2,001 research outputs found
A phenomenological representation of iridescent colors in butterfly wings
The representation of the color of butterflies has always
been a challenge to artis
ts, whatever the medium
involved. These colors are highly complex to reproduce, even with the use of computer generated images. This
article introduces a new algorithm developed to simulate and generate the iridescent colors that are found on the
wings of particular butterflies. The model presented here
is based on the scientific description of the butterfly
Morpho menelaus
. Wing color is determined by interference, diffraction, absorption and reflection of light on
microscopic wing's structures. The color varies dependi
ng on a combination of the following parameters: view
angle, incidence and characteristics of the light source, and surrounding medium. This algorithm which tends to
real-time imaging required by computer graphics artis
ts still renders images with a fairly high degree of
accuracy
The Brown-dwarf Atmosphere Monitoring (BAM) Project II: Multi-epoch monitoring of extremely cool brown dwarfs
With the discovery of Y dwarfs by the WISE mission, the population of field
brown dwarfs now extends to objects with temperatures comparable to those of
Solar System planets. To investigate the atmospheres of these newly identified
brown dwarfs, we have conducted a pilot study monitoring an initial sample of
three late T-dwarfs (T6.5, T8 and T8.5) and one Y-dwarf (Y0) for infrared
photometric variability at multiple epochs. With J-band imaging, each target
was observed for a period of 1.0h to 4.5h per epoch, which covers a significant
fraction of the expected rotational period. These measurements represent the
first photometric monitoring for these targets. For three of the four targets
(2M1047, Ross 458C and WISE0458), multi-epoch monitoring was performed, with
the time span between epochs ranging from a few hours to ~2 years. During the
first epoch, the T8.5 target WISE0458 exhibited variations with a remarkable
min-to-max amplitude of 13%, while the second epoch light curve taken ~2 years
later did not note any variability to a 3% upper limit. With an effective
temperature of ~600 K, WISE0458 is the coldest variable brown dwarf published
to-date, and combined with its high and variable amplitude makes it a
fascinating target for detailed follow-up. The three remaining targets showed
no significant variations, with a photometric precision between 0.8% and 20.0%,
depending on the target brightness. Combining the new results with previous
multi-epoch observations of brown dwarfs with spectral types of T5 or later,
the currently identified variables have locations on the colour-colour diagram
better matched by theoretical models incorporating cloud opacities rather than
cloud-free atmospheres. This preliminary result requires further study to
determine if there is a definitive link between variability among late-T dwarfs
and their location on the colour-colour diagram.Comment: 9 pages, 6 figures, 3 tables, accepted for publication in MNRA
The `666' collaboration on OGLE transits: I. Accurate radius of the planets OGLE-TR-10b and OGLE-TR-56b with VLT deconvolution photometry
Transiting planets are essential to study the structure and evolution of
extra-solar planets. For that purpose, it is important to measure precisely the
radius of these planets. Here we report new high-accuracy photometry of the
transits of OGLE-TR-10 and OGLE-TR-56 with VLT/FORS1. One transit of each
object was covered in Bessel V and R filters, and treated with the
deconvolution-based photometry algorithm DECPHOT, to ensure accurate
millimagnitude light curves. Together with earlier spectroscopic measurements,
the data imply a radius of 1.22 +0.12-0.07 R_J for OGLE-TR-10b and 1.30 +- 0.05
R_J for OGLE-TR-56b. A re-analysis of the original OGLE photometry resolves an
earlier discrepancy about the radius of OGLE-TR-10. The transit of OGLE-TR-56
is almost grazing, so that small systematics in the photometry can cause large
changes in the derived radius. Our study confirms both planets as inflated hot
Jupiters, with large radii comparable to that of HD 209458 and at least two
other recently discovered transiting gas giants.Comment: Fundamental updates compared to previous version; accepted for
publication in Astronomy & Astrophysic
The spin-orbit angle of the transiting hot jupiter CoRoT-1b
We measure the angle between the planetary orbit and the stellar rotation
axis in the transiting planetary system CoRoT-1, with new HIRES/Keck and
FORS/VLT high-accuracy photometry. The data indicate a highly tilted system,
with a projected spin-orbit angle lambda = 77 +- 11 degrees. Systematic
uncertainties in the radial velocity data could cause the actual errors to be
larger by an unknown amount, and this result needs to be confirmed with further
high-accuracy spectroscopic transit measurements.
Spin-orbit alignment has now been measured in a dozen extra-solar planetary
systems, and several show strong misalignment. The first three misaligned
planets were all much more massive than Jupiter and followed eccentric orbits.
