We report the discovery of a compact multi-planet system orbiting the relatively nearby (78pc) and bright (\(K=8.9\)) K-star, K2-266 (EPIC248435473). We identify up to six possible planets orbiting ...K2-266 with estimated periods of P\(_b\) = 0.66, P\(_{.02}\) = 6.1, P\(_c\) = 7.8, P\(_d\) = 14.7, P\(_e\) = 19.5, and P\(_{.06}\) = 56.7 days and radii of R\(_P\) = 3.3 R\(_{\oplus}\), 0.646 R\(_{\oplus}\), 0.705 R\(_{\oplus}\), 2.93 R\(_{\oplus}\), 2.73 R\(_{\oplus}\), and 0.90 R\(_{\oplus}\), respectively. We are able to confirm the planetary nature of two of these planets (d & e) from analyzing their transit timing variations (\(m_d= 8.9_{-3.8}^{+5.7} M_\oplus\) and \(m_e=14.3_{-5.0}^{+6.4} M_\oplus\)), confidently validate the planetary nature of two other planets (b & c), and classify the last two as planetary candidates (K2-266.02 & .06). From a simultaneous fit of all 6 possible planets, we find that K2-266 b's orbit has an inclination of 75.32\(^{\circ}\) while the other five planets have inclinations of 87-90\(^{\circ}\). This observed mutual misalignment may indicate that K2-266 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 K2-266.
K2-138 is a moderately bright (V = 12.2, K = 10.3) main sequence K-star observed in Campaign 12 of the NASA K2 mission. It hosts five small (1.6-3.3R_Earth) transiting planets in a compact ...architecture. The periods of the five planets are 2.35 d, 3.56 d, 5.40 d, 8.26 d, and 12.76 d, forming an unbroken chain of near 3:2 resonances. Although we do not detect the predicted 2-5 minute transit timing variations with the K2 timing precision, they may be observable by higher cadence observations with, for example, Spitzer or CHEOPS. The planets are amenable to mass measurement by precision radial velocity measurements, and therefore K2-138 could represent a new benchmark systems for comparing radial velocity and TTV masses. K2-138 is the first exoplanet discovery by citizen scientists participating in the Exoplanet Explorers project on the Zooniverse platform.
We present high-resolution observations of a sample of 75 K2 targets from Campaigns 1-3 using speckle interferometry on the Southern Astrophysical Research (SOAR) telescope and adaptive optics (AO) ...imaging at the Keck II telescope. The median SOAR \(I\)-band and Keck \(K_s\)-band detection limits at 1" were \(\Delta m_{I}=4.4\)~mag and \(\Delta m_{K_s}=6.1\)~mag, respectively. This sample includes 37 stars likely to host planets, 32 targets likely to be eclipsing binaries (EBs), and 6 other targets previously labeled as likely planetary false positives. We find nine likely physically bound companion stars within 3" of three candidate transiting exoplanet host stars and six likely EBs. Six of the nine detected companions are new discoveries; one of the six, EPIC 206061524, is associated with a planet candidate. Among the EB candidates, companions were only found near the shortest period ones (\(P<3\) days), which is in line with previous results showing high multiplicity near short-period binary stars. This high-resolution data, including both the detected companions and the limits on potential unseen companions, will be useful in future planet vetting and stellar multiplicity rate studies for planets and binaries.
We report the discovery of 14 new transiting planet candidates in the Kepler field from the Planet Hunters citizen science program. None of these candidates overlapped with Kepler Objects of Interest ...(KOIs) at the time of submission. We report the discovery of one more addition to the six planet candidate system around KOI-351, making it the only seven planet candidate system from Kepler. Additionally, KOI-351 bears some resemblance to our own solar system, with the inner five planets ranging from Earth to mini-Neptune radii and the outer planets being gas giants; however, this system is very compact, with all seven planet candidates orbiting \(\lesssim 1\) AU from their host star. A Hill stability test and an orbital integration of the system shows that the system is stable. Furthermore, we significantly add to the population of long period transiting planets; periods range from 124-904 days, eight of them more than one Earth year long. Seven of these 14 candidates reside in their host star's habitable zone.
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