K2 News and Results

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Post by Sirius_Alpha on 6th September 2018, 8:36 pm

The two-planet Praesepe system reported here is independently confirmed.

EPIC 211964830: A transiting multi-planet system in the Praesepe open cluster
https://arxiv.org/abs/1809.01968

Also, apparently the safe-mode earlier was triggered by a bad thruster.  Kepler is back in science mode, though who knows for how much longer.
https://spacenews.com/kepler-resumes-operations-despite-malfunctioning-thruster/

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Post by Sirius_Alpha on 24th September 2018, 9:28 pm

A couple new Kepler-K2 transiting planets.

K2-265 b: A Transiting Rocky Super-Earth
https://arxiv.org/abs/1809.08869

EPIC 249451861b: an Eccentric Warm Saturn transiting a G-dwarf
https://arxiv.org/abs/1809.08879

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Post by Led_Zep on 1st October 2018, 2:19 pm

Crying or Very sad Crying or Very sad Crying or Very sad

https://www.nasa.gov/feature/ames/kepler-put-into-sleep-mode-as-telescope-s-pointing-performance-degrades

Sept. 28, 2018

Kepler Put Into Sleep Mode As Telescope’s Pointing Performance Degrades

NASA’s Kepler team has received data showing that the spacecraft’s ability to point precisely has degraded. In order to preserve high-value science data collected during its latest observation campaign, the Kepler team has placed the spacecraft in a stable, no-fuel-use sleep mode.
During Kepler’s allotted Deep Space Network time, scheduled to begin October 10, the Kepler team will “wake up” the spacecraft and direct it to point its large antenna back to Earth and transmit the science data home. Due to uncertainties about the remaining available fuel, there is no guarantee that NASA will be able to download the science data. If successful the Kepler team will attempt to start the next observing campaign with the remaining fuel.

EDIT : (Twitter)

Natalie Batalha‏ @nbatalha · 3 minil y a 3 minutes
Kepler Put Into Sleep Mode As Telescope’s Pointing Performance Degrades (but spends 27 days observing TRAPPIST-1 first!!)

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Post by Sirius_Alpha on 9th October 2018, 8:35 pm

60 Validated Planets from K2 Campaigns 5-8
https://arxiv.org/abs/1810.04074

We present a uniform analysis of 155 candidates from the second year of NASA's K2 mission (Campaigns 5 - 8 ), yielding 60 statistically validated planets spanning a range of properties, with median values of Rp = 2.5 R⊕, P = 7.1 d, Teq = 811 K, and J = 11.3 mag. The sample includes 24 planets in 11 multi-planetary systems, as well as 18 false positives, and 77 remaining planet candidates. Of particular interest are 18 planets smaller than 2 R⊕, five orbiting stars brighter than J = 10 mag, and a system of four small planets orbiting the solar-type star EPIC 212157262. We compute planetary transit parameters and false positive probabilities using a robust statistical framework and present a complete analysis incorporating the results of an intensive campaign of high resolution imaging and spectroscopic observations. This work brings the K2 yield to over 360 planets, and by extrapolation we expect that K2 will have discovered ∼600 planets before the expected depletion of its on-board fuel in late 2018.

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Post by Sirius_Alpha on 10th October 2018, 8:42 pm

K2-140b and K2-180b -- Characterization of a hot Jupiter and a mini-Neptune from the K2 mission
https://arxiv.org/abs/1810.04601

We report the independent discovery and characterization of two \ktwo\ planets: K2-180b, a mini-Neptune-size planet in an 8.9-day orbit transiting a V\,=\,12.6\,mag, metal-poor ([Fe/H]\,=\,−0.65±0.10) K2V star in \ktwo\ campaign 5; K2-140b, a transiting hot Jupiter in a 6.6-day orbit around a V\,=\,12.6\,mag G6V ([Fe/H]\,=\,+0.10±0.10) star in \ktwo\ campaign 10. Our results are based on \ktwo\ time-series photometry combined with high-spatial resolution imaging and high-precision radial velocity measurements. We present the first mass measurement of K2-180b. K2-180b has a mass of Mp=11.3±1.9\,\Mearth\ and a radius of Rp=2.2±0.1\,\Rearth, yielding a mean density of ρp=5.6±1.9\,\gcm, suggesting a rock composition. Given its radius, K2-180b is above the region of the so-called ``planetary radius gap''. K2-180b is in addition not only one of the densest mini-Neptune-size planets, but also one of the few mini-Neptune-size planets known to transit a metal-poor star. We also constrain the planetary and orbital parameters of K2-140b and show that, given the currently available Doppler measurements, the eccentricity is consistent with zero, contrary to the results of a previous study.

