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Technical Review of Residential Programmable Communicating Thermostat Implementation for Title 24-2008
Adaptive Optics Observations of the Galactic Center Young Stars
Adaptive Optics observations have dramatically improved the quality and
versatility of high angular resolution measurements of the center of our
Galaxy. In this paper, we quantify the quality of our Adaptive Optics
observations and report on the astrometric precision for the young stellar
population that appears to reside in a stellar disk structure in the central
parsec. We show that with our improved astrometry and a 16 year baseline,
including 10 years of speckle and 6 years of laser guide star AO imaging, we
reliably detect accelerations in the plane of the sky as small as 70
microarcsec/yr/yr (~2.5 km/s/yr) and out to a projected radius from the
supermassive black hole of 1.5" (~0.06 pc). With an increase in sensitivity to
accelerations by a factor of ~6 over our previous efforts, we are able to
directly probe the kinematic structure of the young stellar disk, which appears
to have an inner radius of 0.8". We find that candidate disk members are on
eccentric orbits, with a mean eccentricity of = 0.30 +/- 0.07. Such
eccentricities cannot be explained by the relaxation of a circular disk with a
normal initial mass function, which suggests the existence of a top-heavy IMF
or formation in an initially eccentric disk.Comment: 7 pages, 4 figures, SPIE Astronomical Telescopes and Instrumentation
201
Disentangling Confused Stars at the Galactic Center with Long Baseline Infrared Interferometry
We present simulations of Keck Interferometer ASTRA and VLTI GRAVITY
observations of mock star fields in orbit within ~50 milliarcseconds of Sgr A*.
Dual-field phase referencing techniques, as implemented on ASTRA and planned
for GRAVITY, will provide the sensitivity to observe Sgr A* with infrared
interferometers. Our results show an improvement in the confusion noise limit
over current astrometric surveys, opening a window to study stellar sources in
the region. Since the Keck Interferometer has only a single baseline, the
improvement in the confusion limit depends on source position angles. The
GRAVITY instrument will yield a more compact and symmetric PSF, providing an
improvement in confusion noise which will not depend as strongly on position
angle. Our Keck results show the ability to characterize the star field as
containing zero, few, or many bright stellar sources. We are also able to
detect and track a source down to mK~18 through the least confused regions of
our field of view at a precision of ~200 microarcseconds along the baseline
direction. This level of precision improves with source brightness. Our GRAVITY
results show the potential to detect and track multiple sources in the field.
GRAVITY will perform ~10 microarcsecond astrometry on a mK=16.3 source and ~200
microarcsecond astrometry on a mK=18.8 source in six hours of monitoring a
crowded field. Monitoring the orbits of several stars will provide the ability
to distinguish between multiple post-Newtonian orbital effects, including those
due to an extended mass distribution around Sgr A* and to low-order General
Relativistic effects. Early characterizations of the field by ASTRA including
the possibility of a precise source detection, could provide valuable
information for future GRAVITY implementation and observation.Comment: Accepted for publication in Ap
Shallow extra mixing in solar twins inferred from Be abundances
Lithium and beryllium are destroyed at different temperatures in stellar
interiors. As such, their relative abundances offer excellent probes of the
nature and extent of mixing processes within and below the convection zone. We
determine Be abundances for a sample of eight solar twins for which Li
abundances have previously been determined. The analyzed solar twins span a
very wide range of age, 0.5-8.2 Gyr, which enables us to study secular
evolution of Li and Be depletion. We gathered high-quality UVES/VLT spectra and
obtained Be abundances by spectral synthesis of the Be II 313 nm doublet. The
derived beryllium abundances exhibit no significant variation with age. The
more fragile Li, however, exhibits a monotonically decreasing abundance with
increasing age. Therefore, relatively shallow extra mixing below the convection
zone is necessary to simultaneously account for the observed Li and Be behavior
in the Sun and solar twins
Phase diagram of a model for a binary mixture of nematic molecules on a Bethe lattice
We investigate the phase diagram of a discrete version of the Maier-Saupe
model with the inclusion of additional degrees of freedom to mimic a
distribution of rodlike and disklike molecules. Solutions of this problem on a
Bethe lattice come from the analysis of the fixed points of a set of nonlinear
recursion relations. Besides the fixed points associated with isotropic and
uniaxial nematic structures, there is also a fixed point associated with a
biaxial nematic structure. Due to the existence of large overlaps of the
stability regions, we resorted to a scheme to calculate the free energy of
these structures deep in the interior of a large Cayley tree. Both
thermodynamic and dynamic-stability analyses rule out the presence of a biaxial
phase, in qualitative agreement with previous mean-field results
Active swarms on a sphere
Here we show that coupling to curvature has profound effects on collective
motion in active systems, leading to patterns not observed in flat space.
Biological examples of such active motion in curved environments are numerous:
curvature and tissue folding are crucial during gastrulation, epithelial and
endothelial cells move on constantly growing, curved crypts and vili in the
gut, and the mammalian corneal epithelium grows in a steady-state vortex
pattern. On the physics side, droplets coated with actively driven microtubule
bundles show active nematic patterns. We study a model of self-propelled
particles with polar alignment on a sphere. Hallmarks of these motion patterns
are a polar vortex and a circulating band arising due to the incompatibility
between spherical topology and uniform motion - a consequence of the hairy ball
theorem. We present analytical results showing that frustration due to
curvature leads to stable elastic distortions storing energy in the band.Comment: 5 pages, 4 figures plus Supporting Informatio
The solar, exoplanet and cosmological lithium problems
We review three Li problems. First, the Li problem in the Sun, for which some
previous studies have argued that it may be Li-poor compared to other Suns.
Second, we discuss the Li problem in planet hosting stars, which are claimed to
be Li-poor when compared to field stars. Third, we discuss the cosmological Li
problem, i.e. the discrepancy between the Li abundance in metal-poor stars
(Spite plateau stars) and the predictions from standard Big Bang
Nucleosynthesis. In all three cases we find that the "problems" are naturally
explained by non-standard mixing in stars.Comment: Astrophysics and Space Science, in press. New version has one
reference correcte
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