2024MNRAS.535.1123U

Here, we present the low-resolution transmission spectroscopy of three giant planets using the Himalayan Faint Object Spectrograph Camera (HFOSC) on the 2 m Himalayan Chandra Telescope (HCT) in Hanle, India. It is the first application of transmission spectroscopy with HCT. This study presents results from a single transit, each for three planets: HAT-P-1b, KELT-18b, and WASP-127b. The selection of suitable reference stars assisted in accurately tracking slit losses for the long cadence observations that are needed to achieve the required signal-to-noise ratio (SNR). We employ the common mode correction technique, utilizing a white light transit curve to minimize time-dependent systematic errors. The observed spectra for WASP-127b and HAT-P-1b agree with previous low-resolution transit spectroscopic observations using other observing facilities. We confirm the presence of Rayleigh scattering in the atmosphere of WASP-127b. In addition, we provide the first low-resolution transmission spectrum for KELT-18b. Modelling the exoplanet atmosphere with HFOSC and available IR observations from HST and Spitzer for WASP-127b and HAT-P-1b shows that HFOSC can be an alternative optical instrument to use in conjunction with IR observations to constrain the atmospheric parameters better.