[en] Initially designed to discover short-period planets, the N2K campaign has since evolved to discover new worlds at large separations from their host stars. Detecting such worlds will help determine the giant planet occurrence at semi-major axes beyond the ice line, where gas giants are thought to mostly form. Here we report four newly discovered gas giant planets (with minimum masses ranging from 0.4 to 2.1 M _Jup) orbiting stars monitored as part of the Next 2000 target stars (N2K) Doppler Survey program. Two of these planets orbit stars already known to host planets: HD 5319 and HD 11506. The remaining discoveries reside in previously unknown planetary systems: HD 10442 and HD 75784. The refined orbital period of the inner planet orbiting HD 5319 is 641 days. The newly discovered outer planet orbits in 886 days. The large masses combined with the proximity to a 4:3 mean motion resonance make this system a challenge to explain with current formation and migration theories. HD 11506 has one confirmed planet, and here we confirm a second. The outer planet has an orbital period of 1627.5 days, and the newly discovered inner planet orbits in 223.6 days. A planet has also been discovered orbiting HD 75784 with an orbital period of 341.7 days. There is evidence for a longer period signal; however, several more years of observations are needed to put tight constraints on the Keplerian parameters for the outer planet. Lastly, an additional planet has been detected orbiting HD 10442 with a period of 1043 days

[en] We present initial results from a new high-contrast imaging program dedicated to stars that exhibit long-term Doppler radial velocity accelerations (or ''trends''). The goal of the TRENDS (TaRgetting bENchmark-objects with Doppler Spectroscopy) imaging survey is to directly detect and study the companions responsible for accelerating their host star. In this first paper of the series, we report the discovery of low-mass stellar companions orbiting HD 53665, HD 68017, and HD 71881 using NIRC2 adaptive optics (AO) observations at Keck. Follow-up imaging demonstrates association through common proper motion. These comoving companions have red colors with estimated spectral types of K7-M0, M5, and M3-M4, respectively. We determine a firm lower limit to their mass from Doppler and astrometric measurements. In the near future, it will be possible to construct three-dimensional orbits and calculate the dynamical mass of HD 68017 B and possibly HD 71881 B. We already detect astrometric orbital motion of HD 68017 B, which has a projected separation of 13.0 AU. Each companion is amenable to AO-assisted direct spectroscopy. Further, each companion orbits a solar-type star, making it possible to infer metallicity and age from the primary. Such benchmark objects are essential for testing theoretical models of cool dwarf atmospheres.

[en] We report the detection of three new exoplanets from Keck Observatory. HD 163607 is a metal-rich G5IV star with two planets. The inner planet has an observed orbital period of 75.29 ± 0.02 days, a semi-amplitude of 51.1 ± 1.4 m s^–1, an eccentricity of 0.73 ± 0.02, and a derived minimum mass of M_P sin i = 0.77 ± 0.02 M_Jup. This is the largest eccentricity of any known planet in a multi-planet system. The argument of periastron passage is 78.7 ± 2.⁰0; consequently, the planet's closest approach to its parent star is very near the line of sight, leading to a relatively high transit probability of 8%. The outer planet has an orbital period of 3.60 ± 0.02 years, an orbital eccentricity of 0.12 ± 0.06, and a semi-amplitude of 40.4 ± 1.3 m s^–1. The minimum mass is M_P sin i = 2.29 ± 0.16 M_Jup. HD 164509 is a metal-rich G5V star with a planet in an orbital period of 282.4 ± 3.8 days and an eccentricity of 0.26 ± 0.14. The semi-amplitude of 14.2 ± 2.7 m s^–1 implies a minimum mass of 0.48 ± 0.09 M_Jup. The radial velocities (RVs) of HD 164509 also exhibit a residual linear trend of –5.1 ± 0.7 m s^–1 year^–1, indicating the presence of an additional longer period companion in the system. Photometric observations demonstrate that HD 163607 and HD 164509 are constant in brightness to submillimagnitude levels on their RV periods. This provides strong support for planetary reflex motion as the cause of the RV variations.

