59 research outputs found
LRG-BEASTS: Evidence for clouds in the transmission spectrum of HATS-46 b
We have performed low-resolution ground-based spectroscopy of HATS-46 b in
transmission, using the EFOSC2 instrument on the ESO New Technology Telescope
(NTT). HATS-46 b is a highly-inflated exoplanet that is a prime target for
transmission spectroscopy, having a Jupiter-like radius (0.95 R)
but a much lower mass (0.16 M). It orbits a G-type star with a
4.7 d period, giving an equilibrium temperature of 1100 K. We observed one
transit of HATS-46 b with the NTT, with the time-series spectra covering a
wavelength range of 3900 - 9000 Angstrom at a resolution of . We
achieved a remarkably precise transmission spectrum of 1.03 photon
noise, with a median uncertainty of ppm for Angstrom wide
bins, despite the relative faintness of the host star with . The transmission spectrum does not show strong absorption features and
retrievals favour a cloudy model, ruling out a clear atmosphere with
confidence. We also place a conservative upper limit on the sodium
abundance under the alternative scenario of a clear atmosphere. This is the
eighth planet in the LRG-BEASTS survey, which uses 4m-class telescopes such as
the NTT to obtain low-resolution transmission spectra of hot Jupiters with
precisions of around one atmospheric scale height.Comment: 10 pages, 7 figures, 4 tables, accepted for publication in MNRA
The HARPS search for southern extra-solar planets XLV. Two Neptune mass planets orbiting HD 13808: a study of stellar activity modelling's impact on planet detection
We present a comprehensive analysis of 10 years of HARPS radial velocities of
the K2V dwarf star HD 13808, which has previously been reported to host two
unconfirmed planet candidates. We use the state-of-the-art nested sampling
algorithm PolyChord to compare a wide variety of stellar activity models,
including simple models exploiting linear correlations between RVs and stellar
activity indicators, harmonic models for the activity signals, and a more
sophisticated Gaussian process regression model. We show that the use of
overly-simplistic stellar activity models that are not well-motivated
physically can lead to spurious `detections' of planetary signals that are
almost certainly not real. We also reveal some difficulties inherent in
parameter and model inference in cases where multiple planetary signals may be
present. Our study thus underlines the importance both of exploring a variety
of competing models and of understanding the limitations and precision settings
of one's sampling algorithm. We also show that at least in the case of HD
13808, we always arrive at consistent conclusions about two particular signals
present in the RV, regardless of the stellar activity model we adopt; these two
signals correspond to the previously-reported though unconfirmed planet
candidate signals. Given the robustness and precision with which we can
characterize these two signals, we deem them secure planet detections. In
particular, we find two planets orbiting HD 13808 at distances of 0.11, 0.26 AU
with periods of 14.2, 53.8 d, and minimum masses of 11, 10 Earth masses
Исследование элементного состава проб твердой фазы снега в окрестностях цементного завода (Кемеровская область)
The objectives and methodology of the EU-funded research project HYVOLUTION devoted to hydrogen production from biomass are reviewed. The main scientific objective of this project is the development of a novel two-stage bioprocess employing thermophilic and phototrophic bacteria, for the cost-effective production of pure hydrogen from multiple biomass feedstocks in small-scale, cost-effective industries. Results are summarised of the work on pretreatment technologies for optimal biodegradation of energy crops and bio-residues, conditions for maximum efficiency in conversion of fermentable biomass to hydrogen and CO2, concepts of dedicated installations for optimal gas cleaning and gas quality protocols, as well as innovative system integration aimed at minimizing energy demand and maximizing product output. The main technological objective is the construction of prototype modules of the plant which, when assembled, form the basis of a blueprint for the whole chain for converting biomass to pure hydrogen. A brief outline is presented of the progress made towards developing reactors for thermophilic hydrogen production, reactors for photoheterotrophic hydrogen production and equipment for optimal gas cleaning procedures
ACCESS, LRG-BEASTS, & MOPSS: Featureless Optical Transmission Spectra of WASP-25b and WASP-124b
We present new optical transmission spectra for two hot Jupiters: WASP-25b (M
= 0.56~M; R = 1.23 R; P =~3.76 days) and WASP-124b (M = 0.58~M; R =
1.34 R; P = 3.37 days), with wavelength coverages of 4200 - 9100\AA\ and
4570 - 9940\AA, respectively. These spectra are from the ESO Faint Object
Spectrograph and Camera (v.2) mounted on the New Technology Telescope (NTT) and
Inamori-Magellan Areal Camera & Spectrograph on Magellan Baade. No strong
spectral features were found in either spectra, with the data probing 4 and 6
scale heights, respectively. \texttt{Exoretrievals} and \texttt{PLATON}
retrievals favor stellar activity for WASP-25b, while the data for WASP-124b
did not favor one model over another. For both planets the retrievals found a
wide range in the depths where the atmosphere could be optically thick
( - 0.2 bars for WASP-25b and 1.6 -- 32 bars for WASP-124b)
and recovered a temperature that is consistent with the planets' equilibrium
temperatures, but with wide uncertainties (up to 430K). For
WASP-25b, the models also favor stellar spots that are 500-3000K
cooler than the surrounding photosphere. The fairly weak constraints on
parameters are owing to the relatively low precision of the data, with an
average precision of 840 and 1240 ppm per bin for WASP-25b and WASP-124b,
respectively. However, some contribution might still be due to an inherent
absence of absorption or scattering in the planets' upper atmospheres, possibly
because of aerosols. We attempt to fit the strength of the sodium signals to
the aerosol-metallicity trend proposed by McGruder et al. 2023, and find
WASP-25b and WASP-124b are consistent with the prediction, though their
uncertainties are too large to confidently confirm the trend.Comment: Accepted in AJ July 202
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
Identification of carbon dioxide in an exoplanet atmosphere
Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (that is, elements heavier than helium, also called 'metallicity')1-3, and thus the formation processes of the primary atmospheres of hot gas giants4-6. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets7-9. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification10-12. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science programme13,14. The data used in this study span 3.0-5.5 micrometres in wavelength and show a prominent CO2 absorption feature at 4.3 micrometres (26-sigma significance). The overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 micrometres that is not reproduced by these models
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