PEPSI

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

by Silva Järvinen on 2020-08-31

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 profile on the other hand showed only a few km/s broadening comparable with the synthetic line profiles. 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 different temperature, which could explain the differences 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 fit. 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.