4,655 research outputs found
Collective Excitations, NMR, and Phase Transitions in Skyrme Crystals
At Landau level filling factors near nu =1, quantum Hall ferromagnets form a
Skyrme crystal state with quasi-long-range translational and non-collinear
magnetic order. We develop an effective low energy theory which explains the
presence in these systems of magnetic excitations at low energies below the
Larmor gap (Delta) and which predicts a dramatic enhancement of the nuclear
spin relaxation rate by a factor of 1000. The effective theory predicts a rich
set of quantum and classical phase transitions. Based in part on accurate
time-dependent Hartree-Fock calculations of the ordered state collective
excitation spectrum, we discuss aspects of the T-nu-Delta crystal phase
diagram.Comment: 4 pages REVTEX file and 3 postscript figure
Photoassociative spectroscopy at long range in ultracold strontium
We report photoassociative spectroscopy of Sr in a magneto-optical
trap operating on the intercombination line at 689 nm.
Photoassociative transitions are driven with a laser red-detuned by 600-2400
MHz from the atomic resonance at 461 nm. Photoassociation
takes place at extremely large internuclear separation, and the
photoassociative spectrum is strongly affected by relativistic retardation. A
fit of the transition frequencies determines the atomic lifetime
( ns) and resolves a discrepancy between experiment and
recent theoretical calculations.Comment: 4 pages, 4 figures, submitte
Phases of the 2D Hubbard model at low doping
We show that the planar spiral phase of the 2D Hubbard model at low doping,
x, is unstable towards a noncoplanar spin configuration. The novel equilibrium
state we found at low doping is incommensurate with the inverse pitch of the
spiral varying as x^(1/2), but nevertheless has a dominant peak in the
susceptibility at (\pi,\pi). Relevance to the NMR and neutron scattering
experiments in La_2-xSr_xCuO_4 is disccussed.Comment: 12 pages, emtex v.3.
Correlations of Globular Cluster Properties: Their Interpretations and Uses
Correlations among the independently measured physical properties of globular
clusters (GCs) can provide powerful tests for theoretical models and new
insights into their dynamics, formation, and evolution. We review briefly some
of the previous work, and present preliminary results from a comparative study
of GC correlations in the Local Group galaxies. The results so far indicate
that these diverse GC systems follow the same fundamental correlations,
suggesting a commonality of formative and evolutionary processes which produce
them.Comment: An invited review, to appear in "New Horizons in Globular Cluster
Astronomy", eds. G. Piotto, G. Meylan, S.G. Djorgovski, and M. Riello, ASPCS,
in press (2003). Latex file, 8 pages, 5 eps figures, style files include
From Cooper Pairs to Composite Bosons: A Generalized RPA Analysis of Collective Excitations
The evolution of the ground state and the excitation spectrum of the two and
three dimensional attractive Hubbard model is studied as the system evolves
from a Cooper pair regime for weak attraction to a composite boson regime for a
strong attraction.Comment: 20 pages RevTex, 7 figures on reques
The Kepler DB, a Database Management System for Arrays, Sparse Arrays and Binary Data
The Kepler Science Operations Center stores pixel values on approximately six million pixels collected every 30-minutes, as well as data products that are generated as a result of running the Kepler science processing pipeline. The Kepler Database (Kepler DB) management system was created to act as the repository of this information. After one year of ight usage, Kepler DB is managing 3 TiB of data and is expected to grow to over 10 TiB over the course of the mission. Kepler DB is a non-relational, transactional database where data are represented as one dimensional arrays, sparse arrays or binary large objects. We will discuss Kepler DB's APIs, implementation, usage and deployment at the Kepler Science Operations Center
The Environment of M85 optical transient 2006-1: constraints on the progenitor age and mass
M85 optical transient 2006-1 (M85 OT 2006-1) is the most luminous member of
the small family of V838 Mon-like objects, whose nature is still a mystery.
This event took place in the Virgo cluster of galaxies and peaked at an
absolute magnitude of I~-13. Here we present Hubble Space Telescope images of
M85 OT 2006-1 and its environment, taken before and after the eruption, along
with a spectrum of the host galaxy at the transient location. We find that the
progenitor of M85 OT 2006-1 was not associated with any star forming region.
The g and z-band absolute magnitudes of the progenitor were fainter than about
-4 and -6 mag, respectively. Therefore, we can set a lower limit of ~50 Myr on
the age of the youngest stars at the location of the progenitor that
corresponds to a mass of <7 solar mass. Previously published line indices
suggest that M85 has a mean stellar age of 1.6+/-0.3 Gyr. If this mean age is
representative of the progenitor of M85 OT 2006-1, then we can further
constrain its mass to be less than 2 solar mass. We compare the energetics and
mass limit derived for the M85 OT 2006-1 progenitor with those expected from a
simple model of violent stellar mergers. Combined with further modeling, these
new clues may ultimately reveal the true nature of these puzzling events.Comment: 4 pages, accepted to Ap
The infrared imaging spectrograph (IRIS) for TMT: the science case
The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument being
designed for the Thirty Meter Telescope (TMT). IRIS is a combination of an
imager that will cover a 16.4" field of view at the diffraction limit of TMT (4
mas sampling), and an integral field unit spectrograph that will sample objects
at 4-50 mas scales. IRIS will open up new areas of observational parameter
space, allowing major progress in diverse fields of astronomy. We present the
science case and resulting requirements for the performance of IRIS.
Ultimately, the spectrograph will enable very well-resolved and sensitive
studies of the kinematics and internal chemical abundances of high-redshift
galaxies, shedding light on many scenarios for the evolution of galaxies at
early times. With unprecedented imaging and spectroscopy of exoplanets, IRIS
will allow detailed exploration of a range of planetary systems that are
inaccessible with current technology. By revealing details about resolved
stellar populations in nearby galaxies, it will directly probe the formation of
systems like our own Milky Way. Because it will be possible to directly
characterize the stellar initial mass function in many environments and in
galaxies outside of the the Milky Way, IRIS will enable a greater understanding
of whether stars form differently in diverse conditions. IRIS will reveal
detailed kinematics in the centers of low-mass galaxies, allowing a test of
black hole formation scenarios. Finally, it will revolutionize the
characterization of reionization and the first galaxies to form in the
universe.Comment: to appear in Proc. SPIE 773
Infrared Excess in the Be Star Delta Scorpii
We present infrared photometric observations of the Be binary system delta
Scorpii obtained in 2006. The J,H and K magnitudes are the same within the
errors compared to observations taken 10 months earlier. We derive the infrared
excess from the observation and compare this to the color excess predicted by a
radiative equilibrium model of the primary star and its circumstellar disk. We
use a non-LTE computational code to model the gaseous envelope concentrated in
the star's equatorial plane and calculate the expected spectral energy
distribution and Halpha emission profile of the star with its circumstellar
disk. Using the observed infrared excess of delta Sco, as well as Halpha
spectroscopy bracketing the IR observations in time, we place constraints on
the radial density distribution in the circumstellar disk. Because the disk
exhibits variability in its density distribution, this work will be helpful in
understanding its dynamics.Comment: 12 pages, 14 figures, to be published in PASP May 200
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