8,842 research outputs found
Discerning Exoplanet Migration Models Using Spin-Orbit Measurements
We investigate the current sample of exoplanet spin-orbit measurements to
determine whether a dominant planet migration channel can be identified, and at
what confidence. We use the predictions of Kozai migration plus tidal friction
(Fabrycky and Tremaine 2007) and planet-planet scattering (Nagasawa et al.
2008) as our misalignment models, and we allow for a fraction of intrinsically
aligned systems, explainable by disk migration. Bayesian model comparison
demonstrates that the current sample of 32 spin-orbit measurements strongly
favors a two-mode migration scenario combining planet-planet scattering and
disk migration over a single-mode Kozai migration scenario. Our analysis
indicates that between 34% and 76% of close-in planets (95% confidence)
migrated via planet-planet scattering. Separately analyzing the subsample of 12
stars with T_eff > 6250 K---which Winn et al. (2010) predict to be the only
type of stars to maintain their primordial misalignments---we find that the
data favor a single-mode scattering model over Kozai with 81% confidence. We
also assess the number of additional hot star spin-orbit measurements that will
likely be necessary to provide a more confident model selection, finding that
an additional 20-30 measurements has a >50% chance of resulting in a
95%-confident model selection, if the current model selection is correct. While
we test only the predictions of particular Kozai and scattering migration
models in this work, our methods may be used to test the predictions of any
other spin-orbit misaligning mechanism.Comment: 9 pages, 8 figures, ApJ responded to refere
Understanding Legislator Experiences of Family-Friendly Working Practices in Political Institutions
This is a post-peer-review, pre-copy edit version of an article published in Politics and Gender. © 2015, Cambridge University Press
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
Orbital Orientations of Exoplanets: HAT-P-4b is Prograde and HAT-P-14b is Retrograde
We present observations of the Rossiter-McLaughlin effect for two
exoplanetary systems, revealing the orientations of their orbits relative to
the rotation axes of their parent stars. HAT-P-4b is prograde, with a
sky-projected spin-orbit angle of lambda = -4.9 +/- 11.9 degrees. In contrast,
HAT-P-14b is retrograde, with lambda = 189.1 +/- 5.1 degrees. These results
conform with a previously noted pattern among the stellar hosts of close-in
giant planets: hotter stars have a wide range of obliquities and cooler stars
have low obliquities. This, in turn, suggests that three-body dynamics and
tidal dissipation are responsible for the short-period orbits of many
exoplanets. In addition, our data revealed a third body in the HAT-P-4 system,
which could be a second planet or a companion star.Comment: AJ, in press [8 pages
HATS-1b: The First Transiting Planet Discovered by the HATSouth Survey
We report the discovery of HATS-1b, a transiting extrasolar planet orbiting
the moderately bright V=12.05 G dwarf star GSC 6652-00186, and the first planet
discovered by HATSouth, a global network of autonomous wide-field telescopes.
HATS-1b has a period P~3.4465 d, mass Mp~1.86MJ, and radius Rp~1.30RJ. The host
star has a mass of 0.99Msun, and radius of 1.04Rsun. The discovery light curve
of HATS-1b has near continuous coverage over several multi-day periods,
demonstrating the power of using a global network of telescopes to discover
transiting planets.Comment: Submitted to AJ 10 pages, 5 figures, 6 table
Radiation Damage and Recovery Properties of Common Plastics PEN (Polyethylene Naphthalate) and PET (Polyethylene Terephthalate) Using a 137Cs Gamma Ray Source Up To 1 MRad and 10 MRad
Polyethylene naphthalate (PEN) and polyethylene teraphthalate (PET) are cheap
and common polyester plastics used throughout the world in the manufacturing of
bottled drinks, containers for foodstuffs, and fibers used in clothing. These
plastics are also known organic scintillators with very good scintillation
properties. As particle physics experiments increase in energy and particle
flux density, so does radiation exposure to detector materials. It is therefore
important that scintillators be tested for radiation tolerance at these
generally unheard of doses. We tested samples of PEN and PET using laser
stimulated emission on separate tiles exposed to 1 MRad and 10 MRad gamma rays
with a 137Cs source. PEN exposed to 1 MRad and 10 MRad emit 71.4% and 46.7% of
the light of an undamaged tile, respectively, and maximally recover to 85.9%
and 79.5% after 5 and 9 days, respectively. PET exposed to 1 MRad and 10 MRad
emit 35.0% and 12.2% light, respectively, and maximally recover to 93.5% and
80.0% after 22 and 60 days, respectively
Line-profile tomography of exoplanet transits I: The Doppler shadow of HD 189733b
We present a direct method for isolating the component of the starlight
blocked by a planet as it transits its host star, and apply it to spectra of
the bright transiting planet HD 189733b. We model the global shape of the
stellar cross-correlation function as the convolution of a limb-darkened
rotation profile and a gaussian representing the Doppler core of the average
photospheric line profile. The light blocked by the planet during the transit
is a gaussian of the same intrinsic width, whose trajectory across the line
profile yields a precise measure of the misalignment angle and an independent
measure of v sin I. We show that even when v sin I is less than the width of
the intrinsic line profile, the travelling Doppler "shadow" cast by the planet
creates an identifiable distortion in the line profiles which is amenable to
direct modelling. Direct measurement of the trajectory of the missing starlight
yields self-consistent measures of the projected stellar rotation rate, the
intrinsic width of the mean local photospheric line profile, the projected
spin-orbit misalignment angle, and the system's centre-of-mass velocity.
Combined with the photometric rotation period, the results give a geometrical
measure of the stellar radius which agrees closely with values obtained from
high-precision transit photometry if a small amount of differential rotation is
present in the stellar photosphere.Comment: 8 pages, 5 figures, 2 tables; accepted by MNRA
Processing spatial media
Despite increasing interest in non-verbal media, they are still less well understood than forms of verbal communication
Obliquities of Hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments
We provide evidence that the obliquities of stars with close-in giant planets
were initially nearly random, and that the low obliquities that are often
observed are a consequence of star-planet tidal interactions. The evidence is
based on 14 new measurements of the Rossiter-McLaughlin effect (for the systems
HAT-P-6, HAT-P-7, HAT-P-16, HAT-P-24, HAT-P-32, HAT-P-34, WASP-12, WASP-16,
WASP-18, WASP-19, WASP-26, WASP-31, Gl 436, and Kepler-8), as well as a
critical review of previous observations. The low-obliquity (well-aligned)
systems are those for which the expected tidal timescale is short, and likewise
the high-obliquity (misaligned and retrograde) systems are those for which the
expected timescale is long. At face value, this finding indicates that the
origin of hot Jupiters involves dynamical interactions like planet-planet
interactions or the Kozai effect that tilt their orbits, rather than
inspiraling due to interaction with a protoplanetary disk. We discuss the
status of this hypothesis and the observations that are needed for a more
definitive conclusion.Comment: Accepted for publication in ApJ; typos corrected, 2 broken references
fixed, 26 pages, 25 figure
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