38 research outputs found
Quantifying the Transit Light Source Effect: Measurements of Spot Temperature and Coverage on the Photosphere of AU Microscopii with High-Resolution Spectroscopy and Multi-Color Photometry
AU Mic is an active 24 Myr pre-main sequence M dwarf in the stellar
neighborhood (d9.7 pc) with a rotation period of 4.86 days. The two
transiting planets orbiting AU Mic, AU Mic b and c, are warm sub-Neptunes on
8.5 and 18.9 day periods and are targets of interest for atmospheric
observations of young planets. Here we study AU Mic's unocculted starspots
using ground-based photometry and spectra in order to complement current and
future transmission spectroscopy of its planets. We gathered multi-color LCO
0.4m SBIG photometry to study the star's rotational modulations and LCO NRES
high-resolution spectra to measure the different spectral components within the
integrated spectrum of the star, parameterized by 3 spectral components and
their coverage fractions. We find AU Mic's surface has at least 2 spectral
components, a K ambient photosphere with cool spots that have a
temperature of K and cover percent of the surface,
increasing and decreasing by 5 from the average throughout a rotation. We
also detect a third flux component with a filling factor less than 0.5 and
a largely uncertain temperature that we attribute to flare flux not entirely
omitted in the time-averaged spectra. We include measurements of spot
temperature and coverage fraction from both 2- and 3- temperature models, which
we find agree with each other strongly. Our expanded use of various techniques
to study starspots will help us better understand this system and may have
applications for interpreting the transmission spectra for exoplanets
transiting stars of a wide range of activity levels.Comment: 25 pages, 13 figures, Accepted to Ap
Importance of Sample Selection in Exoplanet Atmosphere Population Studies
Understanding planet formation requires robust population studies, which are
designed to reveal trends in planet properties. In this work, we aim to
determine if different methods for selecting populations of exoplanets for
atmospheric characterization with JWST could influence population-level
inferences. We generate three hypothetical surveys of
super-Earths/sub-Neptunes, each spanning a similar radius-insolation flux
space. The survey samples are constructed based on three different selection
criteria (evenly-spaced-by-eye, binned, and a quantitative selection function).
Using an injection-recovery technique, we test how robustly individual-planet
atmospheric parameters and population-level parameters can be retrieved. We
find that all three survey designs result in equally suitable targets for
individual atmospheric characterization, but not equally suitable targets for
constraining population parameters. Only samples constructed with a
quantitative method or that are sufficiently evenly-spaced-by-eye result in
robust population parameter constraints. Furthermore, we find that the sample
with the best targets for individual atmospheric study does not necessarily
result in the best constrained population parameters. The method of sample
selection must be considered. We also find that there may be large variability
in population-level results with a sample that is small enough to fit in a
single JWST cycle (12 planets), suggesting that the most successful
population-level analyses will be multi-cycle. Lastly, we infer that our
exploration of sample selection is limited by the small number of transiting
planets with measured masses around bright stars. Our results can guide future
development of programs that aim to determine underlying trends in exoplanet
atmospheric properties and, by extension, formation and evolution processes.Comment: 16 pages, 7 figures, accepted Ap
Double Trouble: Two Transits of the Super-Earth GJ 1132 b Observed with JWST NIRSpec G395H
The search for rocky planet atmospheres with JWST has focused on planets
transiting M dwarfs. Such planets have favorable planet-to-star size ratios,
enhancing the amplitude of atmospheric features. Since the expected signal
strength of atmospheric features is similar to the single-transit performance
of JWST, multiple observations are required to confirm any detection. Here, we
present two transit observations of the rocky planet GJ 1132 b with JWST
NIRSpec G395H, covering 2.8-5.2 m. Previous HST WFC3 observations of GJ
1132 b were inconclusive, with evidence reported for either an atmosphere or a
featureless spectrum based on analyses of the same dataset. Our JWST data
exhibit substantial differences between the two visits. One transit is
consistent with either a HO-dominated atmosphere containing ~1% CH and
trace NO ( = 1.13) or stellar contamination from unocculted
starspots ( = 1.36). However, the second transit is consistent
with a featureless spectrum. Neither visit is consistent with a previous report
of HCN. Atmospheric variability is unlikely to explain the scale of the
