133 research outputs found
The Eclipse Mapping Null Space: Comparing Theoretical Predictions with Observed Maps
High-precision exoplanet eclipse light curves, like those possible with JWST,
enable flux and temperature mapping of exoplanet atmospheres. These eclipse
maps will have unprecedented precision, providing an opportunity to constrain
current theoretical predictions of exoplanet atmospheres. However, eclipse
mapping has unavoidable mathematical limitations because many map patterns are
unobservable. This ``null space'' has implications for making comparisons
between predictions from general circulation models (GCMs) and the observed
planet maps, and, thus, affects our understanding of the physical processes
driving the observed maps. We describe the eclipse-mapping null space and show
how GCM forward models can be transformed to their observable modes for more
appropriate comparison with retrieved eclipse maps, demonstrated with
applications to synthetic data of an ultra-hot Jupiter and a cloudy warm
Jupiter under JWST-best-case- and extreme-precision observing scenarios. We
show that the effects of the null space can be mitigated and manipulated
through observational design, and JWST exposure times are short enough to not
increase the size of the null space. Furthermore, we show the mathematical
connection between the null space and the ``eigenmapping'' method,
demonstrating how eigenmaps can be used to understand the null space in a
model-independent way. We leverage this connection to incorporate null-space
uncertainties in retrieved maps, which increases the uncertainties to now
encompass the ground truth for synthetic data. The comparisons between observed
maps and forward models that are enabled by this work, and the improved
eclipse-mapping uncertainties, will be critical to our interpretation of
multidimensional aspects of exoplanets in the JWST era.Comment: 20 pages, 12 figures. Accepted for publication in The Astronomical
Journal. Note that PDF readers may blur figures 1 and 3, which can be fixed
by zooming i
Proxima Centauri b is not a transiting exoplanet
We report Spitzer Space Telescope observations during predicted transits of
the exoplanet Proxima Centauri b. As the nearest terrestrial habitable-zone
planet we will ever discover, any potential transit of Proxima b would place
strong constraints on its radius, bulk density, and atmosphere. Subsequent
transmission spectroscopy and secondary-eclipse measurements could then probe
the atmospheric chemistry, physical processes, and orbit, including a search
for biosignatures. However, our photometric results rule out planetary transits
at the 200~ppm level at 4.5, yielding a 3 upper radius limit
of 0.4~R_\rm{\oplus} (Earth radii). Previous claims of possible transits from
optical ground- and space-based photometry were likely correlated noise in the
data from Proxima Centauri's frequent flaring. Follow-up observations should
focus on planetary radio emission, phase curves, and direct imaging. Our study
indicates dramatically reduced stellar activity at near-to-mid infrared
wavelengths, compared to the optical. Proxima b is an ideal target for
space-based infrared telescopes, if their instruments can be configured to
handle Proxima's brightness.Comment: 8 pages, 3 figures, 2 tables, accepted for publication in MNRA
Latitudinal Asymmetry in the Dayside Atmosphere of WASP-43b
We present two-dimensional near-infrared temperature maps of the canonical hot Jupiter WASP-43b using a phase-curve observation with JWST NIRSpec/G395H. From the white-light planetary transit, we improve constraints on the planet’s orbital parameters and measure a planet-to-star radius ratio of 0.15883−0.00053+0.00056 . Using the white-light phase curve, we measure a longitude of maximum brightness of 6.9−0.°5+0.°5 east of the substellar point and a phase-curve offset of 10.0−0.°8+0.°8 . We also find a ≈4σ detection of a latitudinal hotspot offset of −13.4−1.°7+3.°2 , the first significant detection of a nonequatorial hotspot in an exoplanet atmosphere. We show that this detection is robust to variations within planetary parameter uncertainties, but only if the transit is used to improve constraints, showing the importance of transit observations to eclipse mapping. Maps retrieved from the NRS1 and NRS2 detectors are similar, with hotspot locations consistent between the two detectors at the 1σ level. Our JWST data show brighter (hotter) nightsides and a dimmer (colder) dayside at the shorter wavelengths relative to fits to Spitzer 3.6 and 4.5 μm phase curves. Through comparison between our phase curves and a set of general circulation models, we find evidence for clouds on the nightside and atmospheric drag or high metallicity reducing the eastward hotspot offset
On-chain electrodynamics of metallic (TMTSF)_2 X salts: Observation of Tomonaga-Luttinger liquid response
We have measured the electrodynamic response in the metallic state of three
highly anisotropic conductors, (TMTSF)_2 X, where X=PF_6, AsF_6, or ClO_4, and
TMTSF is the organic molecule tetramethyltetraselenofulvalene. In all three
cases we find dramatic deviations from a simple Drude response. The optical
conductivity has two features: a narrow mode at zero frequency, with a small
spectral weight, and a mode centered around 200 cm^{-1}, with nearly all of the
spectral weight expected for the relevant number of carriers and single
particle bandmass. We argue that these features are characteristic of a nearly
one-dimensional half- or quarter-filled band with Coulomb correlations, and
evaluate the finite energy mode in terms of a one-dimensional Mott insulator.