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Post by Sirius_Alpha on 11th October 2018, 8:35 pm

Confirmation of the radial velocity super-Earth K2-18c with HARPS and CARMENES
https://arxiv.org/abs/1810.04731

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Post by Led_Zep on 11th October 2018, 10:42 pm

cheers Twitter :

K2 News and Results - Page 11 L8icOU76_o
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Post by Lazarus on 26th November 2018, 2:44 pm

Cortes et al. "Search for Exoplanetary Transits in the Galactic Bulge"
https://arxiv.org/abs/1811.09174

It's not clear to me which of these are actually in the Galactic Bulge. EPIC 224439122 is in NGC 6530, the open cluster within the Lagoon Nebula so could have some interesting views there. Unfortunately they don't give the Gaia DR2 identifiers or the parallaxes, despite discussing the use of Gaia data.
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Post by Sirius_Alpha on 13th December 2018, 11:55 pm

Apparently exoplanet.eu has identified a problem with the K2 designations.
Warning : Announcements of K2 planets can be duplicated. -The planet of the star EPIC 201498078 has been announced as K2-261 b by Johnson et al., MNRAS, august 2018 and as K2-161 b by Brahms et al. , MNRAS, november 2018. - Mayo et al. 2018 gives also the name K2-161 b to EPIC 201231064 b. - The two planets of the star 2MASS J08452605+1941544 are simultaneously announced by Rizzuto et al. (2018 ) as K2-264 b and c and by Livingston et al. (2018) as EPIC 211964830 b and c.

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Post by Sirius_Alpha on 23rd December 2018, 11:30 pm

Detection and characterization of an ultra-dense sub-Neptune planet orbiting the Sun-like star HD 119130
https://arxiv.org/abs/1812.09242

We present the discovery and characterization of a new transiting planet from Campaign 17 of the Kepler extended mission K2. HD 119130 b is a warm sub-Neptune on a 17-d orbit around a bright (V = 9.9 mag) solar-like G3 V star with a mass and radius of M⋆=1.00±0.03M⊙ and R⋆=1.09±0.03R⊙, respectively. We model simultaneously the K2 photometry and CARMENES spectroscopic data and derive a radius of Rp=2.63+0.12−0.10R⊕ and mass of Mp=24.5+4.4−4.4M⊕, yielding a mean density of ρp=7.4+1.6−1.5gcm−3, which makes it one of the densest sub-Neptune planets known to date. We also detect a linear trend in radial velocities of HD 119130 (γ˙RV=−0.40+0.07−0.07ms−1d−1) that suggests a long-period companion with a minimum mass on the order of 33M⊕. If confirmed, it would support a formation scenario of HD 119130 b by migration caused by Kozai-Lidov oscillations.

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Post by Lazarus on 24th December 2018, 7:44 am

Spitzer+RV characterisation of K2-3 and GJ 3470.

Kosiarek et al. "Bright Opportunities for Atmospheric Characterization of Small Planets: Masses and Radii of K2-3 b, c, d and GJ3470 b from Radial Velocity Measurements and Spitzer Transits"
https://arxiv.org/abs/1812.08241
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Post by Lazarus on 24th December 2018, 11:12 am

Phase curves for several planets using K2: the hot Jupiters K2-31b, HATS-9b, HATS-11b and K2-107b, plus the super-Earths K2-131b and K2-106b. Secondary eclipse is detected for HATS-11b.

Niraula et al. "Discovery of Six Optical Phase Curves with K2"
https://arxiv.org/abs/1812.09227
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Post by Sirius_Alpha on 26th December 2018, 3:35 pm

A transiting super-Earth close to the inner edge of the habitable zone of an M0 dwarf star
https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/sty3467/5259110?redirectedFrom=PDF

We present a super-Earth orbiting close to the inner edge of the habitable zone of the cool dwarf star K2-XX (EPIC 249889081), detected with data from the K2 mission in its 15th campaign. The planet has radius of 2.1 ± 0.2 R⊕, near the 1.5 – 2.0 R⊕ gap in the radii distribution. The equilibrium temperature is 347+21−11 K, cooler than most of the small planets with well measured masses, and the orbital period is 27.359 ± 0.005 days. K2-XX, located at a distance of 76.3 ± 0.3 pc, is an M0V star with estimated effective temperature of 3926 ± 100 K, less active than other M dwarf stars hosting exoplanets. The expected radial velocity semi-amplitude induced by the planet on the star is 1.9+1.3−1.2 m·s−1, and the amplitude of signals in transit transmission spectroscopy is estimated at 5.0 ± 3.0 ppm. Follow-up observations for mass measurements and transit spectroscopy should be desirable for this relatively bright target (mV = 12.76, mKs = 9.32) hosting a transiting super-Earth within the inner edge of the habitable zone.