CoRoT-1, however, is a jovian-mass close-in planet on a circular orbit. If its
strong misalignment is confirmed, it would break this pattern. The high
occurence of misaligned systems for several types of planets and orbits favours
planet-planet scattering as a mechanism to bring gas giants on very close
orbits.Comment: to appear in in MNRAS letters [5 pages
Wall effects on granular heap stability
We investigate the effects of lateral walls on the angle of movement and on
the angle of repose of a granular pile. Our experimental results for beads
immersed in water are similar to previous results obtained in air and to recent
numerical simulations. All of these results, showing an increase of pile angles
with a decreasing gap width, are explained by a model based on the redirection
of stresses through the granular media. Two regimes are observed depending on
the bead diameter. For large beads, the range of wall effects corresponds to a
constant number of beads whereas it corresponds to a constant characteristic
length for small beads as they aggregate via van der Waals forces
The transiting planet OGLE-TR-132b revisited with new spectroscopy and deconvolution photometry
OGLE-TR-132b transits a very metal-rich F dwarf about 2000 pc from the Sun,
in the Galactic disc towards Carina. It orbits very close to its host star (a =
0.03 AU) and has an equilibrium temperature of nearly 2000 K. Using
rapid-cadence transit photometry from the FORS2 camera on the VLT and SUSI2 on
the NTT, and high-resolution spectroscopy with UVES on the VLT, we refine the
shape of the transit light curve and the parameters of the system. In
particular, we improve the planetary radius estimate, R=1.18 +- 0.07 R_J and
provide very precise ephemeris, T_tr=2453142.59123 +- 0.0003 BJD and P=1.689868
+- 0.000003 days. The obtained planetary mass is 1.14 +- 0.12 M_J. Our results
give a slightly smaller and lighter star, and bigger planet, than previous
values. As the VLT/FORS2 light curve obtained in this analysis with the
deconvolution photometry algorithm DECPHOT shows a transit depth in
disagreement with the one obtained by a previous study using the same data, we
analyze them with two other reduction methods (aperture and image subtraction).
The light curves obtained with the three methods are in good agreement, though
deconvolution-based photometry is significantly more precise. It appears from
these results that the smaller transit depth obtained in the previous study was
due to a normalisation problem inherent to the reduction procedure used.Comment: 7 pages, 6 figures. Accepted for publication in A&
The Rotation Period of the Planet-Hosting Star HD 189733
We present synoptic optical photometry of HD 189733, the chromospherically
active parent star of one of the most intensively studied exoplanets. We have
significantly extended the timespan of our previously reported observations and
refined the estimate of the stellar rotation period by more than an order of
magnitude: days. We derive a lower limit on the
inclination of the stellar rotation axis of 56\arcdeg (with 95% confidence),
corroborating earlier evidence that the stellar spin axis and planetary orbital
axis are well aligned.Comment: To appear in A
Blue Dots Team Transits Working Group Review
Transiting planet systems offer an unique opportunity to observationally
constrain proposed models of the interiors (radius, composition) and
atmospheres (chemistry, dynamics) of extrasolar planets. The spectacular
successes of ground-based transit surveys (more than 60 transiting systems
known to-date) and the host of multi-wavelength, spectro-photometric follow-up
studies, carried out in particular by HST and Spitzer, have paved the way to
the next generation of transit search projects, which are currently ongoing
(CoRoT, Kepler), or planned. The possibility of detecting and characterizing
transiting Earth-sized planets in the habitable zone of their parent stars
appears tantalizingly close. In this contribution we briefly review the power
of the transit technique for characterization of extrasolar planets, summarize
the state of the art of both ground-based and space-borne transit search
programs, and illustrate how the science of planetary transits fits within the
Blue Dots perspective.Comment: 9 pages, 3 figures, to be published in the proceedings (ASP Conf.
Ser.) of the "Pathways Towards Habitable Planets" conference, held in
Barcelona (14-18 Sep 2009
Intense field stabilization in circular polarization: 3D time-dependent dynamics
We investigate the stabilization of a hydrogen atom in circularly polarized
laser fields. We use a time-dependent, fully three dimensional approach to
study the quantum dynamics of the hydrogen atom subject to high intensity,
short wavelength laser pulses. We find enhanced survival probability as the
field is increased under fixed envelope conditions. We also confirm wavepacket
dynamics seen in prior time-dependent computations restricted to two
dimensions.Comment: 4 pages, 3 figures, submitte
Hyperspherical partial wave calculation for double photoionization of the helium atom at 20 eV excess energy
Hyperspherical partial wave approach has been applied here in the study of
double photoionization of the helium atom for equal energy sharing geometry at
20 eV excess energy. Calculations have been done both in length and velocity
gauges and are found to agree with each other, with the CCC results and with
experiments and exhibit some advantages of the corresponding three particle
wave function over other wave functions in use.Comment: 11 pages, 1 figure, submitted to J. Phys B: At. Mol. Opt. Phys; v2 -
revised considerably, rewritten using ioplatex clas
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