237 research outputs found
Estimations of orbital parameters of exoplanets from transit photometry by using dynamical constraints
The probability of the detection of Earth-like exoplanets may increase in the
near future after the launch of the space missions using the transit photometry
as observation method. By using this technique only the semi-major axis of the
detected planet can be determined, and there will be no information on the
upper limit of its orbital eccentricity. However, the orbital eccentricity is a
very important parameter, not only from a dynamical point of view, since it
gives also information on the climate and the habitability of the Earth-like
planets. In this paper a possible procedure is suggested for confining the
eccentricity of an exoplanet discovered by transit photometry if an already
known giant planet orbits also in the system.Comment: 16 pages, 10 figures, accepted for Cel. Mech. Dyn. Astro
Eccentricities of Planets in Binary Systems
The most puzzling property of the extrasolar planets discovered by recent
radial velocity surveys is their high orbital eccentricities, which are very
difficult to explain within our current theoretical paradigm for planet
formation. Current data reveal that at least 25% of these planets, including
some with particularly high eccentricities, are orbiting a component of a
binary star system. The presence of a distant companion can cause significant
secular perturbations in the orbit of a planet. At high relative inclinations,
large-amplitude, periodic eccentricity perturbations can occur. These are known
as "Kozai cycles" and their amplitude is purely dependent on the relative
orbital inclination. Assuming that every planet host star also has a (possibly
unseen, e.g., substellar) distant companion, with reasonable distributions of
orbital parameters and masses, we determine the resulting eccentricity
distribution of planets and compare it to observations? We find that
perturbations from a binary companion always appear to produce an excess of
planets with both very high (e>0.6) and very low (e<0.1) eccentricities. The
paucity of near-circular orbits in the observed sample implies that at least
one additional mechanism must be increasing eccentricities. On the other hand,
the overproduction of very high eccentricities observed in our models could be
combined with plausible circularization mechanisms (e.g., friction from
residual gas) to create more planets with intermediate eccentricities
(e=0.1-0.6).Comment: 8 pages, to appear in "Close Binaries in the 21st Century: New
Opportunities and Challenges", ed. A. Gimenez et al. (Springer
Dynamical description of quantum computing: generic nonlocality of quantum noise
We develop dynamical non-Markovian description of quantum computing in weak
coupling limit, in lowest order approximation. We show that long range memory
of quantum reservoir produces strong interrelation between structure of noise
and quantum algorithm, implying nonlocal attacks of noise. We then argue that
the quantum error correction method fails to protect quantum computation
against electromagnetic or phonon vacuum which exhibit memory. This
shows that the implicit assumption of quantum error correction theory --
independence of noise and self-dynamics -- fails in long time regimes. We also
use our approach to present {\it pure} decoherence and decoherence accompanied
by dissipation in terms of spectral density of reservoir. The so-called {\it
dynamical decoupling} method is discussed in this context. Finally, we propose
{\it minimal decoherence model}, in which the only source of decoherence is
vacuum. We optimize fidelity of quantum information processing under the
trade-off between speed of gate and strength of decoherence.Comment: 12 pages, minor corrections, softened interpretation of the result
Vegetation's Red Edge: A Possible Spectroscopic Biosignature of Extraterrestrial Plants
Earth's deciduous plants have a sharp order-of-magnitude increase in leaf
reflectance between approximately 700 and 750 nm wavelength. This strong
reflectance of Earth's vegetation suggests that surface biosignatures with
sharp spectral features might be detectable in the spectrum of scattered light
from a spatially unresolved extrasolar terrestrial planet. We assess the
potential of Earth's step-function-like spectroscopic feature, referred to as
the "red edge", as a tool for astrobiology. We review the basic characteristics
and physical origin of the red edge and summarize its use in astronomy: early
spectroscopic efforts to search for vegetation on Mars and recent reports of
detection of the red edge in the spectrum of Earthshine (i.e., the spatially
integrated scattered light spectrum of Earth). We present Earthshine
observations from Apache Point Observatory to emphasize that time variability
is key to detecting weak surface biosignatures such as the vegetation red edge.
We briefly discuss the evolutionary advantages of vegetation's red edge
reflectance, and speculate that while extraterrestrial "light harvesting
organisms" have no compelling reason to display the exact same red edge feature
as terrestrial vegetation, they might have similar spectroscopic features at
different wavelengths than terrestrial vegetation. This implies that future
terrestrial-planet-characterizing space missions should obtain data that allow
time-varying, sharp spectral features at unknown wavelengths to be identified.
We caution that some mineral reflectance edges are similar in slope and
strength to vegetation's red edge (albeit at different wavelengths); if an
extrasolar planet reflectance edge is detected care must be taken with its
interpretation.Comment: 19 pages, 6 figures, to appear in Astrobiolog
Super-Earths: A New Class of Planetary Bodies
Super-Earths, a class of planetary bodies with masses ranging from a few
Earth-masses to slightly smaller than Uranus, have recently found a special
place in the exoplanetary science. Being slightly larger than a typical
terrestrial planet, super-Earths may have physical and dynamical
characteristics similar to those of Earth whereas unlike terrestrial planets,
they are relatively easier to detect. Because of their sizes, super-Earths can
maintain moderate atmospheres and possibly dynamic interiors with plate
tectonics. They also seem to be more common around low-mass stars where the
habitable zone is in closer distances. This article presents a review of the
current state of research on super-Earths, and discusses the models of the
formation, dynamical evolution, and possible habitability of these objects.
