3,000 research outputs found
Pan-European backcasting exercise, enriched with regional perspective, and including a list of short-term policy options
This deliverable reports on the results of the third and final pan-European stakeholder meeting and secondly, on the enrichment with a Pilot Area and regional perspective. The main emphasis is on backcasting as a means to arrive at long-term strategies and short-term (policy) actions
Carbon monoxide and water vapor in the atmosphere of the non-transiting exoplanet HD 179949 b
(Abridged) In recent years, ground-based high-resolution spectroscopy has
become a powerful tool for investigating exoplanet atmospheres. It allows the
robust identification of molecular species, and it can be applied to both
transiting and non-transiting planets. Radial-velocity measurements of the star
HD 179949 indicate the presence of a giant planet companion in a close-in
orbit. Here we present the analysis of spectra of the system at 2.3 micron,
obtained at a resolution of R~100,000, during three nights of observations with
CRIRES at the VLT. We targeted the system while the exoplanet was near superior
conjunction, aiming to detect the planet's thermal spectrum and the radial
component of its orbital velocity. We detect molecular absorption from carbon
monoxide and water vapor with a combined S/N of 6.3, at a projected planet
orbital velocity of K_P = (142.8 +- 3.4) km/s, which translates into a planet
mass of M_P = (0.98 +- 0.04) Jupiter masses, and an orbital inclination of i =
(67.7 +- 4.3) degrees, using the known stellar radial velocity and stellar
mass. The detection of absorption features rather than emission means that,
despite being highly irradiated, HD 179949 b does not have an atmospheric
temperature inversion in the probed range of pressures and temperatures. Since
the host star is active (R_HK > -4.9), this is in line with the hypothesis that
stellar activity damps the onset of thermal inversion layers owing to UV flux
photo-dissociating high-altitude, optical absorbers. Finally, our analysis
favors an oxygen-rich atmosphere for HD 179949 b, although a carbon-rich planet
cannot be statistically ruled out based on these data alone.Comment: 10 pages, 9 figures. Accepted for publication in Astronomy and
Astrophysic
The GROUSE project III: Ks-band observations of the thermal emission from WASP-33b
In recent years, day-side emission from about a dozen hot Jupiters has been
detected through ground-based secondary eclipse observations in the
near-infrared. These near-infrared observations are vital for determining the
energy budgets of hot Jupiters, since they probe the planet's spectral energy
distribution near its peak. The aim of this work is to measure the Ks-band
secondary eclipse depth of WASP-33b, the first planet discovered to transit an
A-type star. This planet receives the highest level of irradiation of all
transiting planets discovered to date. Furthermore, its host-star shows
pulsations and is classified as a low-amplitude delta-Scuti. As part of our
GROUnd-based Secondary Eclipse (GROUSE) project we have obtained observations
of two separate secondary eclipses of WASP-33b in the Ks-band using the LIRIS
instrument on the William Herschel Telescope (WHT). The telescope was
significantly defocused to avoid saturation of the detector for this bright
star (K~7.5). To increase the stability and the cadence of the observations,
they were performed in staring mode. We collected a total of 5100 and 6900
frames for the first and the second night respectively, both with an average
cadence of 3.3 seconds. On the second night the eclipse is detected at the
12-sigma level, with a measured eclipse depth of 0.244+0.027-0.020 %. This
eclipse depth corresponds to a brightness temperature of 3270+115-160 K. The
measured brightness temperature on the second night is consistent with the
expected equilibrium temperature for a planet with a very low albedo and a
rapid re-radiation of the absorbed stellar light. For the other night the short
out-of-eclipse baseline prevents good corrections for the stellar pulsations
and systematic effects, which makes this dataset unreliable for eclipse depth
measurements. This demonstrates the need of getting a sufficient out-of-eclipse
baseline.Comment: 12 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
Detection of water absorption in the day side atmosphere of HD 189733 b using ground-based high-resolution spectroscopy at 3.2 microns
We report a 4.8 sigma detection of water absorption features in the day side
spectrum of the hot Jupiter HD 189733 b. We used high-resolution (R~100,000)
spectra taken at 3.2 microns with CRIRES on the VLT to trace the
radial-velocity shift of the water features in the planet's day side atmosphere
during 5 h of its 2.2 d orbit as it approached secondary eclipse. Despite
considerable telluric contamination in this wavelength regime, we detect the
signal within our uncertainties at the expected combination of systemic
velocity (Vsys=-3 +5-6 km/s) and planet orbital velocity (Kp=154 +14-10 km/s),
and determine a H2O line contrast ratio of (1.3+/-0.2)x10^-3 with respect to
the stellar continuum. We find no evidence of significant absorption or
emission from other carbon-bearing molecules, such as methane, although we do
note a marginal increase in the significance of our detection to 5.1 sigma with
the inclusion of carbon dioxide in our template spectrum. This result
demonstrates that ground-based, high-resolution spectroscopy is suited to
finding not just simple molecules like CO, but also to more complex molecules
like H2O even in highly telluric contaminated regions of the Earth's
transmission spectrum. It is a powerful tool that can be used for conducting an
immediate census of the carbon- and oxygen-bearing molecules in the atmospheres
of giant planets, and will potentially allow the formation and migration
history of these planets to be constrained by the measurement of their
atmospheric C/O ratios.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Evidence for the disintegration of KIC 12557548 b
Context. The Kepler object KIC 12557548 b is peculiar. It exhibits
transit-like features every 15.7 hours that vary in depth between 0.2% and
1.2%. Rappaport et al. (2012) explain the observations in terms of a
disintegrating, rocky planet that has a trailing cloud of dust created and
constantly replenished by thermal surface erosion. The variability of the
transit depth is then a consequence of changes in the cloud optical depth.