Orbit parameters and physical properties on exoplanet.eu:
http://exoplanet.eu/catalog/epic_249889081_b/

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Post by Sirius_Alpha on 7th January 2019, 4:46 pm

Some Spitzer-aided confirmations of exoplanets being presented at the AAS233 conference.

K2-288 Bb, a 2 Earth-radius planet in/near the HZ of an M dwarf in a binary system.
https://www.jpl.nasa.gov/news/news.php?release=2019-002
http://iopscience.iop.org/article/10.3847/1538-3881/aafa70

K2-138 g, Kepler-K2's first six-planet system.
https://aas233-aas.ipostersessions.com/default.aspx?s=B1-4E-A0-5C-E1-C3-3C-2B-10-73-E2-4A-17-0E-01-88

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Post by Sirius_Alpha on 15th January 2019, 12:40 am

EPIC 249624646: a warm Jupiter and a mini-Neptune in a triple-star system
https://arxiv.org/abs/1901.03716

We report the discovery of two transiting planets orbiting EPIC 249624646, a bright (V=11.11) late F-type star residing in a triple-star system. It was observed during Campaign 15 of the K2 mission, and in order to confirm and characterise the system, follow-up spectroscopy and AO imaging were carried out using the FIES, HARPS, HARPS-N, and IRCS instruments. From AO imaging and Gaia data we identify two M-dwarf companions at a separation of 113±2 AU and 2467+177−155 AU. From radial velocities, K2 photometry, and stellar characterisation of the host star, we find the inner planet to be a mini-Neptune with a radius of 3.06±0.16R⊕ and an orbital period of P=9.2 days. The radius of the mini-Neptune suggests that the planet is located above the radius valley, and with an incident flux of F∼400F⊕, it lies safely outside the super-Earth desert. The outer warm Jupiter has a mass of 0.774±0.047MJ and a radius of 1.006±0.050RJ, and orbits the host star every 48.4 days on an orbit with an eccentricity e<0.241. Its mild eccentricity and mini-Neptune sibling suggest that the warm Jupiter originates from in situ formation or disk migration.

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Post by Lazarus on 16th January 2019, 6:50 pm

A couple more papers:

EPIC 247418783

Kosiarek et al. "EPIC 247418783b: A rocky super-Earth in a 2.2 day orbit"
https://arxiv.org/abs/1901.04558

K2-286=EPIC 29889081

Díez Alonso et al. "A transiting super-Earth close to the inner edge of the habitable zone of an M0 dwarf star"
https://arxiv.org/abs/1901.04739
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Post by Sirius_Alpha on 17th January 2019, 10:26 pm

Refinement of transit ephemereses validation of EPIC 205686202.01 (K2-289 b).

Spitzer transit follow-up of planet candidates from the K2 mission
https://arxiv.org/abs/1901.05855

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Post by Edasich on 12th March 2019, 4:04 pm

Before NASA, Extrasolar Planet Encyclopaedia celebrates the 4,000th Exoplanet by including both previously and recently announced brown dwarf companions to K2-EPIC targets.

New substellar discoveries from Kepler and K2: Is there a brown dwarf desert?

