  Transiting planets provide unique opportunities for the atmospheric
characterization of exoplanets as they can reveal composition and the
temperature structures at the day-night terminator regions in planetary
atmospheres, and help understand the atmospheric process and formation
environments of exoplanets. Here, we present the optical transmission
spectroscopic study of an inflated Saturn-mass planet WASP-69 b, obtained by
the 4-meter ground-based telescope Southern Astrophysical Research Telescope
(SOAR). We obtain spectroscopic transit light curves in 20 passbands from 502
to 890 nm, and fit them using Gaussian Processes and an analytical transit
model to obtain independent transit depths for each. The derived transmission
spectrum of WASP-69 b shows a slope with absorption depth increasing towards
blue wavelengths, indicating a Rayleigh scattering in the atmosphere consistent
with previous works. The retrieval analysis yields a tentative detection of TiO
absorption feature in the transmission spectrum. We present the first results
from the SOAR telescope to characterize exoplanetary atmospheres proving its
capability and precision for hot Jupiters around bright stars in an area
dominated by results from large ground-based telescopes or space telescopes.
