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Neutral metals in the atmosphere of HD149026b

Recent progress in high-dispersion spectroscopy has revealed the presence of vaporized heavy metals and ions in the atmosphere of hot Jupiters whose dayside temperature is larger than 2000 K, categorized as ultra hot Jupiters (UHJs). Using the archival data of high resolution transmission spectroscopy obtained with the Subaru telescope, we searched for neutral metals in HD149026b, a hot Jupiter cooler than UHJs. By removing stellar and telluric absorption and using a cross-correlation technique, we report tentative detection of neutral titanium with 4.4 sigma and a marginal signal of neutral iron with 2.8 sigma in the atmosphere. This is the first detection of neutral titanium in an exoplanetary atmosphere. In this temperature range, titanium tends to form titanium oxide (TiO). The fact that we did not detect any signal from TiO suggests that the C/O ratio in the atmosphere is higher than the solar value. The detection of metals in the atmosphere of hot Jupiters cooler than UHJs will be useful for understanding the atmospheric structure and formation history of hot Jupiters.