Ground-based detection of calcium and possibly scandium and hydrogen in the atmosphere of HD 209458b

Context. Since the first exoplanetary atmosphere detection using the Hubble Space Telescope, characterization of exoplanet atmospheres from the ground have been playing an increasingly important role in the analysis of these atmospheres thanks to the enhancement of telluric correction techniques. At present, several species have been discovered in the atmosphere of HD 209458b, all of them consistent with theoretical models. Aims. Data acquired using the High Dispersion Spectrograph on the Subaru telescope are re-analysed. We expect to discover new species in the atmosphere of the exoplanet HD 209458b. In addition to shedding light on the atmospheric composition, we will derive the radial extension of the absorbents present in the atmosphere of the exoplanet. Methods. We present an alternative method for correcting the telluric effects through the analysis of variations in spectral lines with the airmass. To search for absorptions due to an exoplanetary atmosphere we implemented an algorithm to automatically search for all the features presenting an atmospheric signature in the transmission spectrum and through the wavelength range in the data. To estimate uncertainties we performed a bootstrapping analysis. Results. Absorption excess due to the transitions of calcium at 6162.17 Å and 6493.78 Å, scandium at 5526.79 Å, hydrogen at 6562.8 Å, and the sodium doublet are detected in the transmission spectrum at a level of −0.079 ± 0.012%, −0.138 ± 0.013%, −0.059 ± 0.012%, −0.123 ± 0.012%, −0.071 ± 0.016% using pass-bands of 0.5 Å, 0.4 Å, 0.5 Å, 1.1 Å, and 0.6 Å, respectively. Conclusions. Models predict strong absorption in the sodium resonance doublet which was previously detected, also in this analysis. However, this is the first report of calcium and possibly scandium in HD 209458b, including the possible ground-based detection of hydrogen. Calcium is expected to condense out in the atmosphere of this exoplanet; therefore, confirmation of these results will certainly imply a review of theoretical models.