520 research outputs found
A Phase Transition for Circle Maps and Cherry Flows
We study weakly order preserving circle maps with a flat interval.
The main result of the paper is about a sharp transition from degenerate
geometry to bounded geometry depending on the degree of the singularities at
the boundary of the flat interval. We prove that the non-wandering set has zero
Hausdorff dimension in the case of degenerate geometry and it has Hausdorff
dimension strictly greater than zero in the case of bounded geometry. Our
results about circle maps allow to establish a sharp phase transition in the
dynamics of Cherry flows
The Araucaria project: High-precision orbital parallaxes and masses of binary stars. I. VLTI/GRAVITY observations of ten double-lined spectroscopic binaries
We aim to measure very precise and accurate model-independent masses and
distances of detached binary stars. Precise masses at the % level are
necessary to test and calibrate stellar interior and evolution models, while
precise and independent orbital parallaxes are essential to check for the next
Gaia data releases. We combined RV measurements with interferometric
observations to determine orbital and physical parameters of ten double-lined
spectroscopic systems. We report new relative astrometry from VLTI/GRAVITY and,
for some systems, new VLT/UVES spectra to determine the radial velocities of
each component. We measured the distance of ten binary systems and the mass of
their components with a precision as high as 0.03% (average level 0.2%). They
are combined with other stellar parameters (effective temperatures, radii, flux
ratios, etc.) to fit stellar isochrones and determine their evolution stage and
age. We also compared our orbital parallaxes with Gaia and showed that half of
the stars are beyond with our orbital parallaxes; although, their
RUWE is below the frequently used cutoff of 1.4 for reliable Gaia astrometry.
By fitting the telluric features in the GRAVITY spectra, we also estimated the
accuracy of the wavelength calibration to be % in high and medium
spectral resolution modes. We demonstrate that combining spectroscopic and
interferometric observations of binary stars provides extremely precise and
accurate dynamical masses and orbital parallaxes. As they are detached
binaries, they can be used as benchmark stars to calibrate stellar evolution
models and test the Gaia parallaxes.Comment: Accepted for publication in A&
The Araucaria Project. OGLE-LMC-CEP-1718: An exotic eclipsing binary system composed of two classical overtone Cepheids in a 413-day orbit
We have obtained extensive high-quality spectroscopic observations of the
OGLE-LMC-CEP-1718 eclipsing binary system in the Large Magellanic Cloud which
Soszynski et al. (2008) had identified as a candidate system for containing two
classical Cepheids in orbit. Our spectroscopic data clearly demonstrate binary
motion of the Cepheids in a 413-day eccentric orbit, rendering this eclipsing
binary system the first ever known to consist of two classical Cepheid
variables. After disentangling the four different radial velocity variations in
the system we present the orbital solution and the individual pulsational
radial velocity curves of the Cepheids. We show that both Cepheids are
extremely likely to be first overtone pulsators and determine their respective
dynamical masses, which turn out to be equal to within 1.5 %. Since the
secondary eclipse is not observed in the orbital light curve we cannot derive
the individual radii of the Cepheids, but the sum of their radii derived from
the photometry is consistent with overtone pulsation for both variables.
The existence of two equal-mass Cepheids in a binary system having different
pulsation periods (1.96 and 2.48 days, respectively) may pose an interesting
challenge to stellar evolution and pulsation theories, and a more detailed
study of this system using additional datasets should yield deeper insight
about the physics of stellar evolution of Cepheid variables. Future analysis of
the system using additional near-infrared photometry might also lead to a
better understanding of the systematic uncertainties in current Baade-Wesselink
techniques of distance determinations to Cepheid variables.Comment: accepted to be published in Ap
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