588 research outputs found
Constraining Exoplanet Mass from Transmission Spectroscopy
Determination of an exoplanet's mass is a key to understanding its basic
properties, including its potential for supporting life. To date, mass
constraints for exoplanets are predominantly based on radial velocity (RV)
measurements, which are not suited for planets with low masses, large
semi-major axes, or those orbiting faint or active stars. Here, we present a
method to extract an exoplanet's mass solely from its transmission spectrum. We
find good agreement between the mass retrieved for the hot Jupiter HD189733b
from transmission spectroscopy with that from RV measurements. Our method will
be able to retrieve the masses of Earth-sized and super-Earth planets using
data from future space telescopes that were initially designed for atmospheric
characterization.Comment: 66 pages, 25 figures, published in the December 20, 2013 edition of
Science Magazine. Includes supplementary material
Towards consistent mapping of distant worlds: secondary-eclipse scanning of the exoplanet HD189733b
Mapping distant worlds is the next frontier for exoplanet infrared photometry
studies. Ultimately, constraining spatial and temporal properties of an
exoplanet atmosphere will provide further insight into its physics. For
tidally-locked hot Jupiters that transit and are eclipsed by their host star,
the first steps are now possible.
Our aim is to constrain an exoplanet's shape, brightness distribution (BD)
and system parameters from its light curve. Notably, we rely on the eclipse
scanning.
We use archived Spitzer 8-{\mu}m data of HD189733 (6 transits, 8 secondary
eclipses, and a phase curve) in a global MCMC procedure for mitigating
systematics. We also include HD189733's out-of-transit radial velocity
measurements.
We find a 6-{\sigma} deviation from the expected occultation of a
uniformly-bright disk. This deviation emerges mainly from HD189733b's thermal
pattern, not from its shape. We indicate that the correlation of the orbital
eccentricity, e, and BD (uniform time offset) does also depend on the stellar
density, \rho*, and the impact parameter, b (e-b-\rho*-BD correlation). For
HD189733b, we find that relaxing the e-constraint and using more complex BDs
lead to lower stellar/planetary densities and a more localized and
latitudinally-shifted hot spot. We obtain an improved constraint on the upper
limit of HD189733b's orbital eccentricity, e<0.011 (95%), when including the RV
measurements.
Our study provides new insights into the analysis of exoplanet light curves
and a proper framework for future eclipse-scanning observations. Observations
of the same exoplanet at different wavelengths will improve the constraints on
its system parameters while ultimately yielding a large-scale time-dependent 3D
map of its atmosphere. Finally, we discuss the perspective of extending our
method to observations in the visible, in particular to better understand
exoplanet albedos.Comment: Accepted for publication in A&A. Final version will be available soon
at http://www.aanda.org by Free Open Acces
Towards robust corrections for stellar contamination in JWST exoplanet transmission spectra
Transmission spectroscopy is still the preferred characterization technique
for exoplanet atmospheres, although it presents unique challenges which
translate into characterization bottlenecks when robust mitigation strategies
are missing. Stellar contamination is one of such challenges that can overpower
the planetary signal by up to an order of magnitude, and thus not accounting
for stellar contamination can lead to significant biases in the derived
atmospheric properties. Yet, accounting for stellar contamination may not be
straightforward, as important discrepancies exist between state-of-the-art
stellar models and measured spectra and between models themselves. Here we
explore the extent to which stellar models can be used to reliably correct for
stellar contamination and yield a planet's uncontaminated transmission
spectrum. We find that (1) discrepancies between stellar models can dominate
the noise budget of JWST transmission spectra of planets around stars with
heterogeneous photospheres; (2) the true number of unique photospheric spectral
components and their properties can only be accurately retrieved when the
stellar models have a sufficient fidelity; and (3) under such optimistic
circumstances the contribution of stellar contamination to the noise budget of
a transmission spectrum is considerably below that of the photon noise for the
standard transit observation setup. Therefore, we suggest (1) increased efforts
towards development of model spectra of stars and their active regions in a
data-driven manner; and (2) the development of empirical approaches for
deriving spectra of photospheric components using the observatories with which
the atmospheric explorations are carried out.Comment: 15 pages, 8 figures, 2 table
GPU-based framework for detecting small Solar System bodies in targeted exoplanet surveys
Small Solar System bodies are pristine remnants of Solar System formation,
which provide valuable insights for planetary science and astronomy. Their
discovery and cataloging also have strong practical implications to life on
Earth as the nearest asteroids could pose a serious impact threat. Concurrently
with dedicated observational projects, searches for small bodies have been
performed on numerous archival data sets from different facilities. Here, we
present a framework to increase the scientific return of an exoplanet
transit-search survey by recovering serendipitous detections of small bodies in
its daily and archival data using a GPU-based synthetic tracking algorithm. As
a proof of concept, we analysed sky fields
observed by the 1-m telescopes of the SPECULOOS survey. We analysed 90 sky
fields distributed uniformly across the sky as part of the daily search for
small bodies and 21 archival fields located within 5 deg from the ecliptic
plane as part of the archival search (4.4 deg in total). Overall, we
identified 400 known objects of different dynamical classes from Inner
Main-belt Asteroids to Jupiter Trojans and 43 potentially new small bodies with
no priors on their motion. We were able to reach limiting magnitude for unknown
objects of =23.8 mag, and a retrieval rate of 80% for objects with
22 mag and 23.5 mag for the daily and archival searches, respectively.
