K2 News and Results

A reminder to keep exoplanet count up to date:

- K2-16 d (Heller et al. 2019)
- K2-166 c (Heller et al. 2019)
- K2-297 b (Vanderburg et al. 2016, Heller et al. 2019)
- K2-300 b (Heller et al. 2019)
- K2-306 b (Heller et al. 2019)
- K2-311 b (Giles et al. 2018)

are "confirmed" but not included among confirmed planet list. The last one is the longest period K2 transiting planet.

On the other hand the substellar companion to EPIC 201702477 straddles the BD-M dwarf boundary like NGTS-19 b (or B) due to an estimated mass of 66.9 M_J.

Four new confirmed planets from K2:

The K2-OjOS Project: New and Revisited Planets and Candidates in K2 Campaigns 5, 16 & 18

Quote :

We present the first results of K2-OjOS, a collaborative project between professional and amateur astronomers primarily aimed to detect, characterize and validate new extrasolar planets. For this work, 10 amateur astronomers looked for planetary signals by visually inspecting the 20,427 light curves of K2 campaign 18 (C18). They found 42 planet candidates, of which 18 are new detections and 24 had been detected in the overlapping C5 by previous works. We used archival photometric and spectroscopic observations, as well as new high-spatial resolution images in order to carry out a complete analysis of the candidates found, including a homogeneous characterization of the host stars, transit modeling, search for transit timing variations and statistical validation. As a result, we report four new planets (K2-XXX b, K2-XXX b, K2-XXX b, and K2-XXX b) and 14 planet candidates. Besides, we refine the transit ephemeris of the previously published planets and candidates by modeling C5, C16 (when available) and C18 photometric data jointly, largely improving the period and mid-transit time precision. Regarding individual systems, we highlight the new planet K2-XXX b and candidate EPIC211537087.02 being near a 2:1 period commensurability, the detection of significant TTVs in the bright star K2-184 (V = 10.35), the location of K2-103 b inside the habitable zone according to optimistic models, the detection of a new single transit in the known system K2-274, and the disposition reassignment of K2-120 b, which we consider as a planet candidate as the origin of the signal can not be ascertained.

And further tens of newly confirmed ones with official K2 designation from NASA Exoplanet Archive de Leon et al. (2021):

https://exoplanetarchive.ipac.caltech.edu/docs/exonews_archive.html#26Aug2021

Among these some additional planets to known systems, namely K2-185 c, K2-268 d, e, & f, K2-304 c, K2-307 c, K2-331 c & b.

Edasich wrote:

Four new confirmed planets from K2:

The K2-OjOS Project: New and Revisited Planets and Candidates in K2 Campaigns 5, 16 & 18

Quote :

We present the first results of K2-OjOS, a collaborative project between professional and amateur astronomers primarily aimed to detect, characterize and validate new extrasolar planets. For this work, 10 amateur astronomers looked for planetary signals by visually inspecting the 20,427 light curves of K2 campaign 18 (C18). They found 42 planet candidates, of which 18 are new detections and 24 had been detected in the overlapping C5 by previous works. We used archival photometric and spectroscopic observations, as well as new high-spatial resolution images in order to carry out a complete analysis of the candidates found, including a homogeneous characterization of the host stars, transit modeling, search for transit timing variations and statistical validation. As a result, we report four new planets (K2-355 b, K2-356 b, K2-357 b, and K2-358 b) and 14 planet candidates. Besides, we refine the transit ephemeris of the previously published planets and candidates by modeling C5, C16 (when available) and C18 photometric data jointly, largely improving the period and mid-transit time precision. Regarding individual systems, we highlight the new planet K2-XXX b and candidate EPIC211537087.02 being near a 2:1 period commensurability, the detection of significant TTVs in the bright star K2-184 (V = 10.35), the location of K2-103 b inside the habitable zone according to optimistic models, the detection of a new single transit in the known system K2-274, and the disposition reassignment of K2-120 b, which we consider as a planet candidate as the origin of the signal can not be ascertained.

And further tens of newly confirmed ones with official K2 designation from NASA Exoplanet Archive de Leon et al. (2021):

https://exoplanetarchive.ipac.caltech.edu/docs/exonews_archive.html#26Aug2021

Among these some additional planets to known systems, namely K2-185 c, K2-268 d, e, & f, K2-304 c, K2-307 c, K2-331 c & b.

Additional K2 planets from K2-355 to 358. Updated in the "quote" panel.

Tightened constraints on three K2 planets.
http://arxiv.org/abs/2110.05502v1

New confirmed ultra-short-period planets (K2-359 to K2-363), with additions to known systems too (K2-299 and K2-301).

Updates for K2-99 system: new parameters for the transiting planet and detection of an additional, non-transiting outer planet.

K2-99 revisited: a non-inflated warm Jupiter, and a temperate giant planet on a 522-d orbit around a subgiant

Quote :

We report new photometric and spectroscopic observations of the K2-99 planetary system. Asteroseismic analysis of the short-cadence light curve from K2's Campaign 17 allows us to refine the stellar properties. We find K2-99 to be significantly smaller than previously thought, with R⋆=2.55±0.02 R⊙. The new light curve also contains four transits of K2-99b, which we use to improve our knowledge of the planetary properties. We find the planet to be a non-inflated warm Jupiter, with Rb=1.06±0.01 RJup. Sixty new radial velocity measurements from HARPS, HARPS-N, and HIRES enable the determination of the orbital parameters of K2-99c, which were previously poorly constrained. We find that this outer planet has a minimum mass Mcsinic=8.4±0.2 MJup, and an eccentric orbit (ec=0.210±0.009) with a period of 522.2±1.4 d. Upcoming TESS observations in 2022 have a good chance of detecting the transit of this planet, if the mutual inclination between the two planetary orbits is small.

