1,328 research outputs found
Obliquities of Kepler Stars: Comparison of Single- and Multiple-Transit Systems
The stellar obliquity of a transiting planetary system can be constrained by
combining measurements of the star's rotation period, radius, and projected
rotational velocity. Here we present a hierarchical Bayesian technique for
recovering the obliquity distribution of a population of transiting planetary
systems, and apply it to a sample of 70 Kepler Objects of Interest. With ~95%
confidence we find that the obliquities of stars with only a single detected
transiting planet are systematically larger than those with multiple detected
transiting planets. This suggests that a substantial fraction of Kepler's
single-transiting systems represent dynamically hotter, less orderly systems
than the "pancake-flat" multiple-transiting systems.Comment: 8 pages, 7 figures, accepted to Ap
Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra
We present a technique to extract radial velocity measurements from echelle
spectrograph observations of rapidly rotating stars ( km
s). This type of measurement is difficult because the line widths of
such stars are often comparable to the width of a single echelle order. To
compensate for the scarcity of lines and Doppler information content, we have
developed a process that forward-models the observations, fitting the radial
velocity shift of the star for all echelle orders simultaneously with the
echelle blaze function. We use our technique to extract radial velocity
measurements from a sample of rapidly rotating A- and B-type stars used as
calibrator stars observed by the California Planet Survey observations. We
measure absolute radial velocities with a precision ranging from 0.5-2.0 km
s per epoch for more than 100 A- and B-type stars. In our sample of 10
well-sampled stars with radial velocity scatter in excess of their measurement
uncertainties, three of these are single-lined binaries with long observational
baselines. From this subsample, we present detections of two previously unknown
spectroscopic binaries and one known astrometric system. Our technique will be
useful in measuring or placing upper limits on the masses of sub-stellar
companions discovered by wide-field transit surveys, and conducting future
spectroscopic binarity surveys and Galactic space-motion studies of massive
and/or young, rapidly-rotating stars.Comment: Accepted to ApJ
On the Low False Positive Probabilities of Kepler Planet Candidates
We present a framework to conservatively estimate the probability that any
particular planet-like transit signal observed by the Kepler mission is in fact
a planet, prior to any ground-based follow-up efforts. We use Monte Carlo
methods based on stellar population synthesis and Galactic structure models,
and report a priori false positive probabilities for every Kepler Object of
Interest in tabular form, assuming a 20% intrinsic occurrence rate of close-in
planets in the radius range 0.5 Rearth < Rp < 20 Rearth. Almost every candidate
has FPP <10%, and over half have FPP <5%. This probability varies most strongly
with the magnitude and Galactic latitude of the Kepler target star, and more
weakly with transit depth. We establish that a single deep high-resolution
image will be an extremely effective follow-up tool for the shallowest
(Earth-sized) transits, providing the quickest route towards probabilistically
"validating" the smallest candidates by potentially decreasing the false
positive probability of an earth-sized transit around a faint star from >10% to
<1%. On the other hand, we show that the most useful follow-up observations for
moderate-depth (super-Earth and Neptune-sized) candidates are shallower AO
imaging and high S/N spectroscopy. Since Kepler has detected many more
planetary signals than can be positively confirmed with ground-based follow-up
efforts in the near term, these calculations will be crucial to using the
ensemble of Kepler data to determine population characteristics of planetary
systems. We also describe how our analysis complements the Kepler team's more
detailed BLENDER false positive analysis for planet validation.Comment: Revision including results of calculations of individual FPPs for all
KOIs as well as an additional discussion section regarding the relationship
of our calculations to BLENDER. ApJ in pres
The Radius Distribution of Planets Around Cool Stars
We calculate an empirical, non-parametric estimate of the shape of the
period-marginalized radius distribution of planets with periods less than 150
days using the small yet well-characterized sample of cool (K) dwarf stars in the Kepler catalog. In particular, we present and validate a
new procedure, based on weighted kernel density estimation, to reconstruct the
shape of the planet radius function down to radii smaller than the completeness
limit of the survey at the longest periods. Under the assumption that the
period distribution of planets does not change dramatically with planet radius,
we show that the occurrence of planets around these stars continues to increase
to below 1 , and that there is no strong evidence for a turnover in
the planet radius function. In fact, we demonstrate using many iterations of
simulated data that a spurious turnover may be inferred from data even when the
true distribution continues to rise toward smaller radii. Finally, the sharp
rise in the radius distribution below 3 implies that a large
number of planets await discovery around cool dwarfs as the sensitivities of
ground-based transit surveys increase.Comment: 13 pages, 10 figures, published in Ap
Kepler Planet Reliability Metrics: Astrophysical Positional Probabilities for Data Release 25
This document is very similar to KSCI-19092-003, Planet Reliability Metrics: Astrophysical Positional Probabilities, which describes the previous release of the astrophysical positional probabilities for Data Release 24. The important changes for Data Release 25 are:1. The computation of the astrophysical positional probabilities uses the Data Release 25 processed pixel data for all Kepler Objects of Interest.2. Computed probabilities now have associated uncertainties, whose computation is described in x4.1.3.3. The scene modeling described in x4.1.2 uses background stars detected via ground-based high-resolution imaging, described in x5.1, that are not in the Kepler Input Catalog or UKIRT catalog. These newly detected stars are presented in Appendix B. Otherwise the text describing the algorithms and examples is largely unchanged from KSCI-19092-003
Vitamin D supplementation does not improve human skeletal muscle contractile properties in insufficient young males
Vitamin D may be a regulator of skeletal muscle function, although human trials investigating this hypothesis are limited to predominantly elderly populations. We aimed to assess the effect of oral vitamin D3 in healthy young males upon skeletal muscle function
Observations of X-rays and Thermal Dust Emission from the Supernova Remnant Kes 75
We present Spitzer Space Telescope and Chandra X-ray Observatory observations
of the composite Galactic supernova remnant Kes 75 (G29.7-0.3). We use the
detected flux at 24 microns and hot gas parameters from fitting spectra from
new, deep X-ray observations to constrain models of dust emission, obtaining a
dust-to-gas mass ratio M_dust/M_gas ~0.001. We find that a two-component
thermal model, nominally representing shocked swept-up interstellar or
circumstellar material and reverse-shocked ejecta, adequately fits the X-ray
spectrum, albeit with somewhat high implied densities for both components. We
surmise that this model implies a Wolf-Rayet progenitor for the remnant. We
also present infrared flux upper limits for the central pulsar wind nebula.Comment: 7 pages, 2 tables, 4 figures, uses emulateapj. Accepted for
publication in Ap
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