5,267 research outputs found
Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation
The extended Kepler mission, K2, is now providing photometry of new fields
every three months in a search for transiting planets. In a recent study,
Foreman-Mackey and collaborators presented a list of 36 planet candidates
orbiting 31 stars in K2 Campaign 1. In this contribution, we present stellar
and planetary properties for all systems. We combine ground-based
seeing-limited survey data and adaptive optics imaging with an automated
transit analysis scheme to validate 21 candidates as planets, 17 for the first
time, and identify 6 candidates as likely false positives. Of particular
interest is K2-18 (EPIC 201912552), a bright (K=8.9) M2.8 dwarf hosting a 2.23
\pm 0.25 R_Earth planet with T_eq = 272 \pm 15 K and an orbital period of 33
days. We also present two new open-source software packages which enable this
analysis. The first, isochrones, is a flexible tool for fitting theoretical
stellar models to observational data to determine stellar properties using a
nested sampling scheme to capture the multimodal nature of the posterior
distributions of the physical parameters of stars that may plausibly be
evolved. The second is vespa, a new general-purpose procedure to calculate
false positive probabilities and statistically validate transiting exoplanets.Comment: 17 pages, 5 figures, 5 tables, accepted for publication in the
Astrophysical Journal. Updated to closely reflect published version in ApJ
(2015, 809, 25
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Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets
We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm^(â3), suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than ~2 R_â. Larger planets evidently contain a larger fraction of low-density material (H, He, and H_2O)
Towards a fullerene-based quantum computer
Molecular structures appear to be natural candidates for a quantum
technology: individual atoms can support quantum superpositions for long
periods, and such atoms can in principle be embedded in a permanent molecular
scaffolding to form an array. This would be true nanotechnology, with
dimensions of order of a nanometre. However, the challenges of realising such a
vision are immense. One must identify a suitable elementary unit and
demonstrate its merits for qubit storage and manipulation, including input /
output. These units must then be formed into large arrays corresponding to an
functional quantum architecture, including a mechanism for gate operations.
Here we report our efforts, both experimental and theoretical, to create such a
technology based on endohedral fullerenes or 'buckyballs'. We describe our
successes with respect to these criteria, along with the obstacles we are
currently facing and the questions that remain to be addressed.Comment: 20 pages, 13 figs, single column forma
Forum 2: The migrant climate: resilience, adaptation and the ontopolitics of mobility in the Anthropocene
While modernist or âtop-downâ, âcommand-and-controlâ approaches to climate and migration worked at the surface or ontic level of the redistribution of entities in time and space, resilience approaches call for a different approach to mobility (for an extensive discussion of resilience as a distinctive governance regime see, for example, Grove, 2018; Chandler, 2014). These discourses construct mobilities that are more transformative, in fact, ones that question traditional liberal modernist notions of time and space and of entities with fixed essences. These mobilities do not concern moving entities in space but rethinking mobility in relation to space. Mobility then becomes more a matter of changing the understandings and practices relating to spaces and entities than of moving things from one place to another. Becoming âmobileâ thus would apply to the development of capabilities or âresponse-abilitiesâ (Haraway, 2016: 2) to sense, adapt, recompose, repurpose and reimagine problems and possibilities; taking responses to crises beyond the static and binary conceptions of mobility and space epitomised by The Clash lyrics in the epigraph
Provenance Response to Rifting and Separation at the Jan Mayen Microcontinent Margin
Funding This research received no external funding. Acknowledgments We are grateful to John Still (University of Aberdeen) and Iain Macdonald (Cardiff University) for their assistance with acquisition of mineral chemical data, and to Mick Pointon (CASP) for running the âRâ code to assign apatite provenance. This research was carried out as part of CASPâs Greenland-Norway Project. Our sponsorsâ financial support is gratefully acknowledged. We are grateful for the reviewers comments, which significantly improved the manuscript.Peer reviewedPublisher PD
Econometric forecasts for Scotland
In the first issue (July 1975) of the Fraser of Allander Institute Quarterly Economic Commentary, the special article, by Professor J McGilvray, reviewed the problems associated with constructing regional econometric models to forecast key economic variables. Since that time, a number of forecasts for the Scottish economy have been made in the main text or in special articles of the Quarterly Commentary. Many of these have been underpinned by forecasting relationships which have been estimated for particular sectors of the economy. Up to now we have been unable to produce a set of relationships which could genuinely be described as a 'model' of the Scottish economy. The reason for this is simple, but illustrative of the type of problem discussed by Professor McGilvray. To understand it one must be acquainted with the fundamental differences which exist between national and regional economic models
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