English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present a new Keck/NIRSPEC observation of metastable helium absorptionfrom the upper atmosphere of HD 189733b, a hot Jupiter orbiting a nearbymoderately active star. We measure an average helium transit depth of $0.420\pm 0.013$% integrated over the [-20, 20] km/s velocity range. Comparing thismeasurement to eight previously published transit observations with differentinstruments, we find that our depth is 32% (9$\sigma$) lower than the averageof the three CARMENES transits, but only 16% (4.4$\sigma$) lower than theaverage of the five GIANO transits. We perform 1D hydrodynamical simulations ofthe outflow, and find that XUV variability on the order of 33%--common for thisstar--can change the helium absorption depth by 60%. We conclude that changesin stellar XUV flux can explain the observational variability in heliumabsorption. 3D models are necessary to explore other sources of variability,such as shear instability and changing stellar wind conditions.

More Evidence for Variable Helium Absorption from HD 189733b