Signs of strong Na and K absorption in the transmission spectrum of WASP-103b

Abstract

Context: Transmission spectroscopy has become a prominent tool for characterizing the atmospheric properties on close-in transiting planets. Recent observations have revealed a remarkable diversity in exoplanet spectra, which show absorption signatures of Na, K and ${\mathrm{H}}_2\mathrm{O}$, in some cases partially or fully attenuated by atmospheric aerosols. Aerosols (clouds and hazes) themselves have been detected in the transmission spectra of several planets thanks to wavelength-dependent slopes caused by the particles' scattering properties. Aims: We present an optical 550 - 960 nm transmission spectrum of the extremely irradiated hot Jupiter WASP-103b, one of the hottest (2500 K) and most massive (1.5 $M_J$) planets yet to be studied with this technique. WASP-103b orbits its star at a separation of less than 1.2 times the Roche limit and is predicted to be strongly tidally distorted. Methods: We have used Gemini/GMOS to obtain multi-object spectroscopy hroughout three transits of WASP-103b. We used relative spectrophotometry and bin sizes between 20 and 2 nm to infer the planet's transmission spectrum. Results: We find that WASP-103b shows increased absorption in the cores of the alkali (Na, K) line features. We do not confirm the presence of any strong scattering slope as previously suggested, pointing towards a clear atmosphere for the highly irradiated, massive exoplanet WASP-103b. We constrain the upper boundary of any potential cloud deck to reside at pressure levels above 0.01 bar. This finding is in line with previous studies on cloud occurrence on exoplanets which find that clouds dominate the transmission spectra of cool, low surface gravity planets while hot, high surface gravity planets are either cloud-free, or possess clouds located below the altitudes probed by transmission spectra.

Accepted for publication in A&A

References in corpus (17)

• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• Rayleigh scattering in the transit spectrum of HD 189733b
• The Transit Light Curve Project. IX. Evidence for a Smaller Radius of the Exoplanet XO-3b
• Limb darkening and exoplanets: testing stellar model atmospheres and identifying biases in transit parameters
• HST hot-Jupiter transmission spectral survey: detection of potassium in WASP-31b along with a cloud deck and Rayleigh scattering
• The Transit Light Curve (TLC) Project. I. Four Consecutive Transits of the Exoplanet XO-1b
• A consistent retrieval analysis of 10 Hot Jupiters observed in transmission
• Friends of Hot Jupiters. IV. Stellar companions beyond 50 AU might facilitate giant planet formation, but most are unlikely to cause Kozai-Lidov migration
• On Correlated-noise Analyses Applied To Exoplanet Light Curves
• Rayleigh scattering by H2 in the extrasolar planet HD209458b
• VLT FORS2 comparative transmission spectroscopy: Detection of Na in the atmosphere of WASP-39b from the ground
• A Cloudiness Index for Transiting Exoplanets Based on the Sodium and Potassium Lines: Tentative Evidence for Hotter Atmospheres Being Less Cloudy at Visible Wavelengths
• High-precision photometry by telescope defocussing. VII. The ultra-short period planet WASP-103
• Potassium detection in the clear atmosphere of a hot-Jupiter: FORS2 transmission spectroscopy of WASP-17b
• Near-Infrared Emission Spectrum of WASP-103b using Hubble Space Telescope/Wide Field Camera 3
• Contamination from a nearby star cannot explain the anomalous transmission spectrum of the ultra-short period giant planet WASP-103b

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• Mitigating flicker noise in high-precision photometry. I -- Characterization of the noise structure, impact on the inferred transit parameters, and predictions for CHEOPS observations
• Ground-Based Transmission Spectroscopy with FORS2: A featureless optical transmission spectrum and detection of H${}_2$O for the ultra-hot Jupiter WASP-103b
• Multi-season optical modulation phased with the orbit of the super-Earth 55 Cnc e
• Three Hot-Jupiters on the upper edge of the mass-radius distribution: WASP-177, WASP-181 and WASP-183
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