Search for an exosphere in sodium and calcium in the transmission spectrum of exoplanet 55 Cancri e

• Context. The atmospheric and surface characterization of rocky planets is a key goal of exoplanet science. Unfortunately, the measurements required for this are generally out of reach of present-day instrumentation. However, the planet Mercury in our own solar system exhibits a large exosphere composed of atomic species that have been ejected from the planetary surface by the process of sputtering. Since the hottest rocky exoplanets known so far are more than an order of magnitude closer to their parent star than Mercury is to the Sun, the sputtering process and the resulting exospheres could be orders of magnitude larger and potentially detectable using transmission spectroscopy, indirectly probing their surface compositions. Aims. The aim of this work is to search for an absorption signal from exospheric sodium (Na) and singly ionized calcium (Ca+) in the optical transmission spectrum of the hot rocky super-Earth 55 Cancri e. Although the current best-fitting models to the planet mass and radius require a possible atmospheric component, uncertainties in the radius exist, making it possible that 55 Cancri e could be a hot rocky planet without an atmosphere. Methods. High resolution (R similar to 110 000) time-series spectra of five transits of 55 Cancri e, obtained with three different telescopes (UVES/VLT, HARPS/ESO 3.6 m and HARPS-N/TNG) were analysed. Targeting the sodium D lines and the calcium H and K lines, the potential planet exospheric signal was filtered out from the much stronger stellar and telluric signals, making use of the change of the radial component of the orbital velocity of the planet over the transit from -57 to +57 km s(-1). Results. Combining all five transit data sets, we detect a signal potentially associated with sodium in the planet exosphere at a statistical significance level of 3 sigma. Combining the four HARPS transits that cover the calcium H and K lines, we also find a potential signal from ionized calcium (4.1 sigma). Interestingly, this latter signal originates from just one of the transit measurements with a 4.9 sigma detection at this epoch. Unfortunately, due to the low significance of the measured sodium signal and the potentially variable Ca+ signal, we estimate the p-values of these signals to be too high (corresponding to

Ämnesord

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Nyckelord

techniques: spectroscopic

planetary systems

methods: data analysis

Planets and satellites: atmospheres

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art (ämneskategori)

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