16,574 research outputs found
The Impact of Transiting Planet Science on the Next Generation of Direct-Imaging Planet Searches
Within the next five years, a number of direct-imaging planet search
instruments, like the VLT SPHERE instrument, will be coming online. To
successfully carry out their programs, these instruments will rely heavily on
a-priori information on planet composition, atmosphere, and evolution.
Transiting planet surveys, while covering a different semi-major axis regime,
have the potential to provide critical foundations for these next-generation
surveys. For example, improved information on planetary evolutionary tracks may
significantly impact the insights that can be drawn from direct-imaging
statistical data. Other high-impact results from transiting planet science
include information on mass-to-radius relationships as well as atmospheric
absorption bands. The marriage of transiting planet and direct-imaging results
may eventually give us the first complete picture of planet migration,
multiplicity, and general evolution.Comment: 4 pages, 3 figures, IAU Transiting Planets Proceedings, in pres
Quantum Phonon Optics: Coherent and Squeezed Atomic Displacements
In this paper we investigate coherent and squeezed quantum states of phonons.
The latter allow the possibility of modulating the quantum fluctuations of
atomic displacements below the zero-point quantum noise level of coherent
states. The expectation values and quantum fluctuations of both the atomic
displacement and the lattice amplitude operators are calculated in these
states---in some cases analytically. We also study the possibility of squeezing
quantum noise in the atomic displacement using a polariton-based approach.Comment: 6 pages, RevTe
Phonon Transmission Rate, Fluctuations, and Localization in Random Semiconductor Superlattices: Green's Function Approach
We analytically study phonon transmission and localization in random
superlattices by using a Green's function approach. We derive expressions for
the average transmission rate and localization length, or Lyapunov exponent, in
terms of the superlattice structure factor. This is done by considering the
backscattering of phonons, due to the complex mass density fluctuations, which
incorporates all of the forward scattering processes. These analytical results
are applied to two types of random superlattices and compared with numerical
simulations based on the transfer matrix method. Our analytical results show
excellent agreement with the numerical data. A universal relation for the
transmission fluctuations versus the average transmission is derived
explicitly, and independently confirmed by numerical simulations. The transient
of the distribution of transmission to the log-normal distribution for the
localized phonons is also studied.Comment: 36 pages, Late
ALMA Observations of the Gravitational Lens SDP.9
We present long-baseline ALMA observations of the strong gravitational lens
H-ATLAS J090740.0-004200 (SDP.9), which consists of an elliptical galaxy at
lensing a background submillimeter galaxy into two
extended arcs. The data include Band 6 continuum observations, as well as CO
=65 molecular line observations, from which we measure an updated source
redshift of . The image morphology in the ALMA data is
different from that of the HST data, indicating a spatial offset between the
stellar, gas, and dust component of the source galaxy. We model the lens as an
elliptical power law density profile with external shear using a combination of
archival HST data and conjugate points identified in the ALMA data. Our best
model has an Einstein radius of and a
slightly steeper than isothermal mass profile slope. We search for the central
image of the lens, which can be used constrain the inner mass distribution of
the lens galaxy including the central supermassive black hole, but do not
detect it in the integrated CO image at a 3 rms level of 0.0471 Jy km
s.Comment: Accepted for publication in ApJL; 6 pages, 2 figures, 3 table
Optical Spatial integration methods for ambiguity function generation
A coherent optical spatial integration approach to ambiguity function generation is described. It uses one dimensional acousto-optic Bragg cells as input tranducers in conjunction with a space variant linear phase shifter, a passive optical element, to generate the two dimensional ambiguity function in one exposure. Results of a real time implementation of this system are shown
The SONYC survey: Towards a complete census of brown dwarfs in star forming regions
SONYC, short for "Substellar Objects in Nearby Young Clusters", is a survey
program to provide a census of the substellar population in nearby star forming
regions. We have conducted deep optical and near-infrared photometry in five
young regions (NGC1333, rho Ophiuchi, Chamaeleon-I, Upper Sco, and Lupus-3),
combined with proper motions, and followed by extensive spectroscopic campaigns
with Subaru and VLT, in which we have obtained more than 700 spectra of
candidate low-mass objects. We have identified and characterized more than 60
new substellar objects, among them a handful of objects with masses close to,
or below the Deuterium burning limit. Through SONYC and surveys by other
groups, the substellar IMF is now well characterized down to ~ 5 - 10 MJup, and
we find that the ratio of the number of stars with respect to brown dwarfs lies
between 2 and 6. A comprehensive survey of NGC 1333 reveals that, down to
~5MJup, free-floating objects with planetary masses are 20-50 times less
numerous than stars, i.e. their total contribution to the mass budget of the
clusters can be neglected.Comment: to appear in the proceedings of the conference 'Brown dwarfs come of
age', May 20-24 2013, Memorie della Societa Astronomica Italian
Electron Correlations in the Quasi-Two-Dimensional Organic Conductor -(BEDT-TTF)I investigated by C NMR
We report a C-NMR study on the ambient-pressure metallic phase of the
layered organic conductor -(BEDT-TTF)I [BEDT-TTF:
bisethylenedithio-tetrathiafulvalene], which is expected to connect the physics
of correlated electrons and Dirac electrons under pressure. The orientation
dependence of the NMR spectra shows that all BEDT-TTF molecules in the unit
cell are to be seen equivalent from a microscopic point of view. This feature
is consistent with the orthorhombic symmetry of the BEDT-TTF sublattice and
also indicates that the monoclinic sublattice, which should make three
molecules in the unit cell nonequivalent, is not practically influential on the
electronic state in the conducting BEDT-TTF layers at ambient pressure. There
is no signature of charge disproportionation in opposition to most of the
-type BEDT-TTF salts.
The analyses of NMR Knight shift, , and the nuclear spin-lattice
relaxation rate, , revealed that the degree of electron correlation,
evaluated by the Korringa ratio [)], is in an
intermediate regime. However, NMR relaxation rate is enhanced above
200K, which possibly indicates that the system enters into a quantum
critical regime of charge-order fluctuations as suggested theoretically.Comment: 19pages, 6figure
- …