Aims. We aim to validate the disintegrating-planet scenario by modeling the
detailed shape of the observed light curve, and thereby constrain the cloud
particle properties to better understand the nature of this intriguing object.
Methods. We analysed the six publicly-available quarters of raw Kepler data,
phase-folded the light curve and fitted it to a model for the trailing dust
cloud. Constraints on the particle properties were investigated with a
light-scattering code. Results. The light curve exhibits clear signatures of
light scattering and absorption by dust, including a brightening in flux just
before ingress correlated with the transit depth and explained by forward
scattering, and an asymmetry in the transit light curve shape, which is easily
reproduced by an exponentially decaying distribution of optically thin dust,
with a typical grain size of 0.1 micron. Conclusions. Our quantitative analysis
supports the hypothesis that the transit signal of KIC 12557548 b is due to a
variable cloud of dust, most likely originating from a disintegrating object.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysic
There is no unmet requirement of optical coherence for continuous-variable quantum teleportation
It has been argued [T. Rudolph and B.C. Sanders, Phys. Rev. Lett. 87, 077903
(2001)] that continuous-variable quantum teleportation at optical frequencies
has not been achieved because the source used (a laser) was not `truly
coherent'. Here I show that `true coherence' is always illusory, as the concept
of absolute time on a scale beyond direct human experience is meaningless. A
laser is as good a clock as any other, even in principle, and this objection to
teleportation experiments is baseless.Comment: 6 pages, no figures, no equations, to be published in Journal of
Modern Optics. This is a long version of quant-ph/0104004. I have not
replaced that paper with this one because some authors have referenced that
one approvingly who may feel differently about doing so to this versio
Quantum repeaters and quantum key distribution: analysis of secret key rates
We analyze various prominent quantum repeater protocols in the context of
long-distance quantum key distribution. These protocols are the original
quantum repeater proposal by Briegel, D\"ur, Cirac and Zoller, the so-called
hybrid quantum repeater using optical coherent states dispersively interacting
with atomic spin qubits, and the Duan-Lukin-Cirac-Zoller-type repeater using
atomic ensembles together with linear optics and, in its most recent extension,
heralded qubit amplifiers. For our analysis, we investigate the most important
experimental parameters of every repeater component and find their minimally
required values for obtaining a nonzero secret key. Additionally, we examine in
detail the impact of device imperfections on the final secret key rate and on
the optimal number of rounds of distillation when the entangled states are
purified right after their initial distribution.Comment: Published versio
Geometric derivation of the quantum speed limit
The Mandelstam-Tamm and Margolus-Levitin inequalities play an important role
in the study of quantum mechanical processes in Nature, since they provide
general limits on the speed of dynamical evolution. However, to date there has
been only one derivation of the Margolus-Levitin inequality. In this paper,
alternative geometric derivations for both inequalities are obtained from the
statistical distance between quantum states. The inequalities are shown to hold
for unitary evolution of pure and mixed states, and a counterexample to the
inequalities is given for evolution described by completely positive
trace-preserving maps. The counterexample shows that there is no quantum speed
limit for non-unitary evolution.Comment: 8 pages, 1 figure
Search for an exosphere in sodium and calcium in the transmission spectrum of exoplanet 55 Cancri e
[Abridged] The aim of this work is to search for an absorption signal from
exospheric sodium (Na) and singly ionized calcium (Ca) in the optical
transmission spectrum of the hot rocky super-Earth 55 Cancri e. Although the
current best-fitting models to the planet mass and radius require a possible
atmospheric component, uncertainties in the radius exist, making it possible
that 55 Cancri e could be a hot rocky planet without an atmosphere. High
resolution (R110000) time-series spectra of five transits of 55 Cancri e,
obtained with three different telescopes (UVES/VLT, HARPS/ESO 3.6m &
HARPS-N/TNG) were analysed. Targeting the sodium D lines and the calcium H and
K lines, the potential planet exospheric signal was filtered out from the much
stronger stellar and telluric signals, making use of the change of the radial
component of the orbital velocity of the planet over the transit from -57 to
+57 km/sec. Combining all five transit data sets, we detect a signal
potentially associated with sodium in the planet exosphere at a statistical
significance level of 3. Combining the four HARPS transits that cover
the calcium H and K lines, we also find a potential signal from ionized calcium
(4.1 ). Interestingly, this latter signal originates from just one of
the transit measurements - with a 4.9 detection at this epoch.
Unfortunately, due to the low significance of the measured sodium signal and
the potentially variable Ca signal, we estimate the p-values of these
signals to be too high (corresponding to <4) to claim unambiguous
exospheric detections. By comparing the observed signals with artificial
signals injected early in the analysis, the absorption by Na and Ca are
estimated to be at a level of approximately 2.3 and 7.0 respectively, relative to the stellar spectrum.Comment: 15 pages, 8 figures, submission updated after English language
editing, submission updated to correct a mistaken cross-reference noticed in
A&A proo
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