SPECULOOS and similar exoplanet surveys can thus serve as pencil-beam surveys
for small bodies and probe parameter space beyond =22 mag.Comment: Accepted for publication in MNRAS (Monthly Notices of the Royal
Astronomical Society), 11 pages, 11 figure
Unveiling the atmospheres of giant exoplanets with an EChO-class mission
More than a thousand exoplanets have been discovered over the last decade. Perhaps more excitingly, probing their atmospheres has become possible. With current data we have glimpsed the diversity of exoplanet atmospheres that will be revealed over the coming decade. However, numerous questions concerning their chemical composition, thermal structure, and atmospheric dynamics remain to be answered. More observations of higher quality are needed. In the next years, the selection of a space-based mission dedicated to the spectroscopic characterization of exoplanets would revolutionize our understanding of the physics of planetary atmospheres. Such a mission was proposed to the ESA cosmic vision program in 2014. Our paper is therefore based on the planned capabilities of the Exoplanet Characterization Observatory (EChO), but it should equally apply to any future mission with similar characteristics. With its large spectral coverage (0.4 − 16 μm), high spectral resolution (λ/Δλ > 300 below 5 μm and λ/Δλ > 30 above 5 μm) and 1.5m mirror, a future mission such as EChO will provide spectrally resolved transit lightcurves, secondary eclipses lightcurves, and full phase curves of numerous exoplanets with an unprecedented signal-to-noise ratio. In this paper, we review some of today’s main scientific questions about gas giant exoplanets atmospheres, for which a future mission such as EChO will bring a decisive contribution
Empirically Constraining the Spectra of a Stars Heterogeneities From Its Rotation Lightcurve
Transmission spectroscopy is currently the most powerful technique to study a
wide range of planetary atmospheres, leveraging the filtering of a stars light
by a planets atmosphere rather than its own emission. However, both a planet
and its star contribute to the information encoded in a transmission spectrum
and a particular challenge relate to disentangling their contributions. As
measurements improve, the lack of fidelity of stellar spectra models present a
bottleneck for accurate disentanglement. Considering JWST and future
high-precision spectroscopy missions, we investigate the ability to derive
empirical constraints on the emission spectra of stellar surface
heterogeneities (i.e., spots and faculae) using the same facility as used to
acquire the transmission spectra intended to characterize a given atmosphere.
Using TRAPPIST-1 as a test case, we demonstrate that it is possible to
constrain the photospheric spectrum to 0.2% and the spectra of stellar
heterogeneities to within 1-5%, which will be valuable benchmarks to inform the
new generation of theoretical stellar models. Long baseline of observations
(90% of the stellar rotation period) are necessary to ensure the photon-limited
(i.e., instrument-limited) exploration of exoplanetary atmospheres via
transmission spectroscopy.Comment: 10 pages, 3 figure
Unveiling the atmospheres of giant exoplanets with an EChO-class mission
More than a thousand exoplanets have been discovered over the last decade.
Perhaps more excitingly, probing their atmospheres has become possible. With
current data we have glimpsed the diversity of exoplanet atmospheres that will
be revealed over the coming decade. However, numerous questions concerning
their chemical composition, thermal structure, and atmospheric dynamics remain
to be answered. More observations of higher quality are needed. In the next
years, the selection of a space-based mission dedicated to the spectroscopic
characterization of exoplanets would revolutionize our understanding of the
physics of planetary atmospheres. Such a mission was proposed to the ESA cosmic
vision program in 2014. Our paper is therefore based on the planned
capabilities of the Exoplanet Characterization Observatory (EChO), but it
should equally apply to any future mission with similar characteristics. With
its large spectral coverage (), high spectral resolution
( below and
above ) and mirror, a
future mission such as EChO will provide spectrally resolved transit
lightcurves, secondary eclipses lightcurves, and full phase curves of numerous
exoplanets with an unprecedented signal-to-noise ratio. In this paper, we
review some of today's main scientific questions about gas giant exoplanets
atmospheres, for which a future mission such as EChO will bring a decisive
contribution.Comment: Accepted to the Experimental Journal of Astronom
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