4,308 research outputs found
On the ground electronic states of copper silicide and its ions
The low-lying electronic states of SiCu, SiCu^+, and SiCu^â have been studied using a variety of high-level ab initio techniques. As expected on the basis of simple orbital occupancy and bond forming for Si(s^2p^2)+Cu(s^1) species, ^2Î _r, ^1ÎŁ^+, and ^3ÎŁ^â states were found to be the ground electronic states for SiCu, SiCu^+, and SiCu^â, respectively; the ^2Î _r state is not that suggested in most recent experimental studies. All of these molecules were found to be quite strongly bound although the bond lengths, bond energies, and harmonic frequencies vary slightly among them, as a result of the nonbonding character of the 2Ï-MO (molecular orbital) [composed almost entirely of the Si 3p-AO (atomic orbital)], the occupation of which varies from 0 to 2 within the ^1ÎŁ^+, ^2Î _r, and ^3ÎŁ^â series. The neutral SiCu is found to have bound excited electronic states of ^4ÎŁ^â, ^2Î, ^2ÎŁ^+, and ^2Î _i symmetry lying 0.5, 1.2, 1.8, and 3.2 eV above the ^2Î _r ground state. It is possible but not yet certain that the ^2Î _i state is, in fact, the âB stateâ observed in the recent experimental studies by Scherer, Paul, Collier, and Saykally
The first WASP public data release
The WASP (wide angle search for planets) project is an exoplanet transit survey that has been automatically taking wide field images since 2004. Two instruments, one in La Palma and the other in South Africa, continually monitor the night sky, building up light curves of millions of unique objects. These light curves are used to search for the characteristics of exoplanetary transits. This first public data release (DR1) of the WASP archive makes available all the light curve data and images from 2004 up to 2008 in both the Northern and Southern hemispheres. A web interface () to the data allows easy access over the Internet. The data set contains 3â631â972 raw images and 17â970â937 light curves. In total the light curves have 119â930â299â362 data points available between them
The Doppler Shadow of WASP-3b: A tomographic analysis of Rossiter-McLaughlin observations
Hot-Jupiter planets must form at large separations from their host stars
where the temperatures are cool enough for their cores to condense. They then
migrate inwards to their current observed orbital separations. Different
theories of how this migration occurs lead to varying distributions of orbital
eccentricity and the alignment between the rotation axis of the star and the
orbital axis of the planet. The spin-orbit alignment of a transiting system is
revealed via the Rossiter-McLaughlin effect, which is the anomaly present in
the radial velocity measurements of the rotating star during transit due to the
planet blocking some of the starlight. In this paper we aim to measure the
spin-orbit alignment of the WASP-3 system via a new way of analysing the
Rossiter-McLaughlin observations. We apply a new tomographic method for
analysing the time variable asymmetry of stellar line profiles caused by the
Rossiter-McLaughlin effect. This new method eliminates the systematic error
inherent in previous methods used to analyse the effect. We find a value for
the projected stellar spin rate of v sin i = 13.9 \pm 0.03 km/s which is in
agreement with previous measurements but has a much higher precision. The
system is found to be well aligned which favours an evolutionary history for
WASP-3b involving migration through tidal interactions with a protoplanetary
disc. Using gyrochronology we estimate the age of the star to be ~300 Myr with
an upper limit of 2 Gyr from comparison with isochrones.Comment: Accepted for publication in A&A, 8 pages, 4 figures, 2 table
Civil conflict, federalism and strategic delegation of leadership
This article analyzes negative externalities that policymakers in one region or group may impose upon the citizens of neighboring regions or groups. These externalities may be material, but they may also be psychological (in the form of envy). The latter form of externality may arise from the production of 'conspicuous' public goods. As a result, decentralized provision of conspicuous public goods may be too high. Potentially, a centralized legislature may internalize negative externalities. However, in a model with strategic delegation, we argue that the median voter in each jurisdiction may anticipate a reduction in local public goods supply and delegate to a policymaker who cares more for public goods than she does herself. This last effect mitigates the expected benefits of policy centralization. The authors' theory is then applied to the setting of civil conflict, where they discuss electoral outcomes in Northern Ireland and Yugoslavia before and after significant institutional changes that affected the degree of centralization. These case studies provide support for the authors' theoretical predictions
Force-Free Models of Magnetically Linked Star-Disk Systems
Disk accretion onto a magnetized star occurs in a variety of astrophysical
contexts, from young stars to X-ray pulsars. The magnetohydrodynamic
interaction between the stellar field and the accreting matter can have a
strong effect on the disk structure, the transfer of mass and angular momentum
between the disk and the star, and the production of bipolar outflows, e.g.,
plasma jets. We study a key element of this interaction - the time evolution of
