15,413 research outputs found
Spin-Orbit Alignment for the Circumbinary Planet Host Kepler-16 A
Kepler-16 is an eccentric low-mass eclipsing binary with a circumbinary transiting planet. Here, we investigate the
angular momentum of the primary star, based on Kepler photometry and Keck spectroscopy. The primary star’s
rotation period is 35.1 ± 1.0 days, and its projected obliquity with respect to the stellar binary orbit is 1°.6 ± 2°.4. Therefore, the three largest sources of angular momentum—the stellar orbit, the planetary orbit, and the primary’s rotation—are all closely aligned. This finding supports a formation scenario involving accretion from a single disk. Alternatively, tides may have realigned the stars despite their relatively wide separation (0.2 AU), a hypothesis that is supported by the agreement between the measured rotation period and the “pseudosynchronous” period of tidal evolution theory. The rotation period, chromospheric activity level, and fractional light variations suggest a main-sequence age of 2–4 Gyr. Evolutionary models of low-mass stars can match the observed masses and radii of the primary and secondary stars to within about 3%
Absence of a metallicity effect for ultra-short-period planets
Ultra-short-period (USP) planets are a newly recognized class of planets with
periods shorter than one day and radii smaller than about 2 Earth radii. It has
been proposed that USP planets are the solid cores of hot Jupiters that lost
their gaseous envelopes due to photo-evaporation or Roche lobe overflow. We
test this hypothesis by asking whether USP planets are associated with
metal-rich stars, as has long been observed for hot Jupiters. We find the
metallicity distributions of USP-planet and hot-Jupiter hosts to be
significantly different (), based on Keck spectroscopy of
Kepler stars. Evidently, the sample of USP planets is not dominated by the
evaporated cores of hot Jupiters. The metallicity distribution of stars with
USP planets is indistinguishable from that of stars with short-period planets
with sizes between 2--4~. Thus it remains possible that the USP
planets are the solid cores of formerly gaseous planets smaller than Neptune.Comment: AJ, in pres
A Third Exoplanetary System with Misaligned Orbital and Stellar Spin Axes
We present evidence that the WASP-14 exoplanetary system has misaligned
orbital and stellar-rotational axes, with an angle lambda = 33.1 +/- 7.4 deg
between their sky projections. The evidence is based on spectroscopic
observations of the Rossiter-McLaughlin effect as well as new photometric
observations. WASP-14 is now the third system known to have a significant
spin-orbit misalignment, and all three systems have "super-Jupiter" planets
(M_P > 3 Mjup) and eccentric orbits. This finding suggests that the migration
and subsequent orbital evolution of massive, eccentric exoplanets is somehow
different from that of less massive close-in Jupiters, the majority of which
have well-aligned orbits.Comment: 8 pages, 5 figures, 3 tables, PASP accepte
Orange-Flesh Sweet Potato - Promising Partnerships for Assuring the Integration of Nutritional Concerns into Agricultural Research and Extension
Research Results from the Department of Policy Analysis MARD-Directorate of Economicsfood security, food policy, Mozambique, sweet potato, malnutrition, Crop Production/Industries, Food Security and Poverty, Q18,
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
A low stellar obliquity for WASP-47, a compact multiplanet system with a hot Jupiter and an ultra-short period planet
We have detected the Rossiter-Mclaughlin effect during a transit of WASP-47b,
the only known hot Jupiter with close planetary companions. By combining our
spectroscopic observations with Kepler photometry, we show that the projected
stellar obliquity is . We can firmly exclude a
retrograde orbit for WASP-47b, and rule out strongly misaligned prograde
orbits. Low obliquities have also been found for most of the other compact
multiplanet systems that have been investigated. The Kepler-56 system, with two
close-in gas giants transiting their subgiant host star with an obliquity of at
least 45, remains the only clear counterexample.Comment: 5 pages, 2 figures, Accepted for publication on ApJL, comments
welcom
Beyond Patient Reported Pain: Perfusion Magnetic Resonance Imaging Demonstrates Reproducible Cerebral Representation of Ongoing Post-Surgical Pain
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Constraints on the Obliquities of Kepler Planet-Hosting Stars
Stars with hot Jupiters have obliquities ranging from 0-180 degrees, but
relatively little is known about the obliquities of stars with smaller planets.
Using data from the California-Kepler Survey, we investigate the obliquities of
stars with planets spanning a wide range of sizes, most of which are smaller
than Neptune. First, we identify 156 planet hosts for which measurements of the
projected rotation velocity (vsini) and rotation period are both available. By
combining estimates of v and vsini, we find nearly all the stars to be
compatible with high inclination, and hence, low obliquity (less than about 20
degrees). Second, we focus on a sample of 159 hot stars (> 6000K) for which
vsini is available but not necessarily the rotation period. We find 6 stars for
which vsini is anomalously low, an indicator of high obliquity. Half of these
have hot Jupiters, even though only 3% of the stars that were searched have hot
Jupiters. We also compare the vsini distribution of the hot stars with planets
to that of 83 control stars selected without prior knowledge of planets. The
mean vsini of the control stars is lower than that of the planet hosts by a
factor of approximately pi/4, as one would expect if the planet hosts have low
obliquities. All these findings suggest that the Kepler planet-hosting stars
generally have low obliquities, with the exception of hot stars with hot
Jupiters.Comment: AJ, in pres
HAT-P-7: A Retrograde or Polar Orbit, and a Third Body
We show that the exoplanet HAT-P-7b has an extremely tilted orbit, with a
true angle of at least 86 degrees with respect to its parent star's equatorial
plane, and a strong possibility of retrograde motion. We also report evidence
for an additional planet or companion star. The evidence for the unparalleled
orbit and the third body is based on precise observations of the star's
apparent radial velocity. The anomalous radial velocity due to rotation (the
Rossiter-McLaughlin effect) was found to be a blueshift during the first half
of the transit and a redshift during the second half, an inversion of the usual
pattern, implying that the angle between the sky-projected orbital and stellar
angular momentum vectors is 182.5 +/- 9.4 degreees. The third body is
implicated by excess radial-velocity variation of the host star over 2 yr. Some
possible explanations for the tilted orbit are a close encounter with another
planet, the Kozai effect, and resonant capture by an inward-migrating outer
planet.Comment: ApJ Letters, in press [7 pages
A Comparative Study of Prospective Natural Gas for Vehicle (NGV) Buyers\u27 Behavior Intention in Thailand
This study examines the prospects of how Natural Gas Vehicles (NGV) could gain more popularity, and more consumers, throughout Thailand. A survey of 500 potential consumers, comprising l00 respondents in each of the five separate regions, identified relevant geographic locations, demographic factors and their impact on behavior intention. The results of the study suggest that consumer’s behavioral intentions toward NGV are affected by factors pertaining to social influences and NGV attributes. Each group contains several sub-variables and is used in verifying its individual impact on consumer’s behavioral intention, while the differences in vehicle factors did not strongly affect the behavior intention
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