275 research outputs found
The Metallicities of Stars With and Without Transiting Planets
Host star metallicities have been used to infer observational constraints on
planet formation throughout the history of the exoplanet field. The giant
planet metallicity correlation has now been widely accepted, but questions
remain as to whether the metallicity correlation extends to the small
terrestrial-sized planets. Here, we report metallicities for a sample of 518
stars in the Kepler field that have no detected transiting planets and compare
their metallicity distribution to a sample of stars that hosts small planets
(Rp < 1.7 R_Earth). Importantly, both samples have been analyzed in a
homogeneous manner using the same set of tools (Stellar Parameters
Classification tool; SPC). We find the average metallicity of the sample of
stars without detected transiting planets to be [m/H]_SNTP,dwarf = -0.02 +-
0.02 dex and the sample of stars hosting small planets to be [m/H]_STP = -0.02
+- 0.02 dex. The average metallicities of the two samples are indistinguishable
within the uncertainties, and the two-sample Kolmogorov-Smirnov test yields a
p-value of 0.68 (0.41 sigma), indicating a failure to reject the null
hypothesis that the two samples are drawn from the same parent population. We
conclude that the homogeneous analysis of the data presented here support the
hypothesis that stars hosting small planets have a metallicity similar to stars
with no known transiting planets in the same area of the sky.Comment: Accepted for publication in Ap
Pinning down the mass of Kepler-10c: the importance of sampling and model comparison
Initial RV characterisation of the enigmatic planet Kepler-10c suggested a
mass of M, which was remarkably high for a planet with radius
R; further observations and subsequent analysis hinted at a
(possibly much) lower mass, but masses derived using RVs from two different
spectrographs (HARPS-N and HIRES) were incompatible at a -level. We
demonstrate here how such mass discrepancies may readily arise from sub-optimal
sampling and/or neglecting to model even a single coherent signal (stellar,
planetary, or otherwise) that may be present in RVs. We then present a
plausible resolution of the mass discrepancy, and ultimately characterise
Kepler-10c as having mass M, and mean density
g cm.Comment: 7 pages, 4 figures. Accepted for publication in MNRAS Letter
Modelling the 3D Climate of Venus with OASIS
Flexible 3D models to explore the vast diversity of terrestrial planets and
interpret observational data are still in their early stages. In this work, we
present OASIS: a novel and flexible 3D virtual planet laboratory. With OASIS we
envision a platform that couples self-consistently seven individual modules
representing the main physical and chemical processes that shape planetary
environments. Additionally, OASIS is capable of producing simulated spectra
from different instruments and observational techniques. In this work we focus
on the benchmark test of coupling four of the physical modules: fluid dynamics,
radiation, turbulence and surface/soil. To test the OASIS platform, we produced
3D simulations of the Venus climate and its atmospheric circulation and study
how the modeled atmosphere changes with various cloud covers, atmospheric heat
capacity, and surface friction. 3D simulations of Venus are challenging because
they require long integration times with a computationally expensive radiative
transfer code. By comparing OASIS results with observational data, we verify
that the new model is able to successfully simulate Venus. With simulated
spectra produced directly from the 3D simulations, we explore the capabilities
of future missions, like LUVOIR, to observe Venus analogs located at a distance
of 10 pc. With OASIS, we have taken the first steps to build a sophisticated
and very flexible platform capable of studying the environment of terrestrial
planets, which will be an essential tool to characterize observed terrestrial
planets and plan future observations.Comment: MNRAS published versio
KOI-142, the King of Transit Variations, is a Pair of Planets near the 2:1 Resonance
The Transit Timing Variations (TTVs) can be used as a diagnostic of
gravitational interactions between planets in a multi-planet system. Many
Kepler Objects of Interest (KOIs) exhibit significant TTVs, but KOI-142.01
stands out among them with an unrivaled, 12-hour TTV amplitude. Here we report
a thorough analysis of KOI-142.01's transits. We discover periodic Transit
Duration Variations (TDVs) of KOI-142.01 that are nearly in phase with the
observed TTVs. We show that KOI-142.01's TTVs and TDVs uniquely detect a
non-transiting companion with a mass 0.7 that of Jupiter (KOI-142c).
