Probing the atmosphere of HD 189733b with the Na I and K I spectral lines

A team around Engin Keles (AIP) compared previously observed high resolution Na I and K I absorption in the atmosphere of HD189733b with synthetic transmission spectra modeled for a variety of temperature and abundance values. The comparison showed that the observed Na I-D-line widths are much larger than the modeled ones. The Na I-D-lines had to be broadened by velocities in the order of 10 km/s to match the observations if only rotational broadening is taken into account. The K I line profi le on the other hand showed only a few km/s broadening comparable with the synthetic line pro files. This hints that either the atmosphere of HD 189733b lacks a significant amount of K I or the alkali lines probe different atmospheric regions with diff erent temperature, which could explain the diff erences in the resolved absorption lines.


Transmission spectrum of the KI-line at 7699 A in [%] subtracted from unity. The black solid line shows the Gaussian fi t. The dashed lines show the expected planetary absorption from the synthetic spectra without any broadening (red) and with the best-matching broadening solution of 3.8 km/s (green). The residual spectrum is shifted for clarity. .

Read more: Keles et al., 2020, MNRAS, in press