196 research outputs found
Observing transiting planets with JWST -- Prime targets and their synthetic spectral observations
The James Webb Space Telescope will enable astronomers to obtain exoplanet
spectra of unprecedented precision. Especially the MIRI instrument may shed
light on the nature of the cloud particles obscuring planetary transmission
spectra in the optical and near-infrared. We provide self-consistent
atmospheric models and synthetic JWST observations for prime exoplanet targets
in order to identify spectral regions of interest and estimate the number of
transits needed to distinguish between model setups. We select targets which
span a wide range in planetary temperature and surface gravity, ranging from
super-Earths to giant planets, and have a high expected SNR. For all targets we
vary the enrichment, C/O ratio, presence of optical absorbers (TiO/VO) and
cloud treatment. We calculate atmospheric structures and emission and
transmission spectra for all targets and use a radiometric model to obtain
simulated observations. We analyze JWST's ability to distinguish between
various scenarios. We find that in very cloudy planets such as GJ 1214b less
than 10 transits with NIRSpec may be enough to reveal molecular features.
Further, the presence of small silicate grains in atmospheres of hot Jupiters
may be detectable with a single JWST MIRI transit. For a more detailed
characterization of such particles less than 10 transits are necessary.
Finally, we find that some of the hottest hot Jupiters are well fitted by
models which neglect the redistribution of the insolation and harbor
inversions, and that 1-4 eclipse measurements with NIRSpec are needed to
distinguish between the inversion models. Wet thus demonstrate the capabilities
of JWST for solving some of the most intriguing puzzles in current exoplanet
atmospheric research. Further, by publishing all models calculated for this
study we enable the community to carry out similar or retrieval analyses for
all planets included in our target list.Comment: 24 pages, 7 figures, accepted for publication in A&
Submillimetre/TeraHertz Astronomy at Dome C with CEA filled bolometer array
Submillimetre/TeraHertz (e.g. 200, 350, 450 microns) astronomy is the prime
technique to unveil the birth and early evolution of a broad range of
astrophysical objects. A major obstacle to carry out submm observations from
ground is the atmosphere. Preliminary site testing and atmospheric transmission
models tend to demonstrate that Dome C could offer the best conditions on Earth
for submm/THz astronomy. The CAMISTIC project aims to install a filled
bolometer-array camera with 16x16 pixels on IRAIT at Dome C and explore the
200-m windows for potential ground-based observations.Comment: 6 page
Multi-wavelength observations of Galactic hard X-ray sources discovered by INTEGRAL. II. The environment of the companion star
Context: The INTEGRAL mission has led to the discovery of a new type of
supergiant X-ray binaries (SGXBs), whose physical properties differ from those
of previously known SGXBs. Those sources are in the course of being unveiled by
means of multi-wavelength X-rays, optical, near- and mid-infrared observations,
and two classes are appearing. The first class consists of obscured persistent
SGXBs and the second is populated by the so-called supergiant fast X-ray
transients (SFXTs). Aims: We report here mid-infrared (MIR) observations of the
companion stars of twelve SGXBs from these two classes in order to assess the
contribution of the star and the material enshrouding the system to the total
emission.} Methods: We used data from observations we carried out at ESO/VLT
with VISIR, as well as archival and published data, to perform broad-band
spectral energy distributions of the companion stars and fitted them with a
combination of two black bodies representing the star and a MIR excess due to
the absorbing material enshrouding the star, if there was any. Results: We
detect a MIR excess in the emission of IGR J16318-4848, IGR J16358-4726, and
perhaps IGR J16195-4945. The other sources do not exhibit any MIR excess even
when the intrinsic absorption is very high. (abridged)Comment: A&A in press, The official date of acceptance is 25/01/2008, 17
pages, 4 figures, 9 tables. New version with english language editing
required by editor, note added in proo
Hydrogenated atmospheres of lava planets: atmospheric structure and emission spectra
Hot rocky super-Earths are thought to be sufficiently irradiated by their
host star to melt their surface and thus allow for long-lasting magma oceans.
