Spatial characterization of the trailing and leading limbs of WASP-76 b
Extreme temperature contrasts between the day and nightside of ultra-hot Jupiters (UHJ) result in significantly asymmetric atmospheres, with a region of extreme atmospheric expansion appearing over a small range of latitudes around the terminator. Over the course of a transit, WASP-76 b rotates by about 32° and hence temporal variations of the observable atmosphere could significantly affect the detectability of its constituents. Specifically, the trailing limb of this planet allows us to probe a significant portion of the inflated dayside, resulting in a higher atmospheric detectability. This geometric effect could mimic the observed time-variability of absorption signals due to condensation in the nightside of these planets, which has been recently reported for neutral iron in WASP-76 b. By studying molecules that are not expected to condense in an UHJ, we can isolate the possible effect of different day and nightside scale heights. Here, we will analyze a strong egress water vapor signal, a redshifted hydrogen cyanide signature, and a weak evidence of ammonia during a transit of WASP-76 b and compare the contribution from the leading and trailing limbs.
