Total HST flux of each sub-exposure measured over the 2900 − 3100 Å spectral domain as a function of the HST orbital phase (in erg cm^-2 s^-1). Upper plot: transit #1. During this transit, successive HST orbits are shown (orbit #2, black crosses, orbit #3, blue diamonds, orbit #4, green triangles and orbit #5, red squares). Middle plot: same as upper plot for transit #2. Lower plot: same as upper plot for transit #3.