Some processes have been proposed for such planets to have retained primordial
hydrogen captured during their formation while moving inward in the planetary
system. The new generation of space telescopes such as the JWST may provide
observations precise enough to characterize the atmospheres and perhaps the
interiors of such exoplanets. We use a vaporization model that calculates the
gas-liquid equilibrium between the atmosphere (including hydrogen) and the
magma ocean, to compute the elemental composition of a variety of atmospheres
for different quantities of hydrogen. The elemental composition is then used in
a steady-state atmospheric model to compute the atmospheric structure and
generate synthetic emission spectra. With this method, we confirm previous
results showing that silicate atmospheres exhibit a thermal inversion, with
notably an emission peak of SiO at 9~. We compare our method to the
literature on the inclusion of hydrogen in the atmosphere, and show hydrogen
reduces the thermal inversion, because of the formation of H2O which has a
strong greenhouse potential. However planets that are significantly irradiated
by their host star are sufficiently hot to dissociate H2O and thus also
maintain a thermal inversion. The observational implications are twofold: 1)
H2O is more likely to be detected in colder atmospheres; 2) Detecting a thermal
inversion in hotter atmospheres does not a priori exclude the presence of H (in
its atomic form). Due to the impact of H on the overall chemistry and
atmospheric structure, and therefore observations, we emphasize the importance
of including volatiles in the calculation of the gas-liquid equilibrium.
Finally, we provide a criterion to determine potential targets for observation.Comment: 22 pages, 17 figures + 12 figures in appendices. Accepted for
publication in Astronomy & Astrophysic
Spitzer thermal phase curve of WASP-121 b
Aims. We analyse unpublished Spitzer observations of the thermal phase-curve
of WASP-121 b, a benchmark ultra-hot Jupiter. Methods. We adopted the wavelet
pixel-independent component analysis technique to remove challenging
instrumental systematic effects in these datasets and we fit them
simultaneously with parametric light-curve models. We also performed
phase-curve retrievals to better understand the horizontal and vertical thermal
structure of the planetary atmosphere. Results. We measured planetary
brightness temperatures of 2700\,K (dayside) and 700--1100\,K
(nightside), along with modest peak offsets of 5.91.6
(3.6\,m) and 5.0 (4.5\,m) after
mid-eclipse. These results suggest inefficient heat redistribution in the
atmosphere of WASP-121 b. The inferred atmospheric Bond albedo and circulation
efficiency align well with observed trends for hot giant exoplanets.
Interestingly, the measured peak offsets correspond to a westward hot spot,
which has rarely been observed. We also report consistent transit depths at 3.6
and 4.5\,m, along with updated geometric and orbital parameters. Finally,
we compared our Spitzer results with previous measurements, including recent
JWST observations. Conclusions. We extracted new information on the thermal
properties and dynamics of an exoplanet atmosphere from an especially
problematic dataset. This study probes the reliability of exoplanet phase-curve
parameters obtained from Spitzer observations when state-of-the-art pipelines
are adopted to remove the instrumental systematic effects. It demonstrates that
Spitzer phase-curve observations provide a useful baseline for comparison with
JWST observations, and shows the increase in parameters precision achieved with
the newer telescope.Comment: 14 pages, 10 figure
The effect of a small amount of hydrogen in the atmosphere of ultrahot magma-ocean planets: atmospheric composition and escape
Here we investigate how small amounts of hydrogen (much smaller than the mass
of the exoplanet) above a magma ocean on a rocky exoplanet may modify the
atmospheric chemistry and atmospheric escape.We use a chemical model of a magma
ocean coupled to a gas equilibrium code. An energy-limited model is used to
compute atmospheric escape. The composition of the vapor above a magma ocean is
drastically modified by hydrogen, even for very modest amounts of H ( planetary mass). Hydrogen consumes much of the O(g), which, in
turn, promotes the evaporation of metals and metal oxides (SiO, Mg, Na, K, Fe)
from the magma ocean. Vast amounts of HO are produced by the same process.
