197 Candidates and 102 New Validated Planets in C0-C10 of K2

Since 2014, the K2 mission has observed large portions of the ecliptic plane in search of transiting planets, and thus far discovered over 500 planet candidates in the first 10 campaigns. With observations planned up to at least campaign 16, many more planet candidates will continue to be discovered. We present here our identification of 197 planet candidates suitable for validation from campaigns 0-10 of the K2 mission. We subject these planets to a validation process in order to calculate the false positive probability (FPP), and find that 102 are validated (FPP < 0.001), 61 remain candidates (0.001 < FPP), and 34 are of an unknown disposition (we were unable to or chose not to report the false positive probability). Of the 102 newly validated planets, 32 have already been validated elsewhere, 37 have merely been identified as candidates elsewhere, and 33 have never been identified before. We describe the process of data reduction, candidate identification, and validation. We also explore the demographics of the newly validated planets. This research, in addition to dramatically increasing the population of validated K2 planets, will also provide new targets for follow-up observations, as well as serve as a framework for validating candidates from upcoming K2 campaigns and candidates identified through the Transiting Exoplanet Survey Satellite (TESS), expected to launch in early to mid 2018

Detecting Exomoons Via Doppler Monitoring of Directly Imaged Exoplanets

Recently, Teachey, Kipping, and Schmitt (2018) reported the detection of a candidate exomoon, tentatively designated Kepler-1625b I, around a giant planet in the Kepler field. The candidate exomoon would be about the size and mass of Neptune, considerably larger than any moon in our Solar System, and if confirmed, would be the first in a new class of giant moons or binary planets. Motivated by the large mass ratio in the Kepler-1625b planet and satellite system, we investigate the detectability of similarly massive exomoons around directly imaged exoplanets via Doppler spectroscopy. The candidate moon around Kepler-1625b would induce a radial velocity signal of about 200 m/s on its host planet, large enough that similar moons around directly imaged planets orbiting bright, nearby stars might be detected with current or next generation instrumentation. In addition to searching for exomoons, a radial velocity survey of directly imaged planets could reveal the orientations of the planets' spin axes, making it possible to identify Uranus analogs.Comment: 15 pages, 8 figures, 2 tables. Accepted for publication in A

Constraining Orbital Periods from Nonconsecutive Observations: Period Estimates for Long-Period Planets in Six Systems Observed by K2 During Multiple Campaigns

Most planetary discoveries with the K2 and TESS missions are restricted to short periods because of the limited duration of observation. However, the re-observation of sky area allows for the detection of longer period planets. We describe new transits detected in six candidate planetary systems which were observed by multiple K2 mission campaigns. One of these systems is a multiplanet system with four candidate planets; we present new period constraints for two planets in this system. In the other five systems, only one transit is observed in each campaign, and we derive period constraints from this new data. The period distributions are highly multimodal resulting from missed potential transits in the gap between observations. Each peak in the distribution corresponds to transits at an integer harmonic of the two observed transits. We further detail a generalized procedure to constrain the period for planets with multiple observations with intervening gaps. Because long period photometrically discovered planets are rare, these systems are interesting targets for follow-up observations and confirmation. Specifically, all six systems are bright enough (V = 10.4-12.7) to be amenable to radial velocity follow-up. This work serves as a template for period constraints in a host of similar yet-to-be-discovered planets in long baseline, temporally gapped observations conducted by the TESS mission.Comment: 10 pages, 5 figures; accepted for publication in A

Two Small Planets Transiting HD 3167

We report the discovery of two super-Earth-sized planets transiting the bright (V = 8.94, K = 7.07) nearby late G-dwarf HD 3167, using data collected by the K2 mission. The inner planet, HD 3167 b, has a radius of 1.6 R_e and an ultra-short orbital period of only 0.96 days. The outer planet, HD 3167 c, has a radius of 2.9 R_e and orbits its host star every 29.85 days. At a distance of just 45.8 +/- 2.2 pc, HD 3167 is one of the closest and brightest stars hosting multiple transiting planets, making HD 3167 b and c well suited for follow-up observations. The star is chromospherically inactive with low rotational line-broadening, ideal for radial velocity observations to measure the planets' masses. The outer planet is large enough that it likely has a thick gaseous envelope which could be studied via transmission spectroscopy. Planets transiting bright, nearby stars like HD 3167 are valuable objects to study leading up to the launch of the James Webb Space Telescope.Comment: Accepted by ApJL. 6 pages, 1 figure, 2 table

Distance dependence of photoinduced long-range electron transfer in zinc/ruthenium-modified myoglobins

