We report high-resolution spectroscopic detection of TiO molecular signature in the day-side spectra of WASP-33 b , the second hottest known hot Jupiter .
We used High-Dispersion Spectrograph ( HDS ; R \sim 165,000 ) in the wavelength range of 0.62 – 0.88 \mu m with the Subaru telescope to obtain the day-side spectra of WASP-33 b .
We suppress and correct the systematic effects of the instrument , the telluric and stellar lines by using SYSREM algorithm after the selection of good orders based on Barnard star and other M-type stars .
We detect a 4.8- \sigma signal at an orbital velocity of K _ { p } = +237.5 ^ { +13.0 } _ { -5.0 } km s ^ { -1 } and systemic velocity V _ { sys } = -1.5 ^ { +4.0 } _ { -10.5 } km s ^ { -1 } , which agree with the derived values from the previous analysis of primary transit .
Our detection with the temperature inversion model implies the existence of stratosphere in its atmosphere , however , we were unable to constrain the volume-mixing ratio of the detected TiO .
We also measure the stellar radial velocity and use it to obtain a more stringent constraint on the orbital velocity , K _ { p } = 239.0 ^ { +2.0 } _ { -1.0 } km s ^ { -1 } .
Our results demonstrate that high-dispersion spectroscopy is a powerful tool to characterize the atmosphere of an exoplanet , even in the optical wavelength range , and show a promising potential in using and developing similar techniques with high-dispersion spectrograph on current 10m-class and future extremely large telescopes .