Given the recent advances in detection techniques, the detectability of
super-Earths is also discussed, and a review of the prospects of their
detection in the habitable zones of low-mass stars is presented.Comment: A (non-technical) review of the literature on the current state
ofresearch on super-Earths. The topics include observation, formation,
dynamical evolution, habitability, composition, interior dynamics, magnetic
field, atmosphere, and propsect of detection. The article has 44 pages, 27
figures, and 203 references. It has been accepted for publication in the
journal Contemporary Physics (2011
The distribution of transit durations for Kepler planet candidates and implications for their orbital eccentricities
‘In these times, during the rise in the popularity of institutional repositories, the Society does not forbid authors from depositing their work in such repositories. However, the AAS regards the deposit of scholarly work in such repositories to be a decision of the individual scholar, as long as the individual's actions respect the diligence of the journals and their reviewers.’ Original article can be found at : http://iopscience.iop.org/ Copyright American Astronomical SocietyDoppler planet searches have discovered that giant planets follow orbits with a wide range of orbital eccentricities, revolutionizing theories of planet formation. The discovery of hundreds of exoplanet candidates by NASA's Kepler mission enables astronomers to characterize the eccentricity distribution of small exoplanets. Measuring the eccentricity of individual planets is only practical in favorable cases that are amenable to complementary techniques (e.g., radial velocities, transit timing variations, occultation photometry). Yet even in the absence of individual eccentricities, it is possible to study the distribution of eccentricities based on the distribution of transit durations (relative to the maximum transit duration for a circular orbit). We analyze the transit duration distribution of Kepler planet candidates. We find that for host stars with T > 5100 K we cannot invert this to infer the eccentricity distribution at this time due to uncertainties and possible systematics in the host star densities. With this limitation in mind, we compare the observed transit duration distribution with models to rule out extreme distributions. If we assume a Rayleigh eccentricity distribution for Kepler planet candidates, then we find best fits with a mean eccentricity of 0.1-0.25 for host stars with T ≤ 5100 K. We compare the transit duration distribution for different subsets of Kepler planet candidates and discuss tentative trends with planetary radius and multiplicity. High-precision spectroscopic follow-up observations for a large sample of host stars will be required to confirm which trends are real and which are the results of systematic errors in stellar radii. Finally, we identify planet candidates that must be eccentric or have a significantly underestimated stellar radius.Peer reviewedFinal Accepted Versio
Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation
The fully nonlinear response of a many-level tunneling system to a strong
alternating field of high frequency is studied in terms of the
Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent
tunneling current is calculated exactly and its resonance structure is
elucidated. In particular, it is shown that under certain reasonable conditions
on the physical parameters, the Fourier component is sharply peaked at
, where is the spacing between
two levels. This frequency multiplication results from the highly nonlinear
process of photon absorption (or emission) by the tunneling system. It is
also conjectured that this effect (which so far is studied mainly in the
context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from
[email protected], submitted to Phys.Rev.
Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star
A search of the time-series photometry from NASA's Kepler spacecraft reveals
a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626
with a period of 290 days. The characteristics of the host star are well
constrained by high-resolution spectroscopy combined with an asteroseismic
analysis of the Kepler photometry, leading to an estimated mass and radius of
0.970 +/- 0.060 MSun and 0.979 +/- 0.020 RSun. The depth of 492 +/- 10ppm for
the three observed transits yields a radius of 2.38 +/- 0.13 REarth for the
planet. The system passes a battery of tests for false positives, including
reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A
full BLENDER analysis provides further validation of the planet interpretation
by showing that contamination of the target by an eclipsing system would rarely
mimic the observed shape of the transits. The final validation of the planet is
provided by 16 radial velocities obtained with HIRES on Keck 1 over a one year
span. Although the velocities do not lead to a reliable orbit and mass
determination, they are able to constrain the mass to a 3{\sigma} upper limit
of 124 MEarth, safely in the regime of planetary masses, thus earning the
designation Kepler-22b. The radiative equilibrium temperature is 262K for a
planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is
a rocky planet, it is the first confirmed planet with a measured radius to
orbit in the Habitable Zone of any star other than the Sun.Comment: Accepted to Ap
Quantum Fluctuation Relations for the Lindblad Master Equation
An open quantum system interacting with its environment can be modeled under
suitable assumptions as a Markov process, described by a Lindblad master
equation. In this work, we derive a general set of fluctuation relations for
systems governed by a Lindblad equation. These identities provide quantum
versions of Jarzynski-Hatano-Sasa and Crooks relations. In the linear response
regime, these fluctuation relations yield a fluctuation-dissipation theorem
(FDT) valid for a stationary state arbitrarily far from equilibrium. For a
closed system, this FDT reduces to the celebrated Callen-Welton-Kubo formula
On the reliability of a simple method for scoring phenotypes to estimate heritability: A case study with pupal color in Heliconius erato phyllis, Fabricius 1775 (Lepidoptera, Nymphalidae)
In this paper, two methods for assessing the degree of melanization of pupal exuviae from the butterfly Heliconius erato phyllis, Fabricius 1775 (Lepidoptera, Nymphalidae, Heliconiini) are compared. In the first method, which was qualitative, the exuviae were classified by scoring the degree of melanization, whereas in the second method, which was quantitative, the exuviae were classified by optical density followed by analysis with appropriate software. The heritability (h2) of the degree of melanization was estimated by regression and analysis of variance. The estimates of h 2 were similar with both methods, indicating that the qualitative method could be particularly suitable for field work. The low estimates obtained for heritability may have resulted from the small sample size (n = 7-18 broods, including the parents) or from the allocation-priority hypothesis in which pupal color would be a lower priority trait compared to morphological traits and adequate larval development
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