  An inner companion has recently been discovered orbiting the prototype of
classical Cepheids, delta Cep, whose orbital parameters are still not fully
constrained. We collected new precise radial velocity measurements of delta Cep
in 2019 using the HARPS-N spectrograph mounted at the Telescopio Nazionale
Galileo. Using these radial velocity measurements, we aimed to improve the
orbital parameters of the system. We considered a template available in the
literature as a reference for the radial velocity curve of the pulsation of the
star. We then calculated the residuals between our global dataset (composed of
the new 2019 observations plus data from the literature) and the template as a
function of the pulsation phase and the barycentric Julian date. This provides
the orbital velocity of the Cepheid component. Using a Bayesian tool, we
derived the orbital parameters of the system. Considering priors based on
already published Gaia constraints, we find for the orbital period a maximum a
posteriori probability of Porb=9.32+/-0.03 years (uncertainties correspond to
the 95% highest density probability interval), and we obtain an eccentricity
e=0.71+/-0.02, a semimajor axis a=0.029 +/-0.003 arcsecond, and a
center-of-mass velocity V0=-17.28+/-0.08 km/s, among other parameters. In this
short analysis we derive the orbital parameters of the delta Cep inner binary
system and provide a cleaned radial velocity curve of the pulsation of the
star, which will be used to study its Baade-Wesselink projection factor in a
future publication.
