34,324 research outputs found
Period-Luminosity-Colour distribution and classification of Galactic oxygen-rich LPVs
The absolute K magnitudes and kinematic parameters of about 350 oxygen-rich
Long-Period Variable stars are calibrated, by means of an up-to-date
maximum-likelihood method, using Hipparcos parallaxes and proper motions
together with radial velocities and, as additional data, periods and V-K colour
indices. Four groups, differing by their kinematics and mean magnitudes, are
found. For each of them, we also obtain the distributions of magnitude, period
and de-reddened colour of the base population, as well as de-biased
period-luminosity-colour relations and their two-dimensional projections. The
SRa semiregulars do not seem to constitute a separate class of LPVs. The SRb
appear to belong to two populations of different ages. In a PL diagram, they
constitute two evolutionary sequences towards the Mira stage. The Miras of the
disk appear to pulsate on a lower-order mode. The slopes of their de-biased PL
and PC relations are found to be very different from the ones of the Oxygen
Miras of the LMC. This suggests that a significant number of so-called Miras of
the LMC are misclassified. This also suggests that the Miras of the LMC do not
constitute a homogeneous group, but include a significant proportion of
metal-deficient stars, suggesting a relatively smooth star formation history.
As a consequence, one may not trivially transpose the LMC period-luminosity
relation from one galaxy to the other.Comment: 13 pages, 23 figures. Accepted for publication in A&A
Envelope tomography of long-period variable stars: I. The Schwarzschild mechanism and the Balmer emission lines
This paper is the first one in a series devoted to the study of the dynamics
of the atmospheres of long-period variable stars. Results from a two-month-long
monitoring of the Mira variables RT Cyg and X Oph around maximum light with the
ELODIE spectrograph at the Haute-Provence Observatory are presented. The
monitoring covers phases 0.80 to 1.16 for RT Cyg and phases 0.83 to 1.04 for X
Oph. The cross-correlation profile of the spectrum of RT Cyg with a K0 III mask
confirms that the absorption lines of RT Cyg in the optical domain appear
double around maximum light. No line doubling was found in the optical spectrum
of X Oph around maximum light, indicating that this feature is not common to
all long-period variables. This paper also presents the application to RT Cyg
of a new tomographic technique deriving the velocity field across the
atmosphere by cross-correlating the optical spectrum with numerical masks
constructed from synthetic spectra and probing layers of increasing depths.
This technique reveals that both the temporal evolution of the line doubling,
and its variation with depth in the atmosphere of RT Cyg, are consistent with
the ``Schwarzschild scenario''. This scenario relates the temporal evolution of
the red and blue peaks of the double absorption lines to the progression of a
shock wave in the atmosphere. The temporal evolution of the Balmer Halpha, H
beta, Hgamma and Hdelta emission lines around maximum light is also presented
for RT Cyg and X Oph. The velocity variations of Halpha and of the absorption
lines are discussed in the framework of two competing models for the formation
of Balmer emission lines in long-period variable stars.Comment: 11 pages, 8 figures, Latex, accepted for publication in Astronomy and
Astrophysics main journal. Also available at
http://www-astro.ulb.ac.be/Html/ps.htm
Revisiting Minimal Lepton Flavour Violation in the Light of Leptonic CP Violation
The Minimal Lepton Flavour Violation (MLFV) framework is discussed after the
recent indication for CP violation in the leptonic sector. Among the three
distinct versions of MLFV, the one with degenerate right-handed neutrinos will
be disfavoured, if this indication is confirmed. The predictions for leptonic
radiative rare decays and muon conversion in nuclei are analysed, identifying
strategies to disentangle the different MLFV scenarios. The claim that the
present anomalies in the semi-leptonic -meson decays can be explained within
the MLFV context is critically re-examined concluding that such an explanation
is not compatible with the present bounds from purely leptonic processes.Comment: 36 pages, 4 figures. V2: References added; version accepted for
publication on JHE
Structure and three-body decay of Be resonances
The complex-rotated hyperspherical adiabatic method is used to study the
decay of low-lying Be resonances into one neutron and two
-particles. We investigate the six resonances above the break-up
threshold and below 6 MeV: , and . The
short-distance properties of each resonance are studied, and the different
angular momentum and parity configurations of the Be and He two-body
substructures are determined. We compute the branching ratio for sequential
decay via the Be ground state which qualitatively is consistent with
measurements. We extract the momentum distributions after decay directly into
the three-body continuum from the large-distance asymptotic structures. The
kinematically complete results are presented as Dalitz plots as well as
projections on given neutron and -energy. The distributions are
discussed and in most cases found to agree with available experimental data.Comment: 12 pages, 10 figures. To appear in Physical Review
Momentum distributions from three-body decaying 9Be and 9B resonances
The complex-rotated hyperspherical adiabatic method is used to study the
decay of low-lying Be and B resonances into , and
or . We consider six low-lying resonances of Be (,
and ) and one resonance of B () to compare with. The
properties of the resonances at large distances are decisive for the momentum
distributions of the three decaying fragments. Systematic detailed energy
correlations of Dalitz plots are presented.Comment: 4 pages, 2 figures. Proceedings of the SOTANCP2 conference held in
Brussels in May 201
A Way to Dynamically Overcome the Cosmological Constant Problem
The Cosmological Constant problem can be solved once we require that the full
standard Einstein Hilbert lagrangian, gravity plus matter, is multiplied by a
total derivative. We analyze such a picture writing the total derivative as the
covariant gradient of a new vector field (b_mu). The dynamics of this b_mu
field can play a key role in the explanation of the present cosmological
acceleration of the Universe.Comment: 5 page
Torsion cycles as non-local magnetic sources in non-orientable spaces
Non-orientable spaces can appear to carry net magnetic charge, even in the
absence of magnetic sources. It is shown that this effect can be understood as
a physical manifestation of the existence of torsion cycles of codimension one
in the homology of space.Comment: 17 pages, 4 figure
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