Hunting for Stellar Companions for K2 Mission Exoplanetary Systems

Planet Hunters X: Searching for Nearby Neighbors of 75 Planet and Eclipsing Binary Candidates from the K2 Kepler extended mission

Authors:

Schmitt et al

Abstract:

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 Ks-band detection limits at 1'' were ΔmI=4.4 mag and ΔmKs=6.1 mag, respectively. This sample includes 37 stars likely to host planets, 32 targets likely to be 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 eclipsing binaries (EB). Six of the nine detected companions are new discoveries, one of them associated with a planet candidate (EPIC 206061524). Among the EB candidates, companions were only found near the shortest period ones (P less than 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.

Investigation of 41 Long-Period Kepler Exoplanet Candidates Confirms Seven

Planet Hunters. VIII. Characterization of 41 Long-Period Exoplanet Candidates from Kepler Archival Data

Authors:

Wang et al

Abstract:

The census of exoplanets is incomplete for orbital distances larger than 1 AU. Here, we present 41 long-period planet candidates in 38 systems identified by Planet Hunters based on Kepler archival data (Q0-Q17). Among them, 17 exhibit only one transit, 14 have two visible transits and 10 have more than three visible transits. For planet candidates with only one visible transit, we estimate their orbital periods based on transit duration and host star properties. The majority of the planet candidates in this work (75%) have orbital periods that correspond to distances of 1-3 AU from their host stars. We conduct follow-up imaging and spectroscopic observations to validate and characterize planet host stars. In total, we obtain adaptive optics images for 33 stars to search for possible blending sources. Six stars have stellar companions within 4". We obtain high-resolution spectra for 6 stars to determine their physical properties. Stellar properties for other stars are obtained from the NASA Exoplanet Archive and the Kepler Stellar Catalog by Huber et al. (2014). We validate 7 planet candidates that have planet confidence over 0.997 (3-{\sigma} level). These validated planets include 3 single-transit planets (KIC-3558849c, KIC-5951458b, and KIC-8540376d), 3 planets with double transits (KIC-8540376c, KIC-9663113c, and KIC-10525077b), and 1 planet with 4 transits (KIC-5437945c). This work provides assessment regarding the existence of planets at wide separations and the associated false positive rate for transiting observation (17%-33%). More than half of the long-period planets with at least three transits in this paper exhibit transit timing variations up to 41 hours, which suggest additional components that dynamically interact with the transiting planet candidates. The nature of these components can be determined by follow-up radial velocity and transit observations.

Did F Dwarf KIC 8462852 Have a Comet Breakup?

Planet Hunters X. KIC 8462852 - Where's the Flux?

Authors:

Boyajian et al

Abstract:

Over the duration of the Kepler mission, KIC 8462852 was observed to undergo irregularly shaped, aperiodic dips in flux down to below the 20% level. The dipping activity can last for between 5 and 80 days. We characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, and Fourier analyses of the Kepler light curve. We determine thatKIC 8462852 is a main-sequence F3 V/IV star, with a rotation period ~0.88 d, that exhibits no significant IR excess. In this paper, we describe various scenarios to explain the mysterious events in the Kepler light curve, most of which have problems explaining the data in hand. By considering the observational constraints on dust clumps orbiting a normal main-sequence star, we conclude that the scenario most consistent with the data is the passage of a family of exocomet fragments, all of which are associated with a single previous breakup event. We discuss the necessity of future observations to help interpret the system.

Kepler 289 System Found to Have Three Low Mass, Low Density Planets

PLANET HUNTERS. VII. DISCOVERY OF A NEW LOW-MASS, LOW-DENSITY PLANET (PH3 C) ORBITING KEPLER-289 WITH MASS MEASUREMENTS OF TWO ADDITIONAL PLANETS (PH3 B AND D)

Authors:

Schmitt et al

Abstract:

We report the discovery of one newly confirmed planet (P = 66.06 days, R P = 2.68 ± 0.17 R ⊕) and mass determinations of two previously validated Kepler planets, Kepler-289 b (P = 34.55 days, R P = 2.15 ± 0.10 R ⊕) and Kepler-289-c (P = 125.85 days, R P = 11.59 ± 0.10 R ⊕), through their transit timing variations (TTVs). We also exclude the possibility that these three planets reside in a 1:2:4 Laplace resonance. The outer planet has very deep (~1.3%), high signal-to-noise transits, which puts extremely tight constraints on its host star's stellar properties via Kepler's Third Law. The star PH3 is a young (~1 Gyr as determined by isochrones and gyrochronology), Sun-like star with M * = 1.08 ± 0.02 M ☉, R * = 1.00 ± 0.02 R ☉, and T eff = 5990 ± 38 K. The middle planet's large TTV amplitude (~5 hr) resulted either in non-detections or inaccurate detections in previous searches. A strong chopping signal, a shorter period sinusoid in the TTVs, allows us to break the mass-eccentricity degeneracy and uniquely determine the masses of the inner, middle, and outer planets to be M = 7.3 ± 6.8 M ⊕, 4.0 ± 0.9M ⊕, and M = 132 ± 17 M ⊕, which we designate PH3 b, c, and d, respectively. Furthermore, the middle planet, PH3 c, has a relatively low density, ρ = 1.2 ± 0.3 g cm–3 for a planet of its mass, requiring a substantial H/He atmosphere of $2.1^{+0.8}_{-0.3}\%$ by mass, and joins a growing population of low-mass, low-density planets.

Planet Hunters CSP Find Several Long Period Exoplanets, Some in Multi Planet Systems, Some in the Habitable Zones

PLANET HUNTERS. VI. AN INDEPENDENT CHARACTERIZATION OF KOI-351 AND SEVERAL LONG PERIOD PLANET CANDIDATES FROM THE KEPLER ARCHIVAL DATA*

Authors:

Schmitt et al

Abstract:

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 lsim 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 to 904 days, eight of them more than one Earth year long. Seven of these 14 candidates reside in their host star's habitable zone.