107 research outputs found
Retrieving Temperatures and Abundances of Exoplanet Atmospheres with High-Resolution Cross-Correlation Spectroscopy
Hi-resolution spectroscopy (R > 25,000) has recently emerged as one of the
leading methods to detect atomic and molecular species in the atmospheres of
exoplanets. However, it has so far been lacking in a robust method to extract
quantitative constraints on temperature structure and molecular/atomic
abundances. In this work we present a novel Bayesian atmospheric retrieval
framework applicable to high resolution cross-correlation spectroscopy (HRCCS)
that relies upon the cross-correlation between data and models to extract the
planetary spectral signal. We successfully test the framework on simulated data
and show that it can correctly determine Bayesian credibility intervals on
atmospheric temperatures and abundances allowing for a quantitative exploration
of the inherent degeneracies. Furthermore, our new framework permits us to
trivially combine and explore the synergies between HRCCS and low-resolution
spectroscopy (LRS) to provide maximal leverage on the information contained
within each. This framework also allows us to quantitatively assess the impact
of molecular line opacities at high resolution. We apply the framework to VLT
CRIRES K-band spectra of HD 209458 b and HD 189733 b and retrieve abundant
carbon monoxide but sub-solar abundances for water, largely invariant under
different model assumptions. This confirms previous analysis of these datasets,
but is possibly at odds with detections of water at different wavelengths and
spectral resolutions. The framework presented here is the first step towards a
true synergy between space observatories and ground-based hi-resolution
observations.Comment: Accepted Version (01/16/19
Evidence against a strong thermal inversion in HD 209458 b from high-dispersion spectroscopy
Broadband secondary-eclipse measurements of hot Jupiters have indicated the
existence of atmospheric thermal inversions, but their presence is difficult to
determine from broadband measurements because of degeneracies between molecular
abundances and temperature structure. We apply high-resolution (R = 100 000)
infrared spectroscopy to probe the temperature-pressure profile of HD 209458 b.
This bright, transiting hot-Jupiter has long been considered the gold standard
for a hot Jupiter with an inversion layer, but this has been challenged in
recent publications. We observed the thermal dayside emission of HD 209458 b
with CRIRES / VLT during three nights, targeting the carbon monoxide band at
2.3 microns. Thermal inversions give rise to emission features, which means
that detecting emission lines in the planetary spectrum, as opposed to
absorption lines, would be direct evidence of a region in which the temperature
increases with altitude.
We do not detect any significant absorption or emission of CO in the dayside
spectrum of HD 209458 b, although cross-correlation with template spectra
either with CO absorption lines or with weak emission at the core of the lines
show a low-significance correlation signal with a signal-to-noise ratio of 3 -
3.5. Models with strong CO emission lines show a weak anti-correlation with
similar or lower significance levels. Furthermore, we found no evidence of
absorption or emission from H2O at these wavelengths.
The non-detection of CO in the dayside spectrum of HD 209458 b is interesting
in light of a previous CO detection in the transmission spectrum. That there is
no signal indicates that HD 209458 b either has a nearly isothermal atmosphere
or that the signal is heavily muted. Assuming a clear atmosphere, we can rule
out a full-disc dayside inversion layer in the pressure range 1 bar to 1 mbar.Comment: 11 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
Finding extraterrestrial life using ground-based high-resolution spectroscopy
Exoplanet observations promise one day to unveil the presence of
extraterrestrial life. Atmospheric compounds in strong chemical disequilibrium
would point to large-scale biological activity just as oxygen and methane do in
the Earth's atmosphere. The cancellation of both the Terrestrial Planet Finder
and Darwin missions means that it is unlikely that a dedicated space telescope
to search for biomarker gases in exoplanet atmospheres will be launched within
the next 25 years. Here we show that ground-based telescopes provide a strong
alternative for finding biomarkers in exoplanet atmospheres through transit
observations. Recent results on hot Jupiters show the enormous potential of
high-dispersion spectroscopy to separate the extraterrestrial and telluric
signals making use of the Doppler shift of the planet. The transmission signal
of oxygen from an Earth-twin orbiting a small red dwarf star is only a factor 3
smaller than that of carbon monoxide recently detected in the hot Jupiter tau
Bootis b, albeit such a star will be orders of magnitude fainter. We show that
if Earth-like planets are common, the planned extremely large telescopes can
detect oxygen within a few dozen transits. Ultimately, large arrays of
dedicated flux collector telescopes equipped with high-dispersion spectrographs
can provide the large collecting area needed to perform a statistical study of
life-bearing planets in the solar neighborhood.Comment: 22 pages, 3 figures; published in Ap
Saltire - A model to measure dynamical masses for high-contrast binaries and exoplanets with high-resolution spectroscopy
