The GTC exoplanet transit spectroscopy survey

Abstract

Exoplanets with relatively clear atmospheres are prime targets for detailed studies of chemical compositions and abundances in their atmospheres. Alkali metals have long been suggested to exhibit broad wings due to pressure broadening, but most of the alkali detections only show very narrow absorption cores, probably because of the presence of clouds. We report the strong detection of the pressure-broadened spectral profiles of Na, K, and Li absorption in the atmosphere of the super-Neptune WASP-127b, at 4.1σ, 5.0σ, and 3.4σ, respectively. We performed a spectral retrieval modeling on the high-quality optical transmission spectrum newly acquired with the 10.4 m Gran Telescopio Canarias (GTC), in combination with the re-analyzed optical transmission spectrum obtained with the 2.5 m Nordic Optical Telescope (NOT). By assuming a patchy cloudy model, we retrieved the abundances of Na, K, and Li, which are super-solar at 3.7σ for K and 5.1σ for Li (and only 1.8σ for Na). We constrained the presence of haze coverage to be around 52%. We also found a hint of water absorption, but cannot constrain it with the global retrieval owing to larger uncertainties in the probed wavelengths. WASP-127b will be extremely valuable for atmospheric characterization in the era of James Webb Space Telescope.

The GTC exoplanet transit spectroscopy survey

“…The data for both nights were fitted following the procedure of Chen et al (2018). The analytic transit curve was created using the models of Mandel & Agol (2002) through the batman implementation of Kreidberg (2015).…”

“…This method consists in measuring the change in the planetary radius across wavelengths during a transit event. In the past decade this procedure has been used to detect several planetary atmospheric features such as atomic and molecular absorption lines (e.g., Charbonneau et al 2002;Redfield et al 2008;Snellen et al 2008;Fraine et al 2014;Kreidberg et al 2014a;Chen et al 2017aChen et al , 2018Nikolov et al 2018;Wakeford et al 2018) and scattering features (e.g., Lecavelier Des Etangs et al 2008;Sing et al 2011Sing et al , 2013Sing et al , 2015Pont et al 2013;Nikolov et al 2015;Kirk et al 2017). Thanks to their relatively large atmospheric scale heights most of these detections have been accomplished for Jupiter analogs; however, there has been several efforts in recent years to study the atmospheres of exoplanets with masses around the Saturn/Neptune regime and lower (e.g., Bean et al 2010;Stevenson et al 2010;Fukui et al 2013;Nascimbeni et al 2013;Knutson et al 2014;Kreidberg et al 2014b;Fraine et al 2014;Dragomir et al 2015;Tsiaras et al 2016;Chen et al 2017b;Diamond-Lowe et al 2018).…”

WASP-166b: a bloated super-Neptune transiting a V = 9 star

“…Thus discoveries such as WASP-107b (0.12 MJup; 0.94 RJup; Anderson et al 2017) and WASP-127b (0.18 MJup;1.37 RJup;Lam et al 2017) are prime targets for characterisation (e.g. Kreidberg et al 2018;Spake et al 2018;Palle et al 2017;Chen et al 2018). The importance of such targets, particularly ones transiting bright stars, will increase further with the launch of the James Webb Space Telescope.…”

Mass–Metallicity Trends in Transiting Exoplanets from Atmospheric Abundances of H2O, Na, and K

“…2 O (Rothman et al 2010), Na (Allard et al 2019), K (Allard et al 2016), CH 4 (Yurchenko & Tennyson 2014), NH 3 (Yurchenko et al 2011), HCN (Barber et al 2014), CO (Rothman et al 2010), and H 2 -H 2 and H 2 -He collision induced absorption (CIA;Richard et al 2012). Additionally, following previous studies(Chen et al 2018;von Essen et al 2019;Sedaghati et al 2017;, we include absorption due to Li(Kramida et al 2018) for WASP-127b, AlO(Patrascu et al 2015) …”