Detection of Fe and evidence for TiO in the dayside emission spectrum of WASP-33b
Context. Theoretical studies predict the presence of thermal inversions in the atmosphere of highly irradiated gas giant planets. Recent observations have identified these inversion layers. However, the role of different chemical species in their formation remains unclear. Aims. We search for the signature of the thermal inversion agents TiO and Fe in the dayside emission spectrum of the ultra-hot Jupiter WASP-33b. Methods. The spectra were obtained with CARMENES and HARPS-N, covering different wavelength ranges. Telluric and stellar absorption lines were removed with SYSREM. We cross-correlated the residual spectra with model spectra to retrieve the signals from the planetary atmosphere. Results. We find evidence for TiO at a significance of 4.9σ with CARMENES. The strength of the TiO signal drops close to the secondary eclipse. No TiO signal is found with HARPS-N. An injection-recovery test suggests that the TiO signal is below the detection level at the wavelengths covered by HARPS-N. The emission signature of Fe is detected with both instruments at significance levels of 5.7σ and 4.5σ, respectively. By combining all observations, we obtain a significance level of 7.3σ for Fe. We find the TiO signal at Kp = 248.0-2.5+2.0 km s-1, which is in disagreement with the Fe detection at Kp = 225.0-3.5+4.0 km s-1. The Kp value for Fe is in agreement with prior investigations. The model spectra require different temperature profiles for TiO and Fe to match the observations. We observe a broader line profile for Fe than for TiO. Conclusions. Our results confirm the existence of a temperature inversion layer in the planetary atmosphere. The observed Kp offset and different strengths of broadening in the line profiles suggest the existence of a TiO-depleted hot spot in the planetary atmosphere. © ESO 2021. ; CARMENES is an instrument at the Centro Astronomico Hispano-Aleman (CAHA) at Calar Alto (Almeria, Spain), operated jointly by the Junta de Andalucia and the Instituto de Astrofisica de Andalucia (CSIC). CARMENES was funded by the Max-Planck-Gesellschaft (MPG), the Consejo Superior de Investigaciones Cientificas (CSIC), the Ministerio de Economia y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through projects FICTS-2011-02, ICTS-2017-07-CAHA-4, and CAHA16-CE-3978, and the members of the CARMENES Consortium (Max-Planck-Institut fur Astronomie, Instituto de Astrofisica de Andalucia, Landessternwarte Konigstuhl, Institut de Ciencies de l'Espai, Institut fur Astrophysik Gottingen, Universidad Complutense de Madrid, Thuringer Landessternwarte Tautenburg,Instituto de Astrofisica de Canarias, Hamburger Sternwarte, Centro de Astrobiologia and Centro Astronomico Hispano-Aleman), with additional contributions by the MINECO, the Deutsche Forschungsgemeinschaft through the Major Research Instrumentation Programme and Research Unit FOR2544 "Blue Planets around Red Stars", the Klaus Tschira Stiftung, the states of Baden-Wurttemberg and Niedersachsen, and by the Junta de Andalucia. We acknowledge financial support from the Deutsche Forschungsgemeinschaft through the priority program SPP 1992 "Exploring the Diversity of Extrasolar Planets" (RE 1664/16-1), the Research Unit FOR2544 "Blue Planets around Red Stars" (RE 1664/21-1), and grant CA 1795/3, the Agencia Estatal de Investigacion of the Ministerio de Ciencia, Innovacion y Universidades and the ERDF through projects PID2019-109522GB-C5[1:4]/AEI/10.13039/501100011033, PID2019-110689RB-I00/AEI/10.13039/501100011033, and the Centre of Excellence "Severo Ochoa" and "Maria de Maeztu" awards to the Instituto de Astrofisica de Canarias (SEV-2015-0548), Instituto de Astrofisica de Andalucia (SEV-2017-0709), and Centro de Astrobiologia (MDM-2017-0737), the European Research Council under the European Union's Horizon 2020 research and innovation program (832428), and the Generalitat de Catalunya/CERCA programme. This work is based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundacion Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. ; Peer reviewed