1,757 research outputs found
The PHASES Differential Astrometry Data Archive. I. Measurements and Description
The Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES)
monitored 51 sub-arcsecond binary systems to determine precision binary orbits,
study the geometries of triple and quadruple star systems, and discover
previously unknown faint astrometric companions as small as giant planets.
PHASES measurements made with the Palomar Testbed Interferometer (PTI) from
2002 until PTI ceased normal operations in late 2008 are presented. Infrared
differential photometry of several PHASES targets were measured with Keck
Adaptive Optics and are presented.Comment: 33 pages emulateapj, Accepted to A
Masses, luminosities, and orbital coplanarities of the ” Orionis quadruple-star system from phases differential astrometry
ÎŒ Orionis was identified by spectroscopic studies as a quadruple-star system. Seventeen high-precision differential astrometry measurements of ÎŒ Ori have been collected by the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES). These show both the motion of the long-period binary orbit and short-period perturbations superimposed on that caused by each of the components in the long-period system being themselves binaries. The new measurements enable the orientations of the long-period binary and short-period subsystems to be determined. Recent theoretical work predicts the distribution of relative inclinations between inner and outer orbits of hierarchical systems to peak near 40 and 140 degrees. The degree of coplanarity of this complex system is determined, and the angle between the planes of the AâB and AaâAb orbits is found to be 136.7 ± 8.3 degrees, near the predicted distribution peak at 140 degrees; this result is discussed in the context of the handful of systems with established mutual inclinations. The system distance and masses for each component are obtained from a combined fit of the PHASES astrometry and archival radial velocity observations. The component masses have relative precisions of 5% (component Aa), 15% (Ab), and 1.4% (each of Ba and Bb). The median size of the minor axes of the uncertainty ellipses for the new measurements is 20 micro-arcseconds (ÎŒas). Updated orbits for ÎŽ Equulei, Îș Pegasi, and V819 Herculis are also presented
On the algebra of local unitary invariants of pure and mixed quantum states
We study the structure of the inverse limit of the graded algebras of local
unitary invariant polynomials using its Hilbert series. For k subsystems, we
conjecture that the inverse limit is a free algebra and the number of
algebraically independent generators with homogenous degree 2m equals the
number of conjugacy classes of index m subgroups in a free group on k-1
generators.
Similarly, we conjecture that the inverse limit in the case of k-partite
mixed state invariants is free and the number of algebraically independent
generators with homogenous degree m equals the number of conjugacy classes of
index m subgroups in a free group on k generators. The two conjectures are
shown to be equivalent.
To illustrate the equivalence, using the representation theory of the unitary
groups, we obtain all invariants in the m=2 graded parts and express them in a
simple form both in the case of mixed and pure states. The transformation
between the two forms is also derived. Analogous invariants of higher degree
are also introduced.Comment: 14 pages, no figure
Unusual metallic phase in a chain of strongly interacting particles
We consider a one-dimensional lattice model with the nearest-neighbor
interaction and the next-nearest neighbor interaction with filling
factor 1/2 at zero temperature. The particles are assumed to be spinless
fermions or hard-core bosons. Using very simple assumptions we are able to
predict the basic structure of the insulator-metal phase diagram for this
model. Computations of the flux sensitivity support the main features of the
proposed diagram and show that the system maintains metallic properties at
arbitrarily large values of and along the line ,
where is the hopping amplitude, and . We think that close
to this line the system is a ``weak'' metal in a sense that the flux
sensitivity decreases with the size of the system not exponentially but as
with .Comment: To appear in J. Phys. C; 9 revtex preprint pages + 4 ps figures,
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Silicon isotopes in Antarctic sponges : an interlaboratory comparison
Cycling of deepwater silicon (Si) within the Southern Ocean, and its transport into other ocean basins, may be an important player in the uptake of atmospheric carbon, and global climate. Recent work has shown that the Si isotope (denoted by ÎŽ29Si or ÎŽ30Si) composition of deep sea sponges reflects the availability of dissolved Si during growth, and is a potential proxy for past deep and intermediate water silicic acid concentrations. As with any geochemical tool, it is essential to ensure analytical precision and accuracy, and consistency between methodologies and laboratories. Analytical bias may exist between laboratories, and sponge material may have matrix effects leading to offsets between samples and standards. Here, we report an interlaboratory evaluation of Si isotopes in Antarctic and sub-Antarctic sponges. We review independent methods for measuring Si isotopes in sponge spicules. Our results show that separate subsamples of non-homogenized sponges measured by three methods yield isotopic values within analytical error for over 80% of specimens. The relationship between ÎŽ29Si and ÎŽ30Si in sponges is consistent with kinetic fractionation during biomineralization. Sponge Si isotope analyses show potential as palaeoceaongraphic archives, and we suggest Southern Ocean sponge material would form a useful additional reference standard for future spicule analyses
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