123 research outputs found
Seeing double with K2: Testing re-inflation with two remarkably similar planets around red giant branch stars
Despite more than 20 years since the discovery of the first gas giant planet
with an anomalously large radius, the mechanism for planet inflation remains
unknown. Here, we report the discovery of EPIC228754001.01, an inflated gas
giant planet found with the NASA K2 Mission, and a revised mass for another
inflated planet, K2-97b. These planets reside on ~9 day orbits around host
stars which recently evolved into red giants. We constrain the irradiation
history of these planets using models constrained by asteroseismology and
Keck/HIRES spectroscopy and radial velocity measurements. We measure planet
radii of 1.31 +\- 0.11 Rjup and and 1.30 +\- 0.07 Rjup, respectively. These
radii are typical for planets receiving the current irradiation, but not the
former, zero age main sequence irradiation of these planets. This suggests that
the current sizes of these planets are directly correlated to their current
irradiation. Our precise constraints of the masses and radii of the stars and
planets in these systems allow us to constrain the planetary heating efficiency
of both systems as 0.03% +0.03%/-0.02%. These results are consistent with a
planet re-inflation scenario, but suggest the efficiency of planet re-inflation
may be lower than previously theorized. Finally, we discuss the agreement
within 10% of stellar masses and radii, and planet masses, radii, and orbital
periods of both systems and speculate that this may be due to selection bias in
searching for planets around evolved stars.Comment: 18 pages, 15 figures, accepted to AJ. Figures 11, 12, and 13 are the
key figures of the pape
Two Transiting Earth-size Planets Near Resonance Orbiting a Nearby Cool Star
Discoveries from the prime Kepler mission demonstrated that small planets (<
3 Earth-radii) are common outcomes of planet formation. While Kepler detected
many such planets, all but a handful orbit faint, distant stars and are not
amenable to precise follow up measurements. Here, we report the discovery of
two small planets transiting K2-21, a bright (K = 9.4) M0 dwarf located
656 pc from Earth. We detected the transiting planets in photometry
collected during Campaign 3 of NASA's K2 mission. Analysis of transit light
curves reveals that the planets have small radii compared to their host star,
2.60 0.14% and 3.15 0.20%, respectively. We obtained follow up NIR
spectroscopy of K2-21 to constrain host star properties, which imply planet
sizes of 1.59 0.43 Earth-radii and 1.92 0.53 Earth-radii,
respectively, straddling the boundary between high-density, rocky planets and
low-density planets with thick gaseous envelopes. The planets have orbital
periods of 9.32414 days and 15.50120 days, respectively, and have a period
ratio of 1.6624, very near to the 5:3 mean motion resonance, which may be a
record of the system's formation history. Transit timing variations (TTVs) due
to gravitational interactions between the planets may be detectable using
ground-based telescopes. Finally, this system offers a convenient laboratory
for studying the bulk composition and atmospheric properties of small planets
with low equilibrium temperatures.Comment: Updated to ApJ accepted version; photometry available alongside LaTeX
source; 10 pages, 7 figure
All Six Planets Known to Orbit Kepler-11 Have Low Densities
The Kepler-11 planetary system contains six transiting planets ranging in
size from 1.8 to 4.2 times the radius of Earth. Five of these planets orbit in
a tightly-packed configuration with periods between 10 and 47 days. We perform
a dynamical analysis of the system based upon transit timing variations
observed in more than three years of \ik photometric data. Stellar parameters
are derived using a combination of spectral classification and constraints on
the star's density derived from transit profiles together with planetary
eccentricity vectors provided by our dynamical study. Combining masses of the
planets relative to the star from our dynamical study and radii of the planets
relative to the star from transit depths together with deduced stellar
properties yields measurements of the radii of all six planets, masses of the
five inner planets, and an upper bound to the mass of the outermost planet,
whose orbital period is 118 days. We find mass-radius combinations for all six
planets that imply that substantial fractions of their volumes are occupied by
constituents that are less dense than rock. The Kepler-11 system contains the
lowest mass exoplanets for which both mass and radius have been measured.Comment: 39 pages, 10 figure
A First Comparison of Kepler Planet Candidates in Single and Multiple Systems
In this letter we present an overview of the rich population of systems with
multiple candidate transiting planets found in the first four months of Kepler
data. The census of multiples includes 115 targets that show 2 candidate
planets, 45 with 3, 8 with 4, and 1 each with 5 and 6, for a total of 170
systems with 408 candidates. When compared to the 827 systems with only one
candidate, the multiples account for 17 percent of the total number of systems,
and a third of all the planet candidates. We compare the characteristics of
candidates found in multiples with those found in singles. False positives due
to eclipsing binaries are much less common for the multiples, as expected.