At high hydrogen pressures, new hydrogenated species such as SiH form in
the atmosphere. In all cases, H, H, and HO are the dominant
nonmetal-bearing volatile species. Sodium is the dominant atmospheric
metal-bearing species at T 2000K and low H content, whereas Fe is dominant
at high H content and low temperature, while SiO predominates at T>3000 K. We
find that the atmospheric Mg/Fe, Mg/Si, and Na/Si ratios deviate from those in
the underlying planet and from the stellar composition. As such, their
determination may constrain the planet's mantle composition and H content. As
the presence of hydrogen promotes the evaporation of silicate mantles, it is
conceivable that some high-density, irradiated exoplanets may have started life
as hydrogen-bearing planets and that part of their silicate mantle evaporated
(up to a few of Si, O, and Fe) and was subsequently lost owing to the
reducing role of H. Even very small amounts of H can alter the atmospheric
composition and promote the evaporation to space of heavy species derived from
the molten silicate mantle of rocky planets.Comment: Accepted for publication in A&
An independent analysis of the Spitzer/IRAC phase curves of WASP43 b
We present here a reanalysis of the Spitzer Space Telescope phase curves of
the hot Jupiter WASP43 b, using the wavelet pixel-Independent Component
Analysis, a blind signal-source separation method. The data analyzed were
recorded with the InfraRed Array Camera and consisted of two visits at 3.6
m, and one visit at 4.5 m, each visit covering one transit and two
eclipse events. To test the robustness of our technique we repeated the
analysis on smaller portions of the phase curves, and by employing different
instrument ramp models. Our reanalysis presents significant updates of the
planetary parameters compared to those reported in the original phase curve
study of WASP43 b. In particular, we found (1) higher nightside temperatures,
(2) smaller hotspot offsets, (3) a greater consistency (1 )
between the two 3.6~m visits, and (4) a greater similarity with the
predictions of the atmospheric circulation models. Our parameter results are
consistent within 1 with those reported by a recent reanalysis of the
same data sets. For each visit we studied the variation of the retrieved
transit parameters as a function of various sets of stellar limb-darkening
coefficients, finding significant degeneracy between the limb-darkening models
and the analysis output. Furthermore, we performed the analysis of the single
transit and eclipse events, and we examined the differences between these
results with the ones obtained with the whole phase curve. Finally we provide a
formula useful to optimize the trade-off between precision and duration of
observations of transiting exoplanets.Comment: published on A
NEAT: a space born astrometric mission for the detection and characterization of nearby habitable planetary systems
The NEAT (Nearby Earth Astrometric Telescope) mission is a proposal submitted
to ESA for its 2010 call for M-size mission within the Cosmic Vision 2015-2025
plan. The main scientific goal of the NEAT mission is to detect and
characterize planetary systems in an exhaustive way down to 1 Earth mass in the
habitable zone and further away, around nearby stars for F, G, and K spectral
types. This survey would provide the actual planetary masses, the full
characterization of the orbits including their inclination, for all the
components of the planetary system down to that mass limit. NEAT will continue
the work performed by Hipparcos and Gaia by reaching a precision that is
improved by two orders of magnitude on pointed targets.Comment: 17 pages, in SPIE 2012 symposium in "Space Telescopes and
Instrumentation 2012: Optical, Infrared, and Millimeter Wave" SPIE Conference
8442, 1
Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST
The TRAPPIST-1 system is remarkable for its seven planets that are similar in
size, mass, density, and stellar heating to the rocky planets Venus, Earth, and
Mars in our own Solar System (Gillon et al. 2017). All TRAPPIST-1 planets have
been observed with the transmission spectroscopy technique using the Hubble or
Spitzer Space Telescopes, but no atmospheric features have been detected or
strongly constrained (Ducrot et al. 2018; de Wit et al. 2018; Zhang et al.
2018; Garcia et al. 2022). TRAPPIST-1 b is the closest planet to the system's M
dwarf star, and it receives 4 times as much irradiation as Earth receives from
the Sun. This relatively large amount of stellar heating suggests that its
thermal emission may be measurable. Here we present photometric secondary
eclipse observations of the Earth-sized TRAPPIST-1 b exoplanet using the F1500W
filter of the MIRI instrument on JWST. We detect the secondary eclipse in each
of five separate observations with 8.7-sigma confidence when all data are
combined. These measurements are most consistent with the re-radiation of the
TRAPPIST-1 star's incident flux from only the dayside hemisphere of the planet.
The most straightforward interpretation is that there is little or no planetary
atmosphere redistributing radiation from the host star and also no detectable
atmospheric absorption from carbon dioxide (CO) or other species.Comment: Submitted to Natur
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