2,143 research outputs found
Pyaneti: a fast and powerful software suite for multi-planet radial velocity and transit fitting
Transiting exoplanet parameter estimation from time-series photometry and
Doppler spectroscopy is fundamental to study planets' internal structures and
compositions. Here we present the code pyaneti, a powerful and user-friendly
software suite to perform multi-planet radial velocity and transit data
fitting. The code uses a Bayesian approach combined with an MCMC sampling to
estimate the parameters of planetary systems. We combine the numerical
efficiency of FORTRAN, the versatility of PYTHON, and the parallelization of
OpenMP to make pyaneti a fast and easy to use code. The package is freely
available at https://github.com/oscaribv/pyaneti.Comment: 15 pages, 6 figures, 2 tables. Accepted for publication in MNRA
Zero-Temperature Dynamics of Plus/Minus J Spin Glasses and Related Models
We study zero-temperature, stochastic Ising models sigma(t) on a
d-dimensional cubic lattice with (disordered) nearest-neighbor couplings
independently chosen from a distribution mu on R and an initial spin
configuration chosen uniformly at random. Given d, call mu type I (resp., type
F) if, for every x in the lattice, sigma(x,t) flips infinitely (resp., only
finitely) many times as t goes to infinity (with probability one) --- or else
mixed type M. Models of type I and M exhibit a zero-temperature version of
``local non-equilibration''. For d=1, all types occur and the type of any mu is
easy to determine. The main result of this paper is a proof that for d=2,
plus/minus J models (where each coupling is independently chosen to be +J with
probability alpha and -J with probability 1-alpha) are type M, unlike
homogeneous models (type I) or continuous (finite mean) mu's (type F). We also
prove that all other noncontinuous disordered systems are type M for any d
greater than or equal to 2. The plus/minus J proof is noteworthy in that it is
much less ``local'' than the other (simpler) proof. Homogeneous and plus/minus
J models for d greater than or equal to 3 remain an open problem.Comment: 17 pages (RevTeX; 3 figures; to appear in Commun. Math. Phys.
CoRoT 102918586: a Gamma Dor pulsator in a short period eccentric eclipsing binary
Pulsating stars in eclipsing binary systems are powerful tools to test
stellar models. Binarity enables to constrain the pulsating component physical
parameters, whose knowledge drastically improves the input physics for
asteroseismic studies. The study of stellar oscillations allows us, in its
turn, to improve our understanding of stellar interiors and evolution. The
space mission CoRoT discovered several promising objects suitable for these
studies, which have been photometrically observed with unprecedented accuracy,
but needed spectroscopic follow-up. A promising target was the relatively
bright eclipsing system CoRoT 102918586, which turned out to be a double-lined
spectroscopic binary and showed, as well, clear evidence of Gamma Dor type
pulsations. We obtained phase resolved high-resolution spectroscopy with the
Sandiford spectrograph at the McDonald 2.1m telescope and the FEROS
spectrograph at the ESO 2.2m telescope. Spectroscopy yielded both the radial
velocity curves and, after spectra disentangling, the component effective
temperatures, metallicity and line-of-sight projected rotational velocities.
The CoRoT light curve was analyzed with an iterative procedure, devised to
disentangle eclipses from pulsations. We obtained an accurate determination of
the system parameters, and by comparison with evolutionary models strict
constraints on the system age. Finally, the residuals obtained after
subtraction of the best fitting eclipsing binary model were analyzed to
determine the pulsator properties. We achieved a quite complete and consistent
description of the system. The primary star pulsates with typical {\gamma} Dor
frequencies and shows a splitting in period which is consistent with high order
g-mode pulsations in a star of the corresponding physical parameters. The value
of the splitting, in particular, is consistent with pulsations in l = 1 modes.Comment: 12 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
Spin Response and Neutrino Emissivity of Dense Neutron Matter
We study the spin response of cold dense neutron matter in the limit of zero
momentum transfer, and show that the frequency dependence of the
long-wavelength spin response is well constrained by sum-rules and the
asymptotic behavior of the two-particle response at high frequency. The
sum-rules are calculated using Auxiliary Field Diffusion Monte Carlo technique
and the high frequency two-particle response is calculated for several
nucleon-nucleon potentials. At nuclear saturation density, the sum-rules
suggest that the strength of the spin response peaks at 40--60
MeV, decays rapidly for 100 MeV, and has a sizable strength below
40 MeV. This strength at relatively low energy may lead to enhanced neutrino
production rates in dense neutron-rich matter at temperatures of relevance to
core-collapse supernova.Comment: 11 pages, 4 figures. Minor change. Published versio
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