693 research outputs found
Tidal interactions of close-in extrasolar planets: the OGLE cases
Close-in extrasolar planets experience extreme tidal interactions with their
host stars. This may lead to a reduction of the planetary orbit and a spin-up
of stellar rotation. Tidal interactions have been computed for a number of
extrasolar planets in circular orbits within 0.06 AU, namely for OGLE-TR-56 b.
We compare our range of the tidal dissipation value with two dissipation models
from Sasselov (2003) and conclude that our choices are equivalent to these
models. However, applied to the planet OGLE-TR-56 b, we find in contrast to
Sasselov (2003) that this planet will spiral-in toward the host star in a few
billion years. We show that the average and maximum value of our range of
dissipation are equivalent to the linear and quadratic dissipation models of
Sasselov (2003). Due to limitations in the observational techniques, we do not
see a possibility to distinguish between the two dissipation models as outlined
by Sasselov (2003). OGLE-TR-56 b may therefore not serve as a test case for
dissipation models. The probable existence of OGLE-TR-3 b at 0.02 AU and the
discovery of OGLE-TR-113 b at 0.023 AU and OGLE-TR-132 b at 0.03 AU may also
counter Sasselovs (2003) assumption of a pile-up stopping boundary at 0.04 AU.Comment: 7 pages, 4 figure
Interplay of tidal evolution and stellar wind braking in the rotation of stars hosting massive close-in planets
This paper deals with the application of the creep tide theory (Ferraz-Mello,
Cel. Mech. Dyn. Astron. vol. 116, 109, 2013) to the study of the rotation of
stars hosting massive close-in planets. The stars have nearly the same tidal
relaxation factors as gaseous planets and the evolution of their rotation is
similar to that of close-in hot Jupiters: they tidally evolve towards a
stationary solution. However, stellar rotation may also be affected by stellar
wind braking. Thus, while the rotation of a quiet host star evolves towards a
stationary attractor with a frequency () times the orbital mean-motion
of the companion, the continuous loss of angular momentum in an active star
displaces the stationary solution towards slower values: Active host stars with
big close-in companions tend to have rotational periods larger than the orbital
periods of their companions. The study of some hypothetical examples shows that
because of tidal evolution, the rules of gyrochronology cannot be used to
estimate the age of one system with a large close-in companion, no matter if
the star is quiet or active, if the current semi-major axis of the companion is
smaller than 0.03--0.04 AU. Details on the evolution of the systems: CoRoT
LRc06E21637, CoRoT-27, Kepler-75, CoRoT-2, CoRoT-18, CoRoT-14 and on
hypothetical systems with planets of mass 1--4 M_Jup in orbit around a star
similar to the Sun are given.Comment: 22 pages, 8 figures; Publication in Ap
Collision damping in the pi 3He -> d'N reaction near the threshold
We present a simple quantum mechanical model exploiting the optical potential
approach for the description of collision damping in the reaction pi 3He -> d'N
near the threshold, which recently has been measured at TRIUMF. The influence
of the open d'N -> NNN channel is taken into account. It leads to a suppression
factor of about ten in the d' survival probability. Applications of the method
to other reactions are outlined.Comment: RevTeX4, 14 pages, 3 Postscript figures, uses epsfig.sty, to appear
in Phys.Rev.