[en] Determining which small exoplanets have stony-iron compositions is necessary for quantifying the occurrence of such planets and for understanding the physics of planet formation. Kepler-10 hosts the stony-iron world Kepler-10b, and also contains what has been reported to be the largest solid silicate-ice planet, Kepler-10c. Using 220 radial velocities (RVs), including 72 precise RVs from Keck-HIRES of which 20 are new from 2014 to 2015, and 17 quarters of Kepler photometry, we obtain the most complete picture of the Kepler-10 system to date. We find that Kepler-10b ($R_{\mathrm{p}}=1.47R_{\oplus <!--\; ???\; -->}$) has mass $3.72\pm <!--\; ??\; -->0.42M_{\oplus <!--\; ???\; -->}$ and density $6.46\pm <!--\; ??\; -->0.73\mathrm{g}{\mathrm{c}\mathrm{m}}^{-<!--\; ???\; -->3}$. Modeling the interior of Kepler-10b as an iron core overlaid with a silicate mantle, we find that the iron core constitutes 0.17 ± 0.11 of the planet mass. For Kepler-10c ($R_{\mathrm{p}}=2.35R_{\oplus <!--\; ???\; -->}$) we measure mass $13.98\pm <!--\; ??\; -->1.79M_{\oplus <!--\; ???\; -->}$ and density $5.94\pm <!--\; ??\; -->0.76\mathrm{g}{\mathrm{c}\mathrm{m}}^{-<!--\; ???\; -->3}$, significantly lower than the mass computed in Dumusque et al. ($17.2\pm <!--\; ??\; -->1.9M_{\oplus <!--\; ???\; -->}$). Our mass measurement of Kepler-10c rules out a pure stony-iron composition. Internal compositional modeling reveals that at least 10% of the radius of Kepler-10c is a volatile envelope composed of hydrogen–helium (0.2% of the mass, 16% of the radius) or super-ionic water (28% of the mass, 29% of the radius). However, we note that analysis of only HIRES data yields a higher mass for planet b and a lower mass for planet c than does analysis of the HARPS-N data alone, with the mass estimates for Kepler-10 c being formally inconsistent at the 3σ level. Moreover, dividing the data for each instrument into two parts also leads to somewhat inconsistent measurements for the mass of planet c derived from each observatory. Together, this suggests that time-correlated noise is present and that the uncertainties in the masses of the planets (especially planet c) likely exceed our formal estimates. Transit timing variations (TTVs) of Kepler-10c indicate the likely presence of a third planet in the system, KOI-72.X. The TTVs and RVs are consistent with KOI-72.X having an orbital period of 24, 71, or 101 days, and a mass from 1 to 7 $M_{\oplus <!--\; ???\; -->}$.

[en] A historical problem for indirect exoplanet detection has been contending with the intrinsic variability of the host star. If the variability is periodic, it can easily mimic various exoplanet signatures, such as radial velocity (RV) variations that originate with the stellar surface rather than the presence of a planet. Here we present an update for the HD 99492 planetary system, using new RV and photometric measurements from the Transit Ephemeris Refinement and Monitoring Survey. Our extended time series and subsequent analyses of the Ca ii H and K emission lines show that the host star has an activity cycle of ∼13 years. The activity cycle correlates with the purported orbital period of the outer planet, the signature of which is thus likely due to the host star activity. We further include a revised Keplerian orbital solution for the remaining planet, along with a new transit ephemeris. Our transit-search observations were inconclusive

[en] This paper reports the discovery and characterization of the transiting hot giant exoplanet Kepler-17b. The planet has an orbital period of 1.486 days, and radial velocity measurements from the Hobby-Eberly Telescope show a Doppler signal of 419.5^+13.3_–15.6 m s^–1. From a transit-based estimate of the host star's mean density, combined with an estimate of the stellar effective temperature T_eff = 5630 ± 100 from high-resolution spectra, we infer a stellar host mass of 1.06 ± 0.07 M_☉ and a stellar radius of 1.02 ± 0.03 R_☉. We estimate the planet mass and radius to be M_P = 2.45 ± 0.11 M_J and R_P = 1.31 ± 0.02 R_J. The host star is active, with dark spots that are frequently occulted by the planet. The continuous monitoring of the star reveals a stellar rotation period of 11.89 days, eight times the planet's orbital period; this period ratio produces stroboscopic effects on the occulted starspots. The temporal pattern of these spot-crossing events shows that the planet's orbit is prograde and the star's obliquity is smaller than 15°. We detected planetary occultations of Kepler-17b with both the Kepler and Spitzer Space Telescopes. We use these observations to constrain the eccentricity, e, and find that it is consistent with a circular orbit (e < 0.011). The brightness temperatures of the planet's infrared bandpasses are T_3.6μm = 1880 ± 100 K and T_4.5μm = 1770 ± 150 K. We measure the optical geometric albedo A_g in the Kepler bandpass and find A_g = 0.10 ± 0.02. The observations are best described by atmospheric models for which most of the incident energy is re-radiated away from the day side.