At high frequencies (\hbar\omega > t_\perp, the transfer integral perpendicular
to the chains), the frequency dependence of the optical conductivity
\sigma_1(\omega) is in agreement with calculations based on an interacting
Tomonaga-Luttinger liquid, and is different from what is expected for an
uncorrelated one-dimensional semiconductor. The zero frequency mode shows
deviations from a simple Drude response, and can be adequately described with a
frequency dependent mass and relaxation rate.Comment: 12 pages, 7 figures, RevTeX; minor corrections to text and
references; To be published in Phys. Rev. B, 15 July 199
Two-dimensional Eclipse Mapping of the Hot-Jupiter WASP-43b with JWST MIRI/LRS
We present eclipse maps of the two-dimensional thermal emission from the dayside of the hot-Jupiter WASP-43b, derived from an observation of a phase curve with the JWST MIRI/LRS instrument. The observed eclipse shapes deviate significantly from those expected for a planet emitting uniformly over its surface. We fit a map to this deviation, constructed from spherical harmonics up to order ℓmax=2 , alongside the planetary, orbital, stellar, and systematic parameters. This yields a map with a meridionally averaged eastward hot-spot shift of (7.75 ± 0.36)°, with no significant degeneracy between the map and the additional parameters. We show the latitudinal and longitudinal contributions of the dayside emission structure to the eclipse shape, finding a latitudinal signal of ∼200 ppm and a longitudinal signal of ∼250 ppm. To investigate the sensitivity of the map to the method, we fix the parameters not used for mapping and derive an “eigenmap” fitted with an optimized number of orthogonal phase curves, which yields a similar map to the ℓmax=2 map. We also fit a map up to ℓmax=3 , which shows a smaller hot-spot shift, with a larger uncertainty. These maps are similar to those produced by atmospheric simulations. We conclude that there is a significant mapping signal which constrains the spherical harmonic components of our model up to ℓmax=2 . Alternative mapping models may derive different structures with smaller-scale features; we suggest that further observations of WASP-43b and other planets will drive the development of more robust methods and more accurate maps
Thermal Imaging of Nanostructures by Quantitative Optical Phase Analysis
International audienceWe introduce an optical microscopy technique aimed at characterizing the heat generation arising from nanostructures, in a comprehensive and quantitative manner. Namely, the technique permits (i) mapping the temperature distribution around the source of heat, (ii) mapping the heat power density delivered by the source, and (iii) retrieving the absolute absorption cross section of light-absorbing structures. The technique is based on the measure of the thermal-induced refractive index variation of the medium surrounding the source of heat. The measurement is achieved using an association of a regular CCD camera along with a modified Hartmann diffraction grating. Such a simple association makes this technique straightforward to implement on any conventional microscope with its native broadband illumination conditions. We illustrate this technique on gold nanoparticles illuminated at their plasmonic resonance. The spatial resolution of this technique is diffraction limited, and temperature variations weaker than 1 K can be detected
Maskless Plasmonic Lithography at 22 nm Resolution
Optical imaging and photolithography promise broad applications in nano-electronics, metrologies, and single-molecule biology. Light diffraction however sets a fundamental limit on optical resolution, and it poses a critical challenge to the down-scaling of nano-scale manufacturing. Surface plasmons have been used to circumvent the diffraction limit as they have shorter wavelengths. However, this approach has a trade-off between resolution and energy efficiency that arises from the substantial momentum mismatch. Here we report a novel multi-stage scheme that is capable of efficiently compressing the optical energy at deep sub-wavelength scales through the progressive coupling of propagating surface plasmons (PSPs) and localized surface plasmons (LSPs). Combining this with airbearing surface technology, we demonstrate a plasmonic lithography with 22 nm half-pitch resolution at scanning speeds up to 10 m/s. This low-cost scheme has the potential of higher throughput than current photolithography, and it opens a new approach towards the next generation semiconductor manufacturing
Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b
Hot Jupiters are among the best-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5-12 μm with JWST's Mid-Infrared Instrument (MIRI). The spectra reveal a large day-night temperature contrast (with average brightness temperatures of 1524±35 and 863±23 Kelvin, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase curve shape and emission spectra strongly suggest the presence of nightside clouds which become optically thick to thermal emission at pressures greater than ~100 mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Contrary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2σ upper limit of 1-6 parts per million, depending on model assumptions)
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