The Reaction 7Li(pi+,pi-)7B and its Implications for 7B
The reaction 7Li(pi+,pi-)7B has been measured at incident pion energies of
30-90 MeV. 7Li constitutes the lightest target nucleus, where the pionic charge
exchange may proceed as a binary reaction to a discrete final state. Like in
the Delta-resonance region the observed cross sections are much smaller than
expected from the systematics found for heavier nuclei. In analogy to the
neutron halo case of 11Li this cross section suppression is interpreted as
evidence for a proton halo in the particle-unstable nucleus 7B.Comment: 4 pages, 4 figure
Classes of sum-of-cisoids processes and their statistics for the modeling and simulation of mobile fading channels
In this paper, we present a fundamental study on the stationarity and ergodicity of eight classes of sum-of-cisoids (SOC) processes for the modeling and simulation of frequency-nonselective mobile Rayleigh fading channels. The purpose of this study is to determine which classes of SOC models enable the design of channel simulators that accurately reproduce the channel’s statistical properties without demanding information on the time origin or the time-consuming computation of an ensemble average. We investigate the wide-sense stationarity, first-order stationarity of the envelope, mean ergodicity, and autocorrelation ergodicity of the underlying random processes characterizing the different classes of stochastic SOC simulators. The obtained results demonstrate that only the class of SOC models comprising cisoids with constant gains, constant frequencies, and random phases is defined by a set of stationary and ergodic random processes. The analysis presented here can easily be extended with respect to the modeling and simulation of frequency-selective single-input single-output (SISO) and multiple-input multiple-output channels. For the case of frequency-selective SISO channels, we investigate the stationarity and ergodicity in both time and frequency of 16 different classes of SOC simulation models. The findings presented in this paper can be used in the laboratory as guidelines to design efficient simulation platforms for the performance evaluation of modern mobile communication systems
Search for Exotic Muon Decays
Recently, it has been proposed that the observed anomaly in the time
distribution of neutrino induced reactions, reported by the KARMEN
collaboration, can be interpreted as a signal from an exotic muon decay branch
mu+ to e+ X. It has been shown that this hypothesis gives an acceptable fit to
the KARMEN data if the boson X has a mass of m_X=103.9MeV/c^2, close to the
kinematical limit. We have performed a search for the X particle by studying
for the first time the very low energy part of the Michel spectrum in mu+
decays. Using a HPGe detector setup at the muE4 beamline at PSI we find
branching ratios BR(mu+ to e+ X)<5.7e-4 (90% C.L.) for most of the region
103MeV/c^2<m_X<105MeV/c^2.Comment: 9 page
An Investigation into the Radial Velocity Variations of CoRoT-7
CoRoT-7b, the first transiting ``superearth'' exoplanet, has a radius of 1.7
R_Earth and a mass of 4.8 M_Earth. Ground-based radial velocity measurements
also detected an additional companion with a period of 3.7 days (CoRoT-7c) and
a mass of 8.4 M_Earth. The mass of CoRoT-7b is a crucial parameter for planet
structure models, but is difficult to determine because CoRoT-7 is a modestly
active star and there is at least one additional companion. A Fourier analysis
was performed on spectral data for CoRoT-7 taken with the HARPS spectrograph.
These data include RV measurements, spectral line bisectors, the full width at
half maximum of the cross-correlation function, and Ca II emission. The latter
3 quantities vary due to stellar activity and were used to assess the nature of
the observed RV variations. An analysis of a sub-set of the RV measurements
where multiple observations were made per night was also used to estimate the
RV amplitude from CoRoT-7b that was less sensitive to activity variations. Our
analysis indicates that the 0.85-d and 3.7-d RV signals of CoRoT-7b and
CoRoT-7c are present in the spectral data with a high degree of statistical
significance. We also find evidence for another significant RV signal at 9
days. An analysis of the activity indicator data reveals that this 9-d signal
most likely does not arise from activity, but possibly from an additional
companion. If due to a planetary companion the mass is m = 19.5 M_Earth,
assuming co-planarity with CoRoT-7b. A dynamical study of the three planet
system shows that it is stable over several hundred millions of years. Our
analysis yields a RV amplitude of 5.04 +/- 1.09 m/s for CoRoT-7b which
corresponds to a planet mass of m = 6.9 +/- 1.4 M_Earth. This increased mass
would make the planet CoRoT-7b more Earth-like in its internal structure.Comment: 20 pages, 20 figure
Search for Narrow NNpi Resonances in Exclusive p p -> p p pi+ pi- Measurements
Narrow structures in the range of a few MeV have been searched for in p p pi+
and p p pi- invariant mass spectra obtained from exclusive measurements of the
p p -> p p pi+ pi- reaction at Tp = 725, 750 and 775 MeV using the PROMICE/WASA
detector at CELSIUS. The selected reaction is particularily well suited for the
search for NN and / or N Delta decoupled dibaryon resonances. Except for a
possible fluctuation at 2087 MeV/c^2 in Mpppi- no narrow structures could be
identified neither in Mpppi+ nor in Mpppi- on the 3 sigma level of statistical
significance, giving an upper limit (95% C.L.) for dibaryon production in this
reaction of sigma < 20 nb for 2020 MeV/c^2 < m(dibaryon) < 2085 MeV/c^2Comment: 3 pages, 4 figure
Steady State of microemulsions in shear flow
Steady-state properties of microemulsions in shear flow are studied in the
context of a Ginzburg-Landau free-energy approach. Explicit expressions are
given for the structure factor and the time correlation function at the one
loop level of approximation. Our results predict a four-peak pattern for the
structure factor, implying the simultaneous presence of interfaces aligned with
two different orientations.
Due to the peculiar interface structure a non-monotonous relaxation of the
time correlator is also found.Comment: 5 pages, 3 figure
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