5,465 research outputs found
Forbidden Line Emission in the Eccentric Spectroscopic Binaries DQ Tauri and UZ Tauri E Monitored over an Orbital Period
We present echelle spectroscopy of the close pre-main-sequence binary star
systems DQ Tau and UZ Tau-E. Over a 16 day time interval we acquired 14 nights
of spectra for DQ Tau and 12 nights of spectra for UZ Tau-E. This represents
the entire phase of DQ Tau, and 63 percent of the phase of UZ Tau-E. As
expected, photospheric lines such as Li I 6707 clearly split into two
components as the primary and secondary orbit one another, as did the permitted
line He I 5876. Unlike the photospheric features, the forbidden lines of [O I]
6300 and [O I] 5577, retain the same shape throughout the orbit. Therefore
these lines must originate outside of the immediate vicinity of the two stars
and any circumstellar disks that participate in the orbital motion of the
stars.Comment: 14 pages including 6 figures, aastex preprint, accepted to
Astronomical Journa
Revisiting the optical -symmetric dimer
Optics has proved a fertile ground for the experimental simulation of quantum
mechanics. Most recently, optical realizations of -symmetric
quantum mechanics have been shown, both theoretically and experimentally,
opening the door to international efforts aiming at the design of practical
optical devices exploiting this symmetry. Here, we focus on the optical
-symmetric dimer, a two-waveguide coupler were the materials show
symmetric effective gain and loss, and provide a review of the linear and
nonlinear optical realizations from a symmetry based point of view. We go
beyond a simple review of the literature and show that the dimer is just the
smallest of a class of planar -waveguide couplers that are the optical
realization of Lorentz group in 2+1 dimensions. Furthermore, we provide a
formulation to describe light propagation through waveguide couplers described
by non-Hermitian mode coupling matrices based on a non-Hermitian generalization
of Ehrenfest theorem.Comment: 25 pages, 12 figure
Intermediate-mass-ratio-inspirals in the Einstein Telescope. II. Parameter estimation errors
We explore the precision with which the Einstein Telescope (ET) will be able
to measure the parameters of intermediate-mass-ratio inspirals (IMRIs). We
calculate the parameter estimation errors using the Fisher Matrix formalism and
present results of a Monte Carlo simulation of these errors over choices for
the extrinsic parameters of the source. These results are obtained using two
different models for the gravitational waveform which were introduced in paper
I of this series. These two waveform models include the inspiral, merger and
ringdown phases in a consistent way. One of the models, based on the transition
scheme of Ori & Thorne [1], is valid for IMBHs of arbitrary spin, whereas the
second model, based on the Effective One Body (EOB) approach, has been
developed to cross-check our results in the non-spinning limit. In paper I of
this series, we demonstrated the excellent agreement in both phase and
amplitude between these two models for non-spinning black holes, and that their
predictions for signal-to-noise ratios (SNRs) are consistent to within ten
percent. We now use these models to estimate parameter estimation errors for
binary systems with masses 1.4+100, 10+100, 1.4+500 and 10+500 solar masses
(SMs), and various choices for the spin of the central intermediate-mass black
hole (IMBH). Assuming a detector network of three ETs, the analysis shows that
for a 10 SM compact object (CO) inspiralling into a 100 SM IMBH with spin
q=0.3, detected with an SNR of 30, we should be able to determine the CO and
IMBH masses, and the IMBH spin magnitude to fractional accuracies of 0.001,
0.0003, and 0.001, respectively. We also expect to determine the location of
the source in the sky and the luminosity distance to within 0.003 steradians,
and 10%, respectively. We also assess how the precision of parameter
determination depends on the network configuration.Comment: 21 pages, 5 figures. One reference corrected in v3 for consistency
with published version in Phys Rev
Condensation in an Economic Model with Brand Competition
We present a linear agent based model on brand competition. Each agent
belongs to one of the two brands and interacts with its nearest neighbors. In
the process the agent can decide to change to the other brand if the move is
beneficial. The numerical simulations show that the systems always condenses
into a state when all agents belong to a single brand. We study the
condensation times for different parameters of the model and the influence of
different mechanisms to avoid condensation, like anti monopoly rules and brand
fidelity.Comment: Accepted in: International Journal of Modern Physics
Entanglement and alpha entropies for a massive scalar field in two dimensions
We find the analytic expression of the trace of powers of the reduced density
matrix on an interval of length L, for a massive boson field in 1+1 dimensions.
