532 research outputs found
Absolute dimensions of solar-type eclipsing binaries. EF Aquarii: a G0 test for stellar evolution models
Recent studies have shown that stellar chromospheric activity, and its effect
on convective energy transport in the envelope, is most likely the cause of
significant radius and temperature discrepancies between theoretical evolution
models and observations. We aim to determine absolute dimensions and abundances
for the solar-type detached eclipsing binary EF Aqr, and to perform a detailed
comparison with results from recent stellar evolutionary models. uvby-beta
standard photometry was obtained with the Stromgren Automatic Telescope. The
broadening function formalism was applied on spectra observed with HERMES at
the Mercator telescope in La Palma, to obtain radial velocity curves. Masses
and radii with a precision of 0.6% and 1.0% respectively have been established
for both components of EF Aqr. The active 0.956 M_sol secondary shows star
spots and strong Ca II H and K emission lines. The 1.224 M_sol primary shows
signs of activity as well, but at a lower level. An [Fe/H] abundance of
0.00+-0.10 is derived with similar abundances for Si, Ca, Sc, Ti, V, Cr, Co,
and Ni. Solar calibrated evolutionary models such as Yonsei-Yale,
Victoria-Regina and BaSTI isochrones and evolutionary tracks are unable to
reproduce EF Aqr, especially for the secondary, which is 9% larger and 400 K
cooler than predicted. Models adopting significantly lower mixing length
parameters l/H_p remove these discrepancies, as seen in other solar type
binaries. For the observed metallicity, Granada models with a mixing length of
l/H_p=1.30 (primary) and 1.05 (secondary) reproduce both components at a common
age of 1.5+-0.6 Gyr. Observations of EF Aqr suggests that magnetic activity,
and its effect on envelope convection, is likely to be the cause of
discrepancies in both radius and temperature, which can be removed by adjusting
the mixing length parameter of the models downwards.Comment: 11 pages, 8 figures, accepted for publication by A&
Observation of Goos-H\"{a}nchen shifts in metallic reflection
We report the first observation of the Goos-Hnchen
shift of a light beam incident on a metal surface. This phenomenon is
particularly interesting because the Goos-Hnchen shift
for polarized light in metals is negative and much bigger than the positive
shift for polarized light. The experimental result for the measured shifts
as a function of the angle of incidence is in excellent agreement with
theoretical predictions. In an energy-flux interpretation, our measurement
shows the existence of a backward energy flow at the bare metal surface when
this is excited by a polarized beam of light.Comment: The parer was published on Optics Express. The new version is
modified according to the reviewers suggestion
CNOT and Bell-state analysis in the weak-coupling cavity QED regime
We propose an interface between the spin of a photon and the spin of an
electron confined in a quantum dot embedded in a microcavity operating in the
weak coupling regime. This interface, based on spin selective photon reflection
from the cavity, can be used to construct a CNOT gate, a multi-photon entangler
and a photonic Bell-state analyzer. Finally, we analyze experimental
feasibility, concluding that the schemes can be implemented with current
technology.Comment: 4 pages, 2 figure
A long trail behind the planetary nebula HFG1 (PK 136+05) and its precataclysmic binary central star V664 Cas
A deep wide-field image in the light of the Halpha+[N II] emission lines, of
the planetary nebula HFG1 which surrounds the precataclysmic binary system V664
Cas, has revealed a tail of emission at least 20' long, at a position angle of
316deg. Evidence is presented which suggests that this is an ~10^5 y old trail
of shocked material, left behind V664 Cas as it ejects matter whilst ploughing
through its local interstellar media at anywhere between 29 and 59 km/s
depending on its distance from the Sun.Comment: 3 pages, 1 figure, accepted for publication in MNRA
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