We present the discoveries of a brown dwarf and a low mass star from the Kepler and K2 missions. The newly discovered brown dwarf is EPIC 212036875b and the low mass star is KOI-607b. EPIC 212036875b has a mass of Mb=47.8±3.1MJ, a radius of Rb=0.819±0.035RJ, and orbits its host star in P=5.17 days. Its host star is a late F-type star with M⋆=1.124±0.11M⊙, R⋆=1.401±0.059R⊙, and Teff=6231±51K. KOI-607b has a mass of Mb=94.4±3.4MJ, a radius of Rb=1.059±0.084RJ, and an orbital period of P=5.89 days. The primary star in the KOI-607 system is a G dwarf with M⋆=0.983±0.053M⊙, R⋆=0.903±0.032R⊙, and Teff=5435±50K. We also revisit a brown dwarf, CWW 89Ab, that was previously published by Nowak et al. (2017) (under the designation EPIC 219388192b) and report a smaller measurement of its radius than the previous work. CWW 89Ab is the only known brown dwarf associated with a star cluster (Ruprecht 147) which illustrates the need for more brown dwarfs with accurate masses and radii and reliable age determinations to test theoretical models. We find that the newly discovered brown dwarf, EPIC 212036875b, falls in the middle of the so-called "brown dwarf desert", indicating that EPIC 212036875b is either a particularly rare object, or the brown dwarf desert may not be so dry after all.

New entries are the following:

http://exoplanet.eu/catalog/ep212_b/
http://exoplanet.eu/catalog/epic_203868608_(ab)_a/
http://exoplanet.eu/catalog/epic_203868608_(ab)_b/

The latter two have confusing designations. The (ab)a is regarded as circum-binary to (AB) M dwarf eclipsing pair, but is in turn orbited by a low-mass companion. Could a designation like this be solving?

1) EPIC 203868608 (AB)b or Ca for the "circum-binary" primary

2) EPIC 203868608 Cb for the secondary.
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Post by Lazarus on 12th March 2019, 5:45 pm

EPIC 203868608 is discussed more in Wang et al. (2018) "EPIC 203868608: A low-mass quadruple star system in the Upper Scorpius OB association"

A is an SB2 binary (P=17.94 days) consisting of components Aa and Ab, with total mass ~0.4–0.6 solar masses.
B is an eclipsing binary (P=4.54 days) consisting of components Ba and Bb, with total mass ~0.3–0.5 solar masses.

The two binaries have a projected separation of 19.3 AU.

The Carmichael et al. (2019) paper uses the earlier David et al. (2016) reference, which Wang et al. (2018) note made an erroneous assumption that the SB2 and the EB were the same signal.

Presumably one or both of these objects should be removed from the EPE catalogue.
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Post by Sirius_Alpha on 26th March 2019, 9:07 pm

Identifying Exoplanets with Deep Learning II: Two New Super-Earths Uncovered by a Neural Network in K2 Data
https://arxiv.org/abs/1903.10507

Two new planets are validated: K2-293 b and K2-294 b.

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Post by Sirius_Alpha on 1st April 2019, 8:57 pm

The Transit Least Squares Survey - I. Discovery and validation of an Earth-sized planet in the four-planet system K2-32 near the 1:2:5:7 resonance
https://arxiv.org/abs/1904.00651

We apply, for the first time, the Transit Least Squares (TLS) algorithm to search for new transiting exoplanets. TLS is a successor to the Box Least Squares (BLS) algorithm, which has served as a standard tool for the detection of periodic transits. In this proof-of-concept paper, we demonstrate how TLS finds small planets that have previously been missed. We showcase TLS' capabilities using the K2 EVEREST-detrended light curve of the star K2-32 (EPIC205071984) that was known to have three transiting planets. TLS detects these known Neptune-sized planets K2-32b, d, and c in an iterative search and finds an additional transit signal with a high signal detection efficiency (SDE_TLS) of 26.1 at a period of 4.34882 (-0.00075, +0.00069) d. We show that this signal remains detectable (SDE_TLS = 13.2) with TLS in the K2SFF light curve of K2-32, which includes a less optimal detrending of the systematic trends. The signal is below common detection thresholds, however, if searched with BLS in the K2SFF light curve (SDE_BLS = 8.9) as in previous searches. Markov Chain Monte Carlo sampling shows that the radius of this candidate is 1.01 (-0.09, +0.10) Earth radii. We analyze its phase-folded transit light curve using the vespa software and calculate a false positive probability FPP = 3.1e-3, formally validating K2-32e as a planet. Taking into account the multiplicity boost of the system, FPP < 3.1e-4. K2-32 now hosts at least four planets that are very close to a 1:2:5:7 mean motion resonance chain. The offset of the orbital periods of K2-32e and b from a 1:2 mean motion resonance is in very good agreement with the sample of transiting multi-planet systems from Kepler, lending further credence to the planetary nature of K2-32e. We expect that TLS can find many more transits of Earth-sized and smaller planets in the Kepler data that have hitherto remained undetected with BLS and similar algorithms.

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