171 research outputs found
Thermal emission from WASP-24b at 3.6 and 4.5 {\mu}m
Aims. We observe occultations of WASP-24b to measure brightness temperatures
and to determine whether or not its atmosphere exhibits a thermal inversion
(stratosphere). Methods. We observed occultations of WASP-24b at 3.6 and 4.5
{\mu}m using the Spitzer Space Telescope. It has been suggested that there is a
correlation between stellar activity and the presence of inversions, so we
analysed existing HARPS spectra in order to calculate log R'HK for WASP-24 and
thus determine whether or not the star is chromospherically active. We also
observed a transit of WASP-24b in the Str\"{o}mgren u and y bands, with the
CAHA 2.2-m telescope. Results. We measure occultation depths of 0.159 \pm 0.013
per cent at 3.6 {\mu}m and 0.202 \pm 0.018 per cent at 4.5 {\mu}m. The
corresponding planetary brightness temperatures are 1974 \pm 71 K and 1944 \pm
85 K respectively. Atmosphere models with and without a thermal inversion fit
the data equally well; we are unable to constrain the presence of an inversion
without additional occultation measurements in the near-IR. We find log R'HK =
-4.98 \pm 0.12, indicating that WASP-24 is not a chromospherically active star.
Our global analysis of new and previously-published data has refined the system
parameters, and we find no evidence that the orbit of WASP-24b is non-circular.
Conclusions. These results emphasise the importance of complementing Spitzer
measurements with observations at shorter wavelengths to gain a full
understanding of hot Jupiter atmospheres.Comment: 7 pages, 4 figures, 3 tables. Accepted for publication in A&
Thermal Emission of WASP-14b Revealed with Three Spitzer Eclipses
Exoplanet WASP-14b is a highly irradiated, transiting hot Jupiter. Joshi et
al. calculate an equilibrium temperature Teq of 1866 K for zero albedo and
reemission from the entire planet, a mass of 7.3 +/- 0.5 Jupiter masses and a
radius of 1.28 +/- 0.08 Jupiter radii. Its mean density of 4.6 g/cm3 is one of
the highest known for planets with periods less than 3 days. We obtained three
secondary eclipse light curves with the Spitzer Space Telescope. The eclipse
depths from the best jointly fit model are +/- at 4.5
{\mu}m and +/- at 8.0 {\mu}m. The corresponding brightness
temperatures are 2212 +/- 94 K and 1590 +/- 116 K. A slight ambiguity between
systematic models suggests a conservative 3.6 {\mu}m eclipse depth of
+/- and brightness temperature of 2242 +/- 55 K. Although extremely
irradiated, WASP-14b does not show any distinct evidence of a thermal
inversion. In addition, the present data nominally favor models with day night
energy redistribution less than . The current data are generally
consistent with oxygen-rich as well as carbon-rich compositions, although an
oxygen-rich composition provides a marginally better fit. We confirm a
significant eccentricity of e = 0.087 +/- 0.002 and refine other orbital
parameters.Comment: 16 pages, 16 figure
The Need for Laboratory Measurements and Ab Initio Studies to Aid Understanding of Exoplanetary Atmospheres
We are now on a clear trajectory for improvements in exoplanet observations
that will revolutionize our ability to characterize their atmospheric
structure, composition, and circulation, from gas giants to rocky planets.