[en] We characterize the star KOI 961, an M dwarf with transit signals indicative of three short-period exoplanets discovered by the Kepler mission. We proceed by comparing KOI 961 to Barnard's Star, a nearby, well-characterized mid-M dwarf. We compare colors, optical and near-infrared spectra, and find remarkable agreement between the two, implying similar effective temperatures and metallicities. Both are metal-poor compared to the Solar neighborhood, have low projected rotational velocity, high absolute radial velocity, large proper motion, and no quiescent Hα emission—all of which are consistent with being old M dwarfs. We combine empirical measurements of Barnard's Star and expectations from evolutionary isochrones to estimate KOI 961's mass (0.13 ± 0.05 M_☉), radius (0.17 ± 0.04 R_☉), and luminosity (2.40 × 10^–3.0±0.3 L_☉). We calculate KOI 961's distance (38.7 ± 6.3 pc) and space motions, which, like Barnard's Star, are consistent with a high scale-height population in the Milky Way. We perform an independent multi-transit fit to the public Kepler light curve and significantly revise the transit parameters for the three planets. We calculate the false-positive probability for each planet candidate, and find a less than 1% chance that any one of the transiting signals is due to a background or hierarchical eclipsing binary, validating the planetary nature of the transits. The best-fitting radii for all three planets are less than 1 R_⊕, with KOI 961.03 being Mars-sized (R_P = 0.57 ± 0.18 R_⊕), and they represent some of the smallest exoplanets detected to date.

[en] We present an investigation of 12 candidate transiting planets from Kepler with orbital periods ranging from 34 to 207 days, selected from initial indications that they are small and potentially in the habitable zone (HZ) of their parent stars. Few of these objects are known. The expected Doppler signals are too small to confirm them by demonstrating that their masses are in the planetary regime. Here we verify their planetary nature by validating them statistically using the BLENDER technique, which simulates large numbers of false positives and compares the resulting light curves with the Kepler photometry. This analysis was supplemented with new follow-up observations (high-resolution optical and near-infrared spectroscopy, adaptive optics imaging, and speckle interferometry), as well as an analysis of the flux centroids. For 11 of them (KOI-0571.05, 1422.04, 1422.05, 2529.02, 3255.01, 3284.01, 4005.01, 4087.01, 4622.01, 4742.01, and 4745.01) we show that the likelihood they are true planets is far greater than that of a false positive, to a confidence level of 99.73% (3σ) or higher. For KOI-4427.01 the confidence level is about 99.2% (2.6σ). With our accurate characterization of the GKM host stars, the derived planetary radii range from 1.1 to 2.7 R _⊕. All 12 objects are confirmed to be in the HZ, and nine are small enough to be rocky. Excluding three of them that have been previously validated by others, our study doubles the number of known rocky planets in the HZ. KOI-3284.01 (Kepler-438b) and KOI-4742.01 (Kepler-442b) are the planets most similar to the Earth discovered to date when considering their size and incident flux jointly

[en] We find transient transit-like dimming events within the K2 time series photometry of the young star RIK-210 in the Upper Scorpius OB association. These dimming events are variable in depth, duration, and morphology. High spatial resolution imaging revealed that the star is single and radial velocity monitoring indicated that the dimming events cannot be due to an eclipsing stellar or brown dwarf companion. Archival and follow-up photometry suggest the dimming events are transient in nature. The variable morphology of the dimming events suggests they are not due to a single spherical body. The ingress of each dimming event is always shallower than egress, as one would expect for an orbiting body with a leading tail. The dimming events are periodic and synchronous with the stellar rotation. However, we argue it is unlikely the dimming events could be attributed to anything on the stellar surface based on the observed depths and durations. Variable obscuration by a protoplanetary disk is unlikely on the basis that the star is not actively accreting and lacks the infrared excess associated with an inner disk. Rather, we explore the possibilities that the dimming events are due to magnetospheric clouds, a transiting protoplanet surrounded by circumplanetary dust and debris, eccentric orbiting bodies undergoing periodic tidal disruption, or an extended field of dust or debris near the corotation radius.

[en] Strongly irradiated giant planets are observed to have radii larger than thermal evolution models predict. Although these inflated planets have been known for over 15 years, it is unclear whether their inflation is caused by the deposition of energy from the host star or the inhibited cooling of the planet. These processes can be distinguished if the planet becomes highly irradiated only when the host star evolves onto the red giant branch. We report the discovery of K2-97b, a 1.31 ± 0.11 R _J, 1.10 ± 0.11 M _J planet orbiting a 4.20 ± 0.14 R _⊙, 1.16 ± 0.12 M _⊙ red giant star with an orbital period of 8.4 days. We precisely constrained stellar and planetary parameters by combining asteroseismology, spectroscopy, and granulation noise modeling along with transit and radial velocity measurements. The uncertainty in planet radius is dominated by systematic differences in transit depth, which we measure to be up to 30% between different light-curve reduction methods. Our calculations indicate the incident flux on this planet was ${170}_{-<!--\; ???\; -->60}^{+140}$ times the incident flux on Earth, while the star was on the main sequence. Previous studies suggest that this incident flux is insufficient to delay planetary cooling enough to explain the present planet radius. This system thus provides the first evidence that planets may be inflated directly by incident stellar radiation rather than by delayed loss of heat from formation. Further studies of planets around red giant branch stars will confirm or contradict this hypothesis and may reveal a new class of re-inflated planets.