16,595 research outputs found
Compatibility of neutron star masses and hyperon coupling constants
It is shown that the modern equations of state for neutron star matter based
on microscopic calculations of symmetric and asymmetric nuclear matter are
compatible with the lower bound on the maximum neutron-star mass for a certain
range of hyperon coupling constants, which are constrained by the binding
energies of hyperons in symmetric nuclear matter. The hyperons are included by
means of the relativistic Hartree-- or Hartree--Fock approximation. The
obtained couplings are also in satisfactory agreement with hypernuclei data in
the relativistic Hartree scheme. Within the relativistic Hartree--Fock
approximation hypernuclei have not been investigated so far.Comment: 12 pages, 3 figures. Dedicated to Prof. Georg Suessmann on the
occasion of his 70th birthday. To be published in Zeitschrift fuer
Naturforschung
Symmetric and asymmetric nuclear matter in the relativistic approach at finite temperatures
The properties of hot matter are studied in the frame of the relativistic
Brueckner-Hartree-Fock theory. The equations are solved self-consistently in
the full Dirac space. For the interaction we used the potentials given by
Brockmann and Machleidt. The obtained critical temperatures are smaller than in
most of the nonrelativistic investigations. We also calculated the
thermodynamic properties of hot matter in the relativistic Hartree--Fock
approximation, where the force parameters were adjusted to the outcome of the
relativistic Brueckner--Hartree--Fock calculations at zero temperature. Here,
one obtains higher critical temperatures, which are comparable with other
relativistic calculations in the Hartree scheme.Comment: 8 pages, 9 figures, submitted in a shorter version to Phys. Rev.
Discovery of the secondary eclipse of HAT-P-11 b
We report the detection of the secondary eclipse of HAT-P-11 b, a
Neptune-sized planet orbiting an active K4 dwarf. Using all available
short-cadence data of the Kepler mission, we derive refined planetary ephemeris
increasing their precision by more than an order of magnitude. Our simultaneous
primary and secondary transit modeling results in improved transit and orbital
parameters. In particular, the precise timing of the secondary eclipse allows
to pin down the orbital eccentricity to . The
secondary eclipse depth of ppm corresponds to a
detection and results in a geometric albedo of for
HAT-P-11 b, close to Neptune's value, which may indicate further resemblances
between these two bodies. Due to the substantial orbital eccentricity, the
planetary equilibrium temperature is expected to change significantly with
orbital position and ought to vary between K and K,
depending on the details of heat redistribution in the atmosphere of HAT-P-11
b.Comment: Accepted by A&A, 27/10/201
A planetary eclipse map of CoRoT-2a. Comprehensive lightcurve modeling combining rotational-modulation and transits
We analyze the surface structure of the planet host star CoRoT-2a using a
consistent model for both the `global' (i.e., rotationally modulated)
lightcurve and the transit lightcurves, using data provided by the CoRoT
mission. Selecting a time interval covering two stellar rotations and six
transits of the planetary companion CoRoT-2b, we adopt a `strip' model of the
surface to reproduce the photometric modulation inside and outside the transits
simultaneously. Our reconstructions show that it is possible to achieve
appropriate fits for the entire sub-interval using a low-resolution surface
model with 36 strips. The surface reconstructions indicate that the brightness
on the eclipsed section of the stellar surface is (6 +/- 1) % lower than the
average brightness of the remaining surface. This result suggests a
concentration of stellar activity in a band around the stellar equator similar
to the behavior observed on the Sun.Comment: accepted by A&A on 12/09/200
Neutron star properties with relativistic equations of state
We study the properties of neutron stars adopting relativistic equations of
state of neutron star matter, calculated in the framework of the relativistic
Brueckner-Hartree-Fock approximation for electrically charge neutral neutron
star matter in beta-equilibrium. For higher densities more baryons (hyperons
etc.) are included by means of the relativistic Hartree- or Hartree-Fock
approximation. The special features of the different approximations and
compositions are discussed in detail. Besides standard neutron star properties
special emphasis is put on the limiting periods of neutron stars, for which the
Kepler criterion and gravitation-reaction instabilities are considered.
Furthermore the cooling behaviour of neutron stars is investigated, too. For
comparison we give also the outcome for some nonrelativistic equations of
state.Comment: 43 pages, 22 ps-figures, to be published in the International Journal
of Modern Physics
R2D2 - a symmetric measurement of reactor neutrinos free of systematical errors
We discuss a symmetric setup for a reactor neutrino oscillation experiment
consisting of two reactors separated by about 1 km, and two symmetrically
placed detectors, one close to each reactor. We show that such a configuration
allows a determination of which is essentially free of
systematical errors, if it is possible to separate the contributions of the two
reactors in each detector sufficiently. This can be achieved either by
considering data when in an alternating way only one reactor is running or by
directional sensitivity obtained from the neutron displacement in the detector.Comment: 11 pages, 3 figures, clarifications added, some numbers in relation
with the neutron displacement corrected, version to appear in JHE
Growth, micro-structuring, spectroscopy, and optical gain in as-deposited waveguides
Deposition and micro-structuring of layers with low background losses (0.11 dB/cm) and lifetimes up to 7 ms have been optimized for active devices. Net gain of 0.7 dB/cm at 1533 nm has been measured.\ud
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Planetary eclipse mapping of CoRoT-2a. Evolution, differential rotation, and spot migration
The lightcurve of CoRoT-2 shows substantial rotational modulation and
deformations of the planet's transit profiles caused by starspots. We
consistently model the entire lightcurve, including both rotational modulation
and transits, stretching over approximately 30 stellar rotations and 79
transits. The spot distribution and its evolution on the noneclipsed and
eclipsed surface sections are presented and analyzed, making use of the high
resolution achievable under the transit path.
We measure the average surface brightness on the eclipsed section to be
(5\pm1) % lower than on the noneclipsed section. Adopting a solar spot
contrast, the spot coverage on the entire surface reaches up to 19 % and a
maximum of almost 40 % on the eclipsed section. Features under the transit
path, i.e. close to the equator, rotate with a period close to 4.55 days.
Significantly higher rotation periods are found for features on the noneclipsed
section indicating a differential rotation of . Spotted
and unspotted regions in both surface sections concentrate on preferred
longitudes separated by roughly 180 deg.Comment: Paper accepted by A&A 17/02/2010. For a better resolution paper
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