However, exoplanet atmospheric models capable of interpreting the upcoming
observations are often limited by insufficiencies in the laboratory and
theoretical data that serve as critical inputs to atmospheric physical and
chemical tools. Here we provide an up-to-date and condensed description of
areas where laboratory and/or ab initio investigations could fill critical gaps
in our ability to model exoplanet atmospheric opacities, clouds, and chemistry,
building off a larger 2016 white paper, and endorsed by the NAS Exoplanet
Science Strategy report. Now is the ideal time for progress in these areas, but
this progress requires better access to, understanding of, and training in the
production of spectroscopic data as well as a better insight into chemical
reaction kinetics both thermal and radiation-induced at a broad range of
temperatures. Given that most published efforts have emphasized relatively
Earth-like conditions, we can expect significant and enlightening discoveries
as emphasis moves to the exotic atmospheres of exoplanets.Comment: Submitted as an Astro2020 Science White Pape
Two nearby sub-Earth-sized exoplanet candidates in the GJ 436 system
We report the detection of UCF-1.01, a strong exoplanet candidate with a
radius 0.66 +/- 0.04 times that of Earth (R_{\oplus}). This sub-Earth-sized
planet transits the nearby M-dwarf star GJ 436 with a period of 1.365862 +/-
8x10^{-6} days. We also report evidence of a 0.65 +/- 0.06 R_{\oplus} exoplanet
candidate (labeled UCF-1.02) orbiting the same star with an undetermined
period. Using the Spitzer Space Telescope, we measure the dimming of light as
the planets pass in front of their parent star to assess their sizes and
orbital parameters. If confirmed, UCF-1.01 and UCF-1.02 would be called GJ 436c
and GJ 436d, respectively, and would be part of the first
multiple-transiting-planet system outside of the Kepler field. Assuming
Earth-like densities of 5.515 g/cm^3, we predict both candidates to have
similar masses (~0.28 Earth-masses, M_{\oplus}, 2.6 Mars-masses) and surface
gravities of ~0.65 g (where g is the gravity on Earth). UCF-1.01's equilibrium
temperature (T_{eq}, where emitted and absorbed radiation balance for an
equivalent blackbody) is 860 K, making the planet unlikely to harbor life as on
Earth. Its weak gravitational field and close proximity to its host star imply
that UCF-1.01 is unlikely to have retained its original atmosphere; however, a
transient atmosphere is possible if recent impacts or tidal heating were to
supply volatiles to the surface. We also present additional observations of GJ
436b during secondary eclipse. The 3.6-micron light curve shows indications of
stellar activity, making a reliable secondary eclipse measurement impossible. A
second non-detection at 4.5 microns supports our previous work in which we find
a methane-deficient and carbon monoxide-rich dayside atmosphere.Comment: Accepted for publication with Ap
Awesome SOSS: atmospheric characterization of WASP-96 b using the JWST early release observations
This is the final version. Available on open access from Oxford University Press via the DOI in this recordData availability: All data used in this study are publicly available from the Barbara A. Mikulski Archive for Space Telescopes;
https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. The models generated in this paper can be made available on request.The newly operational JWST offers the potential to study the atmospheres of distant worlds with precision that has not been achieved before. One of the first exoplanets observed by JWST in the summer of 2022 was WASP-96 b, a hot Saturn orbiting a G8 star. As a part of the Early Release Observations programme, one transit of WASP-96 b was observed with NIRISS/SOSS to capture its transmission spectrum from 0.6 to 2.85 μm. In this work, we utilize four retrieval frameworks to report precise and robust measurements of WASP-96 b's atmospheric composition. We constrain the logarithmic volume mixing ratios of multiple chemical species in its atmosphere, including: H2O =, CO2 =, and K =, thus generally consistent with 1× solar (with the exception of CO2). Notably, our results offer a first abundance constraint on potassium in WASP-96 b's atmosphere and important inferences on carbon-bearing species such as CO2 and CO. Our short wavelength NIRISS/SOSS data are best explained by the presence of an enhanced Rayleigh scattering slope, despite previous inferences of a clear atmosphere - although we find no evidence for a grey cloud deck. Finally, we explore the data resolution required to appropriately interpret observations using NIRISS/SOSS. We find that our inferences are robust against different binning schemes. That is, from low R = 125 to the native resolution of the instrument, the bulk atmospheric properties of the planet are consistent. Our systematic analysis of these exquisite observations demonstrates the power of NIRISS/SOSS to detect and constrain multiple molecular and atomic species in the atmospheres of hot giant planets
Clinical predictors of lacunar syndrome not due to lacunar infarction
