The GTC exoplanet transit spectroscopy survey. VII. An optical transmission spectrum of WASP-48b

TL;DR

This study presents an optical transmission spectrum of exoplanet WASP-48b, revealing a flat spectrum with no significant atmospheric features, achieved through high-precision spectroscopic transit observations with the GTC.

Contribution

First optical transmission spectrum of WASP-48b obtained with the GTC, demonstrating high-precision measurements and analysis of the planet's atmospheric properties.

Findings

Transmission spectrum is relatively flat with no significant atmospheric features.

Measurement precisions between 261 ppm and 755 ppm achieved.

Data are consistent with models including TiO and VO, but no definitive detection.

Abstract

We obtained long-slit optical spectroscopy of one transit of WASP-48b with the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) spectrograph at the 10.4 m Gran Telescopio Canarias (GTC). We integrated the spectrum of WASP-48 and one reference star in several channels with different wavelength ranges, creating numerous color light curves of the transit. We fit analytic transit curves to the data taking into account the systematic effects present in the time series in an effort to measure the change of the planet-to-star radius ratio ($R_p/R_s$) across wavelength. After removing the transit model and systematic trends to the curves we reached precisions between 261 ppm and 455-755 ppm for the white and spectroscopic light curves, respectively. We obtained $R_p/R_s$ uncertainty values between $0.8 \times 10^{-3}$ and $1.5\times 10^{-3}$ for all the curves analyzed in this work. The measured transit depth for the curves made by integrating the wavelength range between 530 nm and 905 nm is in agreement with previous studies. We report a relatively flat transmission spectrum for WASP-48b with no statistical significant detection of atmospheric species, although the theoretical models that fit the data more closely include of TiO and VO.