5,301 research outputs found
Physics of the ALICE Experiment
A short description of the ALICE detector at CERN is given. The experiment is
aiming to study the properties of the quark-gluon plasma by means of a whole
set of probes that can be subdivided into three classes: soft, heavy-flavour
and high-Pt probes. Each of the classes is illustrated by a few typical
examples.Comment: Proceedings of the 41st Rencontres de Moriond, QCD and high energy
hadronic interactions, La Thuile, Italy, 18-25 March 200
Extragalactic Cepheid database
We present in this paper an exhaustive compilation of all published data of
extragalactic Cepheids. We have checked every light curve in order to
characterize the different types of Cepheid and detect potential overtone
pulsators, or to estimate the quality of the data. This compilation of about
3000 photometric measurements will constitute a very useful tool for
astronomers involved for instance in the extragalactic distance scale.Comment: Updated version of this database is now available through WWW at
http://www-obs.univ-lyon1.fr/~planoix/ECD/ . 1321 Cepheids located in 39
galaxies make up the base at the moment. One can also plot PL-relations and
compute distance moduli based on Hipparcos PL-relation
Equivalence Principle Violation in Weakly Vainshtein-Screened Systems
Massive gravity, galileon and braneworld models that modify gravity to
explain cosmic acceleration utilize the nonlinear field interactions of the
Vainshtein mechanism to screen fifth forces in high density regimes. These
source-dependent interactions cause apparent equivalence principle violations.
In the weakly-screened regime violations can be especially prominent since the
fifth forces are at near full strength. Since they can also be calculated
perturbatively, we derive analytic solutions for illustrative cases: the motion
of massive objects in compensated shells and voids and infall toward halos that
are spherically symmetric. Using numerical techniques we show that these
solutions are valid until the characteristic scale becomes comparable to the
Vainshtein radius. We find a relative acceleration of more massive objects
toward the center of a void and a reduction of the infall acceleration that
increases with the mass ratio of the halos which can in principle be used to
test the Vainshtein screening mechanism.Comment: 7 pages, 4 figure
Simulation of a method to directly image exoplanets around multiple stars systems
Direct imaging of extra-solar planets has now become a reality, especially
with the deployment and commissioning of the first generation of specialized
ground-based instruments such as the GPI, SPHERE, P1640 and SCExAO. These
systems will allow detection of planets 1e7 times fainter than their host star.
For space-based missions, such as EXCEDE, EXO-C, EXO-S, WFIRST-AFTA,
different teams have shown in laboratories contrasts reaching 1e-10 within a
few diffraction limits from the star using a combination of a coronagraph to
suppress light coming from the host star and a wavefront control system. These
demonstrations use a deformable mirror (DM) to remove residual starlight
(speckles) created by the imperfections of telescope. However, all these
current and future systems focus on detecting faint planets around a single
host star or unresolved binaries/multiples, while several targets or planet
candidates are located around nearby binary stars such as our neighbor star
Alpha Centauri.
Until now, it has been thought that removing the light of a companion star is
impossible with the current technology, excluding binary star systems from
target lists of direct imaging missions. Direct imaging around binaries or
multiples systems at a level of contrast allowing Earth-like planets detection
is challenging because the region of interest, where a dark zone is essential,
is contaminated by the light coming from the host star's companion. We propose
a method to simultaneously correct aberration sand diffraction of light coming
from the target star. This method works even if the companion star is outside
the control region of the DM (beyond its half-Nyquist frequency), by taking
advantage of aliasing effects.Comment: 8 pages, 13 figures, SPIE Astronomical Telescope and Instrumentation
conferenc
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