ACCESS and LRG-BEASTS: A Precise New Optical Transmission Spectrum of the Ultrahot Jupiter WASP-103b
Nikolov, Nikolay; Gibson, Neale P.; Wilson, Jamie; Kirk, James; López-Morales, Mercedes; MacDonald, Ryan J.; Jordán, Andrés; Espinoza, Néstor; Wheatley, Peter J.; Apai, Dániel; Lendl, Monika; Bixel, Alex; Rackham, Benjamin V.; Lewis, Nikole K.; Louden, Tom; Rodler, Florian; McGruder, Chima D.; Osip, David J.; Weaver, Ian C.; Skillen, Ian
United States, Switzerland, United Kingdom, Chile, Spain, Ireland
Abstract
We present a new ground-based optical transmission spectrum of the ultrahot Jupiter WASP-103b ( ${T}_{\mathrm{eq}}=2484$ K). Our transmission spectrum is the result of combining five new transits from the ACCESS survey and two new transits from the LRG-BEASTS survey with a reanalysis of three archival Gemini/GMOS transits and one VLT/FORS2 transit. Our combined 11-transit transmission spectrum covers a wavelength range of 3900-9450 Å with a median uncertainty in the transit depth of 148 parts per million, which is less than one atmospheric scale height of the planet. In our retrieval analysis of WASP-103b's combined optical and infrared transmission spectrum, we find strong evidence for unocculted bright regions (4.3σ) and weak evidence for H2O ( $1.9\sigma $ ), HCN ( $1.7\sigma $ ), and TiO ( $2.1\sigma $ ), which could be responsible for WASP-103b's observed temperature inversion. Our optical transmission spectrum shows significant structure that is in excellent agreement with the extensively studied ultrahot Jupiter WASP-121b, for which the presence of VO has been inferred. For WASP-103b, we find that VO can only provide a reasonable fit to the data if its abundance is implausibly high and we do not account for stellar activity. Our results highlight the precision that can be achieved by ground-based observations and the impacts that stellar activity from F-type stars can have on the interpretation of exoplanet transmission spectra.