The transmission spectrum of WASP-17 b from the optical to the near-infrared wavelengths: combining STIS, WFC3 and IRAC datasets
- 1Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, United Kingdom
- 2INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
- 3AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, F-91191 Gif-sur-Yvette, France
- 4School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
In the last two decades the Hubble and the Spitzer Space telescopes have pioneered exoplanet atmospheric studies through transit and eclipse spectroscopy. Among the hot-Jupiters, an exotic class of planets that do not have a counterpart in our solar system, we find the so-called ‘puffy’ hot-Jupiters. Their hot inflated atmosphere and consequently large scale height boosts the S/N ratio of the observations, allowing us to easily probe their atmosphere.
In this context, I will present the transmission spectrum of the inflated hot-Jupiter WASP-17 b, one of the least dense gas giants discovered so far. The exoplanet was observed with the STIS (gratings G430L, G750L) and WFC3 (grisms G102, G141) instruments aboard the Hubble Space Telescope, allowing for a continuous wavelength coverage from 0.4 to 1.7 μm. I also include the observations taken with IRAC channel 1 and 2 on the Spitzer Space Telescope, which add photometric measurements at 3.6 and 4.5 μm. Thanks to the availability of a large breadth of observations, this is a rare opportunity to investigate the spectrum of WASP-17 b from the optical to the near-infrared wavelengths.
I will describe how the HST spectral data was analysed with Iraclis, an open-source pipeline specialised on the reduction of STIS and WFC3 observations. Moreover, I will present a machine learning approach to the data reduction of Spitzer photometric data, by employing the Transit Light Curve Detrending LSTM method. The modelling of this exoplanetary spectrum proves challenging, with two of the STIS datasets producing incompatible results. Hence, I will discuss what can be inferred from the spectrum of this intriguing planet, from the potential presence of aluminium oxide (AlO) and titanium hydride (TiH) to an extreme photospheric activity of its companion star.
The study is of particular interest as it: a) demonstrates the issues faced when combining data from a variety of instruments; b) presents the benefits of achieving a large wavelength coverage; c) allows to investigate the activity of the host star.
The lessons learned from the combination of different instruments are exceptionally timely given the similar challenges that JWST data will bring in the near future.
How to cite: Saba, A., Tsiaras, A., Morvan, M., Thompson, A., Changeat, Q., Edwards, B., Jolly, A., Waldmann, I., and Tinetti, G.: The transmission spectrum of WASP-17 b from the optical to the near-infrared wavelengths: combining STIS, WFC3 and IRAC datasets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-30, https://doi.org/10.5194/epsc2022-30, 2022.
