5,372 research outputs found
Measuring stellar differential rotation with high-precision space-borne photometry
We introduce a method of measuring a lower limit to the amplitude of surface
differential rotation from high-precision, evenly sampled photometric time
series. It is applied to main-sequence late-type stars whose optical flux
modulation is dominated by starspots. An autocorrelation of the time series was
used to select stars that allow an accurate determination of starspot rotation
periods. A simple two-spot model was applied together with a Bayesian
information criterion to preliminarily select intervals of the time series
showing evidence of differential rotation with starspots of almost constant
area. Finally, the significance of the differential rotation detection and a
measurement of its amplitude and uncertainty were obtained by an a posteriori
Bayesian analysis based on a Monte Carlo Markov Chain approach. We applied our
method to the Sun and eight other stars for which previous spot modelling had
been performed to compare our results with previous ones. We find that
autocorrelation is a simple method for selecting stars with a coherent
rotational signal that is a prerequisite for successfully measuring
differential rotation through spot modelling. For a proper Monte Carlo Markov
Chain analysis, it is necessary to take the strong correlations among different
parameters that exist in spot modelling into account. For the planet-hosting
star Kepler-30, we derive a lower limit to the relative amplitude of the
differential rotation of \Delta P / P = 0.0523 \pm 0.0016. We confirm that the
Sun as a star in the optical passband is not suitable for measuring
differential rotation owing to the rapid evolution of its photospheric active
regions. In general, our method performs well in comparison to more
sophisticated and time-consuming approaches.Comment: Accepted to Astronomy and Astrophysics, 15 pages, 13 figures, 4
tables and an Appendi
Towards a complete SUSY GUT
We propose a renormalisable model based on family symmetry with an
grand unified theory (GUT) which leads to the minimal supersymmetric
standard model (MSSM) with a two right-handed neutrino seesaw mechanism.
Discrete symmetry provides the fermion mass
hierarchy in both the quark and lepton sectors, while symmetry
is broken to , identified as usual R-parity. Proton decay is
highly suppressed by these symmetries. We discuss both the and
symmetry breaking sectors, including doublet-triplet splitting, Higgs mixing
and the origin of the term. The model provides an excellent fit (better
than one sigma) to all quark and lepton (including neutrino) masses and mixing
with spontaneous CP violation. With the vacuum alignments, and
, the model predicts the entire PMNS mixing matrix with no free
parameters, up to a relative phase, selected to be from a choice of
the nine complex roots of unity, providing a direct link between neutrino
oscillations and leptogenesis.Comment: 30 pages, 17 figures, 7 tables; Minor changes, references added,
version accepted in JHE
Leptogenesis in minimal predictive seesaw models
We estimate the Baryon Asymmetry of the Universe (BAU) arising from
leptogenesis within a class of minimal predictive seesaw models involving two
right-handed neutrinos and simple Yukawa structures with one texture zero. The
two right-handed neutrinos are dominantly responsible for the "atmospheric" and
"solar" neutrino masses with Yukawa couplings to proportional to and , respectively, where
is a positive integer. The neutrino Yukawa matrix is therefore characterised by
two proportionality constants with their relative phase providing a
leptogenesis-PMNS link, enabling the lightest right-handed neutrino mass to be
determined from neutrino data and the observed BAU. We discuss an SUSY
GUT example, where vacuum alignment provides the required Yukawa
structures with , while a symmetry fixes the relatives
phase to be a ninth root of unity.Comment: 16 pages, 2 tables. v2: minor changes, references added, version
accepted in JHE
Condensation of Vortex-Strings: Effective Potential Contribution Through Dual Actions
Topological excitations are believed to play an important role in different
areas of physics. For example, one case of topical interest is the use of dual
models of quantum cromodynamics to understand properties of its vacuum and
confinement through the condensation of magnetic monopoles and vortices. Other
applications are related to the role of these topological excitations,
nonhomogeneous solutions of the field equations, in phase transitions
associated to spontaneous symmetry breaking in gauge theories, whose study is
of importance in phase transitions in the early universe, for instance. Here we
show a derivation of a model dual to the scalar Abelian Higgs model where its
topological excitations, namely vortex-strings, become manifest and can be
treated in a quantum field theory way. The derivation of the nontrivial
contribution of these vacuum excitations to phase transitions and its analogy
with superconductivity is then made possible and they are studied here.Comment: 7 pages. Based on a talk given by R. O. Ramos at the Infrared QCD in
Rio conference, Rio de Janeiro, Brazil, June 5-9, 200
Generalized Miura Transformations, Two-Boson KP Hierarchies and their Reduction to KDV Hierarchies
Bracket preserving gauge equivalence is established between several two-boson
generated KP type of hierarchies. These KP hierarchies reduce under symplectic
reduction (via Dirac constraints) to KdV, mKdV and Schwarzian KdV hierarchies.
Under this reduction the gauge equivalence is taking form of the conventional
Miura maps between the above KdV type of hierarchies.Comment: 12 pgs., LaTeX, IFT-P/011/93, UICHEP-TH/93-
On the link between rotation, chromospheric activity and Li abundance in subgiant stars
The connection rotation-CaII emission flux-lithium abundance is analyzed for
a sample of bona fide subgiant stars, with evolutionary status determined from
HIPPARCOS trigonometric parallax measurements and from the Toulouse-Geneva
code.Comment: 9 pages, 8 figure
Does rotation of B stars depend on metallicity? preliminary results from GIRAFFE spectra
We show the vsini distribution of main sequence B stars in sites of various
metallicities, in the absolute magnitude range -3.34 < Mv < -2.17. These
include Galactic stars in the field measured by Abt et al. (2002), members of
the h & chi Per open clusters measured by North et al. (2004), and five fields
in the SMC and LMC measured at ESO Paranal with the FLAMES-GIRAFFE
spectrograph, within the Geneva-Lausanne guaranteed time. Following the
suggestion by Maeder et al. (1999), we do find a higher rate of rapid rotators
in the Magellanic Clouds than in the Galaxy, but the vsini distribution is the
same in the LMC and in the SMC in spite of their very different metallicities.Comment: 2 pages, 1 figure, poster presented at the ESO/Arcetri Workshop on
"Chemical abundances and mixing in stars in the Milky Way and its
satellites", 13-17 Sept. 200
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