Singles and multiples are both dominated by planets smaller than Neptune; 69
+2/-3 percent for singles and 86 +2/-5 percent for multiples. This result, that
systems with multiple transiting planets are less likely to include a
transiting giant planet, suggests that close-in giant planets tend to disrupt
the orbital inclinations of small planets in flat systems, or maybe even to
prevent the formation of such systems in the first place.Comment: 13 pages, 13 figures, submitted to ApJ Letter
Five Kepler target stars that show multiple transiting exoplanet candidates
We present and discuss five candidate exoplanetary systems identified with
the Kepler spacecraft. These five systems show transits from multiple exoplanet
candidates. Should these objects prove to be planetary in nature, then these
five systems open new opportunities for the field of exoplanets and provide new
insights into the formation and dynamical evolution of planetary systems. We
discuss the methods used to identify multiple transiting objects from the
Kepler photometry as well as the false-positive rejection methods that have
been applied to these data. One system shows transits from three distinct
objects while the remaining four systems show transits from two objects. Three
systems have planet candidates that are near mean motion
commensurabilities---two near 2:1 and one just outside 5:2. We discuss the
implications that multitransiting systems have on the distribution of orbital
inclinations in planetary systems, and hence their dynamical histories; as well
as their likely masses and chemical compositions. A Monte Carlo study indicates
that, with additional data, most of these systems should exhibit detectable
transit timing variations (TTV) due to gravitational interactions---though none
are apparent in these data. We also discuss new challenges that arise in TTV
analyses due to the presence of more than two planets in a system.Comment: Accepted to Ap
Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates
We present the discovery of the Kepler-20 planetary system, which we
initially identified through the detection of five distinct periodic transit
signals in the Kepler light curve of the host star 2MASSJ19104752+4220194. We
find a stellar effective temperature Teff=5455+-100K, a metallicity of
[Fe/H]=0.01+-0.04, and a surface gravity of log(g)=4.4+-0.1. Combined with an
estimate of the stellar density from the transit light curves we deduce a
stellar mass of Mstar=0.912+-0.034 Msun and a stellar radius of
Rstar=0.944^{+0.060}_{-0.095} Rsun. For three of the transit signals, our
results strongly disfavor the possibility that these result from astrophysical
false positives. We conclude that the planetary scenario is more likely than
that of an astrophysical false positive by a factor of 2e5 (Kepler-20b), 1e5
(Kepler-20c), and 1.1e3 (Kepler-20d), sufficient to validate these objects as
planetary companions. For Kepler-20c and Kepler-20d, the blend scenario is
independently disfavored by the achromaticity of the transit: From Spitzer data
gathered at 4.5um, we infer a ratio of the planetary to stellar radii of
0.075+-0.015 (Kepler-20c) and 0.065+-0.011 (Kepler-20d), consistent with each
of the depths measured in the Kepler optical bandpass. We determine the orbital
periods and physical radii of the three confirmed planets to be 3.70d and
1.91^{+0.12}_{-0.21} Rearth for Kepler-20b, 10.85 d and 3.07^{+0.20}_{-0.31}
Rearth for Kepelr-20c, and 77.61 d and 2.75^{+0.17}_{-0.30} Rearth for
Kepler-20d. From multi-epoch radial velocities, we determine the masses of
Kepler-20b and Kepler-20c to be 8.7\+-2.2 Mearth and 16.1+-3.5 Mearth,
respectively, and we place an upper limit on the mass of Kepler-20d of 20.1
Mearth (2 sigma).Comment: accepted by ApJ, 58 pages, 12 figures revised Jan 2012 to correct
table 2 and clarify planet parameter extractio
Planetary Candidates Observed by Kepler. VIII. A Fully Automated Catalog With Measured Completeness and Reliability Based on Data Release 25
We present the Kepler Object of Interest (KOI) catalog of transiting
exoplanets based on searching four years of Kepler time series photometry (Data
Release 25, Q1-Q17). The catalog contains 8054 KOIs of which 4034 are planet
candidates with periods between 0.25 and 632 days. Of these candidates, 219 are
new and include two in multi-planet systems (KOI-82.06 and KOI-2926.05), and
ten high-reliability, terrestrial-size, habitable zone candidates. This catalog
was created using a tool called the Robovetter which automatically vets the
DR25 Threshold Crossing Events (TCEs, Twicken et al. 2016). The Robovetter also
vetted simulated data sets and measured how well it was able to separate TCEs
caused by noise from those caused by low signal-to-noise transits. We discusses
the Robovetter and the metrics it uses to sort TCEs. For orbital periods less
than 100 days the Robovetter completeness (the fraction of simulated transits
that are determined to be planet candidates) across all observed stars is
greater than 85%. For the same period range, the catalog reliability (the
fraction of candidates that are not due to instrumental or stellar noise) is
greater than 98%. However, for low signal-to-noise candidates between 200 and
500 days around FGK dwarf stars, the Robovetter is 76.7% complete and the
catalog is 50.5% reliable. The KOI catalog, the transit fits and all of the
simulated data used to characterize this catalog are available at the NASA
Exoplanet Archive.Comment: 61 pages, 23 Figures, 9 Tables, Accepted to The Astrophysical Journal
Supplement Serie
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