observed differences between the visits. Similarly, our out-of-transit stellar
spectra show no evidence of changing stellar inhomogeneity between the two
visits - observed 8 days apart, only 6.5% of the stellar rotation rate. We
further find no evidence of differing instrumental systematic effects between
visits. The most plausible explanation is an unlucky random noise draw leading
to two significantly discrepant transmission spectra. Our results highlight the
importance of multi-visit repeatability with JWST prior to claiming atmospheric
detections for these small, enigmatic planets.Comment: 22 pages, 10 figures, 2 tables. Accepted for publication in ApJ
Letters. Co-First Authors. Bonus materials and spectral data:
https://doi.org/10.5281/zenodo.1000208
Detection of carbon monoxide's 4.6 micron fundamental band structure in WASP-39b's atmosphere with JWST NIRSpec G395H
Carbon monoxide (CO) is predicted to be the dominant carbon-bearing molecule in giant planet atmospheres and, along with water, is important for discerning the oxygen and therefore carbon-to-oxygen ratio of these planets. The fundamental absorption mode of CO has a broad, double-branched structure composed of many individual absorption lines from 4.3 to 5.1 μm, which can now be spectroscopically measured with JWST. Here we present a technique for detecting the rotational sub-band structure of CO at medium resolution with the NIRSpec G395H instrument. We use a single transit observation of the hot Jupiter WASP-39b from the JWST Transiting Exoplanet Community Early Release Science (JTEC ERS) program at the native resolution of the instrument (R ~ 2700) to resolve the CO absorption structure. We robustly detect absorption by CO, with an increase in transit depth of 264 ± 68 ppm, in agreement with the predicted CO contribution from the best-fit model at low resolution. This detection confirms our theoretical expectations that CO is the dominant carbon-bearing molecule in WASP-39b's atmosphere and further supports the conclusions of low C/O and supersolar metallicities presented in the JTEC ERS papers for WASP-39b
JWST-TST DREAMS: Quartz Clouds in the Atmosphere of WASP-17b
Clouds are prevalent in many of the exoplanet atmospheres that have been
observed to date. For transiting exoplanets, we know if clouds are present
because they mute spectral features and cause wavelength-dependent scattering.
While the exact composition of these clouds is largely unknown, this
information is vital to understanding the chemistry and energy budget of
planetary atmospheres. In this work, we observe one transit of the hot Jupiter
WASP-17b with JWST's MIRI LRS and generate a transmission spectrum from 5-12
m. These wavelengths allow us to probe absorption due to the
vibrational modes of various predicted cloud species. Our transmission spectrum
shows additional opacity centered at 8.6 m, and detailed atmospheric
modeling and retrievals identify this feature as SiO(s) (quartz) clouds.
The SiO(s) clouds model is preferred at 3.5-4.2 versus a cloud-free
model and at 2.6 versus a generic aerosol prescription. We find the
SiO(s) clouds are comprised of small m particles,
which extend to high altitudes in the atmosphere. The atmosphere also shows a
depletion of HO, a finding consistent with the formation of
high-temperature aerosols from oxygen-rich species. This work is part of a
series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we
will use Guaranteed Time Observations to perform Deep Reconnaissance of
Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).Comment: 19 pages, 7 figures, accepted for publication in ApJ
Photochemically produced SO2 in the atmosphere of WASP-39b
Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability1. However, no unambiguous photochemical products have been detected in exoplanet atmospheres so far. Recent observations from the JWST Transiting Exoplanet Community Early Release Science Program2,3 found a spectral absorption feature at 4.05 μm arising from sulfur dioxide (SO2) in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 MJ) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of around 1,100 K (ref. 4). The most plausible way of generating SO2 in such an atmosphere is through photochemical processes5,6. Here we show that the SO2 distribution computed by a suite of photochemical models robustly explains the 4.05-μm spectral feature identified by JWST transmission observations7 with NIRSpec PRISM (2.7σ)8 and G395H (4.5σ)9. SO2 is produced by successive oxidation of sulfur radicals freed when hydrogen sulfide (H2S) is destroyed. The sensitivity of the SO2 feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of about 10× solar. We further point out that SO2 also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations
Photochemically-produced SO in the atmosphere of WASP-39b
Photochemistry is a fundamental process of planetary atmospheres that
regulates the atmospheric composition and stability. However, no unambiguous
photochemical products have been detected in exoplanet atmospheres to date.
