New elements detected in the atmosphere of the hottest exoplanet known so far. The study: “The GAPS programme at TNG LX Atmospheric characterisation of KELT-9 b via single-line analysis: Detection of six H I Balmer lines, Na I, Ca I, Ca II, Fe I, Fe II, Mg I, Ti II, Sc II, and Cr II” of M. D’Arpa (INAF – OAPA/UNIPA) appeared on A&A

One of the most interesting aspects of exoplanetary science is the possibility of studying worlds that are not present in our Solar System (at least, not today). Some of these exoplanets possess such extreme properties that they are of great scientific interest. This is certainly the case for the Ultra-Hot Jupiter KELT-9b. It is a gas giant with a mass 2.8 times that of Jupiter, orbiting a high-mass star (2.52 solar masses, with an effective temperature exceeding 10000 K) at a distance of just 0.03 Astronomical Units (AU; 1 AU is the average distance between Earth and the Sun, about 150 million km; 0.03 AU is less than one-tenth of the average distance between the Sun and Mercury). Being so close to a very hot star, KELT-9b intercepts an intense flow of high-energy stellar radiation, which raises its atmosphere to a temperature of 4600 K, higher than that of many stars. Additionally, KELT-9b orbits in a nearly polar orbit and is tidally locked with its star.

Given its peculiar characteristics, it is not surprising that KELT-9b has attracted the interest of many astronomers specializing in exoplanets. In particular, this exoplanet is one of the targets of the GAPS (Global Architecture of Planetary Systems) project, which aims to characterize the architecture and physical properties of known exoplanetary systems. The project mainly relies on observations made with the HARPS-N high-resolution spectrograph, mounted on the Telescopio Nazionale Galileo.

A team led by astrophysicist M. D’Arpa (INAF – Astronomical Observatory of Palermo and University of Palermo) analyzed a series of HARPS-N observations of KELT-9b taken during the planet’s transit (i.e., when the planet passes in front of its star from our point of view) and outside of the transit. During transit, some of the stellar radiation passes through the planet’s atmosphere before reaching us, interacting with the atoms in the atmosphere, allowing us to observe the absorption and emission of radiation by various atoms (and molecules, in the case of cooler planets). The study identified a rich array of atoms present in the planet’s atmosphere, including neutral atoms like Sodium, Calcium, Iron, and Magnesium, and ionized atoms such as Calcium, Iron, Titanium, Scandium, and Chromium, with the latter two being identified for the first time in an exoplanetary atmosphere.

The spectroscopic signals from many of these atoms show effects related to the rapid movement of the material generating them (i.e., the Doppler effect, due to the motion of the material that emits/absorbs the radiation relative to the observer). This has allowed the measurement of violent winds, with speeds of several km/s (the exact value varies slightly from one atomic species to another), sweeping through KELT-9b’s atmosphere between its day and night sides.

The study is detailed in the article: “The GAPS programme at TNG LX Atmospheric characterisation of KELT-9b via single-line analysis: Detection of six H I Balmer lines, Na I, Ca I, Ca II, Fe I, Fe II, Mg I, Ti II, Sc II, and Cr II,” recently published in Astronomy & Astrophysics. Co-authors include astronomers G. Micela, C. Di Maio, G. Tripodo, L. Affer, S. Benatti, V. Fardella, J. Maldonado, and R. Spinelli from INAF – Osservatorio Astronomico di Palermo.

The attached figure (click here to view it in full) shows an infrared image (obtained from the WISE satellite) of KELT-9, the star at the center of the image, and its rich surrounding environment.