stellar fundamental properties. We analysed the K2 light curve with the Pyaneti software. The radial-velocity measurements were modelled with both a Gaussian process regression and the floating chunk offset technique to simultaneously model the planetary signal and the correlated noise associated with stellar activity. Imaging confirms that K2-216 is a single star. Our analysis discloses that the star is a moderately active K5V star of mass 0.70+/-0.03 Msun and radius 0.72+/-0.05 Rsun. Planet b is found to have a radius of 1.8+0.2-0.1 Rearth and a 2.17 day orbit. These values are in agreement with those of Mayo et al. 2018. We find consistent results for the planet mass from both models: 7.4+/-2.2 Mearth from the Gaussian process regression, and 7.9+/-1.6 Mearth from the floating chunk offset technique which implies that this planet is a super-Earth. The planet parameters put planet b in the middle of, or just below, the gap of the radius distribution of small planets. The density is consistent with a rocky composition of primarily iron and magnesium silicate. In agreement with theoretical predictions, we find that the planet is a remnant core, stripped of its atmosphere, and is one of the largest planets found that have lost its atmosphere.

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Re: K2 News and Results

Post by Sirius_Alpha on 22nd May 2018, 8:27 pm

Sirius_Alpha wrote:K2-229b is a very dense planet in a multiple planet system.An Earth-sized exoplanet with a Mercury-like composition
https://www.nature.com/articles/s41550-018-0420-5
Now on arXiv.

An Earth-sized exoplanet with a Mercury-like composition
https://arxiv.org/abs/1805.08405

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Re: K2 News and Results

Post by Sirius_Alpha on 30th May 2018, 8:26 pm

Masses and eccentricities of Kepler-643b, K2-132b and K2-97b

Do close-in giant planets orbiting evolved stars prefer eccentric orbits?
https://arxiv.org/abs/1805.11620


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Re: K2 News and Results

Post by Sirius_Alpha on 4th June 2018, 9:54 pm

Two planetary systems with transiting Earth-size and super-Earth planets orbiting late-type dwarf stars
https://arxiv.org/abs/1806.01181

We present two new planetary systems found around cool dwarf stars with data from the K2 mission. The first system was found in K2-XX1 (EPIC 248545986), char- acterized in this work as M3.0V and observed in the 14th campaign of K2. It consists of three Earth-size transiting planets with radii of 1.1, 1.0 and 1.1 R Earth, showing a compact configuration with orbital periods of 5.24, 7.78 and 10.1 days, close to 2:3:4 resonance. The second was found in K2-XX2 (EPIC 249801827), characterized in this work as M0.5V and observed in the 15th campaign. It consists of two transiting super-Earths with radii 2.0 and 1.8 R Earth and orbital periods of 6.03 and 20.5 days. The equilibrium temperatures of the atmospheres of these planets are estimated to be in the range of 380-600 K and the amplitudes of signals in transmission spectroscopy are estimated at ~10 ppm.

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Re: K2 News and Results

Post by Edasich on 6th June 2018, 3:55 am

Sirius_Alpha wrote:Two planetary systems with transiting Earth-size and super-Earth planets orbiting late-type dwarf stars
https://arxiv.org/abs/1806.01181

We present two new planetary systems found around cool dwarf stars with data from the K2 mission. The first system was found in K2-XX1 (EPIC 248545986), char- acterized in this work as M3.0V and observed in the 14th campaign of K2. It consists of three Earth-size transiting planets with radii of 1.1, 1.0 and 1.1 R Earth, showing a compact configuration with orbital periods of 5.24, 7.78 and 10.1 days, close to 2:3:4 resonance. The second was found in K2-XX2 (EPIC 249801827), characterized in this work as M0.5V and observed in the 15th campaign. It consists of two transiting super-Earths with radii 2.0 and 1.8 R Earth and orbital periods of 6.03 and 20.5 days. The equilibrium temperatures of the atmospheres of these planets are estimated to be in the range of 380-600 K and the amplitudes of signals in transmission spectroscopy are estimated at ~10 ppm.

Prompt update concerning K2 designation: K2-239 for EPIC 248545986 and K2-240 for EPIC 249801827.
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Re: K2 News and Results

Post by Sirius_Alpha on 18th June 2018, 8:50 pm

Edasich wrote:Prompt update concerning K2 designation: K2-239 for EPIC 248545986 and K2-240 for EPIC 249801827.
Thanks for that!