Recent observations from the JWST Transiting Exoplanet Early Release Science
Program found a spectral absorption feature at 4.05 m arising from SO
in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass
(0.28 M) gas giant exoplanet orbiting a Sun-like star with an equilibrium
temperature of 1100 K. The most plausible way of generating SO in
such an atmosphere is through photochemical processes. Here we show that the
SO distribution computed by a suite of photochemical models robustly
explains the 4.05 m spectral feature identified by JWST transmission
observations with NIRSpec PRISM (2.7) and G395H (4.5). SO
is produced by successive oxidation of sulphur radicals freed when hydrogen
sulphide (HS) is destroyed. The sensitivity of the SO feature to the
enrichment of the atmosphere by heavy elements (metallicity) suggests that it
can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an
inferred metallicity of 10 solar. We further point out that
SO also shows observable features at ultraviolet and thermal infrared
wavelengths not available from the existing observations.Comment: 39 pages, 14 figures, accepted to be published in Natur
Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H
Measuring the abundances of carbon and oxygen in exoplanet atmospheres is
considered a crucial avenue for unlocking the formation and evolution of
exoplanetary systems. Access to an exoplanet's chemical inventory requires
high-precision observations, often inferred from individual molecular
detections with low-resolution space-based and high-resolution ground-based
facilities. Here we report the medium-resolution (R600) transmission
spectrum of an exoplanet atmosphere between 3-5 m covering multiple
absorption features for the Saturn-mass exoplanet WASP-39b, obtained with JWST
NIRSpec G395H. Our observations achieve 1.46x photon precision, providing an
average transit depth uncertainty of 221 ppm per spectroscopic bin, and present
minimal impacts from systematic effects. We detect significant absorption from
CO (28.5) and HO (21.5), and identify SO as the
source of absorption at 4.1 m (4.8). Best-fit atmospheric models
range between 3 and 10x solar metallicity, with sub-solar to solar C/O ratios.
These results, including the detection of SO, underscore the importance of
characterising the chemistry in exoplanet atmospheres, and showcase NIRSpec
G395H as an excellent mode for time series observations over this critical
wavelength range.Comment: 44 pages, 11 figures, 3 tables. Resubmitted after revision to Natur
Early Release Science of the exoplanet WASP-39b with JWST NIRISS
Transmission spectroscopy provides insight into the atmospheric properties
and consequently the formation history, physics, and chemistry of transiting
exoplanets. However, obtaining precise inferences of atmospheric properties
from transmission spectra requires simultaneously measuring the strength and
shape of multiple spectral absorption features from a wide range of chemical
species. This has been challenging given the precision and wavelength coverage
of previous observatories. Here, we present the transmission spectrum of the
Saturn-mass exoplanet WASP-39b obtained using the SOSS mode of the NIRISS
instrument on the JWST. This spectrum spans m in wavelength and
reveals multiple water absorption bands, the potassium resonance doublet, as
well as signatures of clouds. The precision and broad wavelength coverage of
NIRISS-SOSS allows us to break model degeneracies between cloud properties and
the atmospheric composition of WASP-39b, favoring a heavy element enhancement
("metallicity") of the solar value, a sub-solar
carbon-to-oxygen (C/O) ratio, and a solar-to-super-solar potassium-to-oxygen
(K/O) ratio. The observations are best explained by wavelength-dependent,
non-gray clouds with inhomogeneous coverage of the planet's terminator.Comment: 48 pages, 12 figures, 2 tables. Under review at Natur
Early Release Science of the exoplanet WASP-39b with JWST NIRCam
Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet
atmospheres is a fundamental step towards constraining the dominant chemical
processes at work and, if in equilibrium, revealing planet formation histories.
Transmission spectroscopy provides the necessary means by constraining the
abundances of oxygen- and carbon-bearing species; however, this requires broad
wavelength coverage, moderate spectral resolution, and high precision that,
together, are not achievable with previous observatories. Now that JWST has
commenced science operations, we are able to observe exoplanets at previously
uncharted wavelengths and spectral resolutions. Here we report time-series
observations of the transiting exoplanet WASP-39b using JWST's Near InfraRed
Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength
photometric light curves span 2.0 - 4.0 m, exhibit minimal systematics,
and reveal well-defined molecular absorption features in the planet's spectrum.
Specifically, we detect gaseous HO in the atmosphere and place an upper
limit on the abundance of CH. The otherwise prominent CO feature at 2.8
m is largely masked by HO. The best-fit chemical equilibrium models
favour an atmospheric metallicity of 1-100 solar (i.e., an enrichment
of elements heavier than helium relative to the Sun) and a sub-stellar
carbon-to-oxygen (C/O) ratio. The inferred high metallicity and low C/O ratio
may indicate significant accretion of solid materials during planet formation
or disequilibrium processes in the upper atmosphere.Comment: 35 pages, 13 figures, 3 tables, Nature, accepte