KOI-142.01's mass inferred from the transit variations is consistent with the
measured transit depth, suggesting a Neptune class planet (KOI-142b). The
orbital period ratio P_c/P_b=2.03 indicates that the two planets are just wide
of the 2:1 resonance. The present dynamics of this system, characterized here
in detail, can be used to test various formation theories that have been
proposed to explain the near-resonant pairs of exoplanets
Flicker as a tool for characterizing planets through Asterodensity Profiling
Variability in the time series brightness of a star on a timescale of 8
hours, known as 'flicker', has been previously demonstrated to serve as a proxy
for the surface gravity of a star by Bastien et al. (2013). Although surface
gravity is crucial for stellar classification, it is the mean stellar density
which is most useful when studying transiting exoplanets, due to its direct
impact on the transit light curve shape. Indeed, an accurate and independent
measure of the stellar density can be leveraged to infer subtle properties of a
transiting system, such as the companion's orbital eccentricity via
asterodensity profiling. We here calibrate flicker to the mean stellar density
of 439 Kepler targets with asteroseismology, allowing us to derive a new
empirical relation given by
. The calibration is valid for stars with
KK, and flicker estimates corresponding
to stars with . Our relation has a model error in the
stellar density of 31.7% and so has times lower precision than that
from asteroseismology but is applicable to a sample times greater.
Flicker therefore provides an empirical method to enable asterodensity
profiling on hundreds of planetary candidates from present and future missions.Comment: 6 pages, 3 figures, 1 table. Accepted to ApJ Letters. Code available
at https://www.cfa.harvard.edu/~dkipping/flicker.htm
Occurrence and core-envelope structure of 1--4x Earth-size planets around Sun-like stars
Small planets, 1-4x the size of Earth, are extremely common around Sun-like
stars, and surprisingly so, as they are missing in our solar system. Recent
detections have yielded enough information about this class of exoplanets to
begin characterizing their occurrence rates, orbits, masses, densities, and
internal structures. The Kepler mission finds the smallest planets to be most
common, as 26% of Sun-like stars have small, 1-2 R_e planets with orbital
periods under 100 days, and 11% have 1-2 R_e planets that receive 1-4x the
incident stellar flux that warms our Earth. These Earth-size planets are
sprinkled uniformly with orbital distance (logarithmically) out to 0.4 AU, and
probably beyond. Mass measurements for 33 transiting planets of 1-4 R_e show
that the smallest of them, R < 1.5 R_e, have the density expected for rocky
planets. Their densities increase with increasing radius, likely caused by
gravitational compression. Including solar system planets yields a relation:
rho = 2.32 + 3.19 R/R_e [g/cc]. Larger planets, in the radius range 1.5-4.0
R_e, have densities that decline with increasing radius, revealing increasing
amounts of low-density material in an envelope surrounding a rocky core,
befitting the appellation "mini-Neptunes." Planets of ~1.5 R_e have the highest
densities, averaging near 10 g/cc. The gas giant planets occur preferentially
around stars that are rich in heavy elements, while rocky planets occur around
stars having a range of heavy element abundances. One explanation is that the
fast formation of rocky cores in protoplanetary disks enriched in heavy
elements permits the gravitational accumulation of gas before it vanishes,
forming giant planets. But models of the formation of 1-4 R_e planets remain
uncertain. Defining habitable zones remains difficult, without benefit of
either detections of life elsewhere or an understanding of life's biochemical
origins.Comment: 11 pages, 6 figures, accepted for publication Proc. Natl. Acad. Sc
The Hunt for Exomoons with Kepler (HEK): IV. A Search for Moons around Eight M-Dwarfs
With their smaller radii and high cosmic abundance, transiting planets around
cool stars hold a unique appeal. As part of our on-going project to measure the
occurrence rate of extrasolar moons, we here present results from a survey
focussing on eight Kepler planetary candidates associated with M-dwarfs. Using
