HARPSN and the atmospheric characterization of Kelt-9 b

The recent study on the hot Jupiter Kelt-9 b, conducted as part of the GAPS (The Global Architecture of Planetary Systems) programme using the HARPS-N high-resolution spectrograph, offers a valuable contribution to the field of exoplanetary atmospheric characterization.

With a mass 2.8 times greater than the mass of Jupiter and a radius nearly twice that of Jupiter, Kelt-9b orbits the late B-type/early A-type star Kelt-9, located about 650 light-years from Earth in the constellation Cygnus with a temperature of over 10,000 kelvins (almost twice as hot as the Sun). Kelt-9b is the hottest exoplanet known with dayside temperatures approaching 4,000 K.

This research provides a detailed analysis of the atmosphere of the exoplanet, by detecting six H I Balmer lines along with various metal species, including sodium, calcium, and iron. Notably, this study reports the first detection of the Hϵ and Hζ lines, as well as individual lines of Sc II and Cr II in an exoplanet's atmosphere, showcasing the innovativ nature of the research.

The study's approach involved the use of single line analysis to extract the transmission spectrum of each line individually. This method allowed the researchers to confirm the presence of these atomic species and gain insights into the atmospheric dynamics, such as the height distribution of species and the night-to-day side winds. These findings were compared with theoretical models that account for non-local thermodynamic equilibrium (NLTE) effects, further supporting the reliability of the results.

Mattia D'Arpa, the principal investigator of the work, said: "This work helps confirm the presence of NLTE effects in the atmospheres of ultra-hot Jupiters and provides detailed information on the vertical distribution of elements. Additionally, by identifying elements that have never before been detected through individual lines, the study further confirms the presence of atmospheric winds. While this research sets a useful reference point for future atmospheric studies of exoplanets, it is one of many efforts contributing to the ongoing exploration of exoplanetary atmospheres, enhancing our understanding of these distant worlds."

More information in the paper: Link

Height distribution of detected chemical species expressed in planetary radii (Rp) as a function of atmospheric temperature. H I and Ca II lie on top, but still well below the Roche Lobe (1.95 Rp). The other metals are distributed at lower altitudes. The black dashed line represents the model temperature profile accounting for NLTE effects. The full lines representing each species height distribution are shifted with respect to the black dashed line for clarity.