333 research outputs found
On High-Contrast Characterization of Nearby, Short-Period Exoplanets with Giant Segmented-Mirror Telescopes
Measurements of the frequency with which short-period planets occur around
main sequence stars allows a direct prediction of the number and types of such
planets that will be amenable to characterization by high-contrast instruments
on future giant segmented- mirror telescopes (GSMTs). Adopting conservative
assumptions, I predict of order 10 planets with radii R_P=1-8 R_Earth and
equilibrium temperatures <400 K should be accessible around stars within 8 pc
of the Sun. These numbers are roughly the same for both near-infrared
observations of scattered starlight and mid-infrared observations of planetary
thermal emission, with the latter observations demonstrating greater relative
sensitivity to smaller and cooler planets. Adopting the conservative assumption
that planets with R_P=1-2 R_E and 2-4 R_E occur with equal frequency, I predict
a 40% chance that a planet with R_P=1-2 R_E and equilibrium temperature 200-250
K will accessible to high-contrast thermal infrared characterization; this
would be a compelling object for further study. To validate these predictions,
more detailed analyses are needed of the occurrence frequencies of low-mass
planets around M dwarfs, both in the Kepler field and in the solar
neighborhood. Several planets already discovered by radial velocity surveys
will be accessible to near-infrared high-contrast GSMT observations, including
the low-mass planets alpha Cen Bb and (depending on their albedos) GJ 139c and
d, GJ 876b and c, and tau Cet b, c, and d; tau Cet f would be amenable to
thermal infrared characterization. Further efforts to model the near-infrared
reflectance and mid-infrared emission of these and other short-period planets
are clearly warranted, and will pave the way for the interpretation of future
high-contrast characterization of a variety of planets around the nearest
stars.Comment: A&A Accepted. 10 pages, 5 figures, 1 tabl
Doppler Imaging of Exoplanets and Brown Dwarfs
Doppler Imaging produces 2D global maps of rotating objects using
high-dispersion spectroscopy. When applied to brown dwarfs and extrasolar
planets, this technique can constrain global atmospheric dynamics and/or
magnetic effects on these objects in un- precedented detail. I present the
first quantitative assessment of the prospects for Doppler Imaging of
substellar objects with current facilities and with future giant ground-based
telescopes. Observations will have the greatest sensitivity in K band, but the
H and L bands will also be useful for these purposes. To assess the number and
availability of targets, I also present a compilation of all measurements of
photometric variability, rotation period (P), and projected rotational velocity
(v sin i) for brown dwarfs and exoplanets. Several bright objects are already
accessible to Doppler Imaging with currently available instruments. With the
development of giant ground-based telescopes, Doppler Imaging will become
feasible for many dozens of brown dwarfs and for the few brightest directly
imaged extrasolar planets (such as beta Pic b). The present set of measurements
of P, v sin i, and variability are incomplete for many objects, and the sample
is strongly biased toward early-type objects (< L5). Thus, surveys to measure
these quantities for later-type objects will be especially helpful in expanding
the sample of candidates for global weather monitoring via Doppler Imaging.Comment: 11 pages, 4 figures, 1 electronic table. Recommended for publication
in A&A. Includes referee correction
Photometry as a proxy for stellar activity in radial velocity analyses
Stellar activity remains a limiting factor in measuring precise planet
parameters from radial velocity spectroscopy, not least in the search for Earth
mass planets orbiting in the habitable zones of Sun-like stars. One approach to
mitigate stellar activity is to use combined analyses of both radial velocity
and time-series photometry. We present an analysis of simultaneous
disk-integrated photometry and radial velocity data of the Sun in order to
determine the useful limits of a combined analysis. We find that simple
periodogram or autocorrelation analysis of solar photometry give the correct
rotation period <50% of the time. We therefore use a Gaussian process to
investigate the time variability of solar photometry and to directly compare
simultaneous photometry with radial velocity data. We find that the
hyperparameter posteriors are relatively stable over 70 years of solar
photometry and the amplitude tracks the solar cycle. We observe good agreement
between the hyperparameter posteriors for the simultaneous photometry and
radial velocity data. Our primary conclusion is a recommendation to include an
additional prior in Gaussian process fits to constrain the evolutionary
timescale to be greater than the recurrence timescale (ie., the rotation
period) to recover more physically plausible and useful results. Our results
indicate that such simultaneous monitoring may be a useful tool in enhancing
the precision of radial velocity surveys.Comment: 10 pages, accepted in A
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
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 systems1,2. Access to the chemical inventory of an exoplanet requires high-precision observations, often inferred from individual molecular detections with low-resolution space-based3,4,5 and high-resolution ground-based6,7,8 facilities. Here we report the medium-resolution (R ≈ 600) transmission spectrum of an exoplanet atmosphere between 3 and 5 μm covering several absorption features for the Saturn-mass exoplanet WASP-39b (ref. 9), obtained with the Near Infrared Spectrograph (NIRSpec) G395H grating of JWST. Our observations achieve 1.46 times 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 CO2 (28.5σ) and H2O (21.5σ), and identify SO2 as the source of absorption at 4.1 μm (4.8σ). Best-fit atmospheric models range between 3 and 10 times solar metallicity, with sub-solar to solar C/O ratios. These results, including the detection of SO2, underscore the importance of characterizing the chemistry in exoplanet atmospheres and showcase NIRSpec G395H as an excellent mode for time-series observations over this critical wavelength rang
Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM
Transmission spectroscopy1,2,3 of exoplanets has revealed signatures of water vapour, aerosols and alkali metals in a few dozen exoplanet atmospheres4,5. 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 species—in particular the primary carbon-bearing molecules6,7. Here we report a broad-wavelength 0.5–5.5 µm atmospheric transmission spectrum of WASP-39b8, a 1,200 K, roughly Saturn-mass, Jupiter-radius exoplanet, measured with the JWST NIRSpec’s PRISM mode9 as part of the JWST Transiting Exoplanet Community Early Release Science Team Program10,11,12. We robustly detect several chemical species at high significance, including Na (19σ), H2O (33σ), CO2 (28σ) and CO (7σ). The non-detection of CH4, combined with a strong CO2 feature, favours atmospheric models with a super-solar atmospheric metallicity. An unanticipated absorption feature at 4 µm is best explained by SO2 (2.7σ), which could be a tracer of atmospheric photochemistry. These observations demonstrate JWST’s sensitivity to a rich diversity of exoplanet compositions and chemical processes
Early Release Science of the exoplanet WASP-39b with JWST NIRISS
The Saturn-mass exoplanet WASP-39b has been the subject of extensive efforts to determine its atmospheric properties using transmission spectroscopy1,2,3,4. However, these efforts have been hampered by modelling degeneracies between composition and cloud properties that are caused by limited data quality5,6,7,8,9. Here we present the transmission spectrum of WASP-39b obtained using the Single-Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST. This spectrum spans 0.6–2.8 μm in wavelength and shows several water-absorption bands, the potassium resonance doublet and 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, favouring a heavy-element enhancement (‘metallicity’) of about 10–30 times 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 also best explained by wavelength-dependent, non-grey clouds with inhomogeneous coverageof the planet’s terminator
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