454 research outputs found
Inner Planetary System Gap Complexity is a Predictor of Outer Giant Planets
The connection between inner small planets and outer giant planets is crucial
to our understanding of planet formation across a wide range of orbital
separations. While Kepler provided a plethora of compact multi-planet systems
at short separations ( AU), relatively little is known about the
occurrence of giant companions at larger separations and how they impact the
architectures of the inner systems. Here, we use the catalog of systems from
the Kepler Giant Planet Search (KGPS) to study how the architectures of the
inner transiting planets correlate with the presence of outer giant planets. We
find that for systems with at least three small transiting planets, the
distribution of inner-system gap complexity (), a measure of the
deviation from uniform spacings, appears to differ () between
those with an outer giant planet () and those without any outer giants. All four inner systems (with 3+
transiting planets) with outer giant(s) have a higher gap complexity
() than 79% (19/24) of the inner systems without any outer
giants (median ). This suggests that one can predict
the occurrence of outer giant companions by selecting multi-transiting systems
with highly irregular spacings. We do not find any correlation between outer
giant occurrence and the size (similarity or ordering) patterns of the inner
planets. The larger gap complexities of inner systems with an outer giant hints
that massive external planets play an important role in the formation and/or
disruption of the inner systems.Comment: Published in AJ. 16 pages, 6 figures, 1 tabl
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
Personality structure in bottlenose dolphins (Tursiops truncatus).
Comparative studies can help identify selective pressures that contributed to species differences in the number and composition of personality domains. Despite being adapted to an aquatic lifestyle and last sharing a common ancestor with primates some 95 million years ago, bottlenose dolphins (Tursiops truncatus) resemble nonhuman primate species in several behavioral and cognitive traits. For example, like chimpanzees (Pan troglodytes), dolphins live in fission-fusion societies, use tools, and have relatively large brains. To determine the extent to which these and other factors contribute to the evolution of personality structure, we examined personality structure in 134 bottlenose dolphins. Personality was measured in 49 dolphins using a 42-item questionnaire, and in 85 dolphins using a version of the questionnaire that included 7 additional items. We found four domains. Three—openness, sociability, and disagreeableness—resembled personality domains found in nonhuman primates and other species. The fourth, directedness, was a blend of high conscientiousness and low neuroticism, and was unique to dolphins. Unlike other species, dolphins did not appear to have a strong dominance domain. The overlap in personality structure between dolphins and other species suggests that selective pressures, such as those related to group structure, terrestrial lifestyles, morphology, and social learning or tool use are not necessary for particular domains to evolve within a species
Long-Period Giant Companions to Three Compact, Multiplanet Systems
Understanding the relationship between long-period giant planets and multiple smaller short-period planets is critical for formulating a complete picture of planet formation. This work characterizes three such systems. We present Kepler-65, a system with an eccentric (e = 0.28 ± 0.07) giant planet companion discovered via radial velocities (RVs) exterior to a compact, multiply transiting system of sub-Neptune planets. We also use precision RVs to improve mass and radius constraints on two other systems with similar architectures, Kepler-25 and Kepler-68. In Kepler-68 we propose a second exterior giant planet candidate. Finally, we consider the implications of these systems for planet formation models, particularly that the moderate eccentricity in Kepler-65\u27s exterior giant planet did not disrupt its inner system
Three Super-Earths Orbiting HD 7924
We report the discovery of two super-Earth mass planets orbiting the nearby
K0.5 dwarf HD 7924 which was previously known to host one small planet. The new
companions have masses of 7.9 and 6.4 M, and orbital periods of 15.3
and 24.5 days. We perform a joint analysis of high-precision radial velocity
data from Keck/HIRES and the new Automated Planet Finder Telescope (APF) to
robustly detect three total planets in the system. We refine the ephemeris of
the previously known planet using five years of new Keck data and high-cadence
observations over the last 1.3 years with the APF. With this new ephemeris, we
show that a previous transit search for the inner-most planet would have
covered 70% of the predicted ingress or egress times. Photometric data
collected over the last eight years using the Automated Photometric Telescope
shows no evidence for transits of any of the planets, which would be detectable
if the planets transit and their compositions are hydrogen-dominated. We detect
a long-period signal that we interpret as the stellar magnetic activity cycle
since it is strongly correlated with the Ca II H and K activity index. We also
detect two additional short-period signals that we attribute to
rotationally-modulated starspots and a one month alias. The high-cadence APF
data help to distinguish between the true orbital periods and aliases caused by
the window function of the Keck data. The planets orbiting HD 7924 are a local
example of the compact, multi-planet systems that the Kepler Mission found in
great abundance.Comment: Accepted to ApJ on 4/7/201
The California-Kepler Survey. IV. Metal-rich Stars Host a Greater Diversity of Planets
Probing the connection between a star's metallicity and the presence and
properties of any associated planets offers an observational link between
conditions during the epoch of planet formation and mature planetary systems.
We explore this connection by analyzing the metallicities of Kepler target
stars and the subset of stars found to host transiting planets. After
correcting for survey incompleteness, we measure planet occurrence: the number
of planets per 100 stars with a given metallicity . Planet occurrence
correlates with metallicity for some, but not all, planet sizes and orbital
periods. For warm super-Earths having days and , planet occurrence is nearly constant over metallicities spanning
0.4 dex to +0.4 dex. We find 20 warm super-Earths per 100 stars, regardless
of metallicity. In contrast, the occurrence of warm sub-Neptunes () doubles over that same metallicity interval, from 20 to 40
planets per 100 stars. We model the distribution of planets as , where characterizes the strength of any metallicity
correlation. This correlation steepens with decreasing orbital period and
increasing planet size. For warm super-Earths ,
while for hot Jupiters . High metallicities in
protoplanetary disks may increase the mass of the largest rocky cores or the
speed at which they are assembled, enhancing the production of planets larger
than 1.7 . The association between high metallicity and short-period
planets may reflect disk density profiles that facilitate the inward migration
of solids or higher rates of planet-planet scattering.Comment: 32 pages, 15 figures, 9 tables, accepted for publication in The
Astronomical Journa
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