835 research outputs found
Vulnerabilities in first-generation RFID-enabled credit cards
Credit cards ; Radio frequency identification systems
The polarization of the planet-hosting WASP-18 system
We report observations of the linear polarization of the WASP-18 system,
which harbors a very massive ( approx 10 M_J) planet orbiting very close to its
star with an orbital period of 0.94 days. We find the WASP-18 system is
polarized at about 200 parts-per-million (ppm), likely from the interstellar
medium predominantly, with no strong evidence for phase dependent modulation
from reflected light from the planet. We set an upper limit of 40 ppm (99%
confidence level) on the amplitude of a reflected polarized light planetary
signal. We compare the results with models for a number of processes that may
produce polarized light in a planetary system to determine if we can rule out
any phenomena with this limit. Models of reflected light from thick clouds can
approach or exceed this limit, but such clouds are unlikely at the high
temperature of the WASP-18b atmosphere. Additionally, we model the expected
polarization resulting from the transit of the planet across the star and find
this has an amplitude of about 1.6 ppm, which is well below our detection
limits. We also model the polarization due to the tidal distortion of the star
by the massive planet and find this is also too small to be measured currently.Comment: 23 pages, 10 Figures, 6 Tables, Accepted to A
Phase-locked polarization by photospheric reflection in the semidetached eclipsing binary Sco
We report the detection of phase-locked polarization in the bright
(=2.98-3.24) semidetached eclipsing binary Sco (HD 151890). The
phenomenon was observed in multiple photometric bands using two different
HIPPI-class (HIgh Precision Polarimetric Instrument)polarimeters with
telescopes ranging in size from 35-cm to 3.9-m. The peak-to-trough amplitude of
the polarization is wavelength dependent and large, 700 parts-per-million
in green light, and is easily seen with even the smallest telescope. We fit the
polarization phase curve with a SYNSPEC/VLIDORT polarized radiative transfer
model and a Wilson-Devinney geometric formalism, which we describe in detail.
Light from each star reflected by the photosphere of the other, together with a
much smaller contribution from tidal distortion and eclipse effects, wholly
accounts for the polarization amplitude. In the past polarization in
semidetached binaries has been attributed mostly to scattering from
extra-stellar gas. Our new interpretation facilitates determining masses of
such stars in non-eclipsing systems.Comment: 16 pages, 8 figures, 8 tables. Accepted to MNRA
The rotation of alpha Oph investigated using polarimetry
Recently we have demonstrated that high-precision polarization observations
can detect the polarization resulting from the rotational distortion of a
rapidly rotating B-type star. Here we investigate the extension of this
approach to an A-type star. Linear-polarization observations of Oph
(A5IV) have been obtained over wavelengths from 400 to 750 nm. They show the
wavelength dependence expected for a rapidly-rotating star combined with a
contribution from interstellar polarization. We model the observations by
fitting rotating-star polarization models and adding additional constraints
including a measured . However, we cannot fully separate the
effects of rotation rate and inclination, leaving a range of possible
solutions. We determine a rotation rate between
0.83 and 0.98 and an axial inclination i > 60 deg. The rotation-axis position
angle is found to be 142 4 deg, differing by 16 deg from a value obtained
by interferometry. This might be due to precession of the rotation axis due to
interaction with the binary companion. Other parameters resulting from the
analysis include a polar temperature Tp = 8725 175 K, polar gravity
(dex cgs), and polar radius Rsun. Comparison with rotating-star evolutionary models indicates that
Oph is in the later half of its main-sequence evolution and must have
had an initial of 0.8 or greater. The interstellar polarization has a
maximum value at a wavelength () of nm,
consistent with values found for other nearby stars.Comment: 14 pages, 11 figures, 5 tables, Accepted in MNRA
A high-sensitivity polarimeter using a ferro-electric liquid crystal modulator
We describe the HIgh Precision Polarimetric Instrument (HIPPI), a polarimeter built at UNSW (The University of New South Wales) Australia and used on the Anglo-Australian Telescope (AAT). HIPPI is an aperture polarimeter using a ferro-electric liquid crystal modulator. HIPPI measures the linear polarization of starlight with a sensitivity in fractional polarization of ∼4 × 10−6 on low-polarization objects and a precision of better than 0.01 per cent on highly polarized stars. The detectors have a high dynamic range allowing observations of the brightest stars in the sky as well as much fainter objects. The telescope polarization of the AAT is found to be 48 ± 5 × 10−6 in the g′ bandPeer reviewedFinal Accepted Versio
The structure of epitaxial V2O3 films and their surfaces : a medium energy ion scattering study
Medium energy ion scattering, using 100 keV H+ incident ions, has been used to investigate the growth of epitaxial films, up to thicknesses of ~200 Å, of V2O3 on both Pd(111) and Au(111). Scattered-ion energy spectra provide a measure of the average film thickness and the variations in this thickness, and show that, with suitable annealing, the crystalline quality is good. Plots of the scattering yield as a function of scattering angle, so-called blocking curves, have been measured for two different incidence directions and have been used to determine the surface structure. Specifically, scattering simulations for a range of different model structures show poor agreement with experiment for half-metal (….V’O3V) and vanadyl (….V’O3V=O) terminations, with and without surface interlayer relaxations. However, good agreement with experiment is found for the modified oxygen-termination structure, first proposed by Kresse et al., in which a subsurface V half-metal layer is moved up into the outermost V buckled metal layer to produce a VO2 overlayer on the underlying V2O3, with an associated layer structure of ….O3VV’’V’O3
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