# A feature-rich transmission spectrum for WASP-127b

## TL;DR

This study presents the first transmission spectrum of WASP-127b, revealing potential atmospheric components like TiO, VO, and Na, and suggests a cloud-free atmosphere suitable for future detailed characterization.

## Contribution

First low-resolution transmission spectrum of WASP-127b, indicating possible atmospheric constituents and a cloud-free atmosphere, aiding future atmospheric studies.

## Key findings

- Detection of a strong Rayleigh slope at blue wavelengths
- Hint of Na absorption in the spectrum
- Possible presence of TiO and VO absorption features

## Abstract

WASP-127b is one of the lowest density planets discovered to date. With a sub-Saturn mass ($M_{\rm p}=0.18 \pm 0.02 M_J$) and super-Jupiter radius ($R_{\rm p}= 1.37 \pm 0.04 R_J$), it orbits a bright G5 star, which is about to leave the main-sequence. We aim to explore WASP-127b's atmosphere in order to retrieve its main atmospheric components, and to find hints for its intriguing inflation and evolutionary history. We used the ALFOSC spectrograph at the NOT telescope to observe a low resolution ($R\sim330$, seeing limited) long-slit spectroscopic time series during a planetary transit, and present here the first transmission spectrum for WASP-127b. We find the presence of a strong Rayleigh slope at blue wavelengths and a hint of Na absorption, although the quality of the data does not allow us to claim a detection. At redder wavelengths the absorption features of TiO and VO are the best explanation to fit the data. Although higher signal-to-noise ratio observations are needed to conclusively confirm the absorption features, WASP-127b seems to posses a cloud-free atmosphere and is one of the best targets to perform further characterization studies in the near future.