More statistically validated planets (in the right thread this time! :p)

https://arxiv.org/abs/2203.02087

Sirius_Alpha wrote:

More statistically validated planets (in the right thread this time! :p)

https://arxiv.org/abs/2203.02087

There are some interesting new entries: a few Corot-7-analogues, some with way larger radius and several multi-planet systems.

Boyle et al. (2022) "An Updated Ephemeris for K2-138 d"
https://iopscience.iop.org/article/10.3847/2515-5172/ac64fe

Does what it says on the tin.

A Reanalysis of the Composition of K2-106b: an Ultra-short Period Super-Mercury Candidate
https://arxiv.org/abs/2208.07883

TFAW survey II: 6 Newly Validated Planets and 13 Planet Candidates from K2
https://arxiv.org/abs/2210.10805

This one has appeared at EPE, I guess it's from K2-EPIC batch...

http://exoplanet.eu/catalog/hd_73344_b/

It has TOI designation too (TOI-5140.01)

Interesting updates about K2-33 system

A Circumplanetary Dust Ring May Explain the Extreme Spectral Slope of the 10 Myr Young Exoplanet K2-33b
https://arxiv.org/abs/2211.07706

Hazy with a chance of star spots: constraining the atmosphere of the young planet, K2-33b
https://arxiv.org/abs/2211.07728

An Earth-sized Planet around an M5 Dwarf Star at 22 pc
https://arxiv.org/abs/2302.00699

Also known as TOI-5557.

Hyades Member K2-136c: The Smallest Planet in an Open Cluster with a Precisely Measured Mass

Quote :

K2-136 is a late-K dwarf (0.742±0.039 M⊙) in the Hyades open cluster with three known, transiting planets and an age of 650±70 Myr. Analyzing K2 photometry, we found that planets K2-136b, c, and d have periods of 8.0, 17.3, and 25.6 days and radii of 1.014±0.050 R⊕, 3.00±0.13 R⊕, and 1.565±0.077 R⊕, respectively. We collected 93 radial velocity measurements (RVs) with the HARPS-N spectrograph (TNG) and 22 RVs with the ESPRESSO spectrograph (VLT). Analyzing HARPS-N and ESPRESSO data jointly, we found K2-136c induced a semi-amplitude of 5.49±0.53 m s−1, corresponding to a mass of 18.1±1.9 M⊕. We also placed 95% upper mass limits on K2-136b and d of 4.3 and 3.0 M⊕, respectively. Further, we analyzed HST and XMM-Newton observations to establish the planetary high-energy environment and investigate possible atmospheric loss. K2-136c is now the smallest planet to have a measured mass in an open cluster and one of the youngest planets ever with a mass measurement. K2-136c has ∼75% the radius of Neptune but is similar in mass, yielding a density of 3.69+0.67−0.56 g cm−3 (∼2-3 times denser than Neptune). Mass estimates for K2-136b (and possibly d) may be feasible with more RV observations, and insights into all three planets' atmospheres through transmission spectroscopy would be challenging but potentially fruitful. This research and future mass measurements of young planets are critical for investigating the compositions and characteristics of small exoplanets at very early stages of their lives and providing insights into how exoplanets evolve with time.

Scaling K2 VII: Evidence for a high occurrence rate of hot sub-Neptunes at intermediate ages
https://arxiv.org/abs/2311.18709

Quote :

The NASA K2 mission obtained high precision time-series photometry for four young clusters, including the near-twin 600-800 Myr-old Praesepe and Hyades clusters. Hot sub-Neptunes are highly prone to mass-loss mechanisms, given their proximity to the the host star and the weakly bound gaseous envelopes, and analyzing this population at young ages can provide strong constraints on planetary evolution models. Using our automated transit detection pipeline, we recover 15 planet candidates across the two clusters, including 10 previously confirmed planets. We find a hot sub-Neptune occurrence rate of 79-107% for GKM stars in the Praesepe cluster. This is 2.5-3.5 sigma higher than the occurrence rate of 16.54+1.00-0.98% for the same planets orbiting the ~3-9 Gyr-old GKM field stars observed by K2, even after accounting for the slightly super-solar metallicity ([Fe/H]~0.2 dex) of the Praesepe cluster. We examine the effect of adding ~100 targets from the Hyades cluster, and extending the planet parameter space under examination, and find similarly high occurrence rates in both cases. The high occurrence rate of young, hot sub-Neptunes could indicate either that these planets are undergoing atmospheric evolution as they age, or that planetary systems that formed when the Galaxy was much younger are substantially different than from today. Under the assumption of the atmospheric mass-loss scenario, a significantly higher occurrence rate of these planets at the intermediate ages of Praesepe and Hyades appears more consistent with the core-powered mass loss scenario sculpting the hot sub-Neptune population, compared to the photoevaporation scenario.