  We present an atmospheric transmission spectrum of the ultra-hot Jupiter
WASP-76 b by analyzing archival data obtained with the Space Telescope Imaging
Spectrograph (STIS) on board the Hubble Space Telescope (HST). The dataset
spans three transits, two with a wavelength coverage between 2900 and 5700
Armstrong, and the third one between 5250 and 10300 Armstrong. From the
one-dimensional, time dependent spectra we constructed white and chromatic
light curves, the latter with typical integration band widths of ~200
Armstrong. We computed the wavelength dependent planet-to-star radii ratios
taking into consideration WASP-76's companion. The resulting transmission
spectrum of WASP-76 b is dominated by a spectral slope of increasing opacity
towards shorter wavelengths of amplitude of about three scale heights under the
assumption of planetary equilibrium temperature. If the slope is caused by
Rayleigh scattering, we derive a lower limit to the temperature of ~870 K.
Following-up on previous detection of atomic sodium derived from high
resolution spectra, we re-analyzed HST data using narrower bands centered
around sodium. From an atmospheric retrieval of this transmission spectrum, we
report evidence of sodium at 2.9-sigma significance. In this case, the
retrieved temperature at the top of the atmosphere (10-5 bar) is 2300 +412-392
K. We also find marginal evidence for titanium hydride. However, additional
high resolution ground-based data are required to confirm this discovery.
