An extensive search for metallic ions in the exosphere of GJ 436 b

Presenter: Leonardo DOS SANTOS
The M2.5 star GJ 436 hosts a warm Neptune that displays an extended atmosphere that dwarfs its own host star. Predictions of atmospheric escape in such planets state that H atoms escape from the upper atmosphere in a collisional regime and that the flow can drag heavier atoms to the upper atmosphere. We analyzed flux time-series of species present in the FUV spectrum of GJ 436 to search for signals of metallic ions in the upper atmosphere of GJ 436 b, as well as study the activity-induced variability of the star. We found that GJ 436 displays flaring events with a rate of ∼10 events per day. There is evidence for a possibly long-lived active region that modulates the FUV lines of the star with amplitudes up to 20%. Despite the strong geocoronal contamination in the spectra, we detected in-transit excess absorption signals of ∼50% and ∼30% in the blue and red wings, respectively, of the Lyman-alpha line. We did not detect metallic ions in the exosphere of the planet, which could indicate that the atmospheric mixing is not efficient in dragging metals high enough for sublimation to produce a detectable escape rate of ions.