photodynamical modeling and Bayesian multimodal nested sampling, we find no
compelling evidence for an exomoon in these eight systems. Upper limits on the
presence of such bodies probe down to in the best case. For
KOI-314, we are able to confirm the planetary nature of two out of the three
known transiting candidates using transit timing variations. Of particular
interest is KOI-314c, which is found to have a mass of
, making it the lowest mass transiting planet
discovered to date. With a radius of , this
Earth-mass world is likely enveloped by a significant gaseous envelope
comprising % of the planet by radius. We find evidence to
support the planetary nature of KOI-784 too via transit timing, but we advocate
further observations to verify the signals. In both systems, we infer that the
inner planet has a higher density than the outer world, which may be indicative
of photo-evaporation. These results highlight both the ability of Kepler to
search for sub-Earth mass moons and the exciting ancillary science which often
results from such efforts.Comment: 15 pages, 13 figures, 6 tables. Accepted in Ap
The Hunt for Exomoons with Kepler (HEK): II. Analysis of Seven Viable Satellite-Hosting Planet Candidates
From the list of 2321 transiting planet candidates announced by the Kepler
Mission, we select seven targets with favorable properties for the capacity to
dynamically maintain an exomoon and present a detectable signal. These seven
candidates were identified through our automatic target selection (TSA)
algorithm and target selection prioritization (TSP) filtering, whereby we
excluded systems exhibiting significant time-correlated noise and focussed on
those with a single transiting planet candidate of radius less than 6 Earth
radii. We find no compelling evidence for an exomoon around any of the seven
KOIs but constrain the satellite-to-planet mass ratios for each. For four of
the seven KOIs, we estimate a 95% upper quantile of M_S/M_P<0.04, which given
the radii of the candidates, likely probes down to sub-Earth masses. We also
derive precise transit times and durations for each candidate and find no
evidence for dynamical variations in any of the KOIs. With just a few systems
analyzed thus far in the in-going HEK project, projections on eta-moon would be
premature, but a high frequency of large moons around
Super-Earths/Mini-Neptunes would appear to be incommensurable with our results
so far.Comment: 32 pages, 11 figures, 23 tables, Accepted to Ap
The Hunt for Exomoons with Kepler (HEK): III. The First Search for an Exomoon around a Habitable-Zone Planet
Kepler-22b is the first transiting planet to have been detected in the
habitable-zone of its host star. At 2.4 Earth radii, Kepler-22b is too large to
be considered an Earth-analog, but should the planet host a moon large enough
to maintain an atmosphere, then the Kepler-22 system may yet possess a telluric
world. Aside from being within the habitable-zone, the target is attractive due
to the availability of previously measured precise radial velocities and low
intrinsic photometric noise, which has also enabled asteroseismology studies of
the star. For these reasons, Kepler-22b was selected as a target-of-opportunity
by the 'Hunt for Exomoons with Kepler' (HEK) project. In this work, we conduct
a photodynamical search for an exomoon around Kepler-22b leveraging the
transits, radial velocities and asteroseismology plus several new tools
developed by the HEK project to improve exomoon searches. We find no evidence
for an exomoon around the planet and exclude moons of mass >0.5 Earth masses to
95% confidence. By signal injection and blind retrieval, we demonstrate that an
Earth-like moon is easily detected for this planet even when the
time-correlated noise of the data set is taken into account. We provide updated
parameters for the planet Kepler-22b including a revised mass of <53 Earth
masses to 95% confidence and an eccentricity of 0.13(-0.13)(+0.36) by
exploiting Single-body Asterodensity Profiling (SAP). Finally, we show that
Kepler-22b has a >95% probability of being within the empirical habitable-zone
but a <5% probability of being within the conservative habitable-zone.Comment: 19 pages, 11 figures, 7 tables. Accepted in ApJ. Planet-moon transit
animations available at https://www.cfa.harvard.edu/~dkipping/kepler22.htm
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