23,549 research outputs found
Spectroscopic direct detection of reflected light from extra-solar planets
At optical wavelengths, an exoplanet's signature is essentially reflected
light from the host star - several orders of magnitude fainter. Since it is
superimposed on the star spectrum its detection has been a difficult
observational challenge. However, the development of a new generation of
instruments like ESPRESSO and next generation telescopes like the E-ELT put us
in a privileged position to detect these planets' reflected light as we will
have access to extremely high signal-to-noise ratio spectra. With this work, we
propose an alternative approach for the direct detection of the reflected light
of an exoplanet. We simulated observations with ESPRESSO@VLT and HIRES@E-ELT of
several star+planet systems, encompassing 10h of the most favourable orbital
phases. To the simulated spectra we applied the Cross Correlation Function to
operate in a much higher signal-to-noise ratio domain than when compared with
the spectra. The use of the Cross-Correlation Function permitted us to recover
the simulated the planet signals at a level above 3 \sigma_{noise} significance
on several prototypical (e.g., Neptune type planet with a 2 days orbit with the
VLT at 4.4 \sigma_{noise} significance) and real planetary systems (e.g., 55
Cnc e with the E-ELT at 4.9 \sigma_{noise} significance). Even by using a more
pessimistic approach to the noise level estimation, where systematics in the
spectra increase the noise 2-3 times, the detection of the reflected light from
large close-orbit planets is possible. We have also shown that this kind of
study is currently within reach of current instruments and telescopes (e.g., 51
Peg b with the VLT at 5.2 \sigma_{noise} significance), although at the limit
of their capabilities.Comment: Accepted for Publication on MNRAS: 2013 August 29; Online Article:
http://mnras.oxfordjournals.org/content/early/2013/09/27/mnras.stt1642; 5
Figures, 11 page
Further constraints on the optical transmission spectrum of HAT-P-1b
We report on novel observations of HAT-P-1 aimed at constraining the optical
transmission spectrum of the atmosphere of its transiting Hot-Jupiter
exoplanet. Ground-based differential spectrophotometry was performed over two
transit windows using the DOLORES spectrograph at the Telescopio Nazionale
Galileo (TNG). Our measurements imply an average planet to star radius ratio
equal to =(0.11590.0005). This result is consistent
with the value obtained from recent near infrared measurements of this object
but differs from previously reported optical measurements being lower by around
4.4 exoplanet scale heights. Analyzing the data over 5 different spectral bins
600\AA wide we observed a single peaked spectrum (3.7 level)
with a blue cut-off corresponding to the blue edge of the broad absorption wing
of sodium and an increased absorption in the region in between 6180-7400\AA. We
also infer that the width of the broad absorption wings due to alkali metals is
likely narrower than the one implied by solar abundance clear atmospheric
models. We interpret the result as evidence that HAT-P-1b has a partially clear
atmosphere at optical wavelengths with a more modest contribution from an
optical absorber than previously reported.Comment: Accepted by Ap
Vorton Formation
In this paper we present the first analytic model for vorton formation. We
start by deriving the microscopic string equations of motion in Witten's
superconducting model, and show that in the relevant chiral limit these
coincide with the ones obtained from the supersonic elastic models of Carter
and Peter. We then numerically study a number of solutions of these equations
of motion and thereby suggest criteria for deciding whether a given
superconducting loop configuration can form a vorton. Finally, using a recently
developed model for the evolution of currents in superconducting strings we
conjecture, by comparison with these criteria, that string networks formed at
the GUT phase transition should produce no vortons. On the other hand, a
network formed at the electroweak scale can produce vortons accounting for up
to 6% of the critical density. Some consequences of our results are discussed.Comment: 41 pages; color figures 3-6 not included, but available from authors.
To appear in Phys. Rev.
Instalação de granitos pós-tectónicos controlada por falha Varisca profunda no Norte de Portugal
Rossby waves in rapidly rotating Bose-Einstein condensates
We predict and describe a new collective mode in rotating Bose-Einstein
condensates, which is very similar to the Rossby waves in geophysics. In the
regime of fast rotation, the Coriolis force dominates the dynamics and acts as
a restoring force for acoustic-drift waves along the condensate. We derive a
nonlinear equation that includes the effects of both the zero-point pressure
and the anharmonicity of the trap. It is shown that such waves have negative
phase speed, propagating in the opposite sense of the rotation. We discuss
different equilibrium configurations and compare with those resulting from the
Thomas-Fermi approximation.Comment: 4 pages, 2 figures (submitted to PRL
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