Search

Transmission spectroscopy1–3of 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 mode9as part of the JWST Transiting Exoplanet Community Early Release Science Team Program10–12. 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 CO2feature, 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.

This paper reports an investigation of the oxidation state of Cr in samples of natural cements formed 500 ky ago in Maqarin (Jordan). The analyses were conducted using the Scanning Microscope from the ID21 beamline at the ESRF (Grenoble-France) operated in fluorescence mode. Cr(III) and Cr(VI) maps are collected on these samples at a resolution of 1 μm. The results suggest the slow oxidation of Cr(III) to Cr(VI) upon alteration of the cements in conditions of high pH and low to intermediate oxygen fugacity.

Observing sites at the east-Antarctic plateau are considered to provide exceptional conditions for astronomy. The aim of this work is to assess its potential for detecting transiting extrasolar planets through a comparison and combination of photometric data from Antarctica with time series from a midlatitude site. During 2010, the two small aperture telescopes ASTEP 400 (Dome C) and BEST II (Chile) together performed an observing campaign of two target fields and the transiting planet WASP-18b. For the latter, a bright star, Dome C appears to yield an advantageous signal-to-noise ratio. For field surveys, both Dome C and Chile appear to be of comparable photometric quality. However, within two weeks, observations at Dome C yield a transit detection efficiency that typically requires a whole observing season in Chile. For the first time, data from Antarctica and Chile have been combined to extent the observational duty cycle. This approach is both feasible in practice and favorable for transit search, as it increases the detection yield by 12-18%.

Exoplanetary transit and stellar oscillation surveys require a very high precision photometry. The instrumental noise has therefore to be minimized. First, we perform a semi-analytical model of different noise sources. We show that the noise due the CCD electrodes can be overcome using a Gaussian PSF (Point Spread Function) of full width half maximum larger than 1.6 pixels. We also find that for a PSF size of a few pixels, the photometric aperture has to be at least 2.5 times larger than the PSF full width half maximum. Then, we compare a front- with a back-illuminated CCD through a Monte-Carlo simulation. Both cameras give the same results for a PSF full width half maximum larger than 1.5 pixels. All these simulations are applied to the A STEP (Antarctica Search for Transiting Extrasolar Planets) project. As a result, we choose a front-illuminated camera for A STEP because of its better resolution and lower price, and we will use a PSF larger than 1.6 pixels. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Context. The Concordia base in Dome C, Antarctica, is an extremely promising site for photometric astronomy due to the 3-month long night during the Antarctic winter, favorable weather conditions, and low scintillation.Aims. The ASTEP project (Antarctic Search for Transiting ExoPlanets) is a pilot project to discover transiting planets and understand the limits of visible photometry from the Concordia site.Methods. ASTEP South is the first phase of the ASTEP project. The instrument is a fixed 10 cm refractor with a 4k?$\times$?4k CCD camera in a thermalized box, pointing continuously a 3.88 $\times$3.88°2field of view centered on the celestial south pole. We describe the project and report results of a preliminary data analysis.Results. ASTEP South became fully functional in June 2008 and obtained 1592 hours of data during the 2008 Antarctic winter. The data are of good quality but the analysis has to account for changes in the PSF (point spread function) due to rapid ground seeing variations and instrumental effects. The pointing direction is stable within 10 arcsec on a daily timescale and drifts by only 34 arcsec in 50 days. A truly continuous photometry of bright stars is possible in June (the noon sky background peaks at a magnitude R˜15?arcsec-2on June 22), but becomes challenging in July (the noon sky background magnitude is R˜12.5?arcsec-2on July 20). The weather conditions are estimated from the number of stars detected in the field. For the 2008 winter, the statistics are between 56.3% and 68.4% of excellent weather, 17.9% to 30% of veiled weather (when the probable presence of thin clouds implies a lower number of detected stars) and 13.7% of bad weather. Using these results in a probabilistic analysis of transit detection, we show that the detection efficiency of transiting exoplanets in one given field is improved at Dome C compared to a temperate site such as La Silla. For example we estimate that a year-long campaign of 10 cm refractor could reach an efficiency of 69% at Dome C versus 45% at La Silla for detecting 2-day period giant planets around target stars from magnitude 10 to 15. The detection efficiency decreases for planets with longer orbital periods, but in relative sense it is even more favorable to Dome C.Conclusions. This shows the high potential of Dome C for photometry and future planet discoveries.

Context. The Concordia base in Dome C, Antarctica, is an extremely promising site for photometric astronomy due to the 3-month long night during the Antarctic winter, favorable weather conditions, and low scintillation.