EPIC 246911830 b: a hot Jupiter transiting an F star, and EPIC 201498078 b: a warm Saturn around a bright G star
https://arxiv.org/abs/1806.06099

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Re: K2 News and Results

Post by Led_Zep on 21st June 2018, 2:16 pm

MIT press release :

http://news.mit.edu/2018/nearly-80-exoplanet-candidates-identified-record-time-0621

Nearly 80 exoplanet candidates identified in record time
(C16 and C17 campaigns)

« …In a paper that appears online today in The Astronomical Journal, the scientists report the discovery of nearly 80 new planetary candidates, including a particular standout: a likely planet that orbits the star HD 73344, which would be the brightest planet host ever discovered by the K2 mission.
The planet appears to orbit HD 73344 every 15 days, and based on the amount of light that it blocks each time it passes in front of its star, scientists estimate that the planet is about 2.5 times the size of the Earth and 10 times as massive. It is also likely incredibly hot, with a temperature somewhere in the range of 1,200 to 1,300 degrees Celsius, or around 2,000 degrees Fahrenheit — about the the temperature of lava from an erupting volcano.
The planet lies at a relatively close distance of 35 parsecs, or about 114 light years from Earth. Given its proximity and the fact that it orbits a very bright star, scientists believe the planet is an ideal candidate for follow-up studies to determine its atmospheric composition and other characteristics… »

Paper :

http://iopscience.iop.org/article/10.3847/1538-3881/aac6e6

Planetary Candidates from K2 Campaign 16

Abstract
Given that Campaign 16 of the K2 mission is one of just two K2 campaigns observed so far in "forward-facing" mode, which enables immediate follow-up observations from the ground, we present a catalog of interesting targets identified through photometry alone. Our catalog includes 30 high-quality planet candidates (showing no signs of being non-planetary in nature), 48 more ambiguous events that may be either planets or false positives, 164 eclipsing binaries, and 231 other regularly periodic variable sources. We have released light curves for all targets in C16 and have also released system parameters and transit vetting plots for all interesting candidates identified in this paper. Of particular interest is a candidate planet orbiting the bright F dwarf HD 73344 (V = 6.9, K = 5.6) with an orbital period of 15 days. If confirmed, this object would correspond to a 2.56 ± 0.18 R ⊕ planet and would likely be a favorable target for radial velocity characterization. This paper is intended as a rapid release of planet candidates, eclipsing binaries, and other interesting periodic variables to maximize the scientific yield of this campaign, and as a test run for the upcoming TESS mission, whose frequent data releases call for similarly rapid candidate identification and efficient follow up
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Re: K2 News and Results

Post by Sirius_Alpha Today at 9:52 pm

A Compact Multi-Planet System With A Significantly Misaligned Ultra Short Period Planet
https://arxiv.org/abs/1806.08368

We report the discovery of a compact multi-planet system orbiting the relatively nearby (78pc) and bright (K=8.9) K-star, EPIC248435473 (K2-XXX). We identify up to six possible planets orbiting EPIC248435473 with estimated periods of Pb = 0.66, P.02 = 6.1, Pc = 7.8, Pd = 14.7, Pe = 19.5, and P.06 = 56.7 days and radii of RP = 2.9 R⊕, 0.579 R⊕, 0.637 R⊕, 2.644 R⊕, 2.446 R⊕, and 0.81 R⊕, respectively. We are able to confidently validate the planetary nature of four of these planets (Pb = 0.66d, Pc = 7.8d, Pd = 14.7d, and Pe = 19.5d), while classifying the other two as planetary candidates (EPIC248435473.02 & .06). From a simultaneous fit of all 6 possible planets, we find that EPIC248435473 b's orbit has an inclination of 76.5∘ while the other five planets have inclinations of 88-90∘. This observed mutual misalignment may indicate that EPIC248435473 b formed differently from the other planets in the system. The brightness of the host star and the relatively large size of the sub-Neptune sized planets d and e make them well-suited for atmospheric characterization efforts with facilities like the Hubble Space Telescope and upcoming James Webb Space Telescope. We also identify an 8.5-day transiting planet candidate orbiting EPIC248435395, a co-moving companion to EPIC248435473.

The longest period transiting planet candidate from K2
https://arxiv.org/abs/1806.08757

Context: We present the transit and follow-up of a single transit event from Campaign 14 of K2, EPIC248847494b, which has a duration of 54 hours and a 0.18%-depth. Aims: Using photometric tools and conducting radial velocity follow-up, we vet and characterise this very strong candidate. Methods: Due to a long, unknown period, standard follow-up methods need to be adapted. The transit is fitted using Namaste, and the radial velocity slope measured and compared to a grid of planet-like orbits with varying masses and periods. These utilised stellar parameters measured from spectra and the distance as measured by Gaia. Results: Orbiting around a sub-giant star with a radius of 2.70±0.12Rsol, the planet has a radius of 1.11±0.07RJup and a period of 3650+1280−1130 days. The radial velocity measurements constrain the mass to be less than 13MJup, which implies a planetary-like object. Conclusions: We have found a planet at 4.5 AU from a single transit event. After a full radial velocity follow-up campaign, if confirmed, it will be the longest-period transiting planet discovered.

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