An experimental investigation of the distance dependence of long-range electron transfer in zinc/ruthenium-modified myoglobins has been performed. The modified proteins were prepared by substitution of zinc mesoporphyrin IX diacid (ZnP) for the heme in each of four previously characterized pentaammineruthenium(III) (a_5Ru;a = NH_3) derivatives of sperm whale myoglobin (Mb): a_5Ru(His-48)Mb, a_5Ru(His-12)Mb, a_5Ru(His-116)Mb, a_5Ru(His-81)Mb. Electron transfer from the ZnP triplet excited state (^3ZnP*) to Ru^3+, ^3ZnP*-Ru^3+ → ZnP^+-Ru^2+ (ΔE° ~ 0.8V) was measured by time-resolved transient absorption spectroscopy: rate constants (k_f) are 7.0 × 10^4 (His-48), 1.0 × 10^2 (His-12), 8.9 × 10^1 (His-116), and 8.5 × 10^1 (His-81) s^-1 at 25 °C. Activation enthalpies calculated from the temperature dependences of the electron-transfer rates over the range 5-40 °C are 1.7 ± 1.6 (His-48), 4.7 ± 0.9 (His-12), 5.4 ± 0.4 (His-116), and 5.6 ± 2.5 (His-81) kcal mol^-1. Electron-transfer distances (d = closest ZnP edge to a_5Ru(His) edge; angstroms) were calculated to fall in the following ranges: His-48, 11.8-16.6; His-12, 21.5-22.3; His-116, 19.8-20.4; His-81, 18.8-19.3. The rate-distance equation is k_f = 7.8 × 10^8 exp[-0.9l(d - 3)] s^-1 . The data indicate that the ^3ZnP*-Ru(His-12)^3+ electronic coupling may be enhanced by an intervening tryptophan (Trp-14)

WNT-1 Signaling Inhibits Apoptosis by Activating β-Catenin/T Cell Factor–Mediated Transcription

Wnt signaling plays a critical role in development and oncogenesis. Although significant progress has been made in understanding the downstream signaling cascade of Wnt signaling, little is known regarding Wnt signaling modification of the cell death machinery. Given that numerous oncogenes transform cells by providing cell survival function, we hypothesized that Wnt signaling may inhibit apoptosis. Here, we report that cells expressing Wnt-1 were resistant to cancer therapy–mediated apoptosis. Wnt-1 signaling inhibited the cytochrome c release and the subsequent caspase-9 activation induced by chemotherapeutic drugs, including both vincristine and vinblastine. Furthermore, we found that Wnt-1–mediated cell survival was dependent on the activation of β-catenin/T cell factor (Tcf) transcription. Inhibition of β-catenin/Tcf transcription by expression of the dominant-negative mutant of Tcf-4 blocked Wnt-1–mediated cell survival and rendered cells sensitive to apoptotic stimuli. These results provide the first demonstration that Wnt-1 inhibits cancer therapy–mediated apoptosis and suggests that Wnt-1 may exhibit its oncogenic potential through a mechanism of anti-apoptosis

A Closer Look at Exoplanet Occurrence Rates: Considering the Multiplicity of Stars without Detected Planets

One core goal of the Kepler mission was to determine the frequency of Earth-like planets that orbit Sun-like stars. Accurately estimating this planet occurrence rate requires both a well-vetted list of planets and a clear understanding of the stars searched for planets. Previous ground-based follow-up observations have, through a variety of methods, sought to improve our knowledge of stars that are known to host planets. Kepler targets without detected planets, however, have not been subjected to the same intensity of follow-up observations. In this paper, we constrain better the stellar multiplicity for stars around which Kepler could have theoretically detected a transiting Earth-sized planet in the habitable zone. We subsequently aim to improve estimates of the exoplanet search completeness—the fraction of exoplanets that were detected by Kepler—with our analysis. By obtaining adaptive optics observations of 71 Kepler target stars from the Shane 3 m telescope at Lick Observatory, we detected 14 candidate stellar companions within 4'' of 13 target stars. Of these 14 candidate stellar companions, we determine through multiple independent methods that 3 are likely to be bound to their corresponding target star. We then assess the impact of our observations on exoplanet occurrence rate calculations, finding an increase in occurrence of 6% (0.9σ) for various estimates of the frequency of Earth-like planets and an increase of 26% (4.5σ) for super-Earths and sub-Neptunes. These occurrence increases are not entirely commensurate with theoretical predictions, though this discrepancy may be due to differences in the treatment of stellar binarity

A Hot Saturn Near (but Unassociated with) the Open Cluster NGC 1817

We report on the discovery of a hot Saturn-sized planet (9.916 ± 0.985 R ⊕) around a late F-star, K2-308, observed in Campaign 13 of the K2 mission. We began studying this planet candidate because prior to the release of Gaia DR2, the host star was thought to have been a member (⩾90% membership probability) of the ≈1 Gyr open cluster NGC 1817 based on its kinematics and photometric distance. We identify the host star (among three stars within the K2 photometric aperture) using seeing-limited photometry and rule out false-positive scenarios using adaptive optics imaging and radial velocity observations. We statistically validate K2-308b by calculating a false-positive probability rate of 0.01%. However, we also show using new kinematic measurements provided by Gaia DR2 and our measured radial velocity of the system that K2-308 is unassociated with the cluster NGC 1817. Therefore, the long running search for a giant transiting planet in an open cluster remains fruitless. Finally, we note that our use of seeing-limited photometry is a good demonstration of similar techniques that are already being used to follow up Transiting Exoplanet Survey Satellite (TESS) planet candidates, especially in crowded regions