This is given exactly (except for a non universal factor) in terms of a finite
sum of solutions of non linear differential equations of the Painlev\'e V type.
Our method is a generalization of one introduced by Myers and is based on the
explicit calculation of quantities related to the Green function on a plane,
where boundary conditions are imposed on a finite cut. It is shown that the
associated partition function is related to correlators of exponential
operators in the Sine-Gordon model in agreement with a result by Delfino et al.
We also compute the short and long distance leading terms of the entanglement
entropy. We find that the bosonic entropic c-function interpolates between the
Dirac and Majorana fermion ones given in a previous paper. Finally, we study
some universal terms for the entanglement entropy in arbitrary dimensions
which, in the case of free fields, can be expressed in terms of the two
dimensional entropy functions.Comment: 13 pages, 2 figure
Optical Properties of a \theta-Vacuum
Chern-Simons (CS) forms generalize the minimal coupling between gauge
potentials and point charges, to sources represented by charged extended
objects (branes). The simplest example of such a CS-brane coupling is a domain
wall coupled to the electromagnetic CS three-form. This describes a
topologically charged interface where the CS form AdA is supported, separating
two three-dimensional spatial regions in 3+1 spacetime. Electrodynamics at
either side of the brane is described by the same Maxwell's equations, but
those two regions have different vacua, characterized by a different value of
the \theta-parameter multiplying the Pontryagin form F ^ F. The \theta-term is
the abelian version of the concept introduced by 't Hooft for the resolution of
the U(1) problem in QCD. We point out that CS-generalized classical
electrodynamics shows new phenomena when two neighboring regions with different
\theta-vacua are present. These topological effects result from surface effects
induced by the boundary and we explore the consequences of such boundary
effects for the propagation of the electromagnetic field in Maxwell theory.
Several features, including optical and electrostatic/magnetostatic responses,
which may be observable in condensed matter systems, like topological
insulators, are discussed.Comment: 11 pages, no figure
SIM PlanetQuest Key Project Precursor Observations to Detect Gas Giant Planets Around Young Stars
We present a review of precursor observing programs for the SIM PlanetQuest
Key project devoted to detecting Jupiter mass planets around young stars. In
order to ensure that the stars in the sample are free of various sources of
astrometric noise that might impede the detection of planets, we have initiated
programs to collect photometry, high contrast images, interferometric data and
radial velocities for stars in both the Northern and Southern hemispheres. We
have completed a high contrast imaging survey of target stars in Taurus and the
Pleiades and found no definitive common proper motion companions within one
arcsecond (140 AU) of the SIM targets. Our radial velocity surveys have shown
that many of the target stars in Sco-Cen are fast rotators and a few stars in
Taurus and the Pleiades may have sub-stellar companions. Interferometric data
of a few stars in Taurus show no signs of stellar or sub-stellar companions
with separations of <5 mas. The photometric survey suggests that approximately
half of the stars initially selected for this program are variable to a degree
(1 sigma>0.1 mag) that would degrade the astrometric accuracy achievable for
that star. While the precursor programs are still a work in progress, we
provide a comprehensive list of all targets ranked according to their viability
as a result of the observations taken to date. By far, the observable that
moves the most targets from the SIM-YSO program is photometric variability.Comment: Accepted for publication in Publications of the Astronomical Society
of the Pacific, 25 pages, 9 figure
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