High-resolution cross-correlation methods are widely used to discover and to characterise atomic and molecular species in exoplanet atmospheres. The characteristic cross-correlation signal is typically represented as a function of the velocity of the system, and the semi-amplitude of the planet's orbit. We present Saltire, a fast and simple model that accurately reproduces the shape of such cross-correlation signals, allowing a direct fit to the data by using a minimum set of parameters. We show how to use this model on the detection of atmospheric CO in archival data of the hot Jupiter τ Boötis b, and how Saltire can be used to estimate the semi-amplitude and rest velocity of high brightness-ratio binaries. By including the shape of the signal, we demonstrate that our model allows to robustly derive the signal position up to 10 times more accurate, compared to conventional methods. Furthermore, we discuss the impact of correlated noise and demonstrate that Saltire is a robust tool for estimating systematic uncertainties on the signal position. Saltire opens a new door to analyse high signal-to-noise data to accurately study atmospheric dynamics and to measure precise dynamical masses for exoplanets and faint stellar companions. We show, that the phase-resolved shape of the atmospheric CCF signal can accurately be reproduced, allowing studies of phase-dependent signal changes and to disentangle them from noise and data aliases
Component-aware Orchestration of Cloud-based Enterprise Applications, from TOSCA to Docker and Kubernetes
Enterprise IT is currently facing the challenge of coordinating the
management of complex, multi-component applications across heterogeneous cloud
platforms. Containers and container orchestrators provide a valuable solution
to deploy multi-component applications over cloud platforms, by coupling the
lifecycle of each application component to that of its hosting container. We
hereby propose a solution for going beyond such a coupling, based on the OASIS
standard TOSCA and on Docker. We indeed propose a novel approach for deploying
multi-component applications on top of existing container orchestrators, which
allows to manage each component independently from the container used to run
it. We also present prototype tools implementing our approach, and we show how
we effectively exploited them to carry out a concrete case study
Combining high-dispersion spectroscopy (HDS) with high contrast imaging (HCI): Probing rocky planets around our nearest neighbors
Aims: In this work, we discuss a way to combine High Dispersion Spectroscopy
and High Contrast Imaging (HDS+HCI). For a planet located at a resolvable
angular distance from its host star, the starlight can be reduced up to several
orders of magnitude using adaptive optics and/or coronography. In addition, the
remaining starlight can be filtered out using high-dispersion spectroscopy,
utilizing the significantly different (or Doppler shifted) high-dispersion
spectra of the planet and star. In this way, HDS+HCI can in principle reach
contrast limits of ~1e-5 x 1e-5, although in practice this will be limited by
photon noise and/or sky-background.
Methods: We present simulations of HDS+HCI observations with the E-ELT, both
probing thermal emission from a planet at infrared wavelengths, and starlight
reflected off a planet atmosphere at optical wavelengths. For the infrared
simulations we use the baseline parameters of the E-ELT and METIS instrument,
with the latter combining extreme adaptive optics with an R=100,000 IFS. We
include realistic models of the adaptive optics performance and atmospheric
transmission and emission. For the optical simulation we also assume R=100,000
IFS with adaptive optics capabilities at the E-ELT.
Results: One night of HDS+HCI observations with the E-ELT at 4.8 um (d_lambda
= 0.07 um) can detect a planet orbiting alpha Cen A with a radius of R=1.5
R_earth and a twin-Earth thermal spectrum of T_eq=300 K at a signal-to-noise
(S/N) of 5. In the optical, with a Strehl ratio performance of 0.3, reflected
light from an Earth-size planet in the habitable zone of Proxima Centauri can
be detected at a S/N of 10 in the same time frame. Recently, first HDS+HCI
observations have shown the potential of this technique by determining the
spin-rotation of the young massive exoplanet beta Pictoris b. [abridged]Comment: 9 pages, A&A in press: A movie of the simulation can be found at
http://www.strw.leidenuniv.nl/~snellen/simulation.mpe
Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b
[Abridged] After many attempts over more than a decade, high-resolution
spectroscopy has recently delivered its first detections of molecular
absorption in exoplanet atmospheres, both in transmission and thermal emission
spectra. Targeting the combined signal from individual lines in molecular
bands, these measurements use variations in the planet radial velocity to
disentangle the planet signal from telluric and stellar contaminants. In this
paper we apply high resolution spectroscopy to probe molecular absorption in
the day-side spectrum of the bright transiting hot Jupiter HD 189733b. We
observed HD 189733b with the CRIRES high-resolution near-infrared spectograph
on the Very Large Telescope during three nights. We detect a 5-sigma absorption
signal from CO at a contrast level of ~4.5e-4 with respect to the stellar
continuum, revealing the planet orbital radial velocity at 154+4/-3 km s-1.
This allows us to solve for the planet and stellar mass in a similar way as for
stellar eclipsing binaries, resulting in Ms= 0.846+0.068/-0.049 Msun and Mp=
1.162+0.058/-0.039 MJup. No significant absorption is detected from H2O, CO2 or
CH4 and we determined upper limits on their line contrasts here. The detection
of CO in the day-side spectrum of HD 189733b can be made consistent with the
haze layer proposed to explain the optical to near-infrared transmission
spectrum if the layer is optically thin at the normal incidence angles probed
by our observations, or if the CO abundance is high enough for the CO
absorption to originate from above the haze. Our non-detection of CO2 at 2.0
micron is not inconsistent with the deep CO2 absorption from low resolution
NICMOS secondary eclipse data in the same wavelength range. If genuine, the
absorption would be so strong that it blanks out any planet light completely in
this wavelength range, leaving no high-resolution signal to be measured.Comment: A&A, accepted for publication. Fig.1 reduced in qualit
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