Background: Lacunar syndrome not due to lacunar infarct is poorly characterised. This single centre, retrospective study was conducted to describe the clinical characteristics of patients with lacunar syndrome not due to lacunar infarct and to identify clinical predictors of this variant of lacunar stroke. Methods: A total of 146 patients with lacunar syndrome not due to lacunar infarction were included in the "Sagrat Cor Hospital of Barcelona Stroke Registry" during a period of 19 years (1986-2004). Data from stroke patients are entered in the stroke registry following a standardized protocol with 161 items regarding demographics, risk factors, clinical features, laboratory and neuroimaging data, complications and outcome. The characteristics of these 146 patients with lacunar syndrome not due to lacunar infarct were compared with those of the 733 patients with lacunar infarction. Results: Lacunar syndrome not due to lacunar infarct accounted for 16.6% (146/879) of all cases of lacunar stroke. Subtypes of lacunar syndromes included pure motor stroke in 63 patients, sensorimotor stroke in 51, pure sensory stroke in 14, atypical lacunar syndrome in 9, ataxic hemiparesis in 5 and dysarthria-clumsy hand in 4. Valvular heart disease, atrial fibrillation, sudden onset, limb weakness and sensory symptoms were significantly more frequent among patients with lacunar syndrome not due to lacunar infarct than in those with lacunar infarction, whereas diabetes was less frequent. In the multivariate analysis, atrial fibrillation (OR = 4.62), sensorimotor stroke (OR = 4.05), limb weakness (OR = 2.09), sudden onset (OR = 2.06) and age (OR = 0.96) were independent predictors of lacunar syndrome not due to lacunar infarct. Conclusions: Although lacunar syndromes are highly suggestive of small deep cerebral infarctions, lacunar syndromes not due to lacunar infarcts are found in 16.6% of cases. The presence of sensorimotor stroke, limb weakness and sudden onset in a patient with atrial fibrillation should alert the clinician to the possibility of a lacunar syndrome not due to a lacunar infarct
Awesome SOSS: Transmission Spectroscopy of WASP-96b with NIRISS/SOSS
The future is now - after its long-awaited launch in December 2021, JWST
began science operations in July 2022 and is already revolutionizing exoplanet
astronomy. The Early Release Observations (ERO) program was designed to provide
the first images and spectra from JWST, covering a multitude of science cases
and using multiple modes of each on-board instrument. Here, we present
transmission spectroscopy observations of the hot-Saturn WASP-96b with the
Single Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and
Slitless Spectrograph, observed as part of the ERO program. As the SOSS mode
presents some unique data reduction challenges, we provide an in-depth
walk-through of the major steps necessary for the reduction of SOSS data:
including background subtraction, correction of 1/f noise, and treatment of the
trace order overlap. We furthermore offer potential routes to correct for field
star contamination, which can occur due to the SOSS mode's slitless nature. By
comparing our extracted transmission spectrum with grids of atmosphere models,
we find an atmosphere metallicity between 1x and 5x solar, and a solar
carbon-to-oxygen ratio. Moreover, our models indicate that no grey cloud deck
is required to fit WASP-96b's transmission spectrum, but find evidence for a
slope shortward of 0.9m, which could either be caused by enhanced Rayleigh
scattering or the red wing of a pressure-broadened Na feature. Our work
demonstrates the unique capabilities of the SOSS mode for exoplanet
transmission spectroscopy and presents a step-by-step reduction guide for this
new and exciting instrument.Comment: MNRAS, in press. Updated to reflect published versio
Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM
Transmission spectroscopy of exoplanets has revealed signatures of water
vapor, aerosols, and alkali metals in a few dozen exoplanet atmospheres.
However, these previous inferences with the Hubble and Spitzer Space Telescopes
were hindered by the observations' relatively narrow wavelength range and
spectral resolving power, which precluded the unambiguous identification of
other chemical speciesin particular the primary carbon-bearing molecules.
Here we report a broad-wavelength 0.5-5.5 m atmospheric transmission
spectrum of WASP-39 b, a 1200 K, roughly Saturn-mass, Jupiter-radius exoplanet,
measured with JWST NIRSpec's PRISM mode as part of the JWST Transiting
Exoplanet Community Early Release Science Team program. We robustly detect
multiple chemical species at high significance, including Na (19),
HO (33), CO (28), and CO (7). The non-detection
of CH, combined with a strong CO feature, favours atmospheric models
with a super-solar atmospheric metallicity. An unanticipated absorption feature
at 4m is best explained by SO (2.7), which could be a tracer
of atmospheric photochemistry. These observations demonstrate JWST's
sensitivity to a rich diversity of exoplanet compositions and chemical
processes.Comment: 41 pages, 4 main figures, 10 extended data figures, 4 tables. Under
review in Natur
- …