the magnetic field configuration brought about by the relative rotation between
the disk and the star - using simplified, largely semianalytic, models. We
first discuss the rapid inflation and opening up of the magnetic field lines in
the corona above the accretion disk, which is caused by the differential
rotation twisting. Then we consider additional physical effects that tend to
limit this expansion, such as the effect of plasma inertia and the possibility
of reconnection in the disk's corona, the latter possibly leading to repeated
cycles in the evolution. We also derive the condition for the existence of a
steady state for a resistive disk and conclude that a steady state
configuration is not realistically possible. Finally, we generalize our
analysis of the opening of magnetic field lines by using a non-self-similar
numerical model that applies to an arbitrarily rotating (e.g. keplerian) disk.Comment: 75 pages, 22 figures, 2 tables. Submitted to Astrophysical Journa
The 0.5MJ transiting exoplanet WASP-13b
We report the discovery of WASP-13b, a low-mass M_{\rm p} = 0.46 ^_~M_J transiting exoplanet with an orbital period of 4.35298 0.00004 days. The transit has a depth of 9 mmag, and although our follow-up photometry does not allow us to constrain the impact parameter well (0 < b < 0.46), with radius in the range ~ 1.06-1.21 RJ the location of WASP-13b in the mass-radius plane is nevertheless consistent with H/He-dominated, irradiated, low core mass and core-free theoretical models. The G1V host star is similar to the Sun in mass (M__ ~M_{\odot}) and metallicity ([M/H] = 0.00.2), but is possibly older ( 8.5^_{\rm -4.9} Gyr)
SuperWASP: Wide Angle Search for Planets
SuperWASP is a fully robotic, ultra-wide angle survey for planetary transits.
Currently under construction, it will consist of 5 cameras, each monitoring a
9.5 x 9.5 deg field of view. The Torus mount and enclosure will be fully
automated and linked to a built-in weather station. We aim to begin
observations at the beginning of 2003.Comment: 4 pages, 1 figure, to be published in proceedings of "Scientific
Frontiers in Research on Extrasolar Planets
Current Status of the SuperWASP Project
We present the current status of the SuperWASP project, a Wide Angle Search
for Planets. SuperWASP consists of up to 8 individual cameras using ultra-wide
field lenses backed by high-quality passively cooled CCDs. Each camera covers
7.8 x 7.8 sq degrees of sky, for nearly 500 sq degrees of sky coverage.
SuperWASP I, located in LaPalma, is currently operational with 5 cameras and is
conducting a photometric survey of a large numbers of stars in the magnitude
range ~7 to 15. The collaboration has developed a custom-built reduction
pipeline and aims to achieve better than 1 percent photometric precision. The
pipeline will also produce well sampled light curves for all the stars in each
field which will be used to detect: planetary transits, optical transients, and
track Near-Earth Objects. Status of current observations, and expected rates of
extrasolar planetary detections will be presented. The consortium members,
institutions, and further details can be found on the web site at:
http://www.superwasp.org.Comment: 3 pages, 2 figures, submitted to the Proceedings of the 13th Cool
Stars Workshop, Ed. F. Favata, ESA-S
Line-profile tomography of exoplanet transits -- II. A gas-giant planet transiting a rapidly-rotating A5 star
Most of our knowledge of extrasolar planets rests on precise radial-velocity
measurements, either for direct detection or for confirmation of the planetary
origin of photometric transit signals. This has limited our exploration of the
parameter space of exoplanet hosts to solar- and later-type, sharp-lined stars.
Here we extend the realm of stars with known planetary companions to include
hot, fast-rotating stars. Planet-like transits have previously been reported in
the lightcurve obtained by the SuperWASP survey of the A5 star HD15082
(WASP-33; V=8.3, v sin i = 86 km/sec). Here we report further photometry and
time-series spectroscopy through three separate transits, which we use to
confirm the existence of a gas giant planet with an orbital period of 1.22d in
orbit around HD15082. From the photometry and the properties of the planet
signal travelling through the spectral line profiles during the transit we
directly derive the size of the planet, the inclination and obliquity of its
orbital plane, and its retrograde orbital motion relative to the spin of the
star. This kind of analysis opens the way to studying the formation of planets
around a whole new class of young, early-type stars, hence under different
physical conditions and generally in an earlier stage of formation than in
sharp-lined late-type stars. The reflex orbital motion of the star caused by
the transiting planet is small, yielding an upper mass limit of 4.1 Jupiter
masses on the planet. We also find evidence of a third body of sub-stellar mass
in the system, which may explain the unusual orbit of the transiting planet. In
HD 15082, the stellar line profiles also show evidence of non-radial
pulsations, clearly distinct from the planetary transit signal. This raises the
intriguing possibility that tides raised by the close-in planet may excite or
amplify the pulsations in such stars.Comment: 9 pages, 